Brake vibration/shaking - LONG

[Alaskaburb]

I have been reading threads and trying to figure out where to start. I am narrowing it down to the ABS system but I am unsure. The difficulty is live in Nevada and the burb is in Alaska with limited resources for help. The suburban sits most of the year and has only seen 18000 miles in the last 10 years. It currently has 218000 miles.

1993 K2500 heavy with the 5.7 and hydro boost. I don't recall but it was the heaviest axles and brakes available. Government rig

Last month while driving to the cabin on pavement at 60 mph a vibration started. It was very obvious and the kind that shook the mirrors but not yet violent. I pulled over to look at tires etc and when I took off again it was gone. It was driving smooth underway and while no braking. About 30 minutes later it came back so I stepped on the brakes fairly firmly and the car shook fairly violently. I brought it to a complete stop and took off again a minor vibration remained then cleared.

In town while putting the boat in the water and backing down the ramp the ABS and brake light came on and has stayed on. Ever since I had the car when I hit 10 mph for the first time a noise like a spring unwinding goes off only once. I allows assumed it was the ABS. It has stopped.

On the way back to Ketchikan yesterday, in the dark of course, the heavy shakes came back. It is the whole car and not in the brake pedal or steering wheel. What seems to work is if I bring it to a complete stop and back up quickly and lock the brakes I can continue on for a while before it returns. With limited ability to test it seems like if I do not touch the brakes I am good for a while and if I come to a complete stop when I do its fine. I am thinking when I lightly apply the brakes in a curve and continue on the vibration returns until I do the complete stop and back up again. Again, when this begins and I step on the brakes to come to a complete stop it is quite dramatic.

Prior to the last drive to the airport I was leaning towards something sticking in the rear drums so I put parts I had on hand in the car to repair nest trip. I was going to replace the drums, pads and springs. When this occurred last month I thought sticking caliper pins so I pilled them, cleaned them up and lubricated the pins with high temp brake grease.

There are mechanics in Ketchikan but not all of them are fully versed in all cars and I have no idea if anyone has the ABS related electronics to properly bleed the ABS system. I am at a loss of where to begin. I am still going to put the rear drums, spring and pads on when I get back in November but I no longer am convinced its rusted parts and springs in the rear drums.

Thoughts on where to start?

Thanks for any help. I will need to collect parts here in Nevada and attack it in the cold November rain when I get back.

 

[Schurkey]

There is NOTHING in the ABS system that will shake the vehicle BEFORE the brakes are applied. I don't doubt you need ABS work, but I'm gonna be REALLY surprised if it has anything to do with your coming-and-going vibration.

Which ABS system do you have? If this was a pickup, I'd expect RWAL, aluminum-body version. But as an SUV, I'm thinking you've got the EBC4 system, with external wheel speed sensors near the front-outer CV joints.

"I" would be pulling the wheels off, looking at the brakes for obvious issues...and then pulling driveshafts and CV shafts looking for something that could be an intermittent problem--perhaps two or more somewhat minor issues that get "in phase" and shake the vehicle, then go out-of-phase leaving a relatively smooth ride.

 

[pressureangle]

BTDT.
In my case it was a collapsed brake hose to the caliper. After 1/2 hour or so above 45mph-ish, the rotor got hot and pulsed. When you hit the brakes, it really shook. After cooling it was ok. Replaced both hoses and pads, never came back. I was surprised it didn't ruin the rotors, but hey I'll take a free one once in a while.

 

[HotWheelsBurban]

That spring sound, sounds like what my C3500 crew cab does when you stand on the brakes hard(like trying to stop short at a light). I was told that's the ABS cycling, and the shop that finally fixed my hydro boost unit last year, said that that sound is normal. It's only done it a few times, and only under those circumstances.
Five years ago, I had the right front caliper lock up on my Burb, and it caught the brakes on fire. So I replaced both calipers and brake hoses, and put a new set of pads on too. Good on you for catching the caliper pins needing cleaning and relubricating. Many people don't pay any attention to the brake hardware and that neglect can lead to dangerous problems.

 

[GoToGuy]

The ABS light means it's self test found something out of limits, so further diagnostics required. The shaking, vibrations without touching the brakes, is indicating probably something other than brakes. When this condition occurs and you apply braking does the brake pedal pulsate at any time or just vibrates with everything else. Brakes are reactive , you activate braking there is a reaction.
As Shurkey said this is most likely some other system is the cause.
If the vibration cycle increases or decrease with vehicle ground speed the problem is drive train related.
Drive shaft u joint can be felt in the shift stick- manual, and or transfer case shift- stick.
Jumping to " it must be this " without actual confirmation is a waste of time and money.
What system is problematic. What is broken. How do I fix it.

 

[Alaskaburb]

There is NOTHING in the ABS system that will shake the vehicle BEFORE the brakes are applied. I don't doubt you need ABS work, but I'm gonna be REALLY surprised if it has anything to do with your coming-and-going vibration.

Which ABS system do you have? If this was a pickup, I'd expect RWAL, aluminum-body version. But as an SUV, I'm thinking you've got the EBC4 system, with external wheel speed sensors near the front-outer CV joints.

"I" would be pulling the wheels off, looking at the brakes for obvious issues...and then pulling driveshafts and CV shafts looking for something that could be an intermittent problem--perhaps two or more somewhat minor issues that get "in phase" and shake the vehicle, then go out-of-phase leaving a relatively smooth ride.

I am not sure what system I have but I believe it is 4 wheel. The collapsed brake hose mentioned sure sounds like what I have going on. I did replace both front hoses 5 or so years ago.

 

[Alaskaburb]

The ABS light means it's self test found something out of limits, so further diagnostics required. The shaking, vibrations without touching the brakes, is indicating probably something other than brakes. When this condition occurs and you apply braking does the brake pedal pulsate at any time or just vibrates with everything else. Brakes are reactive , you activate braking there is a reaction.
As Shurkey said this is most likely some other system is the cause.
If the vibration cycle increases or decrease with vehicle ground speed the problem is drive train related.
Drive shaft u joint can be felt in the shift stick- manual, and or transfer case shift- stick.
Jumping to " it must be this " without actual confirmation is a waste of time and money.
What system is problematic. What is broken. How do I fix it.

I am asking here and receiving great information on where to look because I want to have an idea of where to start. I need to have a plan that is hopefully correct when I go back to Alaska.

ABS light question. I installed a Posi lock 4x4 front differential actuator on my Suburban this summer. Let's see if I can explain the scenario. I was putting my boat in the water and had another driver backing the trailer in while I was on the boat. My nephew put it in 4 low not knowing about the post lock manual engagement. The boat is large so the front wheels were locked and the rears were turning as the trailer made its way into the water. Would the 4x4 light activate or throw a code when it sees the rear wheels turning and both fronts are not turning at all?

 

[Alaskaburb]

That spring sound, sounds like what my C3500 crew cab does when you stand on the brakes hard(like trying to stop short at a light). I was told that's the ABS cycling, and the shop that finally fixed my hydro boost unit last year, said that that sound is normal. It's only done it a few times, and only under those circumstances.
Five years ago, I had the right front caliper lock up on my Burb, and it caught the brakes on fire. So I replaced both calipers and brake hoses, and put a new set of pads on too. Good on you for catching the caliper pins needing cleaning and relubricating. Many people don't pay any attention to the brake hardware and that neglect can lead to dangerous problems.

My "spring sound" I assumed was an automatic ABS test because it occurred only once at exactly 10 mph on the first acceleration after starting. Well I had the ABS activation noise when the system was actually doing its job like on snow or ice.

 

[GoToGuy]

ABS is not armed , or is in standby until passing 10 mph or more.
The posi lock, which is probably just like the my 93 has. Is just that. A manual engagement device. If you don't use it or engage front axle, and select low range, then you just have a 2 wheel drive low range, there is no conflict. Adding the posi lock actually gave you another low range option. When you select low range the ABS is now selected out of action. No ABS in low range by design. Are you sure the front wheels were locked? Could it have been during brake application while launching the boat , on a slope , light weight front end, all heavy weight at rear, tongue weight, rear motion inertia, that the front wheel braking was just more effective than rear axle brakes? Which appears that there is front brake problem but is normal laws of physics. Weight, mass , inertia, deceleration forces. It happens alot during boat launching at the ramp. You have some information now. But trying to diagnose something far away . We could ask more technical questions but I believe that would be beyond your ability experience level. And yes we all started at zero.
If do not have the OE service manuals, since your gonna be in the great frozen butt north, download the free manuals for your year, search at top " service manuals " get the link, or maybe someone can post the link, please. The GM manuals, get both, Vol 1, or book 1. And Vol 2, or book 2. You need both. Everything is in there, it's your new best friend, sometimes you need to page and read through.
Why did your nephew select low range? What purpose?
Good luck, tell Elmendorf I'm never coming back.

 

[evilunclegrimace]

I don't have any pics right now but perhaps someone here could post a pic of an RWAL system and a 4 wheel system for the OP.