Antilock Brakes causing vibration

elmeeko · #1 11-12-2003, 10:00 PM

I have a '97 silverado with about 43K miles all stock. I have started to feel a wobble while brakeing. I thought it was due to the rotors being warped, but that is not the case. When I take the fuse out for the antilock, the wobble stops. Any idea how I can address this?

GMMerlin · #2 11-13-2003, 10:20 AM

What might be happening is a wheel speed sensor is dropping out and causing the ABS to activate.
Does this happen at low speeds (almost at a complete stop)?

elmeeko · #3 11-16-2003, 09:32 PM

This starts to be noticeable around 30 MPH. But is noticable at slower/ almost a stop as well.

WebDevil · #4 05-20-2004, 11:54 AM

Hi,

I have a 94 Beretta with the same problem.

Initially I thought it to be the rotors (the wife has a major problem with 'jamming' on the brakes, and warping rotors), so I changed them a few times over the years.

This year I started driving it more, and put new brake pads, rotors, drums, complete front end replacement (ball joints, struts, cv's, tie rods, etc), and alignment into it.

I still had a slight wobbling feeling, and thought it to be the front end alignment. When I had the new struts put in, they had to make the adjustment hole on the right strut wider to manage to adjust the alignment into specs.

I had the alignment checked, and it isn't out of specs.
So I put on new front calipers two days ago, and new pads again, noticing the front left was really worn, where the right one was barely worn at all.

Drove it to work with a noticable pulsation, and coming home last night, it got worse, and worse, to the point where when I got home, the front left wheel well started rolling with brake pad smoke.

What I need to know is where are the problem areas I need to look to eliminate this pulsation problem. I've been told by multiple people that I probablt need to change out the ABS Control unit, and that they'd ALL do it for $700 for the unit, and around $75 per hour labor.

I damn near died, lol. I'll fix it myself, if I can find the information on how to do it myself.

Could it be particles, or flakes of corosion on the line of the ABS, or something else? I would think if it wwas the Control unit, that both the front left AND right would be pulsating heavily.

Any wisdom would be most appreciated.

Thanks in advance.

01Blackerado · #5 05-20-2004, 01:21 PM

Does it happen while excelarating or only when breaking and that question goes for both of you?????!!!!!

WebDevil · #6 05-20-2004, 01:49 PM

It happens for me at slow speeds, and while at highway speeds. Naturally, while going at normal highway speeds it isn't as noticable, but is still there. I didn't have the problem near as bad until I put on the new calipers/new pads a couple of days ago, and today... the front left pad is almost halfway gone, and I'm sure it has now warped the fresh rotor.

01Blackerado · #7 05-20-2004, 01:59 PM

get your brakes rebalanced and see if that knocks it out it should anyway

WebDevil · #8 05-20-2004, 02:03 PM

By rebalanced, do you mean bled?

I've bled them multiple times, and have no apparent air in the lines.

I bled them from the individual bleeders are each wheel. Should I be bleeding them from the master cylinder assembly? I noticed it has 2 bleeders on it as well.

Are they one for the front, and one for the rear?

wagslick · #9 07-08-2004, 11:27 AM

Hey, I've been having the same problem. I just got finished turning my rotors and reinstalling them. 2 days later my brakes seemed worse. There was a weird clunking sound when braking. More noticable at low speeds, specially close to a stop. For the record, my ABS light is on and has been on for quite some time.

WebDevil · #10 07-08-2004, 11:39 AM

After replacing my rotors twice, I've found the culprit to be the rubber hose that goes to the calipre from the metal brake line.

Apparently, the rubber hose begins to collapse over time from excessive heat, and this collapsing of the line cause a fluid pressure fluctuation.

As far as your ABS light being on, I would bet that your ABS sensor is going bad on one or both sides of your front brakes.

You will be able to change those rather easily. They are rather in expensive as well.

If these two fixes do not work, you are probably looking at some type of malfunction in the master cylnder itself, and since it is designed for the ABS, it is a pretty penny to buy new. For my Beretta the new master cylinder was $700, but used ones can be found in a local salvage yard for around $50-$100 if you're lucky.

Good Luck.

Powerwagontim · #11 07-15-2004, 08:18 PM

I was having the abs activate almost constantly on applying the brakes. took it to a local dealer who drove it around his lot with a code reader plugged in. he said it was probably my left front abs senser. We stopped and I told him I would buy the part and he saidthat they had received a service bullitin about this and to pull the senser out and really clean the surface of the hub where it seats. I did that and the problem went away immediatly. I was shocked. And the dealer didnt even charge me for the diagnostics!!
Tim

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