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Discussion Starter #1
I've been chasing driveline vibration for a while now!

Lowered the motor with RM mounts. Shimmed the trans up and added lowering blocks in the back. We're now within 1/4 of a degree driveline angle wise. It has a freshly balanced driveshaft with new spicer u joints. New yoke and trans mount when I put the T5 in.

I don't see anything making contact that isn't supposed to.

Rear wheels were straightened and rebalanced.

Rear end was rebuilt last december. However, when we changed the yoke on the pinion to accept the larger u joint this past week, it was noticed that the pinion support bearing had walked forward. Tapped it back into place and replaced the star clip. Didn't look like there was any damage. Didn't think to check it with a dial gauge for roundness.

The driveline angle sorting got rid of a bunch of vibes, but I still have one from about 60mph onward. It annoys me enough that I don't want to take the car on to the highway.

I'm in to see IWE about the rear end issue on wednesday, but I'm guessing that may not be the cause.

Anyone with any thoughts?
 

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were the RM mounts and T-5 put in at the same time ?

does the vibration intensify if you are in 4th instead of 5th at the same speed ?

have the axles been replaced and / or checked to see if they are bent ?


Z
 

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Discussion Starter #4
were the RM mounts and T-5 put in at the same time ?

does the vibration intensify if you are in 4th instead of 5th at the same speed ?

have the axles been replaced and / or checked to see if they are bent ?


Z
The RM mounts were installed after to get the pinion angles right and help clear the TCP monte carlo bar (AC compressor)

Vibration is the same in 4th or 5th. Clutch in or clutch out at those speeds.

I believe they checked everything in the rear end, but they were the original axles.
 

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55 to 60 MPH is classic bad tire resonant mode try swapping fronts to back etc... Good luck
Dobro, that was one of my first thoughts too. The rear wheels were taken to a wheel shop and straightened and everything been balanced. I've swapped front to back too without any luck.
 

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Check that pinion flange that it has no play. Technically you just can't replace the pinion flange and establish correct bearing preload unless you have a solid spacer. But if you have the more common collapsible spacer you only guesstimating. The collapsible spacer is a one time use.

The solid spacer torque is 175 ft lb, some guy's use 124-150 ft lbs for reusing a collapsible spacer. I would be willing to bet you have play in that pinion flange
 

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Discussion Starter #8
Check that pinion flange that it has no play. Technically you just can't replace the pinion flange and establish correct bearing preload unless you have a solid spacer. But if you have the more common collapsible spacer you only guesstimating. The collapsible spacer is a one time use.

The solid spacer torque is 175 ft lb, some guy's use 124-150 ft lbs for reusing a collapsible spacer. I would be willing to bet you have play in that pinion flange
You may be right. I'm curious as to why the pinion bearing had walked.

It now also sounds like the limited slip is doing funny things.
 

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Take the car to a shop that does "on the car" balancing and have the rears done.
The rear wheels were taken to Greens automotive that exclusively does wheel straightening and repairs and they're now straight as an arrow and well balanced.
 

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I was unable to solve 65mph up vibration until I put on new tires and rims even though I had the old combo checked and balanced. Given the power that you are making, a serious wheel and tire upgrade is way past due! Might want to throw a few Moser axles in as well for good measure.
 

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55 to 60 MPH is classic bad tire resonant mode try swapping fronts to back etc... Good luck
I "like" this for the reason, it's quite possible the rim, in a addition to the tire, is at fault too.
 

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Take the car to a shop that does "on the car" balancing and have the rears done.
I remember in 1980 working at a tire place in Ocala that did on vehicle tire balancing using the machine pictured below. While the electric motor was spinning the wheel at speed you would adjust using the 4 little round knobs at the end of the rim adapter the amount and position on the rim of the necessary weight by grabbing them with your bare hand while they were spinning. Looking back, that was friggin stupid! Hopefully the practice has advanced since then.
 

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I chased a vibration for a long time. I finally had a drive shaft made that was a little longer and solved the problem. How much slack do you have in the slip joint after you install the universal into the rear end yoke. It should not be any more than about 3/4". Just something else to check when all else fails. My driveline had been balanced and had new universals also.
 
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