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Driveshaft pinion angle help needed

pearljam724

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When I bought my car, it had bad rear springs. I addressed that soon after I bought it. It rides, drives incredibly smooth and quite as far as vibrations, etc. With exception I get a very small vibration in the tail shaft when I hit 65 mph or hammer down at slower speeds on occasion. Without a doubt, it’s coming from the driveshaft. Because I can see that it tickled the drive shaft tunnel. The motor mounts are brand new and tranny mount seems pretty descent. The U-Joints are brand new and the vibration was there before I replaced them.
I realize the driveshaft could use balanced or bent, yoke could be issue or tail bushing.
Regardless, I know the pinion angle is off a half inch or so in angle at front of drive shaft and the rear is pretty darn close to being perfectly straight. This is with weight on the wheels. I think it’s off enough when the car squats a tad in the rear under acceleration, it’s causing vibration. I need advice on how to straighten pinion angle at front. Can I slightly raise front of engine to drop tranny at the tail ? Is there a way to drop the tail housing by other means ? Drop the tranny crossmember ? Unless, the driveshaft is bent or out of balance. Or yoke is bent. I’m sure the pinion angle needs addressed. Because, visually looking at it in the front. And there is zero slop or movement in the driveshaft or yoke when I grab it. That eliminates the bushing too I believe. That and it doesn’t leak. Any advice or know how to address front pinion angle based on my information would be appreciated.
 
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If something was bent it would do it all the time you would think.

Here’s what I would do - confirm your suspicions and measure. Tremec has a mobile app that uses your phone as an angle finder. It walks you through the measurements. If you come out with any red values, you know where the problem is.

Is this a stock setup or a modified car?
 
If something was bent it would do it all the time you would think.

Here’s what I would do - confirm your suspicions and measure. Tremec has a mobile app that uses your phone as an angle finder. It walks you through the measurements. If you come out with any red values, you know where the problem is.

Is this a stock setup or a modified car?
I agree, I ll look into the app. It’s a stock car. But, the rear ride height may be slightly higher now than when it was originally made. How do I find out the factory angles ? Is it in the manual ? I don’t think it’s a question of it being off in the front, even though it’s not drastic. I just don’t know how to address it best ? Something ain’t right, that would cause the driveshaft to tickle the driveshaft tunnel and vibration I mentioned. In between it vibrating at 65 ever so slightly and very hard acceleration. It’s quite as a church mouse.
 
So your car squats at the hit,does it stay squat or lifts when you hit 2nd?:fool:
It’s an automatic. I stated it squats, simply based on all cars squat under harder acceleration to some degree. If a small block is cruising at 65 and you have to accelerate hard enough to maintain that speed climbing long/gradual steep mountain inclines. It’s squatting to maintain that speed. It may not be noticeable. But, it is.
 
Just a thought is the perches square to the springs. Not rolled up on either side. This would cause a rocking on acceleration and if it is on the power side of the diff can cause vibration. Just a thought.
 
Just a thought is the perches square to the springs. Not rolled up on either side. This would cause a rocking on acceleration and if it is on the power side of the diff can cause vibration. Just a thought.
Thank you, I don’t know. But, I will look at that. I once had a pickup truck that did the same thing. Never made a noise until 55. Then it vibrated like hell. Sold it, the guy who bought it said the drive shaft was bent. So, that’s still a possibility. A bent/unbalanced shaft or yoke may never make a noise or vibrate until it hits certain speeds. So, it’s not out of the question right now. But, something else is off to make driveshaft tickle a tunnel. In my mind, under all circumstances. I’m thinking that is caused by front pinion angle. Maybe tranny mount.
 
Just a thought is the perches square to the springs. Not rolled up on either side. This would cause a rocking on acceleration and if it is on the power side of the diff can cause vibration. Just a thought.
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Thank you, moparsaver.
Based on what you shared. My rear angle is wrong. Not, my front. Because it’s too straight in line with driveshaft at the rear ? Adjusting the rear will make it, right ? What has to be done to adjust it, rotate the rear axle toward the front of the car after you loosen the shackles ? To point the rear yoke downward to get proper angles ?
My rear yoke is in a straight line with drive shaft, pointing up toward tail shaft. The rear needs pointed down and parallel with tail shaft. That’s, my problem.
 
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I’ve found it’s very common to have the angle wrong, I’ve measured enough Mopars that I usually have keep 2 degree shim kit on the shelf...

Only time I’ve needed any other shim was when things are modified...

Just support the car on the frame, loosen the U bolts on both sides of the axle & slip the shims in with the fat end of the wedge to the rear.... Tighten the u bolts & take it for a test drive
 
If the pinion is straight with the driveshaft at the rear, you need to shim the perches as R/T says. The U joint will wear excessively if it is truly straight. U joints NEED angularity. The straight rear angle can cause a vibration. Also Mopars are NOT supposed to squat during acceleration, they should rise. The center diagram in moparsaver's post is what you want. 2-3* nose down for a moderate power application, 4* down for high power good traction.
 
They sell spring perch shims in 2* 4* 6* When I changed leaf springs on my 65 I had to go with 4* down to make a vibration at 60 mph go away.
Just 2 questions for you. Are you using poly engine and tranny mounts ? Also I re-read your posts, are you saying that the driveshaft hits the tunnel during acceleration ?
 
They sell spring perch shims in 2* 4* 6* When I changed leaf springs on my 65 I had to go with 4* down to make a vibration at 60 mph go away.
Just 2 questions for you. Are you using poly engine and tranny mounts ? Also I re-read your posts, are you saying that the driveshaft hits the tunnel during acceleration ?
The new engine mounts were installed by someone else. They appear to be black soft rubber. In fact, the engine mounts might be too soft. I get a small amount of engine shake at idle that can’t be smoothed out unless I idle the car higher than I like. It has a bigger cam in it. It’s not a engine issue. It’s timed and running exceptionally well. I put 2500 miles on it this summer and it runs fantastic.
The tranny mount appears to be an original. The tranny mount appears to show a little wear at the bottom. It’s squished and tore up a little where it sits in the pocket at bottom. The reminder of it looks good and solid.
Yes, I know on one occasion the driveshaft tickled the tunnel. I noticed a fresh bare metal scrape on the tunnel and on drive shaft when I changed U-joints. The small scrape was about a foot away from the front U -joint. I painted both surfaces afterward to keep an eye on it, to see if it happens again.
 
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When in doubt change them out.Before you do anything I would install all new mounts. Like when installing headers and guys say "They rub or hit and just don't fit." Places like TTI and others always recommend new mounts.Yes I failed to read the instructions and beat the crap out of my first set.My car has poly mounts and they cause vibration mainly at idle but because of harmonics, vibrations show up at different RPMs. They can be ever so slight but annoying. Just food for thought.
 
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Is the car below a factory ride height in the rear? Hitting the tunnel on a stock car is a head scratcher.

If you have factory mounts and the perches have not been cut off the housing and repositioned, you have all the ‘correct’ angles. I used to mess with lowered trucks and we had to shim the rears on leaf spring trucks for sure. Usually we went for 5* pinion down for the angle. Leaf spring rears try to point up under hard acceleration or launch.

I would be more worried about the drive shaft in contact with the tunnel. Fix that and your vibration will be fixed too, maybe.
 
Thank you, everyone. I have a complete understanding now how to measure and fix it. I just need a good suggestion on which shims work well with B body stock leaf springs. I appreciate it.
 
The Belltech shims are nice cause you don’t need to loosen the axle much to slide them in... They are slotted, but the slot is from the fat end so once you tighten the U-bolts there’s no way the shim can slip..
 
i got mine at the local auto parts store, you can get them online also. they come in different thicknesses.
 
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