BuiltZ28

I checked the angle of transmission output and found it to be a +1. I set the pinion angle to a -3 with the thinking you take equal but opposite angles then add 2 additional degrees to the pinion to account for the thrust (raising force) on the pinion when power applied.

All in all I have a +1 on my output and a -3 on the pinion with the suspension loaded.



Also slightly unrelated, what is the effect of raising or lowering the front of the torque arm on my BMR crossmember.

84 z28

Auto car you want around a -2 or -3 degrees

84 z28

BuiltZ28

I watched that video earlier I don't really understand it. I have seen a lot of knowledgable people on here saying ignore the driveshaft angle as well.

The car is manual if it matters.

84 z28

You take the numbers from the driveshaft and rearend and adjust the torque arm accordingly to get the numbers you need

Example
Driveshaft +3
Rearend is a -5

That gives you a -2 so you're in the ball park

84 z28

Here is the UMI instructions if it helps, says manual should be between 1-3 degrees negative

https://static.summitracing.com/glob...20-%202203.pdf

BuiltZ28

Ill check it that way tomorrow see where I'm at.

skinny z

No manufacturer can state what the pinion angle should be unless the existing values are supplied. That is to say, you have to know what the angle "down" is of the output shaft/ crankshaft centreline.
There is very little "thrust" in the torque armed 3rd gen. Even less so with poly mounts, etc.
If the crank centreline is down 4 degrees (which is the standard OEM engine angle) then adjust the pinion up 4 degrees. Take 1 degree out (so it's up 3 degrees) if you feel it's necessary.
The real deal here is what the relationship is when you're cruising. There's no upward action on the pinion when at steady state and you want the angles as close as possible for periods where the relationship is extended such as when on the highway.