Pinion angle and diff centering

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clementine

clementine

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Hello FABO!

I'm welding the axle tubes to the perches and i need some affirmation that in not forgetting something

to get the diff centered i can put a straight edge on the drum (with a couple of lugs to make sure its on) and measure from the fender and frame rail to make it even on both sides.

Right?

To get pinion.......uhhhhh, forgive me, i did use search option, but please double check me on this.

Pictures are from front to back.

Engine pan rail

Slip yoke

Driveline

Pinion yoke

Diff housing

What say you?

Welderup?
67 barracuda fastback 383 4speed 8 3/4.

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That's way too complicated. Here's how I do it. I use concrete blocks, because it works for ME. Flat and level concrete floor of course. Set the perches on the blocks and get them to "whatever" width you're needing. Put the rear upside down into the perches. You'll need a third stand under the pinion nose, of course. Now, double check your perch locations are correct center to center and equal distances from either end. Lastly, position the pinion 5 degrees nose DOWN. Double check again that you didn't move on the perches center to center or side to side. Tack the perches on and double check all the measurements again. If they're good, flip the rear end over so you can get to the perches good and weld them on solid. Since you were upside down and nose down 5 degrees, now, when you right side up, you will be 5 degrees pinion up, which is right where you want to be.
 
Thank you guys, this puts me on track!

I think I'm close.

I guess if i don't nail it first time, there is the shim route.
 
I appreciate youz guyz input on this.

One aspect i need to consider is that i do not have that big piece of fastback glass or interior in the car. To add to the situation, the tank is empty.

So ill add 150# to back end to see how much pinion rises from its current position and re calculate (or just wait until the friggin car is together more).

With trans down 3.5 and pinion down 5 that brings my total to 8. Minus what the pinion will rise under acceleration (traction dependant plus it's a street car) I'm guessing with SS springs, the pinion will only rise 4*.

That puts me a bit out at 4*.

I have the trans up a bit to get headers to clear steering gear so i could look into lowering the car a smidge in the rear and re check.

Thanks for listening, just writing this is helping me get my head around what is happening to the suspension under load/ rest.
 
Weight in the car? You're makin this WAY too complicated. Post 3 outlines how the MP suspension manual tells how to do it. 5 degrees nose down. "From there" you can manipulate anywhere you want with shims and it may not even need them. Since the weight of the car is not consistent, that's not a good landmark. But carry on and have fun!
 
On my non-Mopar race truck, I use the ATI Super Damper for my engine/trans angle. Then to the rear with the equal but opposite deal. Has always worked for me.
 
Here's a good utube vid on this: "How to properly setup & measure your pinion angle on your muscle car" though I thought that when you get that right that you lower the pinion a bit more to compensate for pinion rise on acceleration but this might just only be on a muscle/drag car but not on a DD. I'm learning too. EDIT I see that the gauge is hitting the ujoint cap strap in the one pic, I'm assuming that that was only to get a pic of the gauge setting on the bottom of the ujoint not to get an actual measurement. I would not go by the oil pan rail & the next pic after that I would use a round magnet to get to the actual ujoint flat cap itself. Just me I think I would get the angles correct then weld the perches at that point rather than the MP 5 degree setting (how often would you be swapping the rear end into another car)
 
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I would turn the driveshaft till one of the driveshaft ujoints is at 6 o'clock & take a reading on the cap itself then turn the driveshaft 1/4 turn till one of the pinion ujoints is at 6 o'clock & take another reading at the cap itself. you want the difference between the two numbers to be at least .5 degree but not more than 3 degrees but less is better & 2 degrees to .5 degrees is acceptable and then turn the front ujoint till the cap is at 6 o'clock & take a measurement then turn the driveshaft 1/4 turn till the transmission ujoint cap is at 6 o'clock & take a measurement. same as before you want the difference between em to be at least .5 degrees not more than 3 degrees & 2 or less is ideal & when done you want the 2 angles front and rear to be no more than 1 degree different from each other. now looking at this from the side of the car are the angles at the (front driveshaft/transmission ujoints) "up" or "down" and is the triangle of the driveshaft/pinion ujoints pointing "up" or "down" & you want one of these triangles to be "up" & the other "down" & you would shim the trans mount up or mill it down and or rotate the housing before you weld it to achieve that. However in the vid he states that these specs are for coil spring cars & leaf spring specs are different (I'm looking for em). just my OCD!
 
clementine said:
Hello FABO!

I'm welding the axle tubes to the perches and i need some affirmation that in not forgetting something

to get the diff centered i can put a straight edge on the drum (with a couple of lugs to make sure its on) and measure from the fender and frame rail to make it even on both sides.

Right?

To get pinion.......uhhhhh, forgive me, i did use search option, but please double check me on this.

Pictures are from front to back.

Engine pan rail

Slip yoke

Driveline

Pinion yoke

Diff housing

What say you?

Welderup?
67 barracuda fastback 383 4speed 8 3/4.

View attachment 1716175475

View attachment 1716175477

View attachment 1716175478

View attachment 1716175479

View attachment 1716175480
Click to expand...



This is a good video to explain pinion angle.
 
clementine said:
Hello FABO!

I'm welding the axle tubes to the perches and i need some affirmation that in not forgetting something

to get the diff centered i can put a straight edge on the drum (with a couple of lugs to make sure its on) and measure from the fender and frame rail to make it even on both sides.

Right?

To get pinion.......uhhhhh, forgive me, i did use search option, but please double check me on this.

Pictures are from front to back.

Engine pan rail

Slip yoke

Driveline

Pinion yoke

Diff housing

What say you?

Welderup?
67 barracuda fastback 383 4speed 8 3/4.

View attachment 1716175475

View attachment 1716175477

View attachment 1716175478

View attachment 1716175479

View attachment 1716175480
Click to expand...



Here is a video of my circle track car on my chassis dyno measuring pinion rotation on acceleration and deacceleration. It's a metric 4 link rear suspension and the pinion wraps about 2.3 degrees on acceleration under full load.
 
Thank you @92b ......very informational. I believe my pinion has too much angle (down or up is a matter of opinion.......see what I did there?....eh? OH PINION.....yeah ok.....that is bad....and makes little sense....).

but thanks!!
 
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