Need Help!!! Can't fix brake pulsation

[coollx]

I have a 97 Tahoe 4 dr 4x4 that I bought new that now has 108k.

Here are the details:

- ever since it had 20k I've had to reface or replace the rotors every 12-15k due to brake pulsation

- at about 90k and at the recommendation of a napa brake rep I replaced everything, ie. calipers, rotors, pads, rear drums, rear shoes and whl cylinders. His opinion was that with high mileage the calipers do not fully retract and heat builds up which in turn warps the rotors and pulsation set in. After replacing everything, the brakes worked perfectly for about 10-12k then started to pulse again only worse than ever.

- now at 108k the pulsation/vibration is worse when you just lightly touch the brake pedal to start slowing down when your traveling between 35-50 mph. under 35mph the pulsation isn't bad.

- The mechanic I've been going to for 20 years who has historically been a super trouble shooter said he believes the problem is that the front hubs are worn and that we'll never be able to straighten out the pulsation problem unless we replace them next ($700.00)

So my question is whether anyone on the forum has had a similar problem and has replaced the hubs and solved the pulsation problem?

Or, are there some techs that frequent this forum that can provide an opinion or insight on the likelihood that worn hubs could in fact be the underlying problem.

I'd really like some help on this since I've thrown a lot of money at this problem and would like to keep this vehicle another couple of years at least.

Thanks.

Dom

[GMMerlin]

I guess I would start by checking the front suspension componants for wear.
You can check the hubs for play with a dial indicator..also check them for lateral runout..this could cause your pulsation.
Also check the parrellism of the rotors (check in at least 4 places..should be less than .0015"

Some brake pulsations can be caused by the way you drive..aggressive braking can overheat the rotors and cause them to warp..also the introduction of cold water to a hot rotor can cause this too. (hot brakes cold puddle)
Also aggressive use of the park brake on hot drums can cause the drum to warp.

[ec437]

Drums can warp. Rotors don't. Have your new pads always been broken in properly? I would now suspect things other than brake components. Suspension components, mounts, steering components, alignment, balancing, etc etc.

Is the pulsation coming mostly from front or rear? Right side or left? Have you tried different brands of pads, rotors, etc? Check for any recalls. Perhaps weight transfer during braking is accentuating a problem that exists elsewhere?

[coollx]

Thanks for the quick responses.

To answer some of the questions you raised.

I do not brake aggressively...probably just the opposite.

All the front end components have been checked and are tight.

When we replaced or resurfaced the rotors, we always used new pads (napa ceramic).

We have tried both composite rotors and the other type whatever they call them.

The pulsation is definitely coming from the front wheels, and there's no pulling the left or right.

I have always rotated tires every 6k and computer balanced them each time.

The alignment has been done and frankly the vehicle runs and drives like new until you touch the brake pedal.

One other thing I should mention, the ABS has been deactivated by pulling the fuse out. I did this 20k ago because it had a bad front sensor, but replacing it didn't solve the problem.

GMMERLIN, how do I go about checking the front hubs? I have a dial indicator, but have not tried to check anything myself up to now.

ec437, what do you mean, drums can warp, rotors don't?

[rrousou]

I had this same problem a long time ago with a 1983 GMC Sierra. I replaced the front rotors 2 times and had them machined several times. I finally gave up and bought aftermarket rotors and the problem never happened again. I suspect that the OEM rotors were not heavy enough

[Thunderbolt]

Originally Posted by coollx

Thanks for the quick responses.

To answer some of the questions you raised.

I do not brake aggressively...probably just the opposite.

All the front end components have been checked and are tight.

When we replaced or resurfaced the rotors, we always used new pads (napa ceramic).

We have tried both composite rotors and the other type whatever they call them.

The pulsation is definitely coming from the front wheels, and there's no pulling the left or right.

I have always rotated tires every 6k and computer balanced them each time.

The alignment has been done and frankly the vehicle runs and drives like new until you touch the brake pedal.

One other thing I should mention, the ABS has been deactivated by pulling the fuse out. I did this 20k ago because it had a bad front sensor, but replacing it didn't solve the problem.

GMMERLIN, how do I go about checking the front hubs? I have a dial indicator, but have not tried to check anything myself up to now.

ec437, what do you mean, drums can warp, rotors don't?

Do a search on the internet for info on bedding brakes. This is what will stop the pulsating. Brake pads embed material in the rotor and if not properly bedded or when stopping completly after driving in stop and go traffic it can cause a high spot on the rotor. It will not be visible to the eye, But trust me it is there. The brakes need to be brought up to temp and then cooled without making a complete stop several times to fix it. I do not know how to explain it, But there is info on the net and at aplsweb.com/Topics/Topics.htm and it does work. I went through the same thing as you and after doing this it goes away. When it comes back I repeat the bedding and it is gone. The same goes for brake squeal, I have heard many people say it is normal for semi- metallic pads to squeal sometimes and it is not. If the brakes squeal make three or four panic stops and it should quit. As I said I am not very good at explaining the process, But many sources on the net do. Good Luck.

[GMMerlin]

Originally Posted by ec437

Drums can warp. Rotors don't.

What makes you the expert? Would you say that a rotor with .005" of lateral runout is not warped?

[GMMerlin]

Originally Posted by coollx

GMMERLIN, how do I go about checking the front hubs? I have a dial indicator, but have not tried to check anything myself up to now.

One thing you want to watch is the lug nut torque! 125ft/lbs is the spec.
Using an impact wrench can cause a rotor to warp by uneven clamping forces on the rotor and hub.
Also if the rotrs have been turned, check the thickness. If they are close to discard thickness they are too thin and can warp.

First you would check the face of the hub for lateral runout....should be no more than .0015"
Fasten a dial indicator to the steering knuckle so that the indicator button contacts the rotor surface about 13 mm (0.5 in) from the outer edge.
Set the dial indicator to zero.
Turn the wheel one complete revolution and observe the runout indicated on the dial.
The total indicated runout (TIR) for front disc brake rotors must not exceed 0.08 mm (0.003 in). The TIR for rear disc brakes and for C3500 HD Models must not exceed 0.25 mm (0.010 in).
Refinish or replace any rotor which is not within the lateral runout specifications.
In some cases, indexing the rotor on the hub by one or two bolt positions away from the original position will reduce the lateral runout. If it is impossible to correct the amount of lateral runout by indexing the rotor, then check the hub and bearing assembly for excessive lateral runout or looseness. If the hub and the bearing assembly lateral runout exceeds 0.040 mm (0.0015 in), then repair or replace the hub and the bearing assembly.

[jthomp23777]

Lets go back to basic physics. When metal heats up, it expands and when it is cooled it contracts. And so metal, when hot can warp if cooled down quickly.And rotors which are metal tend to heat up due to brake pads create friction against the rotor when you apply pressure at the brake petal. Case and point. My wife is a hard braker, and I know when its rainy season because that when I have to have her calipers on her hoe turn to may them true. This probaly has no bearing, but I don't know how long Tahoe has had rear rotors. I had a 95 Jeep Grand Cherokee. Had that pusation in the front, put new front pads,top of the line new rotors and had them turn prior to putting them on. Still had the pusation in the front end. Again turn the rotors and still had the problem. Put another set of rotors on, still the pusation in the brake petal. Fustrating it was, I finally figure out the problem was in the rear rotors, duh, didn't I feel like a dumba#@. They were WARPED. So yes, rotors will warp. Maybe BMW vehicles don't.Oh thats right, thier rotors are made out of plastic. Thanks for supporting the american economy.. Just kidding there EC437, I'am sure everybody is trying to help Coollx solve his problem..

[coollx]

Today, I had a few minutes so I pulled the right front wheel off and checked the runout of the rotor. I mounted the dial indicator to the caliper and checked the rotor in 3 or 4 different places. GMMERLIN said to attach it to the steering knuckle so I wonder whether it matters? If so, I'll have to fab something up to mount it on the knuckle.

The reading went from .000 to -.005, then swung to +.010 then back to .000 during one revolution.

I presume this variation is enough to cause significant pulsation?

As GMMERLIN suggests, before I replace any parts I'm going to take the time to remove the calipers and carefully check the hubs for any looseness and runout.

By the way, does anyone know the size of the bolts holding the calipers on? Is it a hex head? Sae or metric?

Thanks.

[southernhonke]

I have the exact same problem on a 98 Yukon 4X4. Did you ever come up with a fix?

BTW, the calipers are held on with a 3/8 inch allen wrench.

Thanks

[coollx]

southernhonke, I haven't fixed it yet but I'm going to keep trying. I spoke with my mechanic a few days ago about his hub theory which is that there is a buildup of uneven scaley rust on the face of the hub where the rotor mounts and that's probably the problem. I live in the northeast and my tahoe has already been through 7 winters so he may be right. After the first of the year I plan to take the calipers and rotors off, remove the wheel studs on the front hubs and clean the rotor mounting surface real good to see if that makes a BIG difference.

I'll report back here once I do it. In the meantime, if you or anyone else with the same problem finds a solution, let us all know.

Thanks.

[southernhonke]

I took my rotors off and found a stud on the right side that was replaced by a mechanic a year or so ago with the shoulder of the stud sticking out past the hub. It in effect kept the rotor from seating. I am hoping that was my problem.

[2kflhr]

Originally Posted by ec437

Drums can warp. Rotors don't.

B.S.

[decoy86]

You need to replace the caliper mount bushings. Each caliper has 4 bushings along with 4 dust caps. You may have to replace the mount bolts too. I have a 99 Tahoe and a 91 GMC and have seen this problem on both of them. Just remove the caliper and remove the 4 dust caps. Remove teh 4 rubber type bushings. They can be bought at your local parts store or at the dealer. You will need to grease the parts before installing. I just bought a set of Raybetos Ceramic brakes for the Tahoe and all these parts were included.

Replacing the bushings is overlooked by everyone. Do not replace the rotors. I did that once with the tahoe and they sucked.