HELP pinion angle

[68400BIRD]

1968 Firebird 400-400 combo
solid GW body mounts at stock heigth, not wedged.
Stock subframe
stock motor mounts and tranny mount
QA1 coil over front suspension
The front sub frame,motor,and tranny should be close to what came from the factory for ride heigth.

The rear has a leaf spring suspension with I think a 1 1/2" drop spring.

The floor in my garage is not level and I do not have a spot that is level as of right now. Still snow in the driveway. LOL

The car is not completely loaded. But I have tried applying several hundred pounds to the rear of the car and the pinion angle does not change. The body of the car just seems to sink down.

I had to weld on new perches to the rearend. I used a 1973 nova rearend as a reference point for mounting the perches and spot welding them on.

I installed the driveshaft last night and here is what I have for measurements.

I put a angle finder on the driveshaft right in front of the rear pinion. I have 3 degrees angling down to the floor.

Next I put the u joint that is bolted into the rear pinion so it was pointing straight down. I put a socket and my angle finder on the cap of the u-joint. I came up with a 5-5 1/2 negative degrees (pinion is angling down to the floor) Does this sound close enough for me to weld the perches up solid? If I have to I can always add a shim if needed.

Just wanted to make sure that I am not way off.

Thanks in advance for any help.

[BMR Tech]

If both are pointing downward basically creating a "V", one angle is 3 degrees and the other 5-1/2 then you actually have 8-1/2 degrees of u-joint angle which is excessive. You could shim it later but I would correct it now before you fully weld the perches on. Typically a u-joint does not like to see much more than 4 degrees. I would knock those tacks loose and shoot for somewhere around 2-3 degrees of combined angle.

[68400BIRD]

If both are pointing downward basically creating a "V", one angle is 3 degrees and the other 5-1/2 then you actually have 8-1/2 degrees of u-joint angle which is excessive. You could shim it later but I would correct it now before you fully weld the perches on. Typically a u-joint does not like to see much more than 4 degrees. I would knock those tacks loose and shoot for somewhere around 2-3 degrees of combined angle.

Thanks for the advice. I just got off the phone with someone over at Currie and thats exactly what they told me. Better to fix it now than later when it's all painted. Like you mentioned I can always add a shim later to dial it in.

[John Wright]

Rob, is it too late to raise the rear of the tranny up a degree or two?

Maybe I mis-read what you were saying....the tranny mount and cross member is in the stock location? But just the spring perches are way off?

[68400BIRD]

Rob, is it too late to raise the rear of the tranny up a degree or two?

Maybe I mis-read what you were saying....the tranny mount and cross member is in the stock location? But just the spring perches are way off?


John, if I raise the tranny up it will make the driveshaft have even more negative degrees. I need to raise the pinion up on the rearend. Just need to grind out a few spot welds reposition and tack back in place. Should have it done this weekend. Then I can get onto my rear disc brakes.

[John Wright]

Ah...I see, I was mis-reading your conditions....I took it as you had the tailshaft pointing down 5.5° and had the pinion shaft pointing down 3°.

[Skip Fix]

There are some 4 wheel truck sources that have larger pinion angle shims. I had a 12 bolt I'm putting in a 79 Camaro that a shop welded perches on for me. It was 12-13 down! It's about right at 3.5 with a 8 degree shim.

[68400BIRD]

Worked on the car last night. Broke all the welds free and now have the drive shaft angling down 1 degree and the pinion angling down 3 degrees.

[old66tiger]

What is the degree of the tranny output shaft? You can't figure final angle without knowing that piece of information. The tranny and rear end should have equal and opposite angles to them otherwise you will have un-even driveshaft velocities at each end which will lead to massive vibrations. Check out this article and make sure you have all the facts.

http://www.markwilliams.com/driveshafttech.aspx

Also, an angle finder like this one makes setting DL angles a breeze

http://www.wixey.com/anglegauge/index.html

Yea, it's for the woodworker, but it is small and works great for the Dl work.

[68400BIRD]

Driveshaft is at about 1-2 degrees angling down. With a load on the drivetrain the rear should come up a few degrees.

[John Wright]

Rob, Take out the drive shaft and put the angle finder on the very end of the tail shaft of the transmission(output shaft)...this will tell you what the angle of the tail shaft is.

[68400BIRD]

The tail shaft never moved it's still at 3 degrees angling down. I now have a few options. I can raise the tranny with a small shim to get to 0 or angling up. and I can shim the rear either way. From what I have read and heard you never want the pinion angling up. Now remember this is on an uneven floor. I'm just making comparisions between the two. I'm real close to having it all straight back with just a little angle down on the pinion. If I have any problems I should be able to shim from here. Unless someone sees something wrong. LOL

[John Wright]

If you zero your angle finder out on the bottom of the rocker panel/door sill or frame rail...everything should be relative to those points so you can compare apples to apples, and the level of the floor shouldn't matter.