pinion angle

[WSSix]

I've been reading so much on this subject trying to figure out the "correct" settings that my head is spinning. I'm tired of reading and would like to minimize the amount of adjusting I need to do so I figured I'd just ask which way should I go.

With the car sitting on it's wheels, the rear of the transmission is pointing down 3*, the pinion is pointing down in the front 2.5*, the drive shaft at the rear is pointing down 0.5*, and is at 0* in the front.

Should I rotate the rear end up or down or adjust the transmission up or down? Can't really go up with the transmission honestly. Keep in mind I'm still riding on leaf springs. 200 lb/in if that matters

The symptoms are I have a bad vibration that comes in around 60 mph. Clutch in/out throttle on/off doesn't matter. The old rear end did this as well only I think it was a slightly higher mph since that was a 3.42 gear and not the 3.90 I have now. It's been too long since I had the car up to those speeds for me to remember exactly though.

In good news, this is the 4th rear I've set up and so far it's dead quiet. Thank you US Gear. The Tru Trac makes for a squirrely good time with my 180k mile stock LT1 Good bye Sumitomos. Your days are numbered.

Thanks

[Vince@Meanstreets]

Originally Posted by WSSix

I've been reading so much on this subject trying to figure out the "correct" settings that my head is spinning. I'm tired of reading and would like to minimize the amount of adjusting I need to do so I figured I'd just ask which way should I go.

With the car sitting on it's wheels, the rear of the transmission is pointing down 3*, the pinion is pointing down in the front 2.5*, the drive shaft at the rear is pointing down 0.5*, and is at 0* in the front.

Should I rotate the rear end up or down or adjust the transmission up or down? Can't really go up with the transmission honestly. Keep in mind I'm still riding on leaf springs. 200 lb/in if that matters

The symptoms are I have a bad vibration that comes in around 60 mph. Clutch in/out throttle on/off doesn't matter. The old rear end did this as well only I think it was a slightly higher mph since that was a 3.42 gear and not the 3.90 I have now. It's been too long since I had the car up to those speeds for me to remember exactly though.

In good news, this is the 4th rear I've set up and so far it's dead quiet. Thank you US Gear. The Tru Trac makes for a squirrely good time with my 180k mile stock LT1 Good bye Sumitomos. Your days are numbered.

Thanks

@ 60 i'd be looking at your tire balance. Them Sumi's suck big time. I had them on my Chevelle and it sound like a Toyota with 35's going down the road.

[Vince@Meanstreets]

[WSSix]

Thanks Vince. It's a bad, high frequency vibration and it started immediately after I finished the suspension work. I figured the ride height changes finally caused the pinion to move enough that it's misaligned.

Yeah, I put the Sumitomos on because I couldn't afford anything better at the time. They will be replaced soon enough.

[Chad-1stGen]

Inland Empire Driveline know a lot about this subject. They have released a few different guides on setup. Here is one. It covers a few different things but page 3 has the info on proper angles to minimize vibration.

http://www.iedls.com/asp/admin/getFi...&TID=28&FN=PDF

[GregWeld]

From your explanation --- your pinion angle is exactly OPPOSITE of where it should be --- if the trans is DOWN 3* --- then your pinion should be UP about 1 or 2*

IIRC you said your pinion angle was DOWN.... and that would be where you're having issues.

You need some working angle on the driveline --- So I'd start by putting the pinion angle UP 1*.... and see if that changes your problem.

Don't over tighten the U-joint U-bolts (straps). Just tighten until the split washer closes and go about another 1/4 turn.

[WSSix]

Thanks guys. I appreciate the feedback. Part of the problem I'm having is so many people refer to the angles in different terms. Not only that but people insist that the nose of the diff should be facing down. So that hopefully I can learn something from this, let me say what I'm thinking in terms that I understand. Please tell me if this makes sense and is correct of not.

The idea is for the trans and diff to be in a parallel plane when under load/power. Because I'm a leaf spring car, the diff needs to be 2-3* down relative to this parallel plane when the car is simply sitting on the cribbing. In this case, I'm 3* down on the trans so I need to be at 0 to1* up on the pinion which is 2-3* down from the parallel plane. Is this correct?

What about the drive shaft's angle? I measured the height of the trans and the diff in the car. The diff is only slightly lower than the trans, less than an inch. Does it matter that the drive shaft will be basically level while in the car, or is it strictly the angles between the trans and drive shaft and diff and drive shaft that matters?

Thanks

[GregWeld]

Under really HARD acceleration the pinion may climb 2* on a leaf spring car... Thus my UP 1* to start - and under acceleration when it climbs it will be up a little more. It's okay to have 1 to 2* of "difference" between the angle of the trans and the pinion.... these change under various conditions to begin with!


In an effort to be on parallel plane -- if the trans is down then the pinion must be up... Extend a line from the back of the trans to the rear end -- and then do the same forward with the pinion.... You can't have the trans DOWN and the Rear end down and end up parallel.

[WSSix]

Thanks, Greg. I read the Inland Empire link Chad gave me after posting my last response. That's the first time I've seen it referenced with the rear higher than the trans. I guess I was getting hung up on the differences instead of just doing the math. I'll get some shims in here and get this dialed in hopefully. The car is fun to drive so long as I stay on surface streets. I'll have to get some seats in here pronto because I can hang on and steer at the same time

[GregWeld]

One of the reasons the vibration may be at a lower speed now - is because with the gear change you driveline is spinning at a higher RPM.