Stock ride height

[Schurkey]

"Z height" is the official, specified ride-height. It's what GM wants your truck to ride at.

If you deliberately screw-up the "Z height" by raising or lowering the suspension, (not a body lift or body drop via the body bushings, or lifting/lowering the truck using only goofball tire/wheel sizing) whatever your ride height ends up at, is where you want the control arms to be torqued at. Control arms mounted on BONDED RUBBER bushings must be torqued at whatever the ride-height is. None of this matters if you have non-bonded (Polyurethane or Delron, or whatever) bushings.

 

[scott2093]

If you deliberately screw-up the "Z height" by raising or lowering the suspension, (not a body lift or body drop via the body bushings, or lifting/lowering the truck using only goofball tire/wheel sizing) whatever your ride height ends up at, is where you want the control arms to be torqued at

I had just edited my post when you were responding I guess...
I found what I did from my post on another forum...does this sound right?

I then put the axles in and the tires back on, and put the truck on the ground. When I measured the z height, it was off by 2". So I adjusted the torsion keys to get the z height where it is supposed to be and torqued down the control arms while it was on the ground.

 

[Schurkey]

Yup, that'll work.

Hopefully, you bounced the suspension a few times after changing the torsion bar adjustment.

 

[scott2093]

Hopefully, you bounced the suspension a few times after changing the torsion bar adjustment.

I did not iirc.
Would that mean having to loosen both control arms, getting the z height where it needs to be with bouncing, then re-torquing control arms?

 

[Schurkey]

You'd loosen all four control arms, not just two. That would be "best practice".

In truth, I'd have trouble justifying the effort at this point. You got the "Z-height" close if not exact. I don't think the bushings were in any danger. OTOH, given the time lapse since then, if there were going to be any damage to the bushings, it's already happened.

 

[scott2093]

You'd loosen all four control arms, not just two. That would be "best practice".

Yes, sorry. Was talking about the side I'm working on... of course upper and lower...

In truth, I'd have trouble justifying the effort at this point. You got the "Z-height" close if not exact. I don't think the bushings were in any danger. OTOH, given the time lapse since then, if there were going to be any damage to the bushings, it's already happened.

Thank you. Was kinda wondering the same thing.

 

[scott2093]

In truth, I'd have trouble justifying the effort at this point. You got the "Z-height" close if not exact. I don't think the bushings were in any danger. OTOH, given the time lapse since then, if there were going to be any damage to the bushings, it's already happened.

I am going to replace my front differential driver's side axle bearing and seal. Need to scooch some things out of the way. Figured it would be a good time to check my z height. I am going to loosen the sway bar, move the end links... also want to loosen upper and lower ca bushings to address proper preload on them...... I've already released the tension on the torsion bars.....

So , I have slightly larger tires than stock...285/75/16..a 3" body lift...... not sure it matters as it relates to setting z height?

I can obviously get z height very easily by jacking up the lower ca since the torsion bar is unloaded.... this would make things easier to get to with wheels off.......
But, considering my tires, is it just better to set everything down on wheels and tires under truck's weight, then torque all the ca bushings and sway bar links etc.... then crank the torsion keys to get at the factory 6"ish z height? I don't feel like I can ever understand the best way since I don't have a stock set up as it relates to tires and the 3" body lift...

 

[Schurkey]

I am going to replace my front differential driver's side axle bearing and seal.

I'm not clear on this. Are you replacing the bearing and seal for the differential output shaft; or are you replacing the more-common hub and bearing assembly in the steering knuckle?

Figured it would be a good time to check my z height. I am going to loosen the sway bar, move the end links... also want to loosen upper and lower ca bushings to address proper preload on them...... I've already released the tension on the torsion bars...

Not sure why you're doing all that if you're replacing the hub and bearing assembly. If you're digging into the differential, some of that might be needed to get the CV shaft out of the way.

So , I have slightly larger tires than stock...285/75/16..

Tires mean NOTHING in terms of "Z-height". The tires raise or lower the vehicle depending on their compressed radius, but that doesn't change the suspension settings.

a 3" body lift...... not sure it matters as it relates to setting z height?

Body lift means NOTHING in terms of "Z-height". The body lift doesn't screw with the suspension.

I can obviously get z height very easily by jacking up the lower ca since the torsion bar is unloaded.... this would make things easier to get to with wheels off.......

OK. How do you plan to match the "Z-height" once the vehicle is supported by the torsion bars?

But, considering my tires, is it just better to set everything down on wheels and tires under truck's weight, then torque all the ca bushings and sway bar links etc.... then crank the torsion keys to get at the factory 6"ish z height?

You tighten the control arm bushings AFTER getting "Z-height". DO NOT tighten them BEFORE getting "Z-height".

My '88 service manual shows "Z-height" should be 73.6mm + or - .6mm. That's nowhere near 6", not even half that. Z-height would be 2.87 inches + or - 1/4 inch.

Z-height is measured from the bottom of the steering knuckle at the ball-joint area, to the center of the lower control arm bushing. The angle of the control arm matters. The angle of the control arm is affected by the tension on the torsion bar, and vehicle weight. The control arm and torsion bar matters, as does the NORMAL loading on the suspension.

 

[scott2093]

I'm not clear on this. Are you replacing the bearing and seal for the differential output shaft

Yes this... the needles were kinda crunchy feeling while spinning and there is a bit of vertical/rotational wallered feeling slop once the cv axle is mounted..but it's actually not as noticeable with just the flange mounted....idk....Hearing groaning and am suspect of it.... thinking about hacking my old cv axle to put in place to hold the wheel bearings together and give it a ride...But my old cv axles are oem and was kinda hoping to have them rebuilt down the road....

Not sure why you're doing all that if you're replacing the hub and bearing assembly. If you're digging into the differential, some of that might be needed to get the CV shaft out of the way.

Yeah, just to get cv axle out...and I want to re address the ride height and bushing torque even though I know it could be moot after riding around for as long as I have....

Tires mean NOTHING in terms of "Z-height". The tires raise or lower the vehicle depending on their compressed radius, but that doesn't change the suspension settings.

Body lift means NOTHING in terms of "Z-height". The body lift doesn't screw with the suspension.

Great. I was assuming that from what I've read. Just wanted to verify.

OK. How do you plan to match the "Z-height" once the vehicle is supported by the torsion bars?

This is where I get confused because I know if I torque everything at z height before adding wheels and the weight of the vehicle, I have to go back in a futz with the torsion keys to get the ride height correct because it changes once the vehicle is down. I don't understand this yet.

You tighten the control arm bushings AFTER getting "Z-height". DO NOT tighten them BEFORE getting "Z-height".

So, everything loose, torsion bars unloaded (or I can preset them to the 34mm), set the vehicle on it's weight, adjust the torsion keys to get z height correct( I'll keep weight off when cranking keys and keep checking), then torque all bushings...even sway bar and end links in this case?

My '88 service manual shows "Z-height" should be 73.6mm + or - .6mm. That's nowhere near 6", not even half that. Z-height would be 2.87 inches + or - 1/4 inch.

93 k1500 and k2500 is 157mm +-6mm

 

[Schurkey]

So, everything loose, torsion bars unloaded (or I can preset them to the 34mm), set the vehicle on it's weight, adjust the torsion keys to get z height correct( I'll keep weight off when cranking keys and keep checking), then torque all bushings...even sway bar and end links in this case?

Get the torsion bar adjusters approximately correct by pre-setting the adjustment. Adjust from there as needed to get "Z-height" correct. You're right about actually making the adjustment with the suspension unloaded so the adjuster bolts aren't stressed as much. Bounce the suspension a couple times, or roll the vehicle forward and back a few feet to "settle" the suspension.

Then tighten the control arm bushings--8 places; and assure that the eccentrics on the upper bushings are set for proper camber/caster. Either put them where they were, or allow the alignment shop to adjust the eccentrics and tie rod sleeves as needed to get camber/caster/toe set properly.

IN GENERAL, nobody loosens the sway bar mounts or end links when setting "Z-height", but it can't hurt. The mounts would matter more than the end-links. The end-links can be tightened at any point in the process.

This is another in a list of items why I use non-bonded control arm bushings (Polyurethane inserts instead of bonded rubber) whenever possible. With non-bonded bushings, the control arms can be torqued in ANY position. Saves a bunch of hassle.

93 k1500 and k2500 is 157mm +-6mm

Okay. You're more correct than I was. The '88 service manual is FILLED with errors. I just looked at the '88 Service Manual SUPPLEMENT, and it's got corrected figures of:
K1,2 without F60 135 ± 6.0mm
K1,2 with F60 161 + 6.0mm

"F60" being "Heavy duty suspension", I guess.