Dragula

iTrader: (5)

I've been having a vibration issue with my mods listed below. I've finally got it to only vibrate under acceleration above 75mph. It no longer vibrates when I'm cruising at speeds above 75 or when I deaccelerating.

Rotated tires = No change

Had gear reset due to unrelated issue = no change.

Adjusted pinion angle = I don't know the DS angle before the change but the pinion was originally at 1* positive (nose up). I was getting horrible fluttering underneath the car that was on accel, cruising and deaccel.

I adjusted the pinion angle to -2.5* (nose down) and the DS is at 1* maybe 1.5* positive.

Is a combined angle of 4* to much? I tried it with the pinion at -1.5*, which reduced the vibration on deaccel and cruising but didn't eliminate it.

Also, with vibration only on accel, do you think this is just engine / tranny vibration?

Dragula

iTrader: (5)

No one knows???

BOWTIE

Another thing to look at is the tranny output shaft angle. It should be the same as the pinion angle or at least with in a degree or two. I have had to shim my tranny mount to try and raise the back of the tranny get mine closer to that of the rear end, but it is still not there. You really need a drive on lift to get these things set up correctly. When I jack up the rear, the pinion angle changes and I am never sure if it is back to normal when lowered onto the stands. I guess thearetically with the suspension loaded (under power) you would want the tranny output shaft and pinion angle parallel with the driveshaft angle up about 1-1.5 degree. This means that you would set the pinion angle somewaht negative in the relaxed state. I plan on using a drive on lift and ramps to try and simulated the loaded state to dial mine in.

peterock98

iTrader: (25)

I'am having the same problem.

Dragula

iTrader: (5)

I did the measurements on a level surface. I just lifted the rear up to make the adjustment and lowered it back down to remeasure.

Is there any surfaces on the tranny to take the measurement w/o removing the DS?

SlickVert

iTrader: (5)

Just Park car on a level ground and place the rear yoke a 0 to start with.
-2 is the recommended setting, but put it at 0 and see if the vibration goes away.
Then next time at the track start lowering the pionon angle and see what the sixty do. I had mine set at -2.5 and it sixty ok 1.65 first time out. need to dail-in the shocks and pionon and looking for 1.5. I just reduced my pinion to -1 and it hooks a lot better on the street. You will need to play with it to see what your car likes.

Dragula

iTrader: (5)

The vibration was during accecl, cruising, and deaccel when at +1* and -1.5*. The only other increment I did was -2.5* which only vibrates on accel, not cruisiung and deaccel.

James B.

iTrader: (1)

Get yourself an angle locator. I found this one at Lowe's, with a magnetic base for less than $20.



Like Bowtie already said, match the angle of the pinion to the angle of the transmission output shaft. With this instrument you should be able to get a good reading right off the flat end of the tailshaft once the driveshaft yoke is pulled out. The angle of the tailshaft versus the angle of the pinion shaft is much more critical than the angle or either or those versus the driveshaft angle.

If the angles of the pinion and the tailshaft do not match then the pinion will accellerate and decellerate relative to the output shaft through the rotation. The more off the driveshaft angle is from the pinion and tailshaft angle the more the driveshaft will accellerate and decellerate though the revolutions, but the u-joint at the other end cancels it out so the pinion remains a "constant velocity" relative to the tailshaft.

peterock98

iTrader: (25)

I'am going to get under there and check it.

Dragula

iTrader: (5)

James B. - Good point on the uneven speed of the driveshaft. I guess I was trying to avoid pulling the DS to get the tranny yoke measurement. I have the angle locator. It's just going to take me a few hours of work.

That leads to my next question:

What is the torque spec on the DS u-joint caps on the diff. I'll call strange tomorrow.

glennster

iTrader: (1)

17 pds ft

Dragula

iTrader: (5)

I pulled the DS to check the Tranny output shaft angle. Bad news, 5 degrees down. If I'm trying to get the tranny output shaft parallel to the pinion and I want that at -2* i now need to shim my tranny up 7*. I got over an inch of washers, unbolted the rear tranny mount, supported the tranny and removed the cross brace. I put 6, then 8, and then 10 washers in and reinstalled everything. The output shaft angle only changed 1* to 4*. I couldn't even install the 18mm nut to hold the tranny down b/c there was so many washers.

I took all of the washers out, and reinstalled everything. I played with the pinion angle to get to a point where it only vibrates above 95 mph.

Any suggestions? This is really pissing me off. I did all this work with out a lift and on the ground, so you can image what a pain in the *** this was.

James B.

iTrader: (1)

7 degrees difference is huge. What got so far out of whack? Is there something custom about your transmission? What about the rear end? From the factory those angles match. What's changed?

Dragula

iTrader: (5)

All stock except the mods listed. I checked the tranny angle 10 times. I was so confused when the shims didn't do the trick. I wonder if the original TA helped hold down the tail of the tranny up. Once that's removed I wonder if it began to sag (sp?).

BOWTIE

From what it sounds like you are saying, you have the pinion pointed down towards the ground -1 deg. This should not be the case. all of the angles in our cars are actually pointing up towards the front of the car. You want the rearend pointing up about 1 degree less than the tranny, and a few degrees less than the driveshaft. If you are trying to follow the Spohn pinion angle adjustment instruction, don't. I am not sure who wrote them, but they are wacked. I actually checked my car when it was still bone stock as far as the rear and T/A were concerned and it was +2 degrees on the pinion and +2.5 degrees on the driveshaft (Unfortunately I did not think to check the tranny output shaft angle) so in reference to those two angles, I had a negative .5 deg pinion angle.

Dragula

iTrader: (5)

To better simplify the situation, If I set my diff to 5* up from horizontal then my diff input will be parallel to the tranny output shaft.

Would I then lower the diff down 2* to get a diff angle of +3* to make a 2* difference from the tranny output shaft????????????

James B.

iTrader: (1)

The transmission is your angle reference point. Start by finding the angle of the tailshaft and then match the rear end to it, not the other way around. Leave the angle of the engine and trans alone.