Low Speed Rear Brake Lock Up

[brsllc]

2000 Chevy 3500 with front disc and rear drums. When this truck is first started in the morning you can gurantee the first time you hit the brakes it will almost throw you into the windshield. The lock up comes from the rear brakes, you can see the skid marks in gravel. Once you have driven above twenty miles an hour or so the truck does not do it when coming to a stop. After driving it above twenty mph for a half our or so it stops acting up completly. Let the truck sit for an hour or two and we are back to rear brakes locking up when any amount of pressure is applied. It does this regardless of going in drive or reverse and only at low speeds. I have inspected the drums, shoes, wheel seals, and wheel cylinders and all are fine.

 

Any ideas on this one?

[cammiller]

Is there any leaking axle seal or wheel cylinder, or possibly an accumulation of brake dust.

[Zembonez]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

[brsllc]

Is there any leaking axle seal or wheel cylinder, or possibly an accumulation of brake dust.

 

 

no leaking seals and all componets have been removed and cleaned.

[brsllc]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

[Zembonez]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

 

Hydroboost systems have lines from the PS pump running to the area near the master cylinder instead of the typical big round vacuum booster. Fairly common on 3500 trucks.

[brsllc]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

 

Hydroboost systems have lines from the PS pump running to the area near the master cylinder instead of the typical big round vacuum booster. Fairly common on 3500 trucks.

 

 

I will check on that and see in the morning.

 

Any chnace it could be a front wheel abs sensor. I have read other post about these causing problems.

[Zembonez]

Any chnace it could be a front wheel abs sensor. I have read other post about these causing problems.

I really doubt it. Usually a bad ABS sensor just triggers a light.

[brsllc]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

 

Hydroboost systems have lines from the PS pump running to the area near the master cylinder instead of the typical big round vacuum booster. Fairly common on 3500 trucks.

 

 

 

This is a hydroboost system. what could be causing the system to overboost. Are there things I can look for to help determine if this is the cause or not.

[brsllc]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

 

Hydroboost systems have lines from the PS pump running to the area near the master cylinder instead of the typical big round vacuum booster. Fairly common on 3500 trucks.

 

 

 

This is a hydroboost system. what could be causing the system to overboost. Are there things I can look for to help determine if this is the cause or not.

 

 

 

 

CAN ANYONE ELSE HELP ME WITH THIS SITUATION.

 

[Zembonez]

Is this a hydroboost system? Possibly an overboost when the PS fluid is cold...?

 

 

How would i tell if it is a hydrboost system.

 

Hydroboost systems have lines from the PS pump running to the area near the master cylinder instead of the typical big round vacuum booster. Fairly common on 3500 trucks.

 

 

 

This is a hydroboost system. what could be causing the system to overboost. Are there things I can look for to help determine if this is the cause or not.

 

 

 

 

CAN ANYONE ELSE HELP ME WITH THIS SITUATION.

 

 

I don't know how the boost is controlled at the master cylinder but from what you are saying I would look into it. There has to be a pressure relieve valve in the system for when the fluid is cold and thicker.

 

Here's a free bump back to the top of the heap so maybe we can gat a more educated opinion.

[cammiller]

Any chnace it could be a front wheel abs sensor. I have read other post about these causing problems.

I really doubt it. Usually a bad ABS sensor just triggers a light.

 

I had one that was the sensors. It had no ABS concerns. The truck has no proportioning valve, instead it uses dynamic rear proportioning controlled by the ABS. Not sure how to diagnose that without replacing the sensors.