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'94 Sonoma having braking problem!


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#1 94sonoma

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Posted 17 July 2013 - 01:56 PM

I having problems with my ABS front disc brakes, (I think it's the brakes!). It seems while HARD BRAKING over ruff pavement, (like if I'm rolling over uneven asphalt, railroad tracks, concrete or small pot holes), my brake pedal seems to pulsate and loses all stiffness and goes to the floor. During normal stopping while applying the brake pedal, all is ok, ABS works fine when on smooth pavement. Anyone have any
ideas what might be causing this dilemma?

Thanks,

Darryl
'94 Sonoma



#2 Carder

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Posted 17 July 2013 - 02:04 PM

It sounds as if your brakes are working correctly to me. You did state hard braking in both situations and to my knowledge, abs vibrates/pulsates rapidly when braking as so. Being that loose gravel or any rough terrain that has yet been paved should require more "help" to keep control of the vehicle so unless I happen to be incorrect, I apologize in advance for being unable to assist you.

Main ride: 2013 Vee-Dub GTI

 

Other ride: 1994 atoyoT MR2 Jap Spec G-Limited


#3 94sonoma

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Posted 17 July 2013 - 06:21 PM

Maybe I can be a little more specific in my explanation of what is happening with the braking system.  If I'm traveling over a bumpy terrain, and my suspension is being compromised, i.e., (uneven travel of the front tires going up and down), when I push the brake pedal while traveling over a bumpy terrain, the brakes will start to grab in their ABS mold, but a split second later, you can feel the brake pedal starts to pulsate, you can feel the brakes let loose under your foot and the ABS system just seems to release while the brake pedal will suddenly go towards the floor in the next second.  Now it doesn't go all the way to the floor completely, (maybe a couple of inches away from the floor, and I'm stretching that only because I have not measured the distance), but if your applying that HARD BRAKING FORCE on the brake pedal, the ABS stops working and the vehicle is not stopping as it should.  It more or less starts to glide.  This can happen at any speed.  It's a feeling like the brakes just stopped working.

 

Now if I'm on a relatively smooth surface, the ABS system works just fine and none of the above explanation happens.

 

One other note; brakes and fluid were changed about ten months ago.  No fluid leaks then, no fluid leaks now and the master cylinder reservoir is topped off.

 

Thanks,

 

Darryl



#4 Carder

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Posted 17 July 2013 - 07:37 PM

Maybe a brake proportioning valve? Other than that, I would highly recommend you take it to a dealer or your mechanic. You could be putting someone else's life in danger to include you OWN! Good Luck!


Main ride: 2013 Vee-Dub GTI

 

Other ride: 1994 atoyoT MR2 Jap Spec G-Limited


#5 94sonoma

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Posted 18 July 2013 - 04:47 AM

Carder, Thank You for the advice.  I'll check on what kind symptoms the brake proportioning valve gives when or if it starts to go bad.  I was doing a little reading and it mentioned speed sensors at each wheel that sends signals to a control unit that accepts and process information received from the speed sensors during braking to control the hydraulic line pressure when braking avoiding wheel lockup.  I need to find a good mechanic who knows GMC ABS braking systems.  Because sometimes I've noticed that some mechanics just don't diagnose the problem correctly and throw parts in there thinking that will solve the problem, That I can do myself.

 

Again, Thank You for your advice,

 

Darryl






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