97 K2500 Suburban shaking when braking(not rotors)

[Boon44]

I have a K2500 suburban that has a rather aggressive/violent "vertical" shake when braking above 30mph... I bought it about 6 months ago and was told it just had a full brake job all around(receipts provided). The shake has been off and on, mostly reserved to highway speeds, however recently it has been constant at any speed above 30mph... Thinking it may be the rotors. I pulled the wheels off and even though everything looked brand new (as described) I replaced the rotors and put on new pads... did not fix the shake... and I had the old rotors mic'd and they came back good as new with zero need to turn/resurface.

I was told it may be the ABS, So I pulled the fuse... and it didn't fix the issue also I have no light on the dash

I was told it may be a flat spot on the rear drums, so I replaced the rear drums and it didn't fix the problem... the shoes looked brand new and had just as much pad left as the set i was replacing them with, so I left them alone.

I had happened to have new tires put on it, and they advised my pitman arm and idler arm were shot and that they couldn't do an alignment, so I replaced the pitman and idler and brought it back to be aligned which they did... this did not resolve any issues...

I spoke with the previous owner and he said he had the same issues and couldnt figure it.. he said his mechanic replaced the wheel bearings, rotors, pads, calipers, brake lines, ball joints(all receipts provided, and all these parts look brand new)...

At this point I have no idea what it could be so any suggestions would be greatly appreciated as the shake is very aggressive it makes the dash jump up and down and vibrates the hood to the point where it looks like it will rattle off.. the pedal doesn't pulse and the steering wheel aside from vibrating up and down doesn't pull or shake one way or the other... truck doesn't pull when braking or during this shake... and the second you let off the brake the shaking stops... and only ever shakes when you hit the brakes...it rides as smooth as can be when not braking...

Any ideas?

[j cAT]

Originally Posted by Boon44

I have a K2500 suburban that has a rather aggressive/violent "vertical" shake when braking above 30mph... I bought it about 6 months ago and was told it just had a full brake job all around(receipts provided). The shake has been off and on, mostly reserved to highway speeds, however recently it has been constant at any speed above 30mph... Thinking it may be the rotors. I pulled the wheels off and even though everything looked brand new (as described) I replaced the rotors and put on new pads... did not fix the shake... and I had the old rotors mic'd and they came back good as new with zero need to turn/resurface.

I was told it may be the ABS, So I pulled the fuse... and it didn't fix the issue also I have no light on the dash

I was told it may be a flat spot on the rear drums, so I replaced the rear drums and it didn't fix the problem... the shoes looked brand new and had just as much pad left as the set i was replacing them with, so I left them alone.

I had happened to have new tires put on it, and they advised my pitman arm and idler arm were shot and that they couldn't do an alignment, so I replaced the pitman and idler and brought it back to be aligned which they did... this did not resolve any issues...

I spoke with the previous owner and he said he had the same issues and couldnt figure it.. he said his mechanic replaced the wheel bearings, rotors, pads, calipers, brake lines, ball joints(all receipts provided, and all these parts look brand new)...

At this point I have no idea what it could be so any suggestions would be greatly appreciated as the shake is very aggressive it makes the dash jump up and down and vibrates the hood to the point where it looks like it will rattle off.. the pedal doesn't pulse and the steering wheel aside from vibrating up and down doesn't pull or shake one way or the other... truck doesn't pull when braking or during this shake... and the second you let off the brake the shaking stops... and only ever shakes when you hit the brakes...it rides as smooth as can be when not braking...

Any ideas?

so to get this minimized as to the issue .... the vehicle vibs bad when braking....

this can be the brake pads in the front binding. pads should set in the front calipers with finger effort only..if they are too tight , file off the excess pad steel backing plate. burrs on these most always even GM ac delco brake pads..

next would be a park/emergency brake cable too tight. this must have slack when off... what happens is new drums installed and the cable is now keeping the rear shoes on the drums then the drums get distorted .. when braking you get the vibs...

have drums checked if distorted with the lathe test , micrometer then they need be replaced.. once these are cut they are not very good for braking...

[Boon44]

Originally Posted by j cAT

so to get this minimized as to the issue .... the vehicle vibs bad when braking....

Sorry for the lengthy post, I tried to explain the base of the issue in the first paragraph... wanted to provide enough details to explain where we stand in an attempt of trying to forego the obvious responses.

Originally Posted by j cAT

this can be the brake pads in the front binding. pads should set in the front calipers with finger effort only..if they are too tight , file off the excess pad steel backing plate. burrs on these most always even GM ac delco brake pads..

Pads were just changed, they went in with normal effort

Originally Posted by j cAT

next would be a park/emergency brake cable too tight. this must have slack when off... what happens is new drums installed and the cable is now keeping the rear shoes on the drums then the drums get distorted .. when braking you get the vibs..

The cable was adjusted along with the rear brakes when the drums were replaced... it should also be noted that the vehicle can be stopped with only using the parking brake without creating the vibrations

Originally Posted by j cAT

have drums checked if distorted with the lathe test , micrometer then they need be replaced.. once these are cut they are not very good for braking...

The drums are new and the problem remained unaffected post them being replaced.

[777stickman]

Welcome to the AF forum. You did a great job of explaining the issues!!

After all you've replaced there's some other things to look at.

1. Shocks (just a WAG).
2. A busted wheel? Did you swap wheels front to rear?
3. You pulled the ABS fuse. Did you get an ABS amber light on the dash with the fuse out?
4. Does your Sub have the Hydro-Boost or the Vacuum Boost for the power brakes?

[Boon44]

Originally Posted by 777stickman

Welcome to the AF forum.

After all you've replaced there's only a few other things to look at.

1. Front hubs & bearings.
2. Steering linkages, although the alignment shop should have informed you of an issue there.
3. Shocks (just a WAG).
4. A busted wheel? Did you swap wheels front to rear?
5. You pulled the ABS fuse. Did you get an ABS amber light on the dash with the fuse out?
6. Does your Sub have the Hydro-Boost or the Vacuum Boost for the power brakes?

1.Hubs/Bearings are new
2. I didn't see anything with the linkage when i was replacing the pitman/idler. And the alignment shop did not raise any concerns (also no shakes outside of braking)
3. This is something we have considered replacing but have not as of yet.
4. Wheels were rotated issue still present.
5. Yes when i pulled the fuse the amber light on the dash appeared. Disappeared when replacing the fuse
6. It is a hydroboost

We assumed one caliper was biting harder than the other but all the wear on the pads are matched...

I was told that if there was air in the abs system it could cause a shake... not sure if pulling the fuse would test this cause if so then that isnt the issue as we pulled the fuse.

I appreciate the ideas!

[jerryg2112]

I would try looking at the rotor and drum run out if it were me. Even though the rotors look good thickness wise and true on the lathe they may run out on the car. A lot of side to side movement could cause vibration and at higher speeds it would be worse. You need a dial indicator to check.

[j cAT]

since the rears when the drum emergency brake is applied does not cause this problem and the steering wheel when the brake pedal is applied to stop the vehicle does not cause the steering to vibrate you have a very strange problem.

the only other thing I would say to check is the rear wheel bearings and the pinion for wear ...

[Boon44]

Originally Posted by j cAT

since the rears when the drum emergency brake is applied does not cause this problem and the steering wheel when the brake pedal is applied to stop the vehicle does not cause the steering to vibrate y

You have a very strange problem.

the only other thing I would say to check is the rear wheel bearings and the pinion for wear ...

I very much agree, it has been to the reputable shops around town and absolutely no luck in fixing the issue.

[777stickman]

Pulling the ABS fuse just deactivates it. It won't test for air in the system. If you suspect air it would have to be bled using a high end scan tool that can access the ABS.

The hydro-boost could be an issue but I don't have a clue how you would test it. Maybe a weak power steering pump.

Just another WAG, but how are the motor and tranny mounts?

Good luck to you as it's a real mystery.

[ASJT3]

Originally Posted by 777stickman

Pulling the ABS fuse just deactivates it. It won't test for air in the system. If you suspect air it would have to be bled using a high end scan tool that can access the ABS.

The hydro-boost could be an issue but I don't have a clue how you would test it. Maybe a weak power steering pump.

Just another WAG, but how are the motor and tranny mounts?

Good luck to you as it's a real mystery.

Could bad control arm bushings be causing this? I wanna say from his description that the bulk of the shaking is coming from the front. If CA bushings are bad, during braking could CA be vibrating excessively in the fore/aft direction?

[j cAT]

Originally Posted by ASJT3

Could bad control arm bushings be causing this? I wanna say from his description that the bulk of the shaking is coming from the front. If CA bushings are bad, during braking could CA be vibrating excessively in the fore/aft direction?

good point on the front suspension wear. with these worn bad also idler arms/tie rods you can get this violent shaking. though I remember this need not be only in brake mode. you hit a bump in the road and the steering wheel goes nuts...

[macser]

Any resolution to this problem?

[Boon44]

Not to resurrect a dead post, apologies.


In short, No - I never was able to fix/identify this problem( I even did some more trouble shooting beyond this post, such as replacing the aluminum wheels with steel wheels(thinking one may have been cracked or something). I still have the Truck and it runs and I drive it every so often, but for the most part it has been parked for the last 3 years or so.


The braking is just far too violent, aside from a quick drive around town, any highway or back road travel is just too much.


Oddly enough, I have recently decided to just sell it - as it has just been sitting and its been registered/insured this whole time, despite never really using it. I was sitting here and decided to research into it one last time and came across this old thread of when I first bought it.


It's a great truck, starts up every time, runs just fine - but using the brakes is just teeth rattling to say the least lol. It oddly has not gotten any worse or better over the time it has sat - which is why I just use it around town once or twice every few months or so; just to keep it moving.

[j cAT]

you stated the vehicle sits for more than a month well you said 3 yrs LOL!!!!!!


the rotors/drums rust up then the braking vibs.. another add on to this is tires when sitting will cause vibs at hywy speeds...


I have a 1996 IMPALA and do not drive it in rain or snow .. so when it sits for a couple of months I get the brake vibs and then drive it on the hyway 100 MPH the tires vib then slowly goes away...


my 1996 is a power house ride .. I got to be careful if I put the gas pedal down ...

[Boon44]

Not sure what you are getting at - I posted the issue back in 2014; at that time the truck had just been purchased and was driven frequently, in addition I stated almost all of the braking components(including rotors, calipers, shoes and drums) had been replaced. I only re responded because I am selling the truck and was researching the problem again and came across this thread, where someone had asked if I ever solved it.



I bought a Brand new truck in 2015, so at that time the suburban became an auxiliary vehicle. I said for the last 3 years it has sat FOR THE MOST PART, meaning I still drive it every now and then to keep it moving, but out of 365 days a year it only gets used a handful of those days. Mostly for jaunts around town, or to move trailers around my lot. The issue was existing with newly replaced braking parts as well as now with the parts being 4-5 years old sitting for the majority of that time... the issue was not due to rusty brake components, nor flat spots in the tires(note my comments about purchasing brand new tires back in 2014, and the problem still persisted)