Pinion angle and drivetrain vibration

-
73SwingerBuild

73SwingerBuild

Well-Known Member
Joined
Feb 22, 2010
Messages
1,004
Reaction score
43
Location
Rhode Island
Hello all.

I've been trying to diagnose a drivetrain vibration that I've had and I think I've narrowed it down to the pinion angle. The vibration only occurs >50-55 mph and gets worse with increased speed, so I know it's not RPM dependent. I took it to a local tire shop and they test drove it and confirmed that it was definitely not a tire issue. However, they wouldn't diagnose it further because it was a "race car" (73 Dart 340 4-speed, 8-1/4" 3.55 sure-grip). I went to a driveshaft company nearby and had them balance the driveshaft and check the ujoints. He said the ujoints were good and the shaft was straight and balanced it. After having the shaft balanced, I still had the same vibration.

I bought a magnetic angle tool and checked my engine, transmission, driveshaft, and pinion angle and found the following:

- Engine (and secondary measurement on transmission): +1* up towards the rear of car

-Driveshaft: -1* down toward the rear of car

-Rear end pinion: -1* down towards rear of car

I know that having the rear pinion and driveshaft at the same angle can definitely cause a vibration. I have read a lot of forums on here and it appears that the pinion angle should match the angle of the engine. To that effect, should I purchase a set of 2* leaf spring shims to bring the rear to +1* towards the rear and should that fix my issue? I've read about "pinion angles" needing to be 3*-4* depending on application. So with the -1* driveshaft and the corrected +1* of the pinion (after I put the shims in), I'd have a 2* pinion angle. Will that be enough?

Thank you all in advance for reading. I know this is lengthy, but it's been driving me nuts and I just want to drive my car on the highway.

-Mike
 
Where are you checking this at? I usually check at the balancer or pulley with straight edge and front of pinion yoke with driveshaft removed both vertically. Driveshaft is not checked has no meaning your looking for the crank and pinion to be the same angle pinion angle up vibration on acceleration down on deceleration
 
Your description is fuzzy. Are you saying that the pinion pointing towards the engine is UP?

-Rear end pinion: -1* down towards rear of car

is what you said...........

What I understood from that is that both the trans and pinion pointing at each other are up?

Don't worry about the driveshaft. Pick a reference like "level" and compare the trans and the pinion. The two of them need to be as close to parallel to each other as possible when under hard acceleration.

When at rest, the pinion FRONT point towards the engine needs to be "down" in relation to the engine / crank/ transmission centerline
 
I know someone already posted on here about the app from Tremec that is used to check driveline angles. It gives you step by step directions. The first measurement is at the back of the engine or bell housing the second measurement is the driveshaft angle and the third is the pinion angle with those measurements it will give you which angle is wrong and how much needs to be changed.
The app is a free download to your smart phone. It works great and has several other features that could be help full. Good Luck on finding your vibration hopefully this is some help
 
Thank you all for your replies.

The Tremec app sounds good if you have access to the bell housing. My engine and transmission are obviously installed and I'm not looking to pull either, so I'm not sure how'd I'd get in there to measure.

I picked "level" as a datum, so those angles are all +/- degrees from dead level. Not sure if that helps my explanation.

To answer one question, yes, the transmission is pointing "up" (front to back) and the pinion is also pointing "up" (back to front).

The vibration occurs under acceleration and deceleration, or even keeping the same speed. It may be a little worse under deceleration, but I can't quite tell.

I'm going to order the Mopar 1*, 2*, and 3* shim kit. It sounds like I need to point the pinion "down" towards the front of the car by 2-3 degrees to match the engine/transmission angle.

Hope to report back with positive results.
Thanks again, and feel free to comment with any additional thoughts.
 
The app is works with the engine and transmission in the car and all the weight has to be on all 4 wheels. You just need flat surfaces like the bottom of the oil pan or the back of the engine. With this app it should only take you 5 mins to find out were your problem is but if the engine and transmission are both angled up and the pinion is up you will not need an app for that most of the time I set the engine and transmission down about 1 degree and on an automatic the pinion is down about 2 degrees and with a stick down 4-6 on a leaf spring car so on acceleration the pinion moves up so the driveshaft is just about straight. That seems to work most of the time if you have ladder bars you can set it were you want it because there is no pinion angle change on acceration but you never want the pinion up it puts the u-joints at an extreme angle which will lead to driveshaft failure.
 
Sounds to me like you need more like 4 If I read that right..... You need the two parallel when under hard power, not when parked. Most recommend something like "2 down" that is the pinion 2 down from the transmission when parked. you are? measuring this with weight on all the wheels, and really, should have a tank of fuel and maybe even a "driver." In other words, "as would be" set to go down the road

You say the transmission shaft points up 1, and (to re-word) the pinion points up 1. To get them parallel means the pinion must go down 2, but that is PARKED. The pinion is going to go up more under power, so you should "start with" adding 2 more I would think
 
Based on what I've read, I believe you're correct 67Dart273.

I picked up some 2" wide 4* shims today and will be putting them in this weekend. 2" seems narrow, but I suppose as long as they're flat and allow the centering pin to reach the leaf spring mounts on the axle, it should work?

Wish me luck, and thanks again everybody.
 
They cannot be so wide that they'll interfere with the U bolts, but if too wide you should be able to cut them down.
 
You must log in or register to reply here.
-

Back
Top