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Rear Suspension Geometry Help.

broncoman6524

broncoman6524

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On my 77 my rear setup is as follows. Stock K20 leafs, the rear hangers are stock front rear spring hangers. (Hope that makes sense) With a 2" block and a 6degree shim installed backwards.

Obviously not the greatest combination.:D

It I use just the blocks the pinion angle is set at 180 degress. IE straight, so with the shims it is at about 200degress? IE bent in an upwards direction.:eek1:

It is the same with a 3" block with the integrated shim.


What would my best decision here be? Get a set of 4" springs and move my hangers until the pinion angle and shackle angle are correct?

Here are some pictures with the 2" and shim.
100_6656.jpg

100_6657.jpg


And because I'm proud that I actually finished it...
100_6654.jpg
 
Your rear pinion angle is not that critical. Just set it up as you want it. I just set mine up higher than stock due to drive shaft angle and clearance. The lower it is the more rocks and other stuff will grab that yoke. Just point it at the xfer case and forget about it.

pinion.JPG
 
Why are your shims in backwards? You're better off w/out them than in backwards.
 
what you should set your pinion angle at depends on what type of rear shaft do you have? If you have a double cardian, you need the pinion at the same angle as the drive shaft or just a few degrees under so under throttle it moves up to the correct position. If you have single cardian you want the angle opposite and equal.
 
The shims are inbackwards, because as I said with out them the angle is set flat.

Since it is a single cardian I was attempting to make the angles opposite, which was done by installing the shims backwards.
 
also in your picture it looks like you are missing a snap ring on the driveshaft slip yoke, post a pic of the tcase and diff together showing the whole shaft then ill have a better idea if it is right
 
have you put an angle finder on the front??i see you have longer shackles and its hard to tell by the pic but looks like your front pinion is angled down causing bad caster
 
I couldnt get a very good picture of both yokes on the shaft. These are the best that I could do.
100_6664.jpg

100_6665.jpg

100_6666.jpg

100_6663.jpg

I do have longer shackles on the front, however the pinion/spring mounts *appear* to be level. No I have not put the angle finder on it. Mostly because I wasn't worried too much about it. The truck doesn't pull horribly so the caster must not be off very badly.
 
your pinion angle looks spot on if you ask me... we would need to have angle finder measurements to say for sure though

whatever you do DONT point your pinion yoke at your tcase as you have single joint shafts... that is only acceptable for a driveshaft with a CV on upper end. what you have done with the block and shims is what your supposed to do. when you install a shackle flip in rotates your pinion angle up and putting blocks in tall side forward gets the pinion back down where it needs to be. i did the same thing with my 2" blocks when i put a shackle flip on my truck 2.5 years ago and have yet to have a single problem
 
rockmad said:
Your rear pinion angle is not that critical. Just set it up as you want it. I just set mine up higher than stock due to drive shaft angle and clearance. The lower it is the more rocks and other stuff will grab that yoke. Just point it at the xfer case and forget about it.
Click to expand...
:eek1: Pinion angle is only important if you care about things like vibrations from the driveline or U-joints lasting more than 100 miles. :rolleyes:
 
Cajun4x4 said:
your pinion angle looks spot on if you ask me... we would need to have angle finder measurements to say for sure though

whatever you do DONT point your pinion yoke at your tcase as you have single joint shafts... that is only acceptable for a driveshaft with a CV on upper end. what you have done with the block and shims is what your supposed to do. when you install a shackle flip in rotates your pinion angle up and putting blocks in tall side forward gets the pinion back down where it needs to be. i did the same thing with my 2" blocks when i put a shackle flip on my truck 2.5 years ago and have yet to have a single problem
Click to expand...

Yeah the angles looks pretty good to me too. Do you have vibes?

You arent going to get a better shackle angle without moving the shackle hangars and/or going to a longer spring. Lift springs will require putting the stock hangars back on and losing the flip.

What are you trying to accomplish?



Your rear pinion angle is not that critical. Just set it up as you want it. I just set mine up higher than stock due to drive shaft angle and clearance. The lower it is the more rocks and other stuff will grab that yoke. Just point it at the xfer case and forget about it.
Click to expand...
Yes it is critical to driveshaft U-joint life and Vibration prevention. If its trail only then not as big of a deal, but if you drive it on the street as well you want the angles correct:wink1:
 
I've posted this many times here, but here it goes again:

In theory, you want the operating angles for each u-joint to be the same (the operating angle is the angle between the yoke and the driveshaft, each at the t-case and pinion). When that is the case, the u-joint vibrations should cancel each other out and the shaft should spin smoothly (u-joints inherently vibrate based on the way they work).

The problem in that theory is that Spicer specs their u-joints at ~3 degrees max, most lifted K5's are more like 15. With angles that extreme, its very difficult to cancel the u-joint vibrations and usually there are driveline vibrations.


IME, pointing my single cardan (non-cv) shaft at the t-case had the least vibrations. If you're running a non-cv shaft you will probably have to experiment to find the point with the least vibrations.

The only guaranteed way to eliminate vibration is to use a cv-shaft.
 
38377k5 said:
I've posted this many times here, but here it goes again:

In theory, you want the operating angles for each u-joint to be the same (the operating angle is the angle between the yoke and the driveshaft, each at the t-case and pinion). When that is the case, the u-joint vibrations should cancel each other out and the shaft should spin smoothly (u-joints inherently vibrate based on the way they work).

The problem in that theory is that Spicer specs their u-joints at ~3 degrees max, most lifted K5's are more like 15. With angles that extreme, its very difficult to cancel the u-joint vibrations and usually there are driveline vibrations.


IME, pointing my single cardan (non-cv) shaft at the t-case had the least vibrations. If you're running a non-cv shaft you will probably have to experiment to find the point with the least vibrations.

The only guaranteed way to eliminate vibration is to use a cv-shaft.
Click to expand...


the 3 degrees is not the angle of the shaft but the angle of the ujoint its self. Shaft angles are greater than 3 degrees from the factory. And for GM testing ujoints angles are run up to 7 degrees and they last for days on end like this.
 
I have run my stock rear drive shaft pointed at the T-case for manny years now and no vibs or problems. If I set it up so they are = I get bind at full drop.
DJ
 
1979jimmy350 said:
the 3 degrees is not the angle of the shaft but the angle of the ujoint its self.
Click to expand...

Right, I was talking about the operating angle of the u-joint.


1979jimmy350 said:
Shaft angles are greater than 3 degrees from the factory. And for GM testing ujoints angles are run up to 7 degrees and they last for days on end like this.
Click to expand...

Hmmm, I don't remember where I got the 3 degree spec but I think its in the link below.

Lots of driveshaft and u-joint info.

Are you the one that works for AAM?
 
Why is it that I cannot use the flip and lift springs?

I have a set of 6" springs that I have been considering puttin back there once I can get larger front springs.
 
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