locked front caliper

[greenstingray]

Finally got to root cause of the problem. Stuck valve in ABS pump. Replaced pump, and bleed the brake system with a pressure bleeder. Everything works fine now. Thanks for all your help.

 

[huntboston]

Finally got to root cause of the problem. Stuck valve in ABS pump. Replaced pump, and bleed the brake system with a pressure bleeder. Everything works fine now. Thanks for all your help.

how did you find out that it was a stuck value in the ABS pump?

 

[greenstingray]

how did you find out that it was a stuck value in the ABS pump?

I called Gordon Kilabrew sorry if I mis-spelled his name. He told me to disconnect the abs if the brake was still stuck then it was the abs pump. He said it is pretty rare, but it happens. Forget about getting a new one the have been out of stock for a long time its a bosce 202 pump. I bought one on ebay installed it and pressure bleed the system. Everything seems to be fine now.

 

[huntboston]

Thanks. it looks like mine is bad also. I can't find one on ebay. can I ask how much you paid for it?

 

[greenstingray]

Thanks. it looks like mine is bad also. I can't find one on ebay. can I ask how much you paid for it?

My car is 87, I paid 100 + shipping the guy included the computer along with it. What year is your car it may be easier to get. Check to see if someone sell rebuilt pumps, my pump is not re-buildable.

 

[Schrade]

ABS has nothing to do with maintaining fluid pressure. It cannot create line pressure under ANY circumstances. It has only something to do with fluid pressure RELEASE. And it cannot release pressure on one wheel and allow pressure to maintain on the other, without ANOTHER pre-existing problem already causing line pressure discrepancies between left and right.

 

[greenstingray]

ABS has nothing to do with maintaining fluid pressure. It cannot create line pressure under ANY circumstances. It has only something to do with fluid pressure RELEASE. And it cannot release pressure on one wheel and allow pressure to maintain on the other, without ANOTHER pre-existing problem already causing line pressure discrepancies between left and right.

What about a stuck valve my pump is bosche 202 pump two lines for the front one for both wheels in the back. And my pump did have a stuck valve. The guy I calledl Gordon Kilabrew used to work at the factory, look him up. He said its rare but does happen. I changed out the pump and the car is fine now how do you explain that then.

 

[Schrade]

What about a stuck valve my pump is bosche 202 pump two lines for the front one for both wheels in the back. And my pump did have a stuck valve. The guy I calledl Gordon Kilabrew used to work at the factory, look him up. He said its rare but does happen. I changed out the pump and the car is fine now how do you explain that then.

The stuck valve if closed would only hold pressure that was created by pressing the pedal. If stuck open, it would not allow pressure build-up in those lines.

The ABS pump is not a 'pump'.

The ABS device is a hydraulic valve controller, and it does NOT in any way increase line pressure. NONE. It only controls valves.

The ABS controller does 3 things in EVERY ABS car -
It registers line pressure at the valve,
It releases line pressure when activated (by opening the valve),
It closes the valve back up, and allows pressure that was there before (by the depressed brake pedal) to be restored. It does not in any way increase pressure beyond what existed before it released the pressure. If there was no pressure before, it couldn't 'create' it afterwards either.

Even if functioning perfectly, it probably cannot exactly restore all pressure that was there before ABS kicked in.

There's no way it can act like a check valve either, because the valve is sort of 'in parallel' with the fluid line, NOT 'in series' with the line. An accumulator is what the valve leads into, kind of like a blister in the line.

I found one web page that said the 3rd step is 'Pressure INcrease' (wrong word). AND, in the same paragraph, it said the Control Module allows 'driver-applied' pressure to RESUME to what it was before the valve opened, if and only if the brake pedal is still pressed. 'Driver-applied' means let off the pedal, the pressure drops. No way the pressure can even be 'retained'. All other pages accurately described it.

There's NO ABS function, or MALfunction, that will maintain hydraulic pressure if the pedal lets off. ABS is all about releasing pressure, working OR broken.

 

[greenstingray]

The stuck valve if closed would only hold pressure that was created by pressing the pedal. If stuck open, it would not allow pressure build-up in those lines.

The ABS pump is not a 'pump'.

The ABS device is a hydraulic valve controller, and it does NOT in any way increase line pressure. NONE. It only controls valves.

The ABS controller does 3 things in EVERY ABS car -
It registers line pressure at the valve,
It releases line pressure when activated (by opening the valve),
It closes the valve back up, and allows pressure that was there before (by the depressed brake pedal) to be restored. It does not in any way increase pressure beyond what existed before it released the pressure. If there was no pressure before, it couldn't 'create' it afterwards either.

Even if functioning perfectly, it probably cannot exactly restore all pressure that was there before ABS kicked in.

There's no way it can act like a check valve either, because the valve is sort of 'in parallel' with the fluid line, NOT 'in series' with the line. An accumulator is what the valve leads into, kind of like a blister in the line.

I found one web page that said the 3rd step is 'Pressure INcrease' (wrong word). AND, in the same paragraph, it said the Control Module allows 'driver-applied' pressure to RESUME to what it was before the valve opened, if and only if the brake pedal is still pressed. 'Driver-applied' means let off the pedal, the pressure drops. No way the pressure can even be 'retained'. All other pages accurately described it.

There's NO ABS function, or MALfunction, that will maintain hydraulic pressure if the pedal lets off. ABS is all about releasing pressure, working OR broken.

My ABS PUMP did not release the pressure on the line, we are not talking about increase pressure we are talking about releasing pressure. That is one of the steps you listed above releasing pressure. Why do my brakes work know that we have the new ABS pump in the car.

 

[Schrade]

I have no clue why yours works with a new 'Pump'. BPM? I am totally clueless, and would REALLY like to see what you had going on.



You said the ABS light is working at start-up, and that you hear it do the self-test when you start moving. That normally means everything is as it should be.

I see no diagnostic situation in the FSM where the ABS BPM - brake PRESSURE (not pump) modulator, which controls (not creates) fluid pressure, can MAINTAIN that pressure when the pedal is let off.

FSM section for 'Brake line restriction' does not indicate BPM failure, only physical inspection of the brake lines.

Finally, the base braking mode descri


edit: I found a possible explanation here...

ASR Acceleration Slip Regulation CAN apply pressure to the REAR wheel calipers, WITHOUT brake pedal pressure, and if ASR is active.

If the previous owner (or a mechanic) has hacked something, or some damage has been done, that could explain dragging front brakes. That is SO much a stretch...

Did you have a 'Service ASR' light?

 

[greenstingray]

I have no clue why yours works with a new 'Pump'. BPM? I am totally clueless, and would REALLY like to see what you had going on.



You said the ABS light is working at start-up, and that you hear it do the self-test when you start moving. That normally means everything is as it should be.

I see no diagnostic situation in the FSM where the ABS BPM - brake PRESSURE (not pump) modulator, which controls (not creates) fluid pressure, can MAINTAIN that pressure when the pedal is let off.

FSM section for 'Brake line restriction' does not indicate BPM failure, only physical inspection of the brake lines.

Finally, the base braking mode descri


edit: I found a possible explanation here...

ASR Acceleration Slip Regulation CAN apply pressure to the REAR wheel calipers, WITHOUT brake pedal pressure, and if ASR is active.

If the previous owner (or a mechanic) has hacked something, or some damage has been done, that could explain dragging front brakes. That is SO much a stretch...

Did you have a 'Service ASR' light?

The car is an 1987 it uses the bosche 202 pump used on several other types of cars. This was the first ABS units aviailable in any US car. So there is no traction control. The unit has lines for the two front brakes and on the unit applies the ABS to two back wheels at once. Nothing was hacked on this car it has 52,000 miles, in fact my local Chevy dealer confirmed that the unit was bad, it did not display any fault light on the dash.