Another Pinion Angle Question

[cv2065]

I'm using a Klein digital angle finder. I tried to use the phone app but can't get repeatable readings as it has no magnet. Keep in mind I 'proactively' installed 3-1/4" shims at the transmission (+.75") when I was installing everything just because.

Measuring at the front of the crank pulley, I'm at 1.3 degrees down. The driveshaft is already installed, so I'm measuring from the topside of the u-joint, which is 4.8 degrees down. I measured from the horizontal casing of the IRS and got zero.

So I'm going to remove my shims to pull the first drivetrain number down, but can one expect a certain amount of degree shift for every 1/4" shim removed?

[rich grsc]

You have IRS, you can't change the pinion angle. Why are you over thinking this? On a scale of 1 to 10 in importance, this is maybe a 2. You aren't going to drive this car a 100,000 miles a year, it's FINE. I have IRS and have NEVER check to see what is is, 20,000+ miles ZERO issues

[PNWTim]

In a prior project I did, 1/8" spacers equated to about a .75 degrees plus or minus a bit. I would simply try removing 1 and see where you land. Even though you can't manipulate the center section doesn't mean you shouldn't get the transmission as close as possible to where you want it. Can also help to eliminate vibration under hard acceleration or decceleration.

[cv2065]

You have IRS, you can't change the pinion angle. Why are you over thinking this? On a scale of 1 to 10 in importance, this is maybe a 2. You aren't going to drive this car a 100,000 miles a year, it's FINE. I have IRS and have NEVER check to see what is is, 20,000+ miles ZERO issues

Thanks Rich. I get it now. The pinion angle really has no bearing on an IRS since the housing does not move with the suspension and has no bearing on the half shafts. I installed the shims to pull the oil pan up into the frame a little higher so I guess the real question is how that will impact my header and side pipe alignment

[cv2065]

In a prior project I did, 1/8" spacers equated to about a .75 degrees plus or minus a bit. I would simply try removing 1 and see where you land. Even though you can't manipulate the center section doesn't mean you shouldn't get the transmission as close as possible to where you want it. Can also help to eliminate vibration on under hard acceleration or decceleration.

By pulling up the oil pan with the spacers, I think it did exactly what you are talking about getting the drive line more in parallel with the frame.

[edwardb]

Thanks Rich. I get it now. The pinion angle really has no bearing on an IRS since the housing does not move with the suspension and has no bearing on the half shafts. I installed the shims to pull the oil pan up into the frame a little higher so I guess the real question is how that will impact my header and side pipe alignment

That's not exactly true. Good to check/know the pinion angle to make sure you're not exceeding the recommended working angles of the driveshaft universal joints. Unlikely you'll be out of range but doesn't hurt to check. But i agree with your setup don't overthink it. It's true with IRS the frame mounted diff doesn't move so it doesn't change under acceleration like a solid axle mounted in a suspension. So it's not necessary to compensate for that.

[rich grsc]

Thanks Rich. I get it now. The pinion angle really has no bearing on an IRS since the housing does not move with the suspension and has no bearing on the half shafts. I installed the shims to pull the oil pan up into the frame a little higher so I guess the real question is how that will impact my header and side pipe alignment
That is really all you need, and it will last long after you have quit driving it. I have 40 yrs experience with PTO drive lines, the U-joints will safely operate at angles far beyond anything you could create on these cars.

[gbranham]

I agree with Rich. I installed 3 Forte's shims on my tranny mount, gave the driveshaft a quick eyeball to make sure nothing looked crazy, and didn't give it another thought. I think folks get too precise with this.

[BRRT]

I spent a couple days measuring and agonizing over my u-joint angles. To make mine perfect was going to require cutting and rewelding the differential mount tubes, or making some sort of offset bushings for the diff mount. Neither solution was workable. I decided to add a few spacers under the trans to get it close and call it done.