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

    Here is a good picture of why you want to check the tooth count ratio of a gear set before purchase to make sure it isn't a non-hunting set if quiet gears are desired:
    Drive Side Paint 3D.png
    This is the Richmond EXCEL 3.89 non-hunting version of Ford 8.8" 3.90 gears (this set is using the Ford OE 9" 35 ring\9 pinion tooth count ratio) that I bought & had installed. This picture was taken while in process of doing the 500 mi break-in fluid changeout\inspection (gotta just love them Lube Locker diff gaskets......makes this easy) after initial install\2nd realignment.

    As you can clearly see, this area is where the installer applied marking compound to check pattern (residue of compound still on tooth crowns). Note how the wear pattern changed on the 2 teeth after the front 2 teeth in the circled area on the ring gear........the clear result of mismatched tooth lapping of ring gear teeth to pinion teeth due to inadvertently being installed out of time (no timing marks on pinion\ring gear teeth to realign the lapping) due to this particular specific gear ratio being a non-hunting gear tooth ratio (description in post #17) thus why this specific 3.89 gear ratio of the "Ford 8.8" 3.90 series" is usually a noisy gear set.......unless you get lucky & unknowingly install into the properly timed tooth pairings of both ring & pinion gears. This could also just be a bad gear cutting as well but if that is so, then Richmond's QA\QC is also poor\non-existent (they claim that EVERY gear set is lapped & checked for proper runout\operation before packaged for sale), so I'll lean on the advent of the non-hunting nature of this 3.89 specific gear ratio as the culprit for the gear whine.

    It's getting closer to the weather patterns getting tolerable enough to start the process of pulling these 3.89 specific gear ratio "Ford 8.8" 3.90's" out (Richmond EXCEL series 3.89 9 pinion\35 ring non-hunting gear set) & install the quieter 3.91 specific gear ratio "Ford 8.8" 3.90's" (Motive Gear F888390 3.91 11 pinion\43 ring full hunting gear set) to rectify the gear whine.

    You can also see how good this Lucas HP 85W-140 GL-5 dino gear fluid lubricates & holds up to fluid temps (notice on teeth what you see is where the teeth cut thru the phosphorus coating but hardly denting the teeth (had hardly any metal collected on the drain plug magnet.....also shows the advantages of running the Ford Performance Track Pack 8.8" Finned Diff Cover controlling fluid temps) so I reloaded diff w\ some Lucas HP 80W-90 GL-5 dino gear fluid to thin it down some when hot to see if this would help to promote gear teeth to mesh better. Noticed the gear whine did reduce more after fluid changeout so at least it is becoming more tolerable until I change them out.

    So, IMHO, you should not lump all 3.90 gear sets for Ford 8.8" axles & label them as bad or noisy.......just know what to look for when considering them to avoid the noisy ones.

    Posted for informational purposes.
    crjackson, MrBhp and dark steed like this.
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.