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Quick list of parts that have been put on my car over the last few months before I go into the issue I'm having:
1996 Trans Am WS6 M6:
UMI upper A-arms rod-rod
UMI boxed lower A-arms rod-rod
UMI road race k-member (with poly engine mounts)
UMI T56 trans crossmember with torque arm relo bracket
UMI adjustable torque arm (poly bushing up front)
Founders rear LCAs rod-rod
Strange S60 rear end (4.10 gears, 35-spline axle, Detroit Tru-Trac) w/ welded on LCA relo brackets + Strange driveshaft (freshly balanced and new Spicer u-joints installed)
Fays2 watts link
Strano hollow 35mm/22mm sway bars with poly bushings
Koni yellows double adjustable fronts and rears
Strano springs
Rear spring isolators removed, heater hose mod done in its place
MWC SFCs
Founders STB
Strano brake MC brace
Pacesetter longtubes
Speed Engineering ORY
Madhammer GMMG catback
Alignment done by Texas Track Works
Ok, now for the problem. My car has a bad drive-line vibration at highway speeds, so I got under it to check the pinion angle, which I asked TTW to set when they aligned everything. Sure enough, it was way off, about 5-6 degrees of difference (guess I should have specified what angle to set the pinion angle to, in hind sight).
Now, I'm trying to get this done in my garage by raising and lowering the rear of the car to put my magnetic angle finder on the driveshaft and the torque arm mounting bracket on the rear end and get readings with it sitting level on the ground and compare. I decided to start by adjusting the torque arm all the way back to bottomed out towards the rear of the car, so the adjustment nut can only move back toward the front of the car at this point. This gives me a rear end angle of -1* currently when sitting on the ground.
With the angle finder on the middle of my driveshaft, however, I'm getting a positive ~3* angle. This is stumping me, how does my driveshaft have a positive angle toward the rear of the car? Did I lower it too much by removing the rear spring rubber isolators when I put my Strano springs in? If I put those back in, will it raise the rear of the car enough to get my driveshaft back into a 0 or negative angle, possibly?
Also, most stuff I've found online refer to setting an automatic car to a -2* pinion angle. Is it different for a T56 car?
Please help, as I'm trying to get this thing sorted out and ready before the first autocross event of the season here on February 25th (2 weeks).
Jesus, stop measuring the driveshaft. Its irrelevant. Second jack the back of the car up, with the rear suspension loaded (or on ramps) and LEAVE IT THERE. Putting it up and down and/or level is just causing more confusion. You arent look for 0, or 2 degrees, or whatever. You just need 2 less degrees in the rear. Meaning if the car is jacked up at a 10 degree angle you're measurements say will be 10 and 12. It doesnt need to "start at 0". So, measure the front, measure the rear, adjust rear to 0-2 degrees pointing down (less) then the front measurement.
Measure Angle A and Angle B. Make sure the DS is rotated properly so you are measuring the sides of the ujoint that are flat with the trans and rearend.
Ok, I measured from the flat side of the u-joints on each end with the rear up in the air /front end on the ground (I don't have ramps, doing all this in a small garage in an apt complex). Rear end is sitting on jack stands so the suspension is still loaded.
Transmission yoke/u-joint angle = -1*
Rear end yoke/u-joint angle = +2*
Based on this, I'm still at +1* pinion angle total. The torque arm adjustment nut is already bottomed out as far as it'll go toward the rear of the car, so I can't get any more negative angle out of the rear end without taking the whole thing apart to adjust the top heim joint length, correct? Moving the adjustment nut toward the front of the car increases my pinion angle even more positive.
It depends, sort of. Are you looking at the dial indicator from the driver or passenger side AND are you looking at it from the same side on both measurements?
From the passenger side you are -3. from the drivers side you are +3. Remember the numbers are not important, its the difference between them.
I'm looking at the angle finder from the driver side on both measurements. I just found another thread which says to look at it from the passenger side on both, though, which just flips the positive and negative around. You're saying they both need to read the same number on the trans and rear end, though?
Should I raise the front of the torque arm up into the next hole on the relo bracket (as this should help pull the rear end up slightly with it, since it's all connected)?
Last edited by BlackHawk96WS6; 02-11-2018 at 01:15 PM.
As a quick update, I just set the pinion angle to -2* when sitting on the ground (irrelevant of the trans angle to start out) and went for a test drive. The vibration is still there, but it's definitely better than it was (no longer violently shaking the whole car). Now, it's just a minor vibration you can still notice whenever off the throttle and above 70-75 mph. I'm headed in the right direction at least, so I'm going to keep adjusting it 1 degree at a time until the vibration stops altogether and see where that angle ends up.
If your trans is in fact pointing down 1 degree, you want the rear end to be up one degree for perfect parallel. Try that to see if your vibes are gone while cruising. If it still vibrates then its not your pinion angle.
If it still vibrates after this, check your 5-6 gear on the main shaft.
If your trans is in fact pointing down 1 degree, you want the rear end to be up one degree for perfect parallel. Try that to see if your vibes are gone while cruising. If it still vibrates then its not your pinion angle.
If it still vibrates after this, check your 5-6 gear on the main shaft.
yea i was gonna suggest the 5/6 as well. im going through this as well. i think my angle was pretty close but still had a vibe. so i bought a trans. won't be installed fort 2 months at least
not to hijack, but is there anything wrong with ignoring what the angle finder says and just keep rotating and rotating the torque arm in the direction that makes it better until it doesn't vibe anymore?
one other thing op, there is an app on ur phone called tremec toolbox that a lot of ppl like as well. maybe try that. its nice it saves ur measurments for you so u just hold it against and it the button
I went through this same type of deal last year, over thinking the driveline angles, buying new driveshaft and yokes ect. Ended up being in the trans. I know its not optimal for the track but just set the angles parallel and if it still vibes pull the trans, you just need some lock ring/snap ring pliers and a tiny bit of mechanical ability to get to the 5-6 gear.
Well, ****, if it ends up being the 5-6 gears in the trans, then the car's going on auto-cross only duty until I can just get a bulletproof/built T56 to swap in (it's next on my upgrade list anyway, looking at Tick level 3 viperized build). I'll find some time after work this week to get back under it and adjust the angle more to get it more parallel and cross my fingers. Thanks for the tips, guys, I'll report back after I get to mess with it some more.
If it is the trans, just take it to Jason at TDP. I want to say hes in fort worth really close to you. He repaired my main shaft really cheap with fast turn around.
Haha touche. Granted, I did drive the car all the way to San Antonio to have Moe Bailey tune it in person, so Fort Worth is a hell of a lot closer by comparison.
I'm looking at the angle finder from the driver side on both measurements. I just found another thread which says to look at it from the passenger side on both, though, which just flips the positive and negative around. You're saying they both need to read the same number on the trans and rear end, though?
Yes they should match for 0. Then down 2 on the rear end and done. If you are at plus 3 thats not good. It will probably effect traction and cause premature ujoint failure during hard launches.
Yes they should match for 0. Then down 2 on the rear end and done. If you are at plus 3 thats not good. It will probably effect traction and cause premature ujoint failure during hard launches.
Thanks. So far I've gone with setting it to matching angles and test driving it. The vibration was considerably less, but still a small vibration left in it above 75. I've gone back and adjusted it to about -1.5* or so from 0* and it's the same as when they were set to 0* delta. Getting much better, but still not gone completely.
Originally Posted by qweedqwag
What driveshaft are you runnin?, you could alway get it checked for balance, I've read where steel driveshaft have more vibs than aluminum.
Strange's driveshaft, which I believe is chrome moly. Their shaft, their yokes, their recommended Spicer 1350 u-joints, and took it to a shop to have new u-joints installed and all balanced just in case. Wheels have been re-balanced as well, just to rule them out, too.
At this point I'm wondering if I should maybe go back to a rubber trans mount instead of the poly and see if that does the trick. Opinions?
02-10-2018, 11:25 PM
Lowered Car + Pinion Angle Troubles 
