Drive Line Harmonics

[2008 V6]

I need some help – Mental but I only care about solving my cars woes now. Most sane people would have thrown in the towel but I have a disorder in not letting a problem go unsolved and it is really bugging me.

2008 V6 Mustang, T5 trans, Astro gear cluster & shaft with 0.8 fifth gear, 8.8 rear end, Torsen T2, 4.1 gear with a Moser 1350 yoke. This vehicle was setup to run in NASA TT events & not completed because of driver & driveline problems.
I swapped the trans, drive shaft, flywheel, pressure plate and rear end at the same time. At a driveshaft rotational speed of 5035 RPM - 95 MPH, we had heavy driveline vibrations.
I pulled the driveshaft out and had it rebalanced. It was out of balance. The vibrations remained - Now kicking in at 5300 RPM – 100 MPH.
I replaced the upper rear control arm with an adjustable one (Heim Joint chassis, stock rubber in differential) and new lower control arms (Stock length with poly bushings) to improve pinion angle.
Now the pinion angle is within 1.5 Degrees – No more adjustment in the upper control arm- not much change.
I was given an aftermarket engine cradle to drop the engine 0.5” and I shimmed the transmission up .1875” - Now the pinion angle within 1.0 degree. I spun the drive shaft myself on a friends machine using dial indicators to check for run out. No run out at 3500 RPM. Vibration now kicks in at 5560 RPM – 105 MPH.
Purchased a helm-jointed rear adjustable lower control arms. I was able to adjust the pinion angle to 0.0 degrees but the lower control arms were short and the bump stops didn’t line up. Pinion angle now 0.0 degrees at ride height (Rear pinion parallel with trans). The vibrations are now at 5830 RPM – 110 MPH.
Purchased a modified part to lengthen the upper control arm and I re-adjusted the lowers to stock length – Stile 0.0 Degrees pinion angle at ride height – Pinion is parallel / in line with trans at ride height.
I called a very good friend of mine to ask for his opinion. He wanted the car because he was having similar problems with a customer’s / project 2006 V6 Mustang. He swapped parts between the 2 cars – no luck. He checked the rear end pinion, ring gears and axles for run out and back Lash on my car with dial indictors– They looked great.
Both cars had drive shafts from the same manufacturer. He pulled both drive shafts and went to his go to Drive shaft shop.
My friend gets a call from a writer / friend looking for filler space for his series in car Magazine. I worked with the writer years ago when he wrote for magazines doing various articles for cars I worked on. He’s a good guy so I told my friend they could use the car for the needed filler space. The new drive shaft shop makes a 4” drive shaft – very nice unit. My friend puts the driveshaft in his car and tests it up to 140 MPH - 6500 RPM shaft speed (27” tire 3.73 gears) - No noticeable vibrations (Soft rear suspension bushings). They call it a day and the article went to print.
My problem 26.2” tire 4.1 gears. I stile see heavy vibrations with the 4” driveshaft at 115 MPH 6049 RPM shaft speed (Solid bushing rear connections - Heim joints ) which are not masking the problems but possibly enhancing them.
I pulled the trans, flywheel and pressure plate and replaced them with loaners just to make sure they were not contributing to the problem - No change in harmonic vibrations.
I purchased a driveshaft 3.5” OD using a CV Joint instead of the common commercial slip joint - Very nice driveshaft but no change. I installed hub centric rings for my lug centric wheels – no change.
I tested at Auto Club / Fontana Speedway a few weeks ago and ran the car up to 125 MPH to see if the harmonic vibrations would cancel out – 6575 rotational shaft speed. The vibrations got aggressively worse.
The car has been sitting since Auto Club – I am at a loss as to how to correct the problem. This has to be basic – What am I missing?
I’m open to all suggestions – Any & all advice would be appreciated.

 

[ArizonaGT]

You want a -1.5 to -2* pinion angle to account for the rear axle torque pointing the diff "up" under load/throttle.

 

[sheizasosay]

You are certain the axle bearings are good?

 

[2008 V6]

You want a -1.5 to -2* pinion angle to account for the rear axle torque pointing the diff "up" under load/throttle.

Thank you mostly solid rear bushings very little axle - pinion rise /rotation. I've tried everything from -2.0 to +2.0 at .02 degree variance.

 

[2008 V6]

You are certain the axle bearings are good?

Thanks
Axle bearings all good.

 

[2013DIBGT]

Is it safe to say that the only thing that has remained constant during the various configuration changes is the rear end itself?

out of curiosity, have you tried removing the rear wheels with the car on VERY sturdy jack stands and ran it up thru the gears to see if the problem is still there?

It may take some bravery (or a camera) but it would be nice to either find someone willing to poke their head under the car while doing the above mentioned test to see if you can spot the excess movement sourcing from a single point as you approach the problem RPM or Speed.

Is it possible that the new rear end was gently dumped on its output flange during assembly or in transit potentially knocking it out of whack not visible to the naked eye but just enough to be the culprit?

 

[2008 V6]

Is it safe to say that the only thing that has remained constant during the various configuration changes is the rear end itself?


Thanks - I agree - But -
Rear end seems to be fine – Checked pinion flange (Moser using a 1350 spicer u-joint), axles, pinion gear & ring gear for run-out with dial indicators. 3+ competent people were present during the examination. I didn’t build the rear end nor was I present during the evaluation.
It isn’t the engine – No discernable vibrations up to 6000 RPM. The car was run on a dyno to verify the vibrations were coming from the back ½ of the vehicle.
My friend wants to put on a dyno and hook up a strobe light to check each components vibration (Have you ever tried to dial in a strobe light (MAJOR PIA + days of work) I’ve never had to pay for dyno time but I can’t screw the shop out of $$$ for the amount of time I think will be necessary. Everyone has too eat no matter how interesting they think a problem is. For a street car /wife’s beater, I really don’t want to sink another $5000.00 + into it but I can’t seem to let a problem go unsolved. The dyno shop & my friend have strobe experience diagnosing and developing valve train components for a local cam manufacturer.
The reason I posted here is because in my experience, a group of people, can look at a problem but can’t see outside of the box. When shown to others looking from a different perspective, BANG Problem solved.
I had another friend send a variation of the original post to his contact a Ford Racing and I was told by another that the new Mustang even with a CV is having similar problems (? IRS rear WTF). An outside source working on the problem - this was 2 or so months ago.
At this point. I feel like a frigin Idiot but solving a problem is more important to me at this point.

 

[sheizasosay]

Tire/wheel balance been checked? I know, I know.....just asking.

 

[2008 V6]

Tire/wheel balance been checked? I know, I know.....just asking.

Thanks - Yes - Multiple times and several sets of tires.

 

[2013DIBGT]

Sounds like a bear of an issue to deal with. Given the fact that the rear or some component inside the pumpkin were the only things that have remained the same during this whole ordeal it would be hard, at least for me, to ignore it as being a potential culprit despite what ever testing was done while it was still assembled.

It's interesting that the point of vibration has progressively moved "UP" in RPM throughout the various stages of testing. I'd be curious to know the weight difference between the various driveshafts that have been tried? If each one was slightly lighter then the one before it an interesting test would be to see where the vibration begins if you were to use a carbon fiber DS instead (assuming you haven't already). I wonder if in doing so you could make the problem "go away" so to speak by moving the vibration higher then the Redline of the car so that you would in effect move it away from concern. Certainly not a fix but sometimes its just easier to deal with an issues just enough so it can be swept under the rug if you know what I'm saying.

 

[sheizasosay]

You changed a lot of things at one time. I would be trying to positively isolate each new component that you added on a different, known "good car". Starting with the easiest one to do. Everything that has changed since the start of the problem has to be suspect within reason.

 

[2008 V6]

Sounds like a bear of an issue to deal with. Given the fact that the rear or some component inside the pumpkin were the only things that have remained the same during this whole ordeal it would be hard, at least for me, to ignore it as being a potential culprit despite what ever testing was done while it was still assembled.

It's interesting that the point of vibration has progressively moved "UP" in RPM throughout the various stages of testing. I'd be curious to know the weight difference between the various driveshafts that have been tried? If each one was slightly lighter then the one before it an interesting test would be to see where the vibration begins if you were to use a carbon fiber DS instead (assuming you haven't already). I wonder if in doing so you could make the problem "go away" so to speak by moving the vibration higher then the Redline of the car so that you would in effect move it away from concern. Certainly not a fix but sometimes its just easier to deal with an issues just enough so it can be swept under the rug if you know what I'm saying.

I never had the stock car past 80MPH. I bought it and swapped out the drivetrain. Suspension was left stock at the time as a learning tool for the wife.

Agreed - I suspect the rear also But I've also suspected and replaced just about everything else so far. Everything I was planning on upgrading anyway within the rule set for the class I wanted her to fall into.
I haven't built a rear end for many a moon. Most of the parts for this one were donated or purchased for pennies on the dollar. Everything new accept for housing, axles & pumpkin. I had the axle tubes welded by the same shop that built it - Local shop. I was planning on shortening the rear in the future to run a much wider square tire set up. I had my friend check the 8.8 rear with his go to group and they said it was set up well. Between all of them, I don't see how they would have missed anything - (2 different groups / shops)
I have the stock rear end 7.5 and stock driveshaft. I'll install it and put it on the dyno so I can run it up to speed - 3.25 rear ratio. I'll check the 8.8 myself but will have to buy a tool to check run out for the pinion flange - something that bolts to the u-joint cup.
I'm going to take a much needed vacation this week end so I won't be responding until next week.
I appreciate all the input from everyone.

 

[2008 V6]

You changed a lot of things at one time. I would be trying to positively isolate each new component that you added on a different, known "good car". Starting with the easiest one to do. Everything that has changed since the start of the problem has to be suspect within reason.

Agree - Most pieces were swapped between 2 cars accept the axle because of Moser Flange.
Not real smart of me because if it brakes, I can't run down to the local Autozone and buy a replacement if I was at an event. I'm usually smarter than that but the flange was just about free - and it used a 1350 Spicer rather than a 1330.

 

[2008 V6]

Update –
I haven’t done SHT – Work 10/6-7. The car has been sitting on a lift since Auto Club. My wife was pissed because it is her daily driver but she commandeered my new travel / light tow vehicle and told me to keep the Mustang as long as I want. (What have I Done -2014 F150 Raptor)

So - I have 3 choices -

(1) Approximately 3 – 5 days FCK time. – Swap Stock 7.5 rear end & driveshaft, dyno to 145 MPH = 6157 RPM (Driveshaft rotational speed), check for harmonics, check / fix possible out of sync 8.8, reinstall 8.8 & driveshaft.
(2) Approximately 2 – 3 days Pull Moser 1350 spicer pinion yoke. measure crush sleeve dimensions, make new billet sleeve matching crush sleeve, install stock 8.8 pinion flange & torque into place, use friends custom driveshaft – proven good, Dyno Test & diagnose car for vibrations. Put original SHT back.
Both these options possibly could find the source of the problem. Your guess is as good as mine
(3) – Beat car of the rest of this year as original planned and convert it back to a 100%
daily driver for the wife.

Track options for the rest of this year -

Auto Club (Kinda boring for me doing HPTDs) the only part of the track I like is turn 13 through 19 depending upon cone layout – Turn 13 & 14 wheels +6” off the ground depending upon how aggressive a line one chooses to take. Between turn 17&18 (Off Preferred Line but much faster) if you want to contend with a big bottoming out low spot and marbles which will cause my car to slide / drift several feet – 1 to 5 seconds faster because you carry your speed for ¼+ of the track. Most of the marbles will be cleaned off your wheels before you enter turn #1. Turns 1 & 2 Insanely fast – Depends upon aero and how light the rear gets. I Held 125MPH constant one lap to see if anything would let go. I didn’t even use the banked section but stayed in the marbles on the lowest flat section of track out of the way but the shortest possible distance traveled. No problem at all - even with my car vibrating to SHT.

Button Willow (I like this track a lot) – Any configuration - I don’t think I will see above 115MPH.

Streets of Willow (I like this track) Same as above.

Big Willow – (Kinda boring track, high speed, easy to learn) 8 & 9 fastest areas would be a problem for me because – Make a mistake / Anything lets loose and a high probability of rolling. I don’t need to run here this year

Chuckawalla – Never run there but I’ll try it this year. I’m told a higher speed track and the track map looks Challenging.

Other tracks I like Laguna Seca, Sears Point, Thunder Hill & Portland – Too far not to tow – no trailer this year – taxes coming up.
My decision / time and cost efficiency at this point - Beat the car though this year and have fun. Solve the harmonic issue when I have more free time. Most free time I’ll be in HPTDs or servicing my wife so I can get my travel / light tow vehicle back at the end of the year.
Signed up for Button Willow CCW15 - 9/21/14.

 

[Mike Rousch]

I did not read everything in the thread so i may have missed something. I have seen this a few times on 05+ cars. First put your stock drive shaft back in, 99% of the time that will fix your issue. If that does not fix the issue take some gear out of the car to slow the shaft speed down ( I know both the above are a step backwards, but that is what its going to take to fix your issue ).

 

[Department Of Boost]

I saw that article in HRM. I thought a few things were overlooked.

On pinion angle. What are they right now.

Is the front pointed "down"? How many deg?

Is the rear pointed "up"? How many deg?

 

[Mach2burnout]

What about that one stock bushing you left in the UCA mount on the rear end? They are known to be problematic and wear out after hard launches, etc. have you checked it or replaced it with a better bushing? Could make it worse, but it's one variable you haven't considered. Also, I had to loosen my engine mounts and pry the engine over to the right slightly to get the vibration out of mine.

 

[dream07]

The s197 has a few known issues and this is one of them. I think you should accept the high shaft speed issue (from your 4.10's) and gear swap to a 3-series gear (3.73 is available cheap from Ford Racing also 3.55's). Personally, I would run 3.55's and get rid of the whole problem. The car's performance won't be that much different and now that you swapped in all of those high quality parts, you should be able to run that car up to its aero-limited top speed without issues.

Look at your friend for example, he has a taller tire and 3.73's and no vibrations. You have a shorter tire (making the effective ratio even past 4.10) and 4.10's. Please, swap in the 3.73's or 3.55's and enjoy your car, like your friend.

 

[2008 V6]

2013DIBGT – I agree – Moving the operational speed of the driveshaft out of the vibration range is the next step after testing the stock 7.5 rear & driveshaft up to a similar rotational speed and checking the 8.8 myself.

Gmitch – I don’t remember off the top of my head (Not in my notes either) how much the trans is pointed down or the rear is pointed up at ride height. The rear pinion is currently at 0 degrees – Meaning it is pointing up to the transmission exactly equal to how much the trans is pointed down at ride height / parallel. This worked best for my application. On gas, of gas & cruse. This showed the least vibration. I tried everything from -2.0 degrees to +1.0 degree. I posted earlier +2.0 but was too lazy to change it. Marlin the author of the article is a good guy. I’ve known him for about 25+ years but he made several mistakes in his article. I got a pre-print but didn’t say anything because what was printed sounded better. Just like the Internet 50% +/- can be considered for advise. Most of what was done is stated in my first post.

Dream07 – That is the next step after a final check of the current 8.8. I estimated RPM, Tire size and final achievable HP of my platform to the tacks I am familiar with - This is how I chose the 4.1 axle ratio.

Mike Roush – I wasn’t comfortable with the stock driveshaft. If I completed the car, the driveshaft rotational speed would be up around 7,600 to 7,700 RPM using a P295-30-18 Hoosier A or R on a square 11” rim setup. The current driveshaft even has a CV and was tested to 9000RPM by the manufacturer.

Mach2 – Rear rubber diff bushing is good. I stopped developing the car. The suspension plan was to lower 3.25” to 3.5”(Depending upon final ride height) and lengthen rear Panhard bar set up parallel to ground at ride height / 3.3 to 4 lbs max increase over the stock panhard bar, lower rear lower control arm pick up points (Depending upon final ride height), replace rubber diff bushing with a solid, replace front lower control arm bushings to solid and install decent coil-overs. Most of the pieces on the car now would have been sacrificial – Wife’s learning tool / daily driver. I can design and fabricate most things given I invest the time. One thing nice about the S197 platform is that most things can be purchased cheaper than it is for me to make. No reason to re-design the wheel for most parts.
The driver / my wife lost interest in racing (She got scared) so I thought I would drive the car the rest of this year to get my legs back. I was SCCA & IMSA licensed and have some seat time just not current. I am now a hazard on the track and need mucho, mocho seat time to become competent. My skill level just isn’t there any more. If I were to be in traffic, it is just not fair to other drivers at this point.

Thanks to everyone for your responses. I have way too much time with this issue but I am exceedingly Anal Retentive and have a difficult time in letting things go / Not being able to solve a problem. I will address this issue but will drive the car for now because my free time is exceedingly limited.

 

[2008 V6]

Button Willow 9/21/14 CCW#15 – Very fun & fast configuration. Faster cars should easily see +150MPH at the end of the drag strip before braking into Riverside – a sweeping left-hander.
My day was cut short unfortunately. I ran in the Blue group / follow the leader session to become familiar with the track and then ran in the Black Group – Intermediate group / point by passing only. After the first session, I was starting to learn the configuration. Second session first 2 laps trying bring the tires & car up to temp – Very heat cycled tires. 3rd lap – the car feels a tad loose – thought the tires were taking along time to come up to temp. 4th Stile a bit loose but I thought I would push it though the sweeper leading into the drag strip and see what kind of speed I could reach before braking into Riverside – Fast sweeping turn. After pushing it though the Sweeper leading up to the Drag Strip, the back end is a bit loose and I put ¼ to a 1/3 of my right rear tire off the track onto the dirt, accelerate up to about 124+ and brake down to 110 to enter Riverside and OOOOOH the rear end is real loose and wants to come around. I figured I was loosing air in the right rear because I put part of the tire off & cut it. After riverside, there is a short straight section you drift though setting up for Truck Stop. (Nope not a flat tire) – Some Dip-Shit must be pissing fluid onto the track but I can’t see any sheen on the surface and no flag from the prior corner worker. I enter truck stop at about 80+ and WOOOOOOOOW my back tires are on ice – nothing – something must have broke but no bang clunk / anything. I scrubbed speed and took Bus Stop trying to stay off line down to ½ speed and the back half of the car is sliddin on ice. I tried to stayed of line, put my arm out and putted to the pits. I have oil pressure, Engine temp fine, no smoke, no smell, no clukin -WTF.
I pull into my spot, popped the hood and low & behold – I’m the DIP-SHIT PISSIN 50% water and 50% radiator fluid – Misting enough to wet my rear tires but not enough to wet the track and screw everyone else. Street car - radiator fluid - I know better.
I lost almost all of my fluid though 3 laps. I spent the next 4 hours pulling the POS injection molded thermostat housing, gluing with 5 minute epoxy and drilling extra screw holes to hold it together – Crack made bigger by me pulling it out. No good – Leaks like an Elephants dick when he’s in rut even with the thermostat out and pressure cap removed. I loaded up, fired the car up, sped up to 10MPH, shut off and coasted out of Button Willow Raceway. I repeated this procedure but up to a higher speed until I reached the on ramp leading to the Freeway home - almost a mile. I then called AAA for a tow home 140 miles to Los Angeles. 100 miles covered by service - 30 miles at $6.00 per mile and 10 miles free. I bought the tow truck driver a Subway Sandwich when he stopped for gas.

For those of you who actually read my rant, I have not diagnosed the vibration problem yet or checked the rear end. When I ran the car up to approximately 124+ and braked to 110MPH the vibration wasn’t enhanced –
At Auto Club I brought the car up to 125 and held it though all of 1 and 2. (Holding it at speed) Was worse than accelerating and decelerating. The harmonics were enhancing themselves at a constant speed of approximately 125MPH. Accelerating and decelerating / The rear pinion was loaded & moving up and down. During Dyno-testing, the speed was held constant also. I have to think about this.