Ok I need all of the best minds on this site to come together on this and help me out your help would be greatly appreciated, I have a 99 Trans Am with a TR6060 swapped out of a 09 Pontiac G8 it has a custom CV driveshaft built by the driveshaft shop and the torque arm is relocated on to the cross member since there is no place to fit the torque arm on to the transmission, I fabricated the torque arm relocation cross member out of the existing cross member and the pinion angle is exactly where it should. For a CV driveshaft the pinion should be inline with the driveshaft, now here is the issue at 70 mph I get a vibration that increases with speed at cruise especially in 6th Gear at 2000 rpm you can start to notice it because in 6th Gear engine rpm will be lower and as speed increases the vibration increases at 120-130 mph it feels like the car will fall apart( I don't drive at that speed I just did it once for the sake of testing this vibration). Now before you that it might be the flywheel engine or transmission go change this and that, I removed the driveshaft got it to 2000 RPM in 6th Gear and there was absolutely no vibration it was very smooth, but as soon as you put the driveshaft back in with the rear jacked up the vibration is there, I knew that what ever it was it was before the transmission like driveshaft/pinion related so this is what I did I jacked up the car from the rear got a dial gauge and took readings of driveshaft runout by turning the wheel, at the front of the driveshaft near the transmission I came up with 0.010 which is fine, in the middle it was 0.015 which is also fine but at the rear close to the pinion it was 0.045 which amazed me, the pinion is inline with the driveshaft so that rules that out and I tried a couple of degrees of variation but the result was the same, I removed the driveshaft put it on a lathe and took several runout reading and they were all fine, around 0.010 at the front, 0.015 in the middle and 0.010 at the rear, now here is where it starts to get more interesting I thought ok maybe the pinion yoke has run out, I took a dial gauge placed the needle.on one Ujoint with the shaft installed slowly pulled the needle back rotated the yoke and got the needle to touch the other ujoint and there was only 0.005 of a difference now at this point I'm baffled, I'll change the yoke tomorrow anyway and before I install the new yoke, with the yoke removed I'll take pinion shaft runout readings what sort of a reading is one that is within tolerance and also after installing the new yoke I'll take runout readings of the circular part of the yoke what sort of reading should I see there?, if all of that checks out ok my other suspicion is that because this is a custom torque arm relocation bracket even though the pinion is aligned in the vertical plane maybe it's misaligned in the horizontal plane, could that cause a high runout reading at the rear of the shaft with the shaft in the car? Your opinions and help would be greatly appreciated, thank you.

 

You need to zero pinion angle out to start. At ride height, position your true flat (the ones that dont swivel) u joint bearing caps facing down. Use a socket or other flat and fitting device to take your measurement off the cap. Measure both front and rear, make adjustments to the rear to make it match identically to the front. Bet your vibe goes away.

 

Red has helped alot of people with this, his advice is solid. If you're off in the horizontal plane, you could still be at zero in the vertical, so to me your thought there has merit.

A dumb question, but would a failed CV joint or U joint cause that runout as well? Mainly, I'm thinking that rear U-joint. could be allowing the driveshaft to move, but still be solid on the yoke side, showing the yoke is still OK?

Another test if you end up ruling the driveshaft out - does it also vibrate in 5th, but not 4th or 3rd at the same speeds with the driveshaft in? The 5/6 gear can come loose on the countershaft resulting in vibrations. Pulling the driveshaft for the test you described also removes the tranny from the equation. I'm not sure you would detect a 5/6 gear vibration by the test you described, as the driveshaft would resonate the vibration, (though I agree, it would not explain the high runout on the rear)

 

I appreciate your input just to clarify this I don't have Ujoints at the front of the shaft, I have a CV joint at the front and Ujoints at the rear this is a custom shaft, pinion angle is at zero it's perfectly inline with the driveshaft, when you say measure from the rear Ujoints measure in relation to what ?I sort of get what your saying but not quite can you please clarify, the only adjusting that is needed is in the horizontal plane in the vertical plane as I have said the pinion is perfectly inline with the driveshaft, so clarify to me how I can get it right in the horizontal plane.

Thank you

 

Thank you for your input Sir it vibrates in all Gears at the same road speed and higher with the driveshaft in, and doesn't vibrate at all in any Gear at any speed without the driveshaft in it, it's just that in 5th and 6th Gear it's much more noticable because your doing the same but with less engine RPM and noise, the issue is definitely backwards of the transmission, pinion area and the sudden change in runout in that area is the biggest sign, I mean 0.040-0.045 at the rear is a lot especially for a M6 car, 3 speed TH350 or 400 wouldn't be a big issue because of the high engine RPMs you would be turning it wouldn't really be noticable but M6, definetly noticeable, uncomfortable and annoying.

 

OK, I missed that you had tried all gears on the road.

I agree the runout at the rear is problematic. The only way I can think that the driveshaft runout would be .045" and the yoke runout would be 0.005" is if that rear U-joint is bad. The two bearings attached to the yoke could be good, but the bearings attached to the driveshaft could be bad. Or a clip could be missing / broken off

 

U joints are new and clips are there this is the second driveshaft with the same results,I think it's either the yoke or a horizontal alignment issue, I think what Red was trying to suggest is to take measurements from the u-joints to the CV plate and verify that they are the same so that alignment in the horizontal plane would be correct, I will give it a try tomorow, by the way I like your Trans Am.

 

 

 

Red this is a CV driveshaft it has a CV at the transmission end and Ujoints at the pinion so traditional pinion angles don't apply the transmission can be anywhere from 0-8 degrees for the CV to work properly but the pinion must be within a degree and a half of the driveshaft mine is perfectly inline with the driveshaft so like I said an issue in the vertical plane is eliminated, it's just the horizontal plane that is still a possibility, have you got any ideas on how to check alignment in the horizontal plane?

 

I'm really glad I saw this thread. I'm having a very slight driveline vibration I'm almost certain has to do with the driveshaft.

The second video on drive shaft velocity is great. I'm surprised when you buy an adjustable torque arm it says nothing about this. Just: set to x for auto & y for manual.

I'll be checking this tomorrow.

 

Thanks! I'm trying to guess at how the horizontal alignment could be off. Either the engine/trans is crooked and the axle is straight? Engine and trans are straight and axle is bent? adjustable rear LCA's making the axle crooked?

The yoke is plausible, and there is a thread where the yoke was the problem for a user named "SpeedTigger"

 

Show us a pic of what your driveshaft looks like. Im obviously not familiar with your setup.

 

The transmission is a TR6060 transmission there is no place to mount the torque arm so I fabbed up a Torque Arm relocation cross member out of the existing tranny cross member, as I have said I positioned the torque arm on the cross member is a way that makes the vertical alignment spot on I checked with an angle finder but with the horizontal alignment I didn't have a way of checking but I've got an idea now I will install the shaft and I will measure the distance between one U-joint and the CV plate then I'll measure the distance between the second Ujoint and the CV plate and compare if the two measurements are different it will mean that one of the Ujoint is closer to the CV plate which will mean it's not aligned in the horizontal plane at least that is the theory I'll give it an attempt, now I know what some people might say they will say that since the torque arm is not on the tranny but the Croome mer more vibration will pass through in some sense it is true but not this much and 0.040 of runout at the rear is the sign.

 

I understand.

Where I'm going is this. It's easy to move your pinion angle vertically. Imagine trying to move it horizontally with a 50' torque arm. You'd have to bend the rear axle assembly to get it to move. My point is that I don't think your body mounted torque arm is going to move the rear pinion against the axle sideways.

If you determine your axle is crooked you will need adjustable rear LCA's and an adjustable pan hard bar to correct it. However if your axle is crooked, your thrust line is off, meaning your car won't track straight, so you'd have an obvious alignment issue. Simply repositioning the torque arm won't move that rear pinion left or right. Only up or down.

If you are 100% certain on your driveline angles, then the yoke makes sense

 

You are right you can't move the the whole rear axle assemble to the left or right because of the LCA'S and panhard bar and even if it were slightly to the left or right it wouldn't be an issue just as long as the yoke is parallel the front yoke, joint, CV plate, but what does happen and you can try this out with the movement of the torque arm tip, the pinion and axle assemble will move in an angular motion sort of like a trolley will.and that sort of misalignment will cause an issue because then the rear yoke is no longer parallel with the front assembly, I have moved it to the left and right and I have seen the axle assembly move that way, I'm going to take measurements today to confirm.

 

Just as I suspected misalignment in the horizontal plane, what I did was I turned the pinion yoke by hand so that the Ujoint caps or straps would be in the horizontal plane, then I measured from the left Ujoint to the CV plate at the transmission and came up with 120 cm, then I measured from the right ujoint to the CV plate and came up with 116 cm, meaning the left ujoint or left side is further away from the CV plate then the right side, meaning the whole yoke and axle assembly is angle to the left off the centre line by a lot, I changed the pinion yoke so that is ruled out, this is the only other possibility to the left, next step is to move the torque arm on the cross member to the right until the measurements are equal.

 

Ok alignment in the horizontal plane has been done and is spot on, and let me tell you the vibration has gone down a lot it's like driving a different car the mirrors are still where as before because of more vibration you could only see a blur when looking at the mirrors, although the vibration has decreased it is still there, I haven't measured runout at the rear of the driveshaft after the Horizontal alignment I will do that soon to see if there is change, I have one question for the people that own torque arm relocation cross members because approaching 110 mph I can feel vibration not terrible but noticeable, my question to the people that own torque arm relocation brackets, do you experience vibration at 110mph+ speeds I thought that maybe because the torque arm is now connected to the cross member that it is transmitting these vibes, your input would greatly be appreciated please let me know what speeds you have been to and what it feels like.

 

I'm glad the vibe has gone down for you. I think that is the next thing I'm going to check. Maybe a slight adjustment to my pan hard rod will get it in line.

I have a T/A relocation crossmember myself. Your idea sounds right. Maybe you just feel the vibes more now that your T/A is mounted to the crossmember.

 

I think that because you have a relocation cross member that is made by a good brand like BMR your horizontal angle will be fine mine was off because I fabricated the relocation cross member myself and had the torque arm bushing sit too far to the left so the whole axle was angled to the left creating a thrust angle very high working angle for the Ujoints the way I measured was by removing the driveshaft rotating the yoke till the ujoint caps sat in the horizontal plane and measured the left ujoint from the joint to the transmission plate and right ujoint to tranny plate at first there was a big difference between them then I made corrections to my crossmember and got them equal, anyway do you feel vibrations in the cabin at 110+mph with your torque arm relocation cross member?