rear end pinion angle issues

[Lookin4the1]

I took my 49 gmc on its maiden voyage today to the muffler shop. on the way back i noticed under acceleration the rear end is literally rotating up to 30 degrees from where it is at stopped. needless to say this scared me to death. I will explain what i've done so far below.

1995 s10 frame
3" Belltech lowering leaf springs
1.5" home made set back plates to center the rear tires in the wheel well.
blisten(sp) drop shocks.

i might need pinion angle shim? whatever it is is scary as hell driving it and it starts vibrating pretty violently around 30mph.

[tinydb84]

Is it moving back and forth of just stuck there? Did you weld the perches on?

[racecougar]

Right, if it's actually rotating back and forth, shims aren't the answer. Are the leaf springs wrapping, is the housing rotating on the tubes, or are the tubes rotating on the spring pads?

[Lookin4the1]

the tubes are rotating on the spring pads. i've got everything bolted down tight. If by chance it is the leaf spring wrapping. i'll have that fixed in a few days. i have a set of cal tracs I'm putting on just to be safe

[PGSigns]

The tubes have to be welded to the spring pads. Also the blocks need to be a bit wider than the spring pads. How much is the rear offset from the locating pin? That can have a effect on the spring.
Jimmy

[Lookin4the1]

right around 1.25 inches. on the spring pad. i plan to eliminate any chance of spring wrap with these caltracs

[mongocanfly]

Pgsign right..you gotta weld the spring pads to the axle tube..don't rely on bolts to hold it..if its moving that much I'm suprised you havnt broke somethimg yet..30 degrees is pretty drastic..make sure your pinion angle matches your trans angle..usually around 3 degrees

[Lookin4the1]

i apologize for my idiocracy, i'll post an image so you guys can clear it up for me. I think you're telling me to weld A to B in this photo?

[racecougar]

To reiterate: The spring pads must be welded to the tubes.

[Lookin4the1]

the perch is secured to the axle tube because it came stock that way. i have no clue why this thing is rotating now.

[mongocanfly]

The way your post #4 read it sounded different.. in your picture the perch lS welded to the axle tube..that's ok .don't weld a to b ..from what I see there should be no way that differential will rotate 30 degrees as long as the perches (a) is welded to the axle tube..if it would rotate 30 degrees i would think your u-joints would be broke..if it is 30 degrees then you've got a serious problem elsewhere

[Lookin4the1]

yeah i'll do some more investigating but I'm pretty sure i have a serious problem. problem is it only does it when accelerating so its hard to actually see my issue.

[mongocanfly]

Hang a gopro underneath..

[PGSigns]

Post pictures of your entire setup if you can. We may be able to see something amiss.
Jimmy

[Keith Seymore]

The pinion nose of the axle moves up and down quite a bit under acceleration and deceleration, due to leaf spring wind up.

I had an opportunity to drive my '87 pickup without the box on it and was surprised at how much motion there was going on back there.

Assuming that the perches are welded to the tube it could very well be normal.

K

[mongocanfly]

This is just a thought..keith is right that there's a lot of movement in the rear..but..does your driveshaft have a slip joint in it? If so do you have the u-joints in time? If not it will shake your teeth out..also, check for bad u-joints

[Lookin4the1]

drive shaft is all new, it is 2 piece from the s10. all the joints are new. i'm not near the truck it will be next week before i can post a few pictures of the entire setup.

[mongocanfly]

Won't matter if its all new or not if it isn't timed correctly...get a good pic of the entire driveshaft...are you familiar with u- joint timing?

[Lookin4the1]

i'll try to phase the U joints on tuesday and take better pictures.

[Lookin4the1]

[mongocanfly]

Were the u joints outta phase?

[Lookin4the1]

i'll be checking on tuesday/wednesday. unfortunately the truck and I don't share the same physical address as my work makes me travel. I'm going to take it apart at the slip shaft and line everything up. i read that < 3 degrees is ok and that I'm just to take a inclinometer and measure on top or bottom of each u joint cup. anything else i should look for?

[mongocanfly]

Yep..3 deg down on trans ..3 deg up on rear diff

[Keith Seymore]

Originally Posted by Lookin4the1

i'll be checking on tuesday/wednesday. unfortunately the truck and I don't share the same physical address as my work makes me travel. I'm going to take it apart at the slip shaft and line everything up. i read that < 3 degrees is ok and that I'm just to take a inclinometer and measure on top or bottom of each u joint cup. anything else i should look for?

...

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

K

[Lookin4the1]

after checking the angles and phasing. they are all correct. What i did notice was something much simpler. I made my own set back place and I believe I made them too short. I'll take some better pictures tomorrow morning.

What I think is happening is under acceleration the rear end rotation upward what would be an acceptable amount nut it basically falls off the back of the setback plates. when i built them i basically did a 2.5" x 5" plate on top of the leaf spring, cut the hole out so it would sit flush and then welded in a 5/8" round stock bar to fit inside the perch. the plate ends about 1/4" after the round stock I welded in so half of the perch on the rear end axle is not touching anything.