Driveline angle questions with Speedtech components

[cpd004]

I have a 71 Firebird with Extreme front sub frame. It has an Ls3 and 4L60e.

I recently had some issues with the original 10 bolt and ended up getting one of their 9" axles.

The rear has their torque arm setup.

There is no way at all to measure the bearing cap of the front U joint as Spicer suggests. Best I could do was at the harmonic balancer face as they list in their Mopar instructions I happened to come across.

I am using a Klein digital angle finder. It is a small square device.

At the balancer, I see 2.8 degrees down. There are several shims between the trans and the trans mount. There is no room to go any higher at the tail of the trans if that's what is needed.

The driveshaft actually runs upward at 1.0 degree.

The center section has approximately 4 washers as shim and runs upward at 1.1 degree.

Their instructions at section 4 on page 20 ( https://speedtechperformance.com/wp-...rm-20300-1.pdf ) say this:

Pinion angle should be within range at the ride height as stated above. If you feel a drive shaft vibration at
speed, you may need to adjust your driveline working angle. We have found this to be at optimum on our
ExtReme products between 1.5-2 degrees. Use shims on either the rear pinion mount as seen in the diagram
70-81 F-Body Torque Arm Page 21
below or at the transmission crossmember until you have the correct angle and any driveline vibrations should
go away.
We have found that in all our installs we have not need to adjust the pinion as it is engineered into the mounts



Not sure how they don't find a need to run them at the center between that mount and the torque arm because mine would point down without these washers.

That would both the trans and center pointing downward. Many websites say this is not acceptable.

I do have an email out to them. The initial email mentioned removing shims at the trans. This doesn't seem correct at all.

I do have the old subframe setup with the very thin tube trans crossmember. Not sure if this has anything to do with anything, but like I said, I can't go any higher with the trans to reduce that downward slope.

[srode1]

I would call them - they are very responsive every time I have called with a question. It's a lot easier and faster to have a conversation than back and forth emails.

[dontlifttoshift]

Can you clarify this?

The driveshaft actually runs upward at 1.0 degree.

Actually, if you clarified all of your angle measurements as either up or down in the rear it would ensure accurate math. I am assuming that these measurements are taken with the rear suspension loaded.

If the driveshaft is running uphill to the rear end, your working angles are 2.1* in the rear and 3.8* in the front.

[cpd004]

Had a little bit of time to try again. The car is on its wheels which are on the 2x4 cribbing that are homemade and then those on rolling dollies. The car has been bounced around on these to hopefully settle it as much as possible. It appears as though it's at ride height but elevated.

Took out the shims at the back between the pinion mount and torque arm.

So this is what I am seeing:

At the crank hub = 3.0 degrees down

Driveshaft = 0.9 degrees up

Center section = 0.9 degrees up

If I'm understanding this correctly now, 3.0 + 0.9 = 3.9 for working angle 1

0.9 - 0.9 = 0.0 for angle 2

So this is far from their 1.5 to 2 degree no noise/vibration suggestion. The zero at the rear is not acceptable at all. The rear can be rotated.

The options I have are to go lower at the trans increasing the downward slope and/or going up at the pinion. A lot would have to be reworked to lift the trans and reduce the slope there.

Maybe I'm misunderstanding something.

The reason I began looking into this is that I have a weird harmonic sound that seems like it comes from the driveshaft off throttle as it coasts down while testing it. The center section builder immediately asked about driveline angles. So looking them over is where I am.

[dontlifttoshift]

Based on that information, you're math is correct.

If you roll the pinion down, working angle at the trans becomes less and working angle at the pinion becomes more.

If you go up on the pinion, angle at the trans is just going to get worse.

[dhutton]

I could be wrong but I think you either need to raise the transmission or increase your ride height.

Don