Tranny mount and pinion angle
11-14-2009, 01:56 PM
#1
Tranny mount and pinion angle I think I have every trans mount made for the A-4, stock, 1LE, anchor, energy-suspension and a couple are different heights, I think only the anchor is the same as stock, the 1le is a little taller and the ES is shorter, my tranny guru says it needs to be the same as the factory and the others he would not put on due to it changing the pinion angle...I can tell he is a bit on the **** side so is the pinion angle that critical? I get a nice double bounce or bump with the anchor on now during/after the 1-2 shift and when this happens it causes the dual exhause pipes to hit the bottom on the car, I assume it's the tranny doing this, I had the ES on for a short time and don't remember it doing this, just alot more vibration.
11-14-2009, 10:34 PM
#2
Transmission height is critical on f-bodies.
I can't tell you anything about other cars and their individual body alignment but I have had drivetrain issues ever since removing the stock A4 transmission mount and installing the Yank transmission mount with stock bushing. It appears the Yank crossmember isn't as high causing the transmission to hang lower when bolted to the bushing and Yank crossmeber. As a result the DS angle goes negative.
After hours of adjusting and measuring it still isn't perfect yet . At certain speeds it still sounds like a bucket of rocks under the car. The bucket of rocks sound is due vibration of the U joints because of the lower transmission height and driveshaft angle back to the rearend.
My installer (30 years of experience) almost refused to believe that just a half inch difference in height of the transmission would make that much difference in causing the front U joint to vibrate violently.
To determine the cause we mounted the car on a drive-on lift with the drive train loaded on stand s on the lift (a special lift). We were able to view the driveshaft rotating up to 80mph. Until we could see the vibration and hear it with our eyes and ears he swore the sound was from the rearend until we actually looked and could see the driveshaft vibrating at the transmission tailshaft.
BTW - a new PST 3.5 driveshaft with new yokes front and rear with a completely rebuilt Moser 12 bolt.
Just a simple 1 or two degree difference in pinion angle at the rearend would start the vibration. We could adjust the pinion anlge as the ds was rotating while the car was on the drive-on lift rather than road testing.
We settled at + 2 on the DS and 0 on the pinion angle giving us -2.
Just a 1/2 degree either way from -2 would start the vibration.
To get the least amount of vibration we had to raise the transmission 1/2 inch with spacers off the Yank cross mount. We couldn't go any higher because of the Spohn driveshaft loop (the loop is made for a 3 inch instead of a 3 1/2).
BTW - everything was perfect with no vibration - all same parts - until we installed the Yank crossmember (many dyno pulls and over 1000 miles of driving).
So to answer your question- IMO - transmission height in relation to the driveshaft and rearend on these cars is extremely critical to minimize driveshaft vibration and harmonics.
I'm putting the stock crossmember back on to test my theory and to get the tranmission height back to where it was before the vibration started.
Note: A4 is a new Performbuilt Level III - transmission rear seal is still good with no play.
Why did I remove the stock crossmount? I wanted to install a body mount torque arm to replace my Spohn adjustable 405 model which is noisey.
After the Yank crossmember install all of the driveshaft and rearend whining started.
I can't tell you anything about other cars and their individual body alignment but I have had drivetrain issues ever since removing the stock A4 transmission mount and installing the Yank transmission mount with stock bushing. It appears the Yank crossmember isn't as high causing the transmission to hang lower when bolted to the bushing and Yank crossmeber. As a result the DS angle goes negative.
After hours of adjusting and measuring it still isn't perfect yet . At certain speeds it still sounds like a bucket of rocks under the car. The bucket of rocks sound is due vibration of the U joints because of the lower transmission height and driveshaft angle back to the rearend.
My installer (30 years of experience) almost refused to believe that just a half inch difference in height of the transmission would make that much difference in causing the front U joint to vibrate violently.
To determine the cause we mounted the car on a drive-on lift with the drive train loaded on stand s on the lift (a special lift). We were able to view the driveshaft rotating up to 80mph. Until we could see the vibration and hear it with our eyes and ears he swore the sound was from the rearend until we actually looked and could see the driveshaft vibrating at the transmission tailshaft.
BTW - a new PST 3.5 driveshaft with new yokes front and rear with a completely rebuilt Moser 12 bolt.
Just a simple 1 or two degree difference in pinion angle at the rearend would start the vibration. We could adjust the pinion anlge as the ds was rotating while the car was on the drive-on lift rather than road testing.
We settled at + 2 on the DS and 0 on the pinion angle giving us -2.
Just a 1/2 degree either way from -2 would start the vibration.
To get the least amount of vibration we had to raise the transmission 1/2 inch with spacers off the Yank cross mount. We couldn't go any higher because of the Spohn driveshaft loop (the loop is made for a 3 inch instead of a 3 1/2).
BTW - everything was perfect with no vibration - all same parts - until we installed the Yank crossmember (many dyno pulls and over 1000 miles of driving).
So to answer your question- IMO - transmission height in relation to the driveshaft and rearend on these cars is extremely critical to minimize driveshaft vibration and harmonics.
I'm putting the stock crossmember back on to test my theory and to get the tranmission height back to where it was before the vibration started.
Note: A4 is a new Performbuilt Level III - transmission rear seal is still good with no play.
Why did I remove the stock crossmount? I wanted to install a body mount torque arm to replace my Spohn adjustable 405 model which is noisey.
After the Yank crossmember install all of the driveshaft and rearend whining started.
Last edited by dlandsvZ28; 11-15-2009 at 09:24 AM.
11-15-2009, 03:01 PM
#3
Wow...I appreciate the info, tells me quite a bit about what might be happening with mine, I have read that with the Energy Suspension solid tranny mount Not to use the spacer that comes with it...I wonder why, the ES mount is shorter without the spacer.