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Brakes Dragging - Hydro Boost System

GMChris

By GMChris
in Ask A GM Technician

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GMChris Enthusiast

GMChris

Posted
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2000 Chevy Silverado 2500 4X4 (6L Gas)

Brakes dragged, rotors got very hot.

All calipers replaced. Master Cylinder replaced. Brake fluid reservoir cleaned and dried. All brake lines flushed & bled. Power steering fluid flushed with one gallon new fluid. Steering works perfectly. (Always has)

With power steering system bled down, new master cylinder sits 1/8 of an inch (same as old one did) away from hydro booster flange due to the booster output push-rod extending out.

Master cylinder mounting bolts will suck it in when tightened but is this pre-loading my M/C and causing it to self apply the brakes?? What is the correct clearance between hydro-booster unit push-rod and M/C?

Is my Hydro boost the problem? There is no adjustment on booster output push-rods these days.

Brakes are fine until 15 minutes or so of driving.

Help!!!!

GMChris Enthusiast

GMChris

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2000 Chevy Silverado 2500 4X4 (6L Gas)

Brakes dragged, rotors got very hot.

All calipers replaced. Master Cylinder replaced. Brake fluid reservoir cleaned and dried. All brake lines flushed & bled. Power steering fluid flushed with one gallon new fluid. Steering works perfectly. (Always has)

With power steering system bled down, new master cylinder sits 1/8 of an inch (same as old one did) away from hydro booster flange due to the booster output push-rod extending out.

Master cylinder mounting bolts will suck it in when tightened but is this pre-loading my M/C and causing it to self apply the brakes?? What is the correct clearance between hydro-booster unit push-rod and M/C?

Is my Hydro boost the problem? There is no adjustment on booster output push-rods these days.

Brakes are fine until 15 minutes or so of driving.

Help!!!!

 

Ok! I drove around for 1/2 hr today and the brakes began to drag harder & harder as the truck warmed up. I parked, then unbolted the NEW master cylinder (when I replaced it I totally bled the brake lines - used 3 quarts dot 3 brake fluid). Now with the master cylinder 1/2 inch away from hydroboost unit, all 4 brakes were still locked up. So HYDROBOOST checks out O.K!---- But brakes are still no good!!!! ABS malfunctioning? Possible water contamination spread to all the new parts I installed?.....LIKE THE ANDROMEDA STRAIN? HELP!!!! PLEASE!!!

markw8 Enthusiast

markw8

Posted
Posted

I can't seem to find it but I seem to remember a recent post with a similar problem. Poster said a new hydro fixed it.

 

Mark

GMChris Enthusiast

GMChris

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Thankyou so much for the great responses. I'm a Newby here. In my 50's and been working lots on cars/trucks all my life, so I may have alot to offer here as time goes by. I'm thinking the Hydroboost is NOT the problem since all brakes are dragging badly (to varying degrees) even when my NEW master cylinder is unbolted and pulled back from my Hydrobooster. I'm a little shakey when it comes to: a)Hydrboost Brakes, and b) ABS brake system. I am however an electronic tech. I'm now going to drive it 'till it's warm so the brakes drag again. Then I'm going to begin releiving brake fluid pressure on each circuit starting with the LH Fr caliper bleed screw & working back up the system towards the master cyl. I WILL NOT LET THIS DEFEAT ME!!!!! there are many, many similar posts with no solutions that satisfy my exact situation, but when I'm done I will post a "Problem w. Symptoms", and "Solution". I've read people's ideas about moisture, foriegn particle, and air contaminated ABS Brake Pressure Modulator Valves. Does anybody know if there's really any truth to this?

DofD Senior Enthusiast

DofD

Posted
Posted

I wish I had some suggestions for you, but it's beyond me. But good luck!

 

Maybe try removing the ABS sensors to see if that makes a difference. It sort of seems like the brake fluid pressure generated during braking is not being fully released with each application of the brakes. So every time the brakes are used increases the base pressure in the system.

markw8 Enthusiast

markw8

Posted
Posted

If your going to troubleshoot by loosening lines, why not start at the hydroboost first. It will effect all four wheels at once. I have never heard of the ABS causing 4 wheel lockup. Also if the ABS malfunctions, it should set a code.

 

Mark

GMChris Enthusiast

GMChris

Posted
  • Author
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If your going to troubleshoot by loosening lines, why not start at the hydroboost first. It will effect all four wheels at once. I have never heard of the ABS causing 4 wheel lockup. Also if the ABS malfunctions, it should set a code.

 

Mark

 

 

As I wrote in my last post:

 

I'm thinking the Hydroboost is NOT the problem since all brakes are dragging badly (to varying degrees) even when my NEW master cylinder is unbolted and pulled back from my Hydrobooster.

markw8 Enthusiast

markw8

Posted
Posted
If your going to troubleshoot by loosening lines, why not start at the hydroboost first. It will effect all four wheels at once. I have never heard of the ABS causing 4 wheel lockup. Also if the ABS malfunctions, it should set a code.

 

Mark

 

 

As I wrote in my last post:

 

I'm thinking the Hydroboost is NOT the problem since all brakes are dragging badly (to varying degrees) even when my NEW master cylinder is unbolted and pulled back from my Hydrobooster.

 

 

 

I don't know how to link the topic, but I found the one I was looking for. It's in the Heavy Duty forum. Feb.13 2009. Poster said brakes would lockup after a little driving, he would bleed off pressure at the master cyl then could drive a little more and it would repeat. He stated he replaced the Hydro-boost and his problem is gone. Also like I said, if it's the ABS you'll get a light and a code.

 

Mark

  • 5 weeks later...
GMChris Enthusiast

GMChris

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It's been a while since my last post. I wanted to be sure my problem was solved. The entire repair job consisted of: Replacing all 4 brake calipers and pads. All 5 flex brake hoses. Master Cylinder. Master Cylinder reservoir - thoroughly cleaned/ dried. Brake fluid replaced. Power Steering fluid flushed and replaced (power steering pump operates the brake Hydro-Boost system). Well it turns out that after replacing the parts and examining the old calipers, 3 YES THAT's RIGHT....3 calipers had siezed within 9 days of each other. As all of the old flexible hoses actually checked out OK, the only reasonable explaination we could come up with is that due to an exceptionally long and cold winter (the cold due to global warming) there's been probably 5x more salt than normally used this past winter and it caused corrosion in the brake caliper piston bores.

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