Ford 8.8" Gear Teeth Cut Process Differences That Affect Setup

Discussion in 'DIY Tech Guides' started by GlassTop09, Nov 12, 2021.

Car Parts
  1. GlassTop09

    GlassTop09 Member

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    Hi All, (warning long post......)

    I recently ran into a gear whine issue when I had a set of Ford Performance 3.73" gears replaced w\ a set of Richmond EXCEL 3.89" gears in my Stang. The shop manager that did the work is a very experienced guy that knows how to properly set up gears (as well as myself) & he knew the gears were whining before I picked up my car (he told me so up front as well) but he couldn't figure out why (he also told me up front that he would prefer me to use Ford Performance 4.10 gears instead but I insisted using these Richmond gears thus understand the risk of potential gear whine).

    So you now know the context up front.

    I have read so many accounts of folks saying that Richmond (or Motive, or US Gear, etc) gears always whine....also certain Ford OE & Ford Performance gears always whine....so it's always the gears are bad, rinse, repeat, etc.

    So I decided to research this issue as I believed that there was more to this than just a lot of references\speculation to specific brand names & a person's knowledge level\competence level in gear setup....what I found out is that, associated w\ the Ford 8.8" axle's appearance, Ford also introduced a new gear tooth cutting process (2-cut face hobbed process....is used to make all current Ford 8.8" OE\Ford Performance gear sets) to make the gear sets for this axle that is different geometrically from the prior 5-cut face milled process Ford used w\ the Ford OE 9" axles (all the aftermarket gear manuf's still use this 5-cut face milled process to make all current Ford-specific 8.8" gear sets) that gives a different pattern checking migration direction & tooth placement position when using gear marking compound to check the same pinion depth\backlash setting procedures used to align the pinion gear teeth chord line to the ring gear teeth chord line (or center if preferred) to achieve proper tooth contact thus mesh quietly under operation (no whining).

    So, unless a person knows which type of gear cut process was used on a particular set of gears being installed in the Ford 8.8" axle in particular, to then know which pattern checking migration & tooth placement position parameters to use w\ marking compound to properly gauge the pinion depth\backlash settings being applied, it will be very easy to make setup mistakes as well as being very hard\frustrating to set them up (think of a busted clock getting the time right 2 times a day scenario.....you'll eventually get there but not w\o a lot of effort & confusion) due to which type gear cut pattern you got used to setting up 1st prior to handling the 2nd type. With the Ford 9" axles this isn't an issue as all Ford 9" gear sets whether OE or aftermarket are made using the same 5-cut face milled gear cutting process so there is no pattern checking parameter differences to account for.....thus much easier & simpler to do. This has been the case until recently when US Gear (Moser) has started making Ford 9" gear sets using the newer 2-cut face hobbed process instead of the older 5-cut face milled process so all you Ford 9" users be warned.............

    The cause is then an identification issue w\ the Ford 8.8" axle of how to recognize which type of gear cut process you're looking at to then know which checking pattern to use to properly interpret the pinion depth\backlash setting movements to properly align the pinion depth\backlash to properly center the pinion to the ring gear to hit the pinion gear\ring gear chord lines so they mesh right thus not whine!

    This is the reason why most proficient shops will have either the high dollar, very accurate pinion depth setting tool (this tool eliminates the gear tooth cut process being a factor in setting the pinion depth.....but the only way it gets you out of the checking pattern issue is if you hit the pinion checking number exactly or within the gear manuf's recommended variation window used to center the pinion gear to the ring gear during QA\QC prior sale) and\or they know how to ID which gear tooth cut process they're working with to then know which pattern checking parameters to use when setting the pinion depth\backlash.

    So from checking this forum & finding nothing to help all us DIY'ers to know\be aware of this concerning the Ford 8.8" axle, here is a link provided to a very good article that explains this w\ very good pictures of these differences showing the pattern migrations from center for both processes when setting pinion depth (called PMD or pinion mounting distance....same thing) or backlash after correct pinion depth is achieved : DIY Ford - Ford Axle Ring and Pinion Assembly How to Guide as well as provided below a .pdf of a Dana Gear Type Interpretation Chart that shows how to ID which type of gear cut process (whether 5-cut face milled or 2-cut face hobbed) was used to make the gears as well as the associated pattern checking parameters to use for both processes so this is not brand dependent (by now I believe most OE gears are being cut using the newer 2-cut face hobbed dry process which is much faster & simpler thus cheaper to make a gear set with than the older 5-cut face milled wet process but most aftermarket manuf's can't afford the expense of a complete equipment swapout to change over based on their existing profit margins so they continue to use the old 5-cut face milled process w\ their Ford 8.8" gears that they sell.....).

    When I showed all this to the shop manager that set up my gears, he admitted that he didn't know this was a thing (I admit I didn't either until I did all the research)....he was always setting up Ford Performance 8.8" gears (his preference & sets them using the old school setting procedures....) so he had unknowingly gotten used to looking at a 2-cut face hobbed process thus gotten familiar w\ the associated pattern checking parameters for a 2-cut face hobbed gear set. The Richmond gears (aftermarket) were cut using the older 5-cut face milled process (but assumed that all gear sets are made the same way.....sound familiar?) which the pattern checking parameters he was accustomed to using w\ the Ford Performance gear sets (2-cut face hobbed) won't respond the same way w\ this Richmond gear set (5-cut face milled).....so he made simple interpretation mistakes due to natural (not willful) ignorance which caused him a lot of headaches trying to get them right (took over 4 days) & still got them wrong in the end (whining).

    1 of my strengths in the profession that I worked in before retirement (Production Specialist for a major oil company) was ability to perform solid & accurate root cause\effect analysis to effectively solve operational issues............IOW's, fixing broke stuff.

    When we got together in person & I showed him the proper pattern checking parameters for a 5-cut face milled gear set (Richmond is an aftermarket gear....1st clue) & used it to compare w\ the pictures of the final gear setting compound pattern markings he sent me, he quickly then recognized that somehow he had lucked out & got the pinion depth set correct (the part that takes the longest time & effort to get right w\o using a pinion depth setting tool) thru a lot of excess time wasted (which I paid for) but had set the final backlash way too loose from trying to match up the pattern shape on both the drive\coast sides from using the wrong 2-cut face hobbed pattern checking parameters which put the pinion tooth chord line high heel on both drive & coast side thus completely off the chord line (true center of teeth or ease-off if you prefer) of the ring gear teeth thus whining on both accel\decel....not because he didn't know HOW TO SET UP GEARS or the BRAND of gear set used, he didn't know the actual gear tooth cut process used w\ the actual gear set he was working with to then know which pattern checking parameters to use to guide him properly w\ their setup!

    So in the end I get a free fix as from the proper comparison using the proper checking parameters that matched the gear set's tooth cutting process in question all we need to do in the end is to just reset the final backlash to the manuf's recommended backlash variation range (we're gonna shoot for the tighter side of the range on purpose) to make it all line up right & I got a big thank you from the shop manager for taking the time to work w\ him in a respectful manner to help him to learn something he didn't know\was unaware of that will help him out going forward (I gave him all of the research materials I had printed out in a packet to have so he could refer back to all this on future jobs) & not being a dick customer blaming him\degrading him for his "lack" of competence in doing his work.

    I'll wager this is a MUCH, MUCH more common issue (on both sides of the aisle) than most would admit concerning setting up gears in the Ford 8.8" axles....

    Hope this helps.
     

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    Last edited: Nov 12, 2021
  2. GlassTop09

    GlassTop09 Member

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    Here is provided a link to an article that explains all the relevant geometrical differences between the 2 gear tooth cutting processes for all those so inclined: Face-off: Face Hobbing vs. Face Milling | Gear Solutions Magazine Your Resource to the Gear Industry

    Enjoy!

    PS-- Also as a piece of advice, don't always count on the gear manuf's setting directions to properly guide you as they are sometimes entirely too generic & lack detail (vague) or leave out needed data that you need to know. The Richmond EXCEL gear installation instructions....while designed for this gear set series doesn't mention anything about a Ford 8.8" axle....only Ford 8"\9" axles....so can easily be misinterpreted (the Ford 9" & Ford 8.8" axles use different gear cutting processes to make their gear sets) & doesn't mention anything about setting pinion depth outside of using a pinion depth setting tool to use the pinion checking distance numbers to set pinion depth.

    So in Richmond's case, they need to revamp all their installation instructions to CLEARLY reflect the differences w\ Ford 8.8" & Ford 9" gear sets so folks won't make these simple but costly mistakes.
     
    Last edited: Nov 12, 2021
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  3. GlassTop09

    GlassTop09 Member

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  4. GlassTop09

    GlassTop09 Member

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  5. MrBhp

    MrBhp Member

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    Thanks for the write up. This explains some perplexing issues I've had with some past setups.
     
  6. Rick Simons

    Rick Simons Member

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    Wow! This perfectly explains why I wasn't getting the contact pattern I was looking for when I set up my diff with the 3:73's. I fussed with that thing for several hours with it in the car, then finally removed the entire axle, put it on the bench to set it up, and then fussed over it for another 4 hours or more. Thank you so much, GlassTop09, for this golden info. The veil has been lifted......
     
  7. RED09GT

    RED09GT Equal Opportunity Offender S197 Team Member

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    That's a great read. I had observed the difference in tooth height but did not know that it basically reverses the steps for correcting the pattern or the name of the process.

    First set of gears I did was a set of Richmond 3.73's in my fox body and used a set of generic set up pictures from an old chilton all makes repair manual and they were quiet- but did have a change in pitch from the 3.08 gears.

    When I did my Ford Racing 4.10's in my car, I set it up like a face milled set, measured the pinion depth, etc... and shimmed the pinion to correct what I thought was the pinion being too shallow on the coast side. I played with it to try and get a decent pattern and settled with a thicker pinion shim than stock. They whined on deceleration.

    I later put the 3.55's back in due to the internet telling me that 3.55's would be better for a turbo car (maybe with an auto and a torque coverter that the motor overpowers, but not the case with a TR6060 and a heavy street car).

    When I put the 4.10's back in, I re-used my thinner shim that came with the factory 3.55's, then adjusted backlash until it had a decent pattern and they are now quiet.

    I had no idea why and assumed that I didn't get the measurements and calculations correct. Now I find out it was because I was trying to set a face hobbed gearset using a face milled method.
    Thanks for the new piece of knowledge!
     
  8. TexasBlownV8

    TexasBlownV8 Formerly TexasBlownV6

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    +1 on the great info! I did not know this either, but always 'preferred' to do FRPP gears just because of the ease of installation and most of the time coming out quiet (with appropriate backlash).
     
  9. Midlife Crises

    Midlife Crises Senior Member

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    After reading the difference in set up procedures I will revisit my differential this winter. Maybe I can get the 4.30s to run quietly.
     
  10. GlassTop09

    GlassTop09 Member

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    This is the problem w\ using other generic pattern checking parameters from all the different manuf's w\ the Ford 7.5" & 8.8" axles......you don't know which gear cutting process they're referencing to as they don't tell you & none of them are consistent in presentation.....even Ford Performance doesn't say but they do give you the proper pattern checking parameters that matches the 2-cut face hobbed cut process used to make the gears in their .pdf's.

    It is this 2-cut face hobbed process & Ford's use of the MHD (master housing dimension) design for the 7.5"\8.8" axle housing (the 4.415" std distance from carrier axle centerline to shim side of the pinion head gear) that makes the advent of using the same pinion shim thickness w\ the original Ford OE or FP gear set installed in a housing for each following Ford OE\FP gear set installed in same housing....even if different ratios up to the 4.56:1 gears.... So this is by design by Ford w\ the 7.5"\8.8" axles........
    Here's an article on this:
    SSOTN - Gear Install (superstallions.com)

    Dana\Spicer Gear is the only 1 I found who made a .pdf specifically devoted to ID'ing the 2 types of gear cutting processes & giving the full pattern checking parameters for both processes....thus can be printed out & kept in a folder to use w\ all other manuf's Ford 7.5"\8.8" specific gear sets.
     
    Last edited: Nov 17, 2021
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  11. 86GT351

    86GT351 forum member

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    I can tell you I have done many sets of gears over the years. I know a lot of shops that would not do a 3:90 Ratio for the 8.8 because of the aggravation while doing them and afterwards with customer concerns.
     
  12. GlassTop09

    GlassTop09 Member

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    Yeah, I kept that in mind as well. During all my research, when I read that DIY Ford article down towards the end of it when the author started explanation of gear ratios falling into "non hunting" or "semi hunting" or "full hunting" (which has to do w\ the pinion gear\ring gear tooth count ratio to determine the amount of revs a pinion gear tooth would have to make to realign w\ the same ring gear tooth grouping as if this happens within a certain # of revs of the gear set the ring gear teeth will have concentric contact wear patterns that will be in harmony thus emit a specific resonance pattern (or noise) as the specific pinion gear teeth rotate thru them.

    So this issue is what makes the 3.89 ratio (9 tooth pinion\35 tooth ring) somewhat suspect as the very next ratio (4.00:1....uses a 9 tooth pinion\36 tooth ring ratio which is a common factor gear set w\ no prime number which is a non-hunting gear...needs to have timing marks cut on pinion gear & ring gear to force the gears to "hunt" & thus stop the resonance issue) thus makes this specific 3.89 ratio-even though the ratio is not a common factor BUT also a non prime number gear set-a semi hunting gear set (means that the same thing can happen as w\ a non hunting gear set but it takes a few more revs than a non hunting gear set to do it) but most gear manuf's won't cut timing marks on these type of gear sets thus the hit\miss issue w\ resonance due to a gear tooth timing pattern issue.

    The gears that are the quietest are full hunting gear sets (these type ratios takes many, many revs to occur for the same teeth patterns to realign thus don't get tooth wear that fall into a resonance emitting pattern).

    They are usually distinguished by the pinion gear tooth count being a two-digit number & none common factor w\ a prime number for both pinion & ring gear (no divisor).

    So if a 3.90 gear set is desired, get the 3.91 ratio gear set (uses a 11 pinion tooth\43 ring tooth count ratio) instead of the 3.89 ratio gear set.

    My issue is that I didn't know this either until after I bought my gears (had them for over a year before install). Richmond usually follows the Ford OE gear pattern (note the 3.89 ratio is a Ford OE pattern for the Ford 9" axle) thus made this for the Ford 8.8" axle as well (ring gear dia was close enough to accommodate this ratio). Now the other aftermarket gear manuf's use the 3.91 ratio instead of the 3.89 ratio for this 8.8" axle.....my read is due to the semi hunting nature of the 3.89 tooth count ratio.

    1 of the side effects of our beloved S197 chassis.....due to it's much improved chassis stiffening....is it is also very susceptible to cabin resonance (why certain exhaust resonance will easily amplify into droning) & when you install stiffer LCA's\UCA's or certain 1-piece driveshafts that use U-joints on each end attached to this 8.8" rear axle you increase the risk of cabin resonance (also associated w\ gear whining even though the gears are properly centered) from a semi hunting\non hunting gear set installed in this 8.8" axle (1 of the reasons why this chassis was designed w\ the infamous 2-piece DS w\ those 2 CV joints...but the DS section between these 2 CV joints is filled w\ a resonance reducing material so the combination of the 2 CV joints (constant load which do not emit a resonance like U-joints when past the 3* angle off) coupled w\ the resonance deadening section between the 2 CV joints effectively cancel some gear set resonance thus prevents cabin amplification of it. This I also did not know.....until now during my research. I made a video of this demonstrating this resonance deadening w\ my OEM 2-piece DS............

    So since I still have my car's original 2-piece DS & all hardware to reinstall it, depending on the outcome of my reset & knowing all this now concerning this 3.89 gear ratio's semi hunting nature I may be reinstalling this 2-piece DS to finish killing this (I have the Ford Racing 1-piece Aluminum DS w\ 2 Spicer 1350 U-joints installed currently....you can clearly hear this DS become a big megaphone which amplifies into the cabin) cause at this time it's a "free" fix & since my goals for this car is now mostly cruiser duty this is IMHO the logical next step.

    Hell of a time to find all this out.....but since I'm blessed at the moment to be able to afford the costs of these lessons learned the hard way I count it all as a positive cause I learned something I didn't know before thus will make me a better "DIY technician" going forward & post all this here to hopefully help others so that they can avoid making these simple but costly mistakes from simple lack of knowledge.
     
    Last edited: Nov 18, 2021
  13. Lime1Gt

    Lime1Gt Junior Member

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    I don't know what technique your installer used to set the pinion depth but Ford uses a set measurement from the large pinion bearing to the bottom of the side bearing saddle. Using their tool positioned, a shim is tried between the tool and bottom of the tube in side bearing saddle until a slight drag is found. If you try to use a measurement from the top of the pinion crown they aren't machined for that propose so errors will occur. I used the Ford tool to install my 4:10's in my previous mustang and there was no noise from them at all. IMHO if a differential shop doesn't have the proper tooling to do Ford rear ends or other manufacturers maybe they shouldn't be doing them. It's the price of doing business and can only give them a bad name if they have multiple failures from guessing or just reusing the original pinion shim. If you look at the FRPP installation instructions for the 8.8 it shows the special tool and pictures of the pieces with their dimensions for stacking together. I had a machinist I know make the tool for me as milling accuracy is needed to meet the specs. I didn't have the correct size tube for the side bearings so I used a smaller tube and shimmed under the caps to hold it in place.
     
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  14. GlassTop09

    GlassTop09 Member

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    Hi Lime1GT,

    That Ford OE pinion depth setting tool you posted about won't work w\ an aftermarket set of gears.....it was specifically designed to work w\ Ford OE or Ford Performance gear sets only (as you have alluded to in your posting).
    My postings here in this thread is concerning the difference between 2 types of gear tooth cutting processes used by gear manuf's to make gear sets for this Ford 8.8" axle when using the old fashioned gear marking compound to check pinion depth & backlash setting cause if you don't ID the type of gear cut to then use the matching checking patterns you'll make the same mistakes & the same can happen to any shop or individual....not due to incompetence but simply lack of knowledge of these differences. Most shop personnel don't go\get sent to formal trade schools (like MIT for example) to get formally trained on this stuff so can easily fall into this unknowingly......no matter how many years experience a person has.....it's about exposure, not experience.

    It will depend on a person's training\background as well as the amount of exposure to both gear tooth cutting processes & the hunting aspects to know about all this..........so because of this most shops since the advent of the Ford 8.8" axle do\have refrain from installing gear sets....in particular aftermarket versions of certain gear ratios due to the expense of this pinion depth setting tool & in addition to this the advent of recognizing whether a particular gear set ratio is non-hunting, semi-hunting or full hunting along w\ very low profit margins. Ford OE & Ford Performance gear sets for this 8.8" are all full hunting ratios by design thus will come in certain ratios only (this has to do w\ the pinion gear & ring gear tooth count ratio used to come up w\ the actual gear ratio number). Most gear whining issues are actually tied to this lack of tooth hunting aspect.....the majority of these will be aftermarket gear sets as most will not inscribe timing marks on the pinion gear\ring gear on gear ratios that are using pinion tooth\ring tooth non-hunting or semi-hunting counts to realign the gears to the original teeth they were lapped with during assembly in the axle to prevent them from whining (essentially you're having to try to "relap" the gear set teeth again to each other during the break in process....w\o any lapping compound). This makes these type of gear sets very hit\miss when installing.....even if you do get the pinion depth\backlash set properly.

    Again it's not about competence\incompetence.......it's about exposure to all this seemingly little known info.
     
  15. GlassTop09

    GlassTop09 Member

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    FYI........
    I got w\ my installer to check this Richmond EXCEL 3.90 (actual 3.89) gear set to see if it is truly a non-hunting\semi-hunting gear set by putting timing marks on a pinion gear tooth & ring gear tooth across from each other, then rotate the ring gear 1 revolution to see how the marked pinion tooth would align itself (9 tooth pinion gear\ 35 tooth ring gear).....it came within 1 ring gear tooth of full realignment (2 of the 3 ring gear teeth were still engaged to this pinion gear tooth which makes this 3.89 gear set a non-hunting set thus tends to be noisy) thus is why it usually has noise issues (there's no way to find the original teeth they were lapped to at Richmond w\o actual timing marks applied to both the ring & pinion gear teeth to match them up during assembly.....the issue then is frequency output from mismatched tooth meshing....a buzzing type of noise--not a roaring\binding type which can indicate improper pinion depth\backlash setting or bearing failure--that operates in much the same way as exhaust resonance does to cause droning).

    The pinion preload was found still holding the 25 in\lb rotational load for new bearings, bearings were rotating smooth & clean so no pinion bearing issues. Same for carrier bearings so no issues. Pinion depth was found still centered thus no reason to mess w\ it so only reset carrier BL from .012" to .007" (Richmond BL spec is .007"-.009") & checked pattern...all was textbook centered for a face milled gear set so buttoned her up at that point. Loaded the axle w\ some Lucas 85W-140 GL-5 spec dino oil & test drove. Whining was much less than before but still present.

    Put her thru a 10 mi break in procedure of 0-45 MPH stop & go, varying speed, low load driving w\ several figure 8's added in to work the Tru-Trac's helical gears & move gear oil down to the outer axle bearings as well & got some positive results as gear whining did start to lessen some (some of the noise was found to actually come from the Tru-Trac while it was unloaded when going in straight line so more figure 8's are needed to finish tuning the Tru-Trac's helical gears as well as more varying low speed stop & go break in driving to allow pinion\ring gear teeth to "lap" themselves to each other again then allow a 30-40 min cooldown in between sessions).

    Time will tell if these will eventually quiet down enough to become acceptable. So far, from this reset, there's some positive promise to work with.

    So in closing, if 3.90's are desired for a Ford 8.8" axle, recommend to get the actual 3.91 ratio gear set (11 pinion tooth, 43 ring tooth, full hunting, face milled so quiet) & stay away from this 3.89 gear ratio set (9 pinion tooth, 35 ring tooth OE Ford 9" pattern, non-hunting, face milled so noisy).
     
  16. Juice

    Juice forum member

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    I have to add, I only ever heard of hunting vs non hunting ratios.

    Non hunting: same teeth mesh over and over. The reason why this is important is when you are installing a used set of gears, you want the same teeth to match up after the second install. It would also matter with new gears if they were lapped in.
    Example: 3.00 gears, 13/39, each tooth on the pinion will mesh with the same 3 ring gear teeth on each and every revolution.
    Hunting: all teeth on both ring and pinion will mesh at some point.
    Example: any ratio that is not an even number.
    Semi hunting, no idea, lol.
    Disclaimer: I only glanced over Glasstop's post. lol
     
  17. GlassTop09

    GlassTop09 Member

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    This is the way I have come to understand all this now as follows:

    Non-hunting:
    1.) Ring\pinion tooth count have common whole number divisor factor (same whole number divisor for both ring\pinion gear tooth counts which makes it a fully timed gear set; example: 3.50 ... 10 pinion\35 ring have common whole divisor of 5) & both are not prime numbers (prime numbers don't have a whole number divisor, say like 11) so will hit the same tooth group pairings within 1 ring gear revolution OR 2.) Ring\pinion tooth count have no common whole number divisor factor BUT both are not prime numbers either so each has a whole number divisor so look for the closest pinion\ring divisor pairing to determine if non-hunting or semi-hunting (3.89 .... 9 pinion\35 ring, both have divisors, pinion is 3, ring has either 5 or 7, closest divisor pairing is 3 to 5 so time spacing is too close so will act as non-hunting within 1 ring gear revolution. My test proved this to be true w\ the Richmond EXCEL 3.89 gears as marked pinion tooth came back within 1 tooth spacing off the marked ring gear tooth thru 1 ring gear revolution). These need timing marks to align the lapped gear teeth pairings back to each other whenever they're taken apart\reassembled or gear noise\whine is suspect regardless of being new or used or pinion depth\backlash settings.

    Semi-hunting:
    Ring\pinion tooth count do not have common whole number divisor factor, 1 side will be a prime number (thus no whole number divisor) but the other side will not be a prime number thus will have a whole number divisor so will have timing but will take more than 1 ring gear revolution to line back up due to the other having no whole number divisor thus no timed pairing (4.10 .... 10 pinion\41 ring, pinion has whole number divisor of either 2 or 5, ring is a prime number so no whole number divisor so pinion tooth will match back up to same ring gear tooth pairing over more than 1 ring gear revolution) OR as laid out in #2 example under non-hunting but the closest divisor pairings are far enough apart (2 to 9 for example) to force the ring gear to have to make more than 1 revolution to get back close enough to remesh in time w\ the pinion gear. These aren't as bad as non-hunting about noise when taken apart\reassembled but are still susceptible to gear noise so timing marks on these will help to align the lapped gear teeth pairings back to each other to prevent inducing gear noise.

    Full hunting:
    Ring\pinion tooth count do not have common whole number divisor factors AND both pinion\ring tooth counts are prime numbers so no whole number divisors so take many, many ring gear revolutions occurring for the same pinion tooth to come close to but never really line back up w\ the same ring gear tooth pairings it started out with during lapping so no timed tooth meshing occurs. These are the desired gears as they are the quietest by far & allow for looser setup. (3.73 .... 11 pinion\41 ring, no whole number divisors of either pinion or ring so no exact timing pattern develops during lapping so no timing marks are needed when taken apart\reassembled whether new or used).

    This is the main advantage w\ Ford OE or Ford Performance 8.8" gear sets vs aftermarket 8.8" gear sets outside of the gear tooth cut process used as Ford will not cut a non-hunting pinion\ring gear tooth count gear ratio for this 8.8" axle .... only either semi-hunting or full hunting pinion\ring gear tooth count gear ratios. This is why w\ Ford Performance there are only certain gear ratios they make available.

    In short, the pinion\ring gear tooth count that is used to make a certain gear ratio gear set is important to know to ensure that you're getting a quiet running, easy to work with (full hunting) set of gears .........

    The 3.89 gear ratio's pinion\ring gear tooth count is a Ford OE 9" pattern (Ford made several gear ratios for the 9" axles using non-hunting gear tooth counts in the past so they tried to not make the same mistake w\ the 8.8" axle) so aftermarkets adopt this pattern to the Ford 8.8" because it's an OE Ford pattern thus the whining issues. Some aftermarkets have fixed this potential whining issue (Motive Gear) by going to the 11 pinion\43 ring gear tooth count pattern to come up w\ the 3.91 gear ratio full hunting gear set .... and it is reflected in it's price (costs about $100.00 more than the Richmond EXCEL 3.89 gear set).

    This is why I made the recommendation to go w\ the 3.91 version of a 3.90 gear set instead of the 3.89 version IF a 3.90 gear set is desired.

    I learned all this too late for this round but will not make any of these mistakes anymore going forward as I now know fully what\how\why to look for & what\how to handle it. I know what needs to be done to fix this 3.89 gear set but it's really not worth it (break it in as best you can then when changing out the gear oil, check BL to see if it has grown from original set, if has then mark gear teeth & reset BL back to original setting to force gear teeth to lap more until they quiet up .... but if you've gone this far just swap out gear set w\ a known full hunting version, set them up & call it a day) so when the time comes to do this I'll have a set of Motive Gear's 3.91 ratio full hunting gears to install cause for a street use, not track use FBO NA 05-10 4.6L-powered S197 I find that these 3.90's IMHO are the best all around gear ratio to run as they fit my engine's TQ output curve to a T thru this Tremec 3650 tran's gear ratios on 26" dia tires so I don't regret going to 3.90's at all .... only regret getting this 3.89 ratio non-hunting version of 3.90 instead of the 3.91 ratio full hunting version. So after I take these 3.89's thru full break in to evaluate any resonance improvement then I will pull my FP 1-piece DS w\ the 2 Spicer 1350 U-joints (gear resonance turns this thing into a big megaphone) & reinstall my OEM 2-piece DS w\ the 2 CV joints & resonance deadened DS section between the CV joints to see if it will fully arrest any left over frequency to stop it from resonating into the cabin (1 of the reasons for this DS design by Ford as I found out later due to the stiffer S197 chassis being more susceptible to cabin resonance or drone if you prefer so anything that creates frequency\resonance attached to this chassis can get amplified into the cabin as a buzzing\droning type noise) since this is a "free fix" at this point & for cruiser duty don't really need the 1-piece DS but I'll keep it as a spare.

    Well I've read, I've studied so thus learned all I need to know going forward so will not get trapped again.
     
    Bullitt2954 likes this.
  18. GlassTop09

    GlassTop09 Member

    553
    203
    Here is a YouTube video of a rock crawler explaining issues concerning gear quality that I found to have some creditability thus something else to look out for:

    The Truth About 4x4 Gears - YouTube

    PS--Due to this video, I'm gonna back off the Motive brand & instead go w\ the Nitro Gear brand. Nitro Gear gives you all this pertinent info on their gear sets up front on their web site (all use the 5-cut face milled process, all gear ratios made for the Ford 8.8" axles are cut using either semi-hunting or full-hunting pinion\ring gear tooth counts just like Ford Performance does but Nitro actually gives the pinion\ring gear tooth counts info on every gear ratio they offer--they also make the 11 pinion\ 43 ring gear tooth count 3.91 ratio full-hunting Ford 8.8" gear set that I want & their installation instructions show clear, distinctive actual gear compound checking patterns based on the 5-cut process) & as the YouTuber posted, I've yet to find a bad review posted anywhere on the Internet out of at least 20 review videos I've seen to date from 10 different posters.

    I've come to suspect going forward any gear set that in their install instructions only says to use a pinion depth setting tool to set pinion depth.........if they have to use this tool there's another reason why they have to be set so accurately thus stay away......

    A big advantage w\ Nitro Gear that the others don't offer is that you can buy direct from them from their web site so can alleviate a lot of the current supply chain issues going on.
     
    Last edited: Dec 4, 2021 at 12:18 PM
  19. Midlife Crises

    Midlife Crises Senior Member

    1,117
    677
    Yep! The Yukon gears I installed in my 8.8 said Made in China right on them and they cost half agin as much as the Motive gears I replaced.
     
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