Vibration after th400 swap
12-01-2014, 09:54 AM
#1
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Vibration after th400 swap 2000 trans am with a heads and cam ls1 and a t56 spun a rod bearing on me. So i pulled the engine and tranny and replaced it with a 6.0 and a th400 from coan. long story short, after the swap I have a terrible pulsating vibration. It comes and goes depending on speed but above about 40 it is a fairly consistent pulsating vibration. The vibration is extremely bad and the car also broke a poly transmission mount. (ripped the stud out) I replaced it with a solid mount (I know this is not the correct fix but it keeps me from going through a tranny mount every 5 seconds) and the vibration feels worse which is expected when more of it is being transferred right into the body of the car. Heres a little background on the car.
Moser 9in rear end
Coan th400
UMI th400 cross member for 4th gen f-body
solid th400 transmission mount from jegs
new custom driveshaft (is correct length, has good u-joints, and the pinion angle is set correctly)
Umi tunnel mount torque arm (Spaced 1/2 inch down to allow clearance between driveshaft loop and driveshaft. torque arm was adjusted so pinion angle is correct)
umi torque arm mount & driveshaft loop
poly motor mounts
I did not just immediately post this thread. I have done endless searches and have been under the car trying everything i can think of to get rid of this vibration. The u-joints are good and the pinion angle is set correctly. I'm pretty much convinced at this point that this is not a drivetrain geometry issue. As far as i'm concerned there is no wrong answer. If you have any idea as to what it might be please post it. I am open to anything and any help is greatly appreciated.
Moser 9in rear end
Coan th400
UMI th400 cross member for 4th gen f-body
solid th400 transmission mount from jegs
new custom driveshaft (is correct length, has good u-joints, and the pinion angle is set correctly)
Umi tunnel mount torque arm (Spaced 1/2 inch down to allow clearance between driveshaft loop and driveshaft. torque arm was adjusted so pinion angle is correct)
umi torque arm mount & driveshaft loop
poly motor mounts
I did not just immediately post this thread. I have done endless searches and have been under the car trying everything i can think of to get rid of this vibration. The u-joints are good and the pinion angle is set correctly. I'm pretty much convinced at this point that this is not a drivetrain geometry issue. As far as i'm concerned there is no wrong answer. If you have any idea as to what it might be please post it. I am open to anything and any help is greatly appreciated.
12-01-2014, 11:20 AM
#2
A pulsating vibration is almost certainly a driveline vibration.
Common to see when transmissions are swapped.
You have to check your trans angle and the pinion angle.
What is the pinion angle and how are you checking it?
Trans angle?
Common to see when transmissions are swapped.
You have to check your trans angle and the pinion angle.
What is the pinion angle and how are you checking it?
Trans angle?
12-02-2014, 12:31 PM
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The trans angle is 2.1 degrees upward when compared to the frame of the car. The pinion angle is -3 degrees. (So down toward the ground). I am setting the pinion angle by putting my digital angle finder on the transmission and then setting it to 0. I am then going to the yoke on the rear end and setting it to negative 3 degrees. I have also set the rear end to 0 degrees (same angle as the transmission) using the same method since it is my understanding that this is the best case scenario for eliminating vibrations in normal driving conditions. This made little to no difference so i set it back to -3 degrees. Thanks for such a quick reply!
12-02-2014, 12:45 PM
#4
The trans angle is 2.1 degrees upward when compared to the frame of the car. The pinion angle is -3 degrees. (So down toward the ground). I am setting the pinion angle by putting my digital angle finder on the transmission and then setting it to 0. I am then going to the yoke on the rear end and setting it to negative 3 degrees. I have also set the rear end to 0 degrees (same angle as the transmission) using the same method since it is my understanding that this is the best case scenario for eliminating vibrations in normal driving conditions. This made little to no difference so i set it back to -3 degrees. Thanks for such a quick reply!
12-02-2014, 02:40 PM
#5
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There is a detailed article about driveline angles in this months issue of Chevy High Performance. It references a free iPhone app from Tremec, but that app requires iOS 7 or later. Nonetheless the article might be useful.