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Old 06-09-2012, 11:23 AM   #1 (permalink)
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Torsion bar fatigue

I dont' know if this is a head's up or what and it's probably not new to anyone ...

I noticed that the front of my 07 2500HD was sagging a little after I bought it from my brother's company. No problem, I'll just add a little on the bolts and level it back out, then put the 285's on it. Nope. Turned the bolts in until the key "bottomed out" in the crossmember and got another 1/4" out of it. No big deal, it's a 3/4 ton truck and 285's should fit easy enough.

Nope. Driver's side makes contact with the inner fender. FFS, I'll just live with it. Order new "lift" keys. Welp, that didn't work either. Ordered new shocks (Bilstin 5100s) and begin to replace them... then we get down to the root of the problem. The shocks were dead. Dead like, you could compress any of them from the front or the rear and they'd stay compressed. I tried the first one with the lower eye on the ground. When I put my weight on it, it collapsed so fast, I almost ate concrete.

Basically, you could compress all of them just by using your hands. Three days later, one of them finally managed to expand almost all the way back to it's original length. A little research and I'm seeing that the factory shocks are only good for 20-30K miles.

In my mind, with no shock to dampen the loads put on the torsion bars, they simply fatigued to the point that they offer no adjustment. Something to think about for those of you who may have noticed your front end sagging a little. I'm gonna have to order new bars or find some out of a junkyard and as I remember it, there's about 2 dozen different GVWR ratings for them.

With the torsion keys turned up as far as they'll go, I'm about 1/4" off the lower bumpstop... well most of the lower bumpstop. It's been eaten into a little.
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Old 06-09-2012, 11:46 AM   #2 (permalink)
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I wonder if the part number for the 3500 torsion bars are the same or different than the bars your have on your 2500?

Might be worth it to check and see......maybe the 3500 bars are different and stronger?
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Old 06-09-2012, 12:39 PM   #3 (permalink)
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I think it depends on how the truck is equipped. I searched a couple of diesel sites, but when you enter "torsion bar rates" in a search, you get back a few thousand Q's about how much lift can they get from cranking up their bars.

SAS would be great, but for right now, I need to buy some new bars. Stealership HAS to have a VIN, which is something I don't understand. Why can't they look up a 2500/3500 truck and tell me what the rating for the bars is?
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Old 06-09-2012, 06:42 PM   #4 (permalink)
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Torsion bars on the 11 and before were all the same I'm 99.9% sure. I remember GM talking about the new (2011+) trucks having 3 different bars available to spec the trucks right. That is why the Diesel's on the 2010 and before couldn't get a snowplow on them in the crew cab without being over weight vs the gassers.

If I were you I'd measure up a 3500HD 2011+ truck's torsion bar and see if it would work. If it does I'd figure out what your trucks actual front weight is and but the next size up.
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Old 06-09-2012, 11:57 PM   #5 (permalink)
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2011 bars are much longer.

The suspension is designed to ride on the "bump stops". It's actually an additional spring to give the suspension a variable spring rate. If your bumpstops are chewed up you may want to replace them first.

Last edited by 73jeep; 06-10-2012 at 12:00 AM.
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Old 06-10-2012, 04:11 PM   #6 (permalink)
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Quote:
Originally Posted by 73jeep View Post

The suspension is designed to ride on the "bump stops". It's actually an additional spring to give the suspension a variable spring rate. If your bumpstops are chewed up you may want to replace them first.

This, and there are a few different bars for different engines etc. A coworker just put lighter bars on his lifted dmax and got a much smoother ride out of it.
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Old 06-10-2012, 05:17 PM   #7 (permalink)
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I remember finding a listing on the Fullsizechevy.com forum for about a dozen different gm torsion bars. I seem to think its a sticky there.

What rims are you running? I fit 285 75 R16s on my 1999 2500 thats stock, but I have the stock aluminum rims. If you have aftermarket rims with a different backspacing then I could see why your eatin the fender. Mine rub slightly.

Kevo

Here you go:http://www.fullsizechevy.com/forum/g...cing-tech.html
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Old 06-11-2012, 05:54 PM   #8 (permalink)
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Some info I found:

CHEVY TORSION BAR CODES AND RATINGS:

15048307-LH (code XK) (Max torque 4553)
15048308-RH (code XK) (Max torque 4553)

15048309-LH (code XL) (Max torque 4626)
15048310-RH (code XL) (Max torque 4626)

15712407-LH (code WX) (Max torque 4863)
15712408-RH (code WX) (Max torque 4863)

15048311-LH (code XM) (Max torque 5638)
15048312-RH (code XM) (Max torque 5638)

15058267-LH (code YH) (Max torque 5913)
15058268-RH (code YH) (Max torque 5913)

15712409-LH (code WY) (Max torque 5913)
15712410-RH (code WY) (Max torque 5913)

15528957-LH (code GG) (Max torque 6709)
15528958-RH (code GG) (Max torque 6709)

15712411-LH (code WZ) (Max torque 7267)
15712412-RH (code WZ) (Max torque 7267)

15528963-LH (code GK) (Max torque 8615)
15528964-RH (code GK) (Max torque 8615)

15528965-LH (code GL) (Max torque 8782)
15528966-RH (code GL) (Max torque 8782)

15732338-LH (code XG) (Max torque 9054)
15732339-RH (code XG) (Max torque 9054)

15528959-LH (code GH) (Max torque 7161)
15528960-RH (code GH) (Max torque 7161)
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Old 06-11-2012, 05:57 PM   #9 (permalink)
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GK = 8615
GL = 8782
XG = 9045
The stock bars for the 2500/3500 are GL


Some good reading:
http://www.dieselplace.com/forum/sho...d.php?t=327156


http://www.gmfullsize.com/tech/torsion401.html
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Old 06-23-2012, 08:48 AM   #10 (permalink)
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Picked up some used bars with 40k miles on them, swapped out last night, vast improvement. Ended up with 10" on the front and 10.5" on the rear between the tire and fender lip. The truck now sits level f to r and side to side.

It was most definitely the bars. The $150 I paid was way cheaper than the dealership and well worth it.
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