Vibration while decelerating?

[bavdrftr318]

Anyone have this issue before? When I lift off throttle and engine brake around a certain spot I'll get a harmonic vibration that can actually get pretty rough at times. Driveshaft was just replaced along with the clutch and flywheel. The diff that I'm running def has a little bit too much lash. Has anyone had diff issues that made this happen?

[5mall5nail5]

Yep - I run UUC racing trans mounts, when the trans moves just right, the vibration is more noticeable. Check your transmission mounts.

[bavdrftr318]

This is more of a substantial vibration... like shakes the whole car. Not just a trans issue.

[milKt]

What is lash? Define
How does one know they have it?

Any diffs I've experienced made more noise when out of load (decel or between gears)
but no vibrations.

[5mall5nail5]

This is more of a substantial vibration... like shakes the whole car. Not just a trans issue.

Yes. Check trans mounts.

[bavdrftr318]

Yes. Check trans mounts.

They are brand new UUC red bolt through with like 100 miles on them.

The diff has lash meaning there is too much play in between the gears. When I turn the input flange by hand there is play.

[DieselGhost]

I'd shoot for the differential being shut if you have loads of play... this can cause vibrations... when decelerating / engine braking...

Although UUC trans-mounts are stiff and could cause minor vibrating feel...

if the whole car vibrates.... i'm betting on the differential...

[marc1119]

Yes. Check trans mounts.

+1

[milKt]

Over-torqued or pre-loaded UUC trans mounts (w/ enforcers) cause vibrations.

also

the red UUC mounts are KNOWN for some good quality vibrations.

[bavdrftr318]

These vibrations shouldn't be enough to shake the seat, steering wheel though should they? When I free rev the car I get a little vibration which I feel like IS because of the red mounts, but the decelerating vibration is pretty substantial.

[m3leistung]

You mentioned changing the driveshaft, clutch, and flywheel. Did the guibo get changed out? When mine went bad, same symptoms: When engine braking after letting off (became more frequent the worse the guibo got), in certain spots in the rev range, it would have very harsh, violent vibration that would shake through the whole car and when accelerating (only sometimes though) it would have light vibration.

So, check the guibo if it hasn't already been replaced recently.

Oh, and was this car at Technica last weekend? I looks identical to the one I saw. I think it was the same car, and it was superclean. Have fun with it!

[5mall5nail5]

These vibrations shouldn't be enough to shake the seat, steering wheel though should they? When I free rev the car I get a little vibration which I feel like IS because of the red mounts, but the decelerating vibration is pretty substantial.

Yes. The red mounts with thru bolts with or without aluminum cups will transmit a lot of vibration through the car. If you over torque its REALLY noticeable.

[bavdrftr318]

You mentioned changing the driveshaft, clutch, and flywheel. Did the guibo get changed out? When mine went bad, same symptoms: When engine braking after letting off (became more frequent the worse the guibo got), in certain spots in the rev range, it would have very harsh, violent vibration that would shake through the whole car and when accelerating (only sometimes though) it would have light vibration.

So, check the guibo if it hasn't already been replaced recently.

Oh, and was this car at Technica last weekend? I looks identical to the one I saw. I think it was the same car, and it was superclean. Have fun with it!

Interesting thought. Pretty positive it was just the guibo that was still attached to the driveshaft I picked up. Def something to look into. Thanks for the help!

Yes. The red mounts with thru bolts with or without aluminum cups will transmit a lot of vibration through the car. If you over torque its REALLY noticeable.

How do I know if they are over torqued? Do these have tq specs or is it just a tighten by feel kinda thing?

[BadBoostedBmwM3]

What about the CSB?

[bavdrftr318]

Could be, I think it's in pretty good shape though...

[milKt]

How do I know if they are over torqued? Do these have tq specs or is it just a tighten by feel kinda thing?

16 ft/lbs is the UUC suggested torque value for their trans mounts with enforcers, I believe.

"Option 2 - street cars that see heavy track use, dedicated track cars:

Red urethane isolated transmission mount bushings, which are replacing our previous-style red neoprene. These are fully isolated, having two seperate mounting bolt hardware pieces embedded in the material just like the black neoprene and OE BMW bushings. The urethane is a higher durometer (stiffer) material than the neoprene and offers nearly the same drivetrain motion control as a solid delrin or aluminum mount, but with significant vibration isolation. That last detail makes it a better choice for a track car that is occassionally street-driven, where cabin noise is a concern. While UUC does expect some vibration transmitted into the cabin, initial user reports say that it is minimal and certainly acceptable."

[YellowBed]

what happens when you torque them over 16ft?

[YellowBed]

what happens when you torque them over 16ft?

[hail2m]

please forgive the thread revival...

bavdrftr - did you resolve this vibration? what was the fix? guibo?

[bavdrftr318]

Actually no it's still there . The only thing that haven't been changed out is completely is the transmission now, which I feel shouldn't have anything to do with it

Had two driveshafts, two diffs, 3 sets of axles, 2 guibos, 2 center support bearings. Only other place it could be coming from is the clutch/flywheel, or the motor itself.

I still have the vibration that is fairly noticeable when free revving the car with the clutch pushed in around 2.2k rpm. I'm lost.....

[pbonsalb]

Could something, typically exhaust but possibly other things, be touching the car body or a subframe or a brace during these conditions? How much clearance do you have around everything under the car?

[95Alpine3]

I have a slight vibration around 2k as well. But only if I hold it there out of gear. I don't have any vibration when decelerating. It sounds like you may have 2 problems. The slight vibration at 2k wouldn't bother me. I don't really give mine too much thought.

Just a shot in the dark here. Are you sure you don't have out of adjustment park brake shoes. Sounds funny but I had a car that would shake real bad when decelerating and that's what it turned out to be. They were partially locked and the P. brake drum was warped. This combined to make a "rattle the interior" kind of vibration.

[bavdrftr318]

Just swapped spindles out back so new p brake everything and the issue is still the same.

Nothing touching the car underneath that isn't supposed to....

[dinanstu]

Did you check the clutch/flywheel combo? It may be worth it to have it removed, inspected and balanced...

[killaM3]

it might be silly, but front control arms bushings and balljoints are known to cause vibrations on braking when they are on the way out. check that.