How to measure pinion flange angle?

jestlurnin

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I have a 78’ 55 with an Alcan lift put on by one of the PO’s. I have no clue what lift height the springs are meant to be.

There are no caster shims currently installed. I’m trying to chase down some serious road wander and think the lack of shims might be part of the issue and or the entire issue as I just rebuilt every steering component from the birfs to the steering wheel.

I downloaded an inclinometer app on my phone and put it on the flange on the diff the red arrow is pointing to in the picture below. It read about 7.2 degrees. Am I measure the angle correctly? Or should I just set my phone flat on the flange and see how far out of plumb it is?


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Usually the wander is from loose, worn trunion bearings. Check upper & lower both sides, check steering arm at top of knuckles for proper tightness. The flat where the arms attach should be 3 or 4 degrees, meaning they should be leaned back towards rear of vehicle. If yours aren't I'd start with a 2 deg. shim and see. I say that because IMO your pinion angle is good now, installing shims to correct steering will roll pinion down a bit, I wouldn't go more than 2 deg.. I would try the trunions first. Although given the list of things done you must have had the trunions out, how did they look ? did you put new bearings in ? shimmed properly ? how much preload did it set up to for rotating the knuckle ?
 

jestlurnin

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If I’m measuring a pinion angle of 7.2 isn’t that bad? From what threads I was able to find I am under the impression it shouldn’t be more than 1 degree.

All bearings are new. Shimmed correctly using SST, preload was set to factory spec. New TRE’s all the way around. Center arm was rebuilt, Mark A rebuilt steering box, intermediate shaft U joints replaced as well.

I’ll measure the angle at the top of the steering arms and see what I get. Hadn’t thought about that one.
 

jestlurnin

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Couldn’t you gain back some positive caster by putting stock length shackles on?
I am a complete nube when it comes to suspension. The deepest I’ve ever dove in before was changing shocks. So I have no idea if going back to stock shackles would help.
 
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I agree that a stock shackle or a set that's about 1" shorter than the ones on there would probably be worth the effort, I hate those fixed with a cross bar shackles anyway.
There are tones of shackles, I like ruff stuff because you can get any length and the size hole you want, fast too. Take them shackles off, inspect bushings, replace if nec.
( might be half yer problem), check bolts used to be sure they fit the hole in bushings correctly, replace if nec., for size, I personally hate the greasable ones. Use correct size hardware for the hole in bushings and get the matching hole punched in your new shackles. The frame side and spring side should be same but who knows whats in there.
A bushing check at frame end of spring wouldn't hurt, could solve wandering with bushings. I use old school drum brake grease on mine, its thicker and stays put longer IMO.
Grease everything, all tubes, spring ends, outside bushings, inside bushings, end of bushings where shackle rubs, bolt, smears like frosting, you'll love it.
don't be silly with it or you'll be wiping off what squishes out forever.
 

jestlurnin

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Ok! We got a plan moving forward. Shackles, gone, new bushings ✅, @Blastservices i usually always go 5ish pounds over what the FSM says but if I’m still having issues after all the other fixes I might go back in there.

Can someone confirm however that my pinion angle needs to be as close to zero as possible after all the fixes?

Thank you everyone.
 

A10Driver

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You are really after caster, not pinion angle. Check your caster and then decide if you want shorter shackles to correct caster, or if you can correct with shims, or a combo. You might need both. Stock should be between 2 and 3 degrees, most people prefer more than 3.
 
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Have you bothered to take your ride to an actual alignment shop that can give you the actual alignment figures? Once you have those you can address what measures are required to make things right. Without them you might as well be pissing into the wind!
 

jestlurnin

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Called 4 alignment shops and all said the 55 is too old for their computers, the one old school shop said their alignment guy is out for 2 months after having neck surgery….thought I’d try and see what I could fix in the mean time.
 

mrboatman

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Called 4 alignment shops and all said the 55 is too old for their computers, the one old school shop said their alignment guy is out for 2 months after having neck surgery….thought I’d try and see what I could fix in the mean time.
Their full of sh!t !! They can give you a read out of your caster/camber/toe. The toe is the only thing they can or will adjust.
 

1911

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Called 4 alignment shops and all said the 55 is too old for their computers, the one old school shop said their alignment guy is out for 2 months after having neck surgery….thought I’d try and see what I could fix in the mean time.

They are lazy, and don't want to mess with old leaf-sprung trucks. Find an old spring shop, there are usually some in any large city. They will know how to do align it.
 

jestlurnin

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They are lazy, and don't want to mess with old leaf-sprung trucks. Find an old spring shop, there are usually some in any large city. They will know how to do align it.
Not disagreeing with this statement at all!
Nearest big city is Portland Oregon if anyone has any recommendations I’m all ears.
 
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There is one factor not discussed yet, wheel bearings ? Have you checked the condition of those ? IMO alignment could tell you if you have a bent axle but other than that you can set toe in easy and the other alignment factors are not easy to change or not changeable. Did you find the deg of caster at the steering arm flat surface ?
Pinion at zero is great if front output is at zero, I'm sure you have read about the " Cut & Turn" which is a process to set the correct pinion angle or should I say the pinion angle you want and maintain caster settings. Need the current caster deg ? FWIW don't be suprised if they are .5 deg different.
 

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