Lower a arm, moved forward for caster

[CarlsLQ9SS]

So I moved the lower a arms forward 3/4" and when I put the spacers and shims on the upper a arms I barely get the full thread of the rear nut on it. I used square body a arms and the stock cross member that come on the truck originally in 1971. Are the studs for the upper a arms shorter on the 71 crossmember than they are on the newer square body a arms. I'm worried about getting the alignment right when the time comes. Hopefully someone that has run into this will chime in. I followed an old thread that someone done a how to on and with the spacers that was recommended I can't get any shims in the rear stud on the upper a arm. Here is a picture of what I have as of now.

[kwmech]

Get rid of the convex washers if there is no concave place for them and just use the shims. Mi-matched parts

And why did you move the lower shaft forward out of the index hole? Should be enough alignment to get the proper caster

[CarlsLQ9SS]

Originally Posted by kwmech

Get rid of the convex washers if there is no concave place for them and just use the shims. Mi-matched parts

And why did you move the lower shaft forward out of the index hole? Should be enough alignment to get the proper caster

I followed an old thread on here called my caster mod I think was the name of it. He drilled a new index hole in the lower a arm shaft to move it forward to gain more caster.

[Boog]

Carlos have you looked in the suspension forum yet? You may get more response down there as it is suspension specific. A number of guys have done this mod but I am unaware of any issues with it.
They say 5 to 6* positive caster is what you want for good return to center and handling. I have not done this yet but will consider it.

[CarlsLQ9SS]

Originally Posted by Boog

Carlos have you looked in the suspension forum yet? You may get more response down there as it is suspension specific. A number of guys have done this mod but I am unaware of any issues with it.
They say 5 to 6* positive caster is what you want for good return to center and handling. I have not done this yet but will consider it.

Thanks Boog, I'll check it out!

[HO455]

I too did the caster modification that involves redrilling the lower control arm shaft. How much is your truck lowered? The lower the truck's ride height is the more shims it takes to get things come around to acceptable specifications. Remember alignment specifications are trade offs. You're looking for the best balance for your intended usage. The factory has it's own parameters in mind when they publish their recommend alignment specifications.
Do not remove the convex washers! They are there so the shims can sit properly against the upper control arm shaft. In order to align the wheel properly the upper control arm shaft will not be parallel to the frame. This means that the shims will only contact on one end. In order to avoid having to make angled shims GM used the convex washer so the shim will seat flat against the control arm shaft and the center part of the shim will seat against the washer securely. It is possible for the shims to work out without the washer. (Something I know from experience )
You can look at the link below for details on what I did with my Burban and it's alignment. Unfortunately it is somewhat spread out in the thread so you will have to do some scrolling.

https://67-72chevytrucks.com/vboard/...698377&page=11

This links to the previous page showing how I modified the index on the shaft.

https://67-72chevytrucks.com/vboard/...698377&page=10

[CarlsLQ9SS]

Thank you for the links, now i get to do some more reading on your awesome build! Read a few pages so far, and looks like alot of good info!

[HO455]

Originally Posted by CarlsLQ9SS

Thank you for the links, now i get to do some more reading on your awesome build! Read a few pages so far, and looks like alot of good info!

Thank you sir. Good luck with yours.

[SCOTI]

Originally Posted by HO455

I too did the caster modification that involves redrilling the lower control arm shaft. How much is your truck lowered? The lower the truck's ride height is the more shims it takes to get things come around to acceptable specifications. Remember alignment specifications are trade offs. You're looking for the best balance for your intended usage. The factory has it's own parameters in mind when they publish their recommend alignment specifications.
Do not remove the convex washers! They are there so the shims can sit properly against the upper control arm shaft. In order to align the wheel properly the upper control arm shaft will not be parallel to the frame. This means that the shims will only contact on one end. In order to avoid having to make angled shims GM used the convex washer so the shim will seat flat against the control arm shaft and the center part of the shim will seat against the washer securely. It is possible for the shims to work out without the washer. (Something I know from experience )
You can look at the link below for details on what I did with my Burban and it's alignment. Unfortunately it is somewhat spread out in the thread so you will have to do some scrolling.

Just to add....
Lowering a truck can impact the quantity of shims required. How it's lowered has more to do w/just how much. Aggressive spring drops usually require more shims vs a drop spindle + mild spring drop.

I believe the truck in question is a 71 but it's using 73 & later arms. The 73 & later arms use the convex washers because the mounting shaft is set-up for them. Earlier trucks or shafts w/o the 'divot' don't require them.

Generic alignment shops will traditionally attempt to get the settings that are "In the Book". You want better settings. Factory stuff calls for (in general): 1-3.5° Caster; .5 - .7 POS Camber; 1/16 - 3/16 Toe-in.

The caster mod will get you easily in to the 5° range. Too aggressive can be too much as well so that 5-6° would do well.

Camber needs to be opposite what the factory specs, Aim for 0 - .7° NEG. I usually request .5 NEG & it works well for daily driving. Go more aggressive if you're building a 'sport' truck. As a side benefit, negative camber requires fewer shims on a set-up like this (C10's).

Toe is kind of regulated to how much tire is involved. I would try to keep it on the lower side of the specs @ 1/16 - 1/8.

[CarlsLQ9SS]

Originally Posted by SCOTI

Just to add....
Lowering a truck can impact the quantity of shims required. How it's lowered has more to do w/just how much. Aggressive spring drops usually require more shims vs a drop spindle + mild spring drop.

I believe the truck in question is a 71 but it's using 73 & later arms. The 73 & later arms use the convex washers because the mounting shaft is set-up for them. Earlier trucks or shafts w/o the 'divot' don't require them.

Generic alignment shops will traditionally attempt to get the settings that are "In the Book". You want better settings. Factory stuff calls for (in general): 1-3.5° Caster; .5 - .7 POS Camber; 1/16 - 3/16 Toe-in.

The caster mod will get you easily in to the 5° range. Too aggressive can be too much as well so that 5-6° would do well.

Camber needs to be opposite what the factory specs, Aim for 0 - .7° NEG. I usually request .5 NEG & it works well for daily driving. Go more aggressive if you're building a 'sport' truck. As a side benefit, negative camber requires fewer shims on a set-up like this (C10's).

Toe is kind of regulated to how much tire is involved. I would try to keep it on the lower side of the specs @ 1/16 - 1/8.

Thank you for all the information, now I know what to ask for when I take it for thame alignment. It is lowered with factory springs that have been cut. And it is a 71 with 73 up a arms. What I was really concerned about was how much thread that would catch on the rear stud on the upper a arm. Thank you for all the numbers you put up, now I can find them easily find them when I get it ready!

[SCOTI]

Originally Posted by CarlsLQ9SS

Thank you for all the information, now I know what to ask for when I take it for thame alignment. It is lowered with factory springs that have been cut. And it is a 71 with 73 up a arms. What I was really concerned about was how much thread that would catch on the rear stud on the upper a arm. Thank you for all the numbers you put up, now I can find them easily find them when I get it ready!

No problem.

Back in the day (>30yrs ago), we would sometimes need to put longer upper shaft bolts in for the excess shims as a result of just cutting coils. With drop spindles & other lowering options, you can keep the spring longer & usually not need the super thick shim stacks.

[gmc684x4]

My question is why not buy new 73 up studs to get longer bolt length
Then there will be less worry of catastrophic failure of thread engagment at say Interstate highway speeds

[CarlsLQ9SS]

Originally Posted by gmc684x4

My question is why not buy new 73 up studs to get longer bolt length
Then there will be less worry of catastrophic failure of thread engagment at say Interstate highway speeds

I was wondering if the 73 up had longer studs. Maybe someone that knows for sure will chime in.

[SCOTI]

Originally Posted by gmc684x4

My question is why not buy new 73 up studs to get longer bolt length
Then there will be less worry of catastrophic failure of thread engagment at say Interstate highway speeds

The point previously being made was a longer stud may not be required. When running NEG vs. POS camber it takes less shims. With the Caster mod it will require fewer shims.
Why put a longer stud in where it's not needed?

[HO455]

There are quite a few threads about "Not enough threads" problem" which I have read and the 1973 stud replacement cure is not one I have heard of. The studs may be longer but maybe the splines are wrong. I'm not saying it isn't a cure but if it was that simple I don't think I would have found so many threads on the issue. The most common replacement cited are ones from Speedway and Jegs. Not vehicle specific so you would have to measure yours to determine if they would not only be longer but that they fit correctly.