1996 GMC Suburban 2500 Violent Wheel Shake Please Help.

[dhollock]

Hi,

 

I have a 1996 GMC Suburban 2500 4wd with disc front brakes and drums on the back.

 

I have replaced the caliper, hoses, rotors, pads in the front. Replaced the shoes, drums, and cylinders in the back.

 

Balanced all tires and had a front end alignment.

 

I still have intermittent violent shaking. Smooth as glass sometimes and then it wants to shake your teeth out.

 

All parts taken off and rechecked. Rotors cut and drums turned just to be sure...

 

Pulled the abs fuse to see if that was the problem no difference.

 

I was wondering if the hydroboost could do this? A friend suggested bad control arm bushings or a steering position sensor?

 

Please any thoughts you have would be greatly appreciated.

[MMC]

Just a thought, check the u joints on the front axel.

[gmtech4]

i road tested a 2013 with 15K Km on it and they complained about stabilitrac light comin on and a dragging like its in low gear ,,,,,i get in and drive away and all is good ,,,,,,until i hit the highway and pin it ,,at 80 km/hr it does the death wobble sumfin awful ,,,,,i turn around and baby it back ,and the stab light came on ,,,i pulled over on base and smelt brake pads ,,,went to each frt tire and right front was hot as a fire cracker lol,,,off to warranty lol for a rather sticky right front caliper ,,

i thought of this thread when it happened !!!! lol

[lee123]

If you work on it ypurself, jack up frontend, put stands under it for safety, set park brake, start, put in 4X4 and hit brakes, see what i does. Irecommend not wasting moneyon parts. If u got new lines hopefuly u got new hoses. Air in lines, bad hoses, and bad bearings are what usualy cause this problem.

[Airwolf2tv]

Gov:

 

Any particular steering components?? I've never had any steering issues....it's pretty tight for nearly 200K...and there hasn't been any changes to steering behavior.

 

This whole deal really seems to be around that left caliper overheating.

 

I think my next step is gonna be to get the entire brake system professionally bled. I'm not sure if that means a vacuum bleed from up top or not?? Since the entire brake lines were replaced, maybe there's some air stuck in the system....even to the rear brakes, causing that front left to be out of balance. I'm not convinced that the traditional two-person pedal bleed is really effective beyond a simple caliper or cylinder change.

 

Thanks

 

Nick

[daxr]

For the left rear to be not braking currently, but braking enough to wear out the shoes at some other point - I'd say the wheel cylinder is most likely. When a cylinder starts to freeze up it will still apply, but it won't back off under spring tension - so your brakes drag on that wheel. When it fully seizes up, then the shoes won't apply at all.

 

Its easy to check - open the bleeder at that corner while someone presses the brake pedal. If fluid squirts out, then its all good up to the cylinder. With the drum off use a screwdriver or prybar to shift the top of the shoes from side to side. They bear on the wheel cylinder pistons, and if they won't budge then the cylinder is frozen.

[00Silverado4x4]

I'd be looking at your front right caliper since your front left is apparently doing all the front end braking. You may have a caliper getting hung up or air in the line.

[Airwolf2tv]

Clarifications on my original post...so everyone has correct information:

 

1. The truck has factory alloy rims with 265/75/16 Michelins. Have always had these on there. In good condition.

2. This is a 100% stock truck. No modifications, lift, etc...

3. No drag on brakes. Calipers take-up fine.

4. I may have mis-stated the upper arm bushing situation. The bushings aren't "missing"!! I've just noticed that the rubber washers where the arm slips into the mounts are severely deteriorated.

 

Thanks again for anyone that can help with some ideas.

 

Nick

[gmtech4]

Did ya get the steering looked at ?

[Airwolf2tv]

Mark:

 

Thanks, that's an excellent point. Behavior hasn't changed going from reman calipers to brand new calipers...maybe there's air in that cross-over brake line....like you said, causing there to always be more brake pressure on the left. That would explain the left lead.

 

The other thing I didn't mention is that a panic stop is really dangerous. The left caliper grabs nasty hard...makes the ABS go nuts trying to recover. Following your thought, it seems like most front brake pressure is going to the left.

 

I'll pursue some extensive bleeding of the right and see if that reveals anything.

 

Thanks

 

Nick

[Airwolf2tv]

Rob:

 

Great story!!...good luck with it. Smoking brakes definitely make things interesting!!

 

Lee - every line is brand new GM parts...other than the pre-formed stainless hard lines from InlineTube...which incidentally fit like a glove, if you need lines. I haven't ruled out bearings....can't say I've ever had one go bad, so I don't know what the behavior would be. The truck runs perfectly smooth and straight at 80MPH for long distances. It only seems to be hard braking that eventually brings on the left-front shudder. Granny drive it or leave out the cargo....and you would probably never know it had a problem....other than very slight brake lead to left.

 

Thanks for everyones input, really appreciate it. My next step is to have someone do a complete flush of brake fluid....just to know that it's done right with the right tools. Hopefully that solves the problem!!

[Airwolf2tv]

Dax:

 

Thanks for the suggestions, this is helpful.

 

My STS guys also suspected the wheel cylinders and replaced them both. Further examination reveals that the left rear drum is twice the temperature of the right side. So it seems like the left rear is inexplicably overheating.....and I guess that is resulting in braking stress on the left front after things get toasty!! It seems like anything can be rationalized!! Also, until that left rear really gets heated up after driving some distance (5-10 miles), the front left/right caliper and rotor temperatures are identical...so I think that rules out problems up front.

 

I saw another forum article about a guy (and dealers and shops) who could not resolve a hot left rear situation on same vehicle. His final root cause ended up being the random brake shoes which were installed or purchased from an auto-parts counter. Three shops later they determined the shoe compostion (or something) was causing them to overheat. Changed shoes and it fixed his problem instantly.

 

I'm ordering all new OEM springs and hardware for my drums....replace shoes with Delco or Raybestos...and see what happens!! I don't recall, but I may have put some PepBoys springs on there in the past. Broke my cardinal rule about "the right part for the right fit"!!

[markw8]

Does this only happen when you apply the brakes? If it happens on uneven surfaces without brake input, you have something worn in the front end. Also is it lifted or have oversized tires.

 

Mark

[ChevyTech77]

What wheels and tires are currently installed on the vehicle?

 

Is there any brake drag on the brake system after the brake pedal is released?

 

Anything loose/worn in the front steering or suspension components?

 

Is there a steering stabilizer installed and if so, is it still good or worn out?

[daxr]

If you work on it ypurself, jack up frontend, put stands under it for safety, set park brake, start, put in 4X4 and hit brakes, see what i does. Irecommend not wasting moneyon parts. If u got new lines hopefuly u got new hoses. Air in lines, bad hoses, and bad bearings are what usualy cause this problem.

If you have four jackstands, put the rear up too and run it in 4wd. If you get a vibration in the wheels then, you know its a rotating part out of round or out of balance (most likely). Having a good lift, that's the first thing I do checking a vibration problem. If a tire is out of round you can usually see it pretty easily. With it in the air you can also apply the brakes, let them off, and hand-spin the wheels to make sure the brakes are releasing, and releasing evenly.

 

If its brakes causing the wobble you can look at the rotors - the color should be a uniform dull grey (if using ceramic pads) or a uniform silver (if using semi-mets). If a rotors is silver on one surface and black on another its usually easy to see, then a resurface on a lathe should take care of if. New rotor doesn't mean its runs true - problems do happen. If you have a rotor problem make sure the caliper pistons and slides aren't bound up, as that can cause rotor overheating and run-out problems.

 

Bearing and bushing problems don't generally cause vibrations, but they can let them propagate more freely.

[Airwolf2tv]

Ok, so I have a brief update after typical delays getting back on this and getting it to the shop.

 

I have a great STS shop near my house, so I decided to have them take a look. One of the managers/mechanics also has a 98 yukon/tahoe, so he's very familiar with the beast.

 

Their discovery is that the left rear shoes are completely shot, while the right rear has full shoes. So after taking a fresh look, doing a skilled ABS bleed, and road testing....they are preliminarily determining that the left rear is actually the root cause of the problem. No left rear braking....causing left front to overheat. Not much unlike the previous hunch above that maybe the right front was weak. Either way, it makes sense that lacking right front or left rear is likely to cause excessive braking up at the left front. I had to take it back for the weekend, but returning it this week so they can finish up.

 

I need to dig out paperwork, but I recall the GM dealer saying they grinded out the grooves in the rear backing plates because it was causing the shoes to stick. So I think it's safe to assume that isn't the current problem. I'm think maybe time for all new hardware in the rear...??? I believe it's all original. Maybe the shoes aren't taking up properly??

 

Anybody have any ideas on this new development?? Good idea to put all new hardware in the drums??

 

Thanks again!!

 

Nick