Learn me Chevy 2500 torsion bars

2008 Duramax. There's no springs under that front end/ just torsion bars.

I'm trying to reestablish a baseline, and understand how to properly adjust these.

I'm pretty sure PO randomly played with them to try to get a "North Carolina squat". Truck sits about 1" higher in the front than the rear (it was more than that before I put some weight permanently on the back). I'd like the truck to sit level.

My understanding is that I should be able to adjust the adjustment bolts on the keys at the rear of the torsion bars to both change the tension and adjust the height (a bit).

I have tried moving the bolts both ways- ride height doesn't change.

The bolts are currently backed out pretty far- nearly 2". I would assume this would mean low tension, and lower ride height. No difference.

I am also noticed some clunking/ looseness in the front end (which makes me think they could be too loose).

So, what's a good starting point? How do I establish a baseline? What's the right way to adjust these? Are they actually supposed to effect ride height?

• signed a Chevy dummy.

Torsion bars on those really don't ever clunk, that I've seen. Only exception was one that had aftermarket keys no bolts in it (for more low) if there was a big rebound/droop event, the suspension would decompress to the point where there was no tension at all on the bar and it would knock against the stop.

Those bolts should absolutely change ride height, but you will have to drive some and remeasure - those trucks have a lot of lateral travel when lifted up because of the A arm travel, so the tires scrub a lot through their travel. You'll probably have to adjust them more than you expect, though. At least on my older truck, I had to back the screws almost all the way out to get it where I wanted it. Doesn't have lift keys in it, does it?

Not sure about your clunk, but could be ball joints or sway bar links. It may also go away if you lower the front - those trucks wear stuff out pretty quick (and ride horribly) with a crank lift and no other supporting work.

Not sure why it wouldn't be changing ride height when you turn the bolts. On my '04, I put some 285/70-17s on it and wanted a bit extra clearance so I turned the bolts in 4 turns, which equaled just under 1.25" higher at the front fender. The ride quality did get a bit harsh I believe due to the aformentioned angle of travel of the control arms.

I'm with gearheadE30 here in that you may have torsion lift keys in there. They're clocked more than the stock ones to provide lift without needing to use the bolts to add preload.

4 turns? No way. I went 10 or 12 in each direction- no change.

Took the weight off before adjusting. Took it for an aggressive drive afterwards- still no change.

I'd guess something was hacked/broken at some point, as there's no real way for those bolts to do nothing. I don't even see how corrosion could cause enough bind to keep the keys from moving the suspension without the bolts also being rusted in place.

I'll be under my K2500 in a few minutes and can take pictures of the stock keys etc if that would help. (Although mines a 97)

My experience is roughly analogous to doc_speeders. 7 turns out brought the front end down almost 2".

Probably lift keys as has been suggested. They're already backed out to the point of being loose and it's still raised?

Do the keys look to be the same age as the truck? Are they rust-colored or are they clean and gray or black?

They look factory.

I didn't say they were loose. I said they were backed out nearly 2".

How can I identify OEM keys?

Can the keys be rotated on the torsion bars?

SVreX wrote: They look factory. I didn't say they were loose. I said they were backed out nearly 2".

Sorry, I assumed the clunking was from being loose from when you wrote:

"I am also noticed some clunking/ looseness in the front end (which makes me think they could be too loose)."

Clunking is probably unrelated

Not sure if the keys can be rotated...on my GMT400, it's a giant 6 point hex on the end of the torsion beam. That reclocks the key so far that there's really only one way you can install it. Not sure if the later ones had more points or were splined, but in that case they could be.

If you look under the upper A arm, I believe there is a droop bump stop (again assuming it's like my older truck). Are your upper arms sitting on those droop stops? That's basically the only way that loosening the screws wouldn't do anything, i.e. they still have enough tension to top out the suspension.

I'm assuming you tried loosening them as far as you could...still very surprised that you're not seeing any change at all, unless you've got aftermarket keys in there.

A popular way to get more lift out of Chevy torsion bars is to swap in Ford torsion keys. The hex is rotated differently so it adds more lift without being out of range of the adjustment bolts. If you back the bolts all the way out and it is still riding high, I would suspect aftermarket/Ford torsion keys. Or the rear of the truck has been lowered. If I remember correctly there should be a 3/4 lift block between the rear springs and the axle.

Edit: All this is true for GMT800 trucks, not sure about the 400's.

aftermarket lift keys can sometimes look pretty similar to factory keys so it may be hard to just look at and be able to tell the difference, but if you have loosened the adjuster all the way and it still sits high i would say they probably are aftermarket

stock vs. aftermarket, besides the surface rust the only visible difference is the clocking of the hex

In reply to edizzle89:

Agreed, that's why I asked what they looked like i.e.: black or silver as opposed to rust-colored to indicate if they were new(er) than the rest of the truck.

The adjustment screw passes through a half moon shaped nut (Part #4), which is inserted in the crossmember.

The key is sitting ON the half moon adjustment nut. There is no additional space for downward movement. The A-arms are NOT sitting on the bump stops.

The ride height is currently 25 1/2" from the fender to the center of the hub. My understanding is that OEM ride height should be about 23 1/2"- 24".

The reason I asked about rotating the key on the torsion bar is because that should give me adjustment which I do not currently have. Whether they are after market or OEM is kinda irrelevant if they are bottomed out with no adjustment space. If I could rotate the key 1 position, it would be clocked 60* from where it is. That would give me adjustment space (unless the key is then outside the range to the opposite direction).

I'm thinking the keys have been swapped, but they were installed incorrectly clocked 60* away from where they should have been.

This is all quite helpful as I've been wanting to drop the front of my truck a touch so it's more even when towing.

If it's still sitting up and the keys are hard against the half moon block, Someone has either swapped keys or swapped the torsion bars in backwards.

Look at the back of the torsion bars near the adjusters, there should be a part number stamped in the end. If there's no stamped number then they're probably in back to front.

There is a number stamped in the end if the torsion bar, but pretty hard to read in place. 985?

There is also a label about 6" from the rear of the bar with a longer number and bar code. Again, hard to read.

Let me go back to those bump stops... the truck is not resting on the bump stops, but it is close. Maybe 1/4" clearance at rest. Those are brand new bump stops I installed a couple weeks ago. The old ones were mangled (I assumed from off-roading).

The keys are held right now by the half moon blocks, and it is sitting about 1 1/2" above stock ride height.

The rear is not blocked. When I got the truck, it sat more level, but a little high. It is now (permanently) carrying about 1500 lbs in the back. It's a better ride height in the rear, so I'd just like to lower the front to match.

If the truck is close to the bumpstops in the front, how will lowering it there help?

In reply to SVreX:

You could certainly try reclocking the key. Worst case is it doesn't work the way you want and you just have to re-do it.

If your torsion keys are resting on the half moons, your as low as your going to get with that setup.

Think of the torsion bar, keys and lower control arm as a flat board. The more you twist the key towards the ground, the more the control arm will twist skyward, and vice versa. So the second that key rests on the half moon, you can't get the control arm to move any further upwards at rest, likewise, if the bolt is screwed all the way in, the key won't move upwards any further and therefore, the control arm won't move any further downwards at rest.

Regarding re indexing or re clocking your keys, I don't see it happening. The next position will be about 60° from where they are now. Even if you can get the adjuster bolts back in, you'll be hard down on the bump stops.

I'd say at this stage, if you want lower, your either in the market for drop arms or drop spindles. That is of course provided that noone has put lifted spindles, arms or balljoint spacers in there?

Some photos might help here?

SVreX wrote: There is a number stamped in the end if the torsion bar, but pretty hard to read in place. 985? There is also a label about 6" from the rear of the bar with a longer number and bar code. Again, hard to read. Let me go back to those bump stops... the truck is not resting on the bump stops, but it is close. Maybe 1/4" clearance at rest. Those are brand new bump stops I installed a couple weeks ago. The old ones were mangled (I assumed from off-roading). The keys are held right now by the half moon blocks, and it is sitting about 1 1/2" above stock ride height. The rear is not blocked. When I got the truck, it sat more level, but a little high. It is now (permanently) carrying about 1500 lbs in the back. It's a better ride height in the rear, so I'd just like to lower the front to match.

dumb question but are you talking about the actual bump stops or do these trucks have 'droop' stops and that is where you are getting that measurement?