Torsion Bar Fatigue

[stevenje98]

2001, Suburban 2500 4x4

 

Torsion bar fatigue?

 

I'm in the processes of replacing all front end parts. everything even the hub bearings. So I'm disconnecting the shocks and notice the jounce \ bumper(s) is really tore up on both sides- ( both are cracked in half and hanging by a thread). I do have a large bush guard bumper on the truck as well and dual batteries. My questions is , Is this a sign of Torsion bar fatigue?

 

The truck has new tires BFG 265-16 and new shock installed last year. this picked up the front end some, but not much. The front end seems like it's a little lower now than before the new tires and shocks. I know I should have measured the Z-hight before putting the Suburban up on jack stands. It just did not dawn on me until I seen how messed up the jounce-bumpers are .

 

I'm going to remove the torsion bars tomorrow in order to take out the lower control arms to replace the bushings and the lower ball joints. I figure since I'm removing the T-bars, would it be better to add new keys or keep the factory ones. What is the best course of action to take here. Crank the factory key or add new keys with a different index and crank it up. I do have the tools to unload the t-bars.

 

 

 

 

Any help is welcome.

[Shaners]

You may be fine just cranking the factory keys and replacing the jounce bumpers. Just remember you will definatly need an alignment after all the work you've done.

[tyhuck]

Ive oftern wondered if you could swap the torsion bars from one side to the other. My theory is that the bars sag because they begin to get a memory and begin to give slightly in the direction of rotation, and that swapping them would reverse the direction of rotation and thus return the bars to their factory straightness. Im not sure if this would work, or even if it would be safe. It just occured to me while driving today. Maybe someone who knows more about the engineering of these bars can tell us if this would work.

[sonjaab]

IIRC the t-bars are side specific.

The part #s are different for left and right.

[steven-je]

You may be fine just cranking the factory keys and replacing the jounce bumpers. Just remember you will definatly need an alignment after all the work you've done.

 

I was think that too , keeping the factory keys. I did remove the both arms form the truck what a pain and the control arms on both sides. After removing everything I can say for sure now the front end definitely is lower than the factory setting. If I keep the factory keys and crank it I wonder if it will sag again? I might just level the Suburban out or replace the torsion bars or both. The right side really took a beating the lower ball joint, upper ball joint, tie rod end, and the inner tie rod had lots of play in it. all those parts are being replaced, I decided to add steering stabilizer while I'm at it.

 

 

 

 

 

I can get some used torsion bars off a Duramax Lb7. I do have to check the letters on them though

 

I have the GK on my truck. 8615 ft lbs. Part numbers LH-15528963 RH-15528964.

[steven-je]

Ive oftern wondered if you could swap the torsion bars from one side to the other. My theory is that the bars sag because they begin to get a memory and begin to give slightly in the direction of rotation, and that swapping them would reverse the direction of rotation and thus return the bars to their factory straightness. Im not sure if this would work, or even if it would be safe. It just occured to me while driving today. Maybe someone who knows more about the engineering of these bars can tell us if this would work.

 

I was looking at the bars when I pulled them out. they are the GK 8615 Torq- ft Lbs. I looked at the GM book and they are different part numbers. both do have the same 8615 torq ft-lbs though. you can see where they are market on the ends left and right. green and red marks form the factory. The part number are also stamped on them. The right side bar is for sure the problem bar.

[steven-je]

I have the GK bars at 8615 torque ft lbs.

 

I'm wondering if the right torsion bar is the problem, I did not see the right side leaning in the front or anything like that , just noticed that is was lower. then again all the joints were really wore out on the right side only. Everything ball joints top and lowers, the idel arm did pop sometimes on the right. the tie rod end seemed ok other than a torn boot. the inner tie rod has about 1\4 inch of play. what would cause all this mess just on the right side.

 

 

 

What would happen if I went up to the next larger torque rating ft/ lbs torsion bars? The next one up is the GL torsion bars at 8782 torq ft lbs; after that it's the XG bars at 9054 Torq-Ft lbs.

[djmercer1]

Ive oftern wondered if you could swap the torsion bars from one side to the other. My theory is that the bars sag because they begin to get a memory and begin to give slightly in the direction of rotation, and that swapping them would reverse the direction of rotation and thus return the bars to their factory straightness. Im not sure if this would work, or even if it would be safe. It just occured to me while driving today. Maybe someone who knows more about the engineering of these bars can tell us if this would work.

 

from a materials standpoint(i understand the bars are physically different), this would be a good concept provided the bars havent been work hardened-----that is overstressed and twisted from a hard bounce. if a bar is workhardened, it should be replaced because it will break.

 

a bar that has been work hardened may not show any obvious signs of sag of softness but may be somewhat brittle or have subsurface flaws---almost impossible to show a bar that has been workardened because it would/may require sonic, magnetic or molecular type scanning to reveal flaws.

[steven-je]

had to change my user name, the system wont let me post with my last name for some reason.

 

 

 

 

Anyway, I found some GL bars with the keys for $50.00 local . guy said that they were half cranked on his truck. Being that they are used would this be a good route to go?

 

GL bars are max torque is 8782.

 

My GX bars max torque is 8615. The difference is 167 on the max torque.