# Transmission angle issue and driveline vibration



## WhittP (Jun 19, 2013)

Recently had a TKX swapped for my automatic in a 67 GTO conv. Transmission mount was replaced and remounted at a different spot which is visibly lower that what the stock unit was. Driveshaft was shortened as well so all the geometry was messed with basically. Surprisingly, the shop that did the work didn't take the necessary steps to dial in the proper driveline angles. I didn't even notice until I drove the car 75 mph for the first time the other day. Lots of vibration and I put the clutch in to make sure it was driveline and not some motor or transmission issue. Tires are brand new and balanced.

Measured the transmission yoke and it's 6 degrees down. Should be about 4 right? Drive shaft is 1.75 degrees down and pinion is zero. Not ideal. I got my adjustable UMI upper control arms installed today and I'm ready to get things set up correctly. My question is should I start by shimming the transmission or crossmember up 2 degrees? If so, how thick are the shims? Everything I read says adjustments must be made at "proper ride height" but my plus sized figure isn't getting under there with no jacks and I don't have a lift. Can I just measure the fender well height and jack up the car to match that front and back? Making sure the rear is loaded of course.


----------



## Mine'sa66 (Oct 30, 2019)

WhittP said:


> Recently had a TKX swapped for my automatic in a 67 GTO conv. Transmission mount was replaced and remounted at a different spot which is visibly lower that what the stock unit was. Driveshaft was shortened as well so all the geometry was messed with basically. Surprisingly, the shop that did the work didn't take the necessary steps to dial in the proper driveline angles. I didn't even notice until I drove the car 75 mph for the first time the other day. Lots of vibration and I put the clutch in to make sure it was driveline and not some motor or transmission issue. Tires are brand new and balanced.
> 
> Measured the transmission yoke and it's 6 degrees down. Should be about 4 right? Drive shaft is 1.75 degrees down and pinion is zero. Not ideal. I got my adjustable UMI upper control arms installed today and I'm ready to get things set up correctly. My question is should I start by shimming the transmission or crossmember up 2 degrees? If so, how thick are the shims? Everything I read says adjustments must be made at "proper ride height" but my plus sized figure isn't getting under there with no jacks and I don't have a lift. Can I just measure the fender well height and jack up the car to match that front and back? Making sure the rear is loaded of course.


Get a pinion angle gauge...they're cheap and easy. At ride height simply means don't jack up the car or put it on a lift to get under it to measure. The weight needs to be on the suspension, it doesn't matter what the actual ride height is, just that you measure when it's there. You are going to take the gauge and measure directly on the pinion and the shaft, while the car is sitting as if you were driving it down the road.
Yes, shimming under the trans mount is a good way to go, adjust yours arms at the same time so that they don't fight with you moving the trans mount.
If you can't slide under the car with it at rest, the easiest way is to jack it up onto four blocks/ramps. Have a few shims on hand, it's more of a trial and error guesstimation. I'm sure the driveline experts are laughing at that, but they can chime in with the math 
Make sure if you adjust the arms, you jounce the car well to settle things.
May the automotive gods smile upon your project.


----------



## O52 (Jan 27, 2019)

Here are the driveline angles for 1970. The 67 should be close to these, at least to get you in the ball park. If you have the 67 assembly manual, you can find the correct angles. 

X2 for putting the car up on blocks or ramps.
There are apps that measure angles using your smart phone.

View attachment 145881


----------



## Sick467 (Oct 29, 2019)

From the 67 Assy Manual.

3.93° for the V8 with a manual, from the transmission yoke to the drive shaft (not from true level).
3.82° for the V8 with the auto transmission yoke to the drive shaft.
(3.48° for the 6 cylinders.)

So, 4° is very close and certainly good enough. The attached page is hard to read as the 67 manual is pretty sketchy when it comes to legibility. I don't see the angles for the driveshaft/rearend, but I think we can assume equal and opposite.

If I'm understanding your numbers...6° down and 1.75° gets pretty close to the prescribed 3.9° at your 4.25°. You're real close. A little shimming of the transmission mount and your good as far as the front is concerned. The attached page shows the transmission angle, measured from level should be more like 4.71°, but this is only with respect to OEM specs. I would concentrate on the angles between the component's centerlines and not from true level.

Something to consider as well...I had a car that vibrated at higher speeds, but the driveline angles were in good order. It turned out that the front yoke was not in the transmission far enough and caused it to wobble at high driveshaft rpms...the drive shaft was 1/2" too short. Just something to check while your down there.


----------



## WhittP (Jun 19, 2013)

I started by shimming the transmission crossmember up .40" to get it back about where the original position was. That brought the angle on the transmission 4.1 degrees down instead of 6. The driveshaft is now 1.4 degrees down and the pinion is 3.5 degrees up after adjusting the upper control arms. Double checked everything was tight and took it for a test drive. The vibration is down tremendously. There is still some that's noticeable should I try to dial things in closer? Maybe I have a lateral alignment issue? It's not bad at all I'm just looking to get it all dialed in correctly.


----------



## BearGFR (Aug 25, 2008)

What you're trying to achieve is to get the centerlines of the transmission output and the pinion input parallel with each other, in "both directions" --- up/down and side/side. The angles between the transmission/driveshaft and again between the driveshaft/pinion gear don't matter.

Support the car on a level surface with its weight on the suspension (for instance jack stands under outsides of the front control arms and also under the rear axle will get you close, but getting all the tires up on blocks, all the same height, would be better.).

Turn the yoke at the trans so that the transmission yoke is perfectly vertical, then measure the angle on the flat of the transmission yoke (not the driveshaft). Make sure you have the tool on the flat part of the yoke. Do the same process and measurement at the pinion, on the pinion yoke. Make those two angles the same.

You're half done at this point.

Harder to get right is the side/side alignment because it's harder to measure and the inclinometer/"angle finder" is no help.

Support the car with its weight on the suspension (for instance jack stands under outsides of the front control arms and also under the rear axle). "Find a way" to make a chalk line, tape line, etc. on the floor that is at a perfect 90-degree angle with the transmission centerline. Measure from that line to the centerline of the rear axle near the rear wheels. Use a framing square or something similar to make sure you're measuring along lines that are at perfect right angles to your chalk line/tape line/ etc. What you're shooting for is getting that distance on both side the same.

There are other posts here on the forum about the process, I know I've written about it more than once myself.

Assuming that your drive shaft itself isn't out of balance, the vibration is caused by not having the trans and the pinion centerlines parallel with each other. If you could watch the ends of the u-joint crosses from the perspective of the driveshaft while it's turning, you'd see that the ends of the cross don't spin in a circle. They spin in a slightly flattened ellipse. They appear to spin in a perfect circle only if you observe them in a perfectly straight line from the center of the trans or pinion. The only way to make those two ellipses to spin "in time" with each other is to make the trans and the rear axle pinion parallel with each other.

Bear


----------



## WhittP (Jun 19, 2013)

Right now it's about half a degree from being parallel. Would getting that perfect completely take this out of the vibration equation? It was bad when it was 6 degrees in front and zero in back but this adjustment got rid of 80-90% of that. Honestly, I really don't have a lot to complain about it's pretty smooth. Not as smooth as my modern drivers but I don't really expect it to be.


----------



## BearGFR (Aug 25, 2008)

Here's a really good video that explains what's going on.





And by the way, even if you get the angles at both ends perfect, if there's any twist at all in the driveshaft such that the crosses at each end don't line up perfectly with each other, that will also cause a vibration.


----------



## WhittP (Jun 19, 2013)

Thanks Bear I actually watched that one several times. Very interesting how that works. I guess it's not as important what angle that driveshaft is compared to the 2 outer angles being parallel to each other. As long as the ujoints can put up with the angle. I see a lot of conflicting info on that. More than 1 degree and less than 3 is the consensus I believe. I'm not one to leave well enough alone so I'm sure I'll be back under there this evening when this Texas heat subsides a little. I'll try to get both sides 4.1 and I'll use the yokes to get my angles like you suggested.


----------



## BearGFR (Aug 25, 2008)

Like you saw in the video, "how much" angle there is doesn't matter at all, as long as the driving and driven components are parallel (and nothing binds). 

Yeah, like everything else on the Internet, you'll get tons of conflicting information and no matter what it is, there'll also be hoards people lined up behind every opinion that swear their opinion alone is "the one true way". The trick is, figuring out which (if any) of them are correct. 

Do you best to understand the "why" behind every answer, and don't feel bad about insisting that the things you're told have to make sense to you.

Bear


----------



## Mine'sa66 (Oct 30, 2019)

BearGFR said:


> Here's a really good video that explains what's going on.
> 
> 
> 
> ...


I've posted that video dozens of times!


----------



## WhittP (Jun 19, 2013)

Just a follow up on this. It turns out the drive shaft was way off. Took it to a shop when I couldn't get the vibration out even after adjusting the angles. He put it up on a rack and ran it and it was obvious. Changed the shaft out and it's 95% smooth. I suspect any remaining vibration is coming from my wobbly steel wheels.


----------



## BearGFR (Aug 25, 2008)

WhittP said:


> Just a follow up on this. It turns out the drive shaft was way off. Took it to a shop when I couldn't get the vibration out even after adjusting the angles. He put it up on a rack and ran it and it was obvious. Changed the shaft out and it's 95% smooth. I suspect any remaining vibration is coming from my wobbly steel wheels.


Great! That's the thing about problems like this: the same set of symptoms can have multiple causes and sometimes, you just have to keep checking them all until you find the culprit.

"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."​Sherlock Holmes / Arthur Conan Doyle​​Bear


----------

