Rear drop - correcting pinion angle

[Chuck U&R]

I've got a '76 C-10 beater / rustbucket I'm hot-rodding on the cheap.
I cut the front coil springs by 1 1/2 coils which got the tops of the
235/75-15's just up under the fender lip - perfect !
To drop the rear I ground the rivets off the front leaf spring hangers and inverted them. That brought the ass end down to level with the front (stock length rear shackles!) but I know I've changed the pinion angle.
So the question is how much wedge do I need to add the pinion to get it
back to the 'correct' angle so that my driveshaft is not a jumprope.
Is there a 'rule-of-thumb' like maybe 1* per inch ?

I'm hoping that someone has done this before and save me the trial and error work.

TIA

[Captkaos]

There is no set shim to tell you. The angle of the trans must match that of the rearend. They typically should be around 2-5 degrees.

[boxrodz]

That's an unique way to drop the rear. I suppose flipping the axle would have given you too much of a drop with respect to your front drop. I don't of anyone who has done this, but like Captkaos stated, you should try to match your pinion angle opposite to that of the transmission angle. To accomplish that, you would have to set it up at ride height and measure the angle of the transmission. I did run some numbers (and assuming you didn't change length between the leaf spring eyelets when you flipped the front hanger and relocated it), I came up with the following table:

[Chuck U&R]

Thanx for the replys -
I seem to remember a post that stated that the deck of the intake manifold was parallel to the crank / tranny and can be used as the reference point to
measure engine angle ?????????

Is this correct or is my memory fuzzy???

[85X3]

If you know of an alignment shop that does big rigs, they will have caster shims that can be used between spring and spring pad. They come in different degree increments. You may have to combine two different shims to get the angle you need. Good luck.

[boxrodz]

Originally Posted by Chuck U&R

Thanx for the replys -
I seem to remember a post that stated that the deck of the intake manifold was parallel to the crank / tranny and can be used as the reference point to
measure engine angle ?????????

Is this correct or is my memory fuzzy???

I vaguely remember reading (or hearing) this.
... or maybe it was the carb.?

[Slonaker]

Originally Posted by Chuck U&R

Thanx for the replys -
I seem to remember a post that stated that the deck of the intake manifold was parallel to the crank / tranny and can be used as the reference point to
measure engine angle ?????????

Is this correct or is my memory fuzzy???

I read something a few months ago that said the intake is designed to be parallel to the ground. We aren't much help on that, are we?

Slonaker

[Chuck U&R]

I guess I'm just gonna have to crawl up under the truck
(now that it's lowered) and measure an imaginary line thru the trans and set the pinion to the opposing angle keeping the two lines parrallel.
I guess the U joints are there to take care of the spacing between the parrallels.

[piecesparts]

Set the vehicle on a set of jack stands (all four points, MAKE SURE that the rear axle is setting on the jack stands) and then use an angle gauge at the rear end (set it on the top of the housing just above the U-joint and then set it on top of the tranny tail shaft housing. Once the angles are determined, then cut and design driveline. I am running a 91 Chevy shortbed with a 1 degree shim installed in my rear axle pads for alignment.

[Canadian72GMC]

Best to have the truck on a drive on 4 post hoist. Measure off the starter, runs parallel to the crank. Then measure off the yokes and shaft/s and subtract measurements to get angles. You need at least 1 degree to keep the needles in the u-joints turning to avoid brinelling the joints. Too much angle = vibration.

[Malo83]

Sheeet!!! you guys gave me a headache just reading this post

[boxrodz]

Originally Posted by Malo83

Sheeet!!! you guys gave me a headache just reading this post

Here's you go, Malo...

BTW Chuck, did you make any progress?