Parallel points for measuring pinion angle...

What are the typical places for mounting the protractor to find pinion angle on rear differential and trans extension housing?

 

on the rear, the flat cover area above the yoke works well.(depending on your rear end type),or,... on mine I used an area on the housing with the carrier removed. there are a couple of places that will work on the rear(or did on mine, but I have an aftermarket housing thats a bit different).

on the tranny, mine has a flat ridge on the top of the tail shaft, that runs parrallel with the tail shaft.

 

Yoke cover (baseball cap) on the back, ridge on top of tail shaft...Thanks

 

I used an u-joint cap with a socket in between the protractor and the u-joint. I set mine this way to neg 4 degrees.

 

Harmonic damper on the front of the engine and the top of the housing or front of the u-joint cups if the driveline is off. Easier (for me) that way. I have it at 1° down right now.

 

Uhm...not to sound dumb here, but the pinion angle is with regard to the driveshaft. Not the transmission. That's how both of my chassis books call it out. The angle between the driveshaft and the pinion. Not the trans and the pinion.

 

Oh and those were referenced from Chris Alston's Drag Race Chassis Tuning Manual and Dorr Slammer: The Chassis Book by Dave Morgan. Oh and I just checked the Mopar performance Chassis book also and it confirms the other two and even goes into more detail if you're interested.

 

Well, the other end of your driveshaft connects to the transmission. The idea is that under acceleration both u-joints on the driveshaft are at a nearly parallel angle. Under power the pinion gear tries to climb up the ring gear, raising the pinion upward. So it's common practice to point the pinion downward a few degrees.

It's best if you put the protractor on a machined surface and not a cast surface. One degree isn't much. How do you know that rib on the tranny is exactly the same angle as the output shaft? I use the machined surfaces on the vertical faces of the u-joint yokes.

 

yes a machined surface is best.

I dont know about every situation, but the rib on my tranny matched up with the same angle and degree as the engine,crank,and output shaft. not saying they cant be different on different applications, but it worked out in mine.

 

I have been looking at -3*, but since my car is not really that powerful, should I shoot for closer to -2 or even closer to parallel?

 

Are you going to be making this adjustment with, Shims, Preload on bars(cal-tracs), removing and rewelding plate on housing, ECT? there are numberous ways to accomplish this. I have found anything over 4 degrees (Negtive or down) will cause a viberation in MOST street driven cars.Im sure there is some that will have more, Mine hooks best with 6 but i can only run 4 with the setup i have now. It to will depend on your traction device and the weight bias on your car, If i were setting up your car i would try at least 4 degrees to start.

 

Honestly, I don't know at this point. I need to verify that it is pinion angle that is causing my "shudder". It could be drive shaft at 180 off, or a bad u-joint or seating of the joint. It hasn't stopped raining long enough for me to get out there and mess with it (that, and my new surfboard came in today:bananaman )

If it comes down to it, I think I will first back off the preload on the caltracs, then start shimming.

 

I can tell you that there will be very little, if any difference between 0°, 4° up, 8° up or 8° down. I've had mine every which way from sunday (as far as 12° down) and it's never changed a thing other than MAYBE a hundredth in the 60' ET. Even then, that was probably due to track conditions. A street car, you may notice some vibration at severe angles but it'd have to be REALLY severe (like 15+).

BTW, it was mentioned that 1° isn't much. Correct, it isn't. But mine is a 4 link car and the rear end simply cannot rotate so I can get away with it. Like I said, I tried it a hundred different ways with no real change. Leaf spring cars need 3-6 down for best performance. I'd keep it about 4 and you should be fine. I think they're about 4° down stock, IIRC.

 

I put mine between 4-5 degrees down.
Dan

 

When I first installed the V8 34 years ago mine was at 0*. When I launced, the car shook and wheel hopped so bad it ripped the rear shock right out the upper mount. 4* wedges under the spring perches solved the problem. One thing that didn't help, I still had the weak 6 cylinder / 7.5" springs under the rear.