Powemaster and S10 wheel cylinders

[Supercomp729l]

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[Keller]

You say your system's behavior passes the test?

The accumulator would be the most likely candidate. Do you know how old it is?

[Supercomp729l]

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[Keller]

Or maybe that round ball is bad?
That is the accumulator. It contains pressurized nitrogen, and it does leak out over time. They simply do not last forever.

[Supercomp729l]

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[Keller]

http://www.kirbanperformance.com/

Dennis Kirban worked with Cardone (who rebuilds Powermasters) to get these built after GM stopped offering them. Sadly, they are a fair bit higher than when GM last sold them. Other vendors may sell them as well, but they are all coming from the same source.

[zeus87gn]

Your accumulator is fine.
You have air in your system.

[Keller]

Certainly possible if you just put the S10 cylinders on. Did you bleed the system after that? You'd have to do all four corners.

[turbodave38]

Based on his description it could be both. I've never had the light behave like that when the system needed bleeding. But the light sympton is certainly indicative of an accumulator starting to go bad.

[zeus87gn]

Supercomp,

I thought about this some more. Does you pedal feel spongy anywhere in it's travel? Once you feel the brakes grab (pedal resistance) is it firm? Please describe this as best you can.

If you think the pedal is normal, and you feel confident that you don't have air in your system, this could be a malfunctioning pressure switch. Your pump up and self cycle times are perfect. I don't really see the accumulator or pump at fault here.

How did you bleed the system?
What method did you use?

Z

[turbodave38]

I don't really see the accumulator or pump at fault here.



Z

Why is that? the brake light flashing on for a short period when the pedal is first depressed is a classic symptom of an accumulator in early stages of giving up the ghost.

[zeus87gn]

Why is that? the brake light flashing on for a short period when the pedal is first depressed is a classic symptom of an accumulator in early stages of giving up the ghost.

If the acc was dying, it wouldn't be holding much pressure. It would also be leaking down somewhere so the pump would have to keep it up almost constantly. It would also take the motor more time to pump it up. It's not happening here based on the description given. It's the basic physics of the unit.

In his situation, the only thing that would "technically" cause the light to flash is a sudden rush of the acc pressure to overcome air somewhere in the system. Depending on how the OP bled the system, and if he feels confident there is no more air left, there isn't anything else left.

If the flash is being caused by the prop valve, there is still air in the system. It's easy enought to figure out with a basic DMM on either the prop valve or the pressure switch.

[Supercomp729l]

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[zeus87gn]

Is there one of your local friends that has a known good working PowerMaster that you can swap the pressure switch out to test? It only takes a few minutes to change it out and you dont' have to bleed the system, only cycle the acc. You can do the same to verify the acc if you like. Probably with the sensor in the prop valve as well (but then you will have to re-bleed the wheels).

Sounds like the system overall is working well short of the light flashing.

[turbodave38]

If the acc was dying, it wouldn't be holding much pressure. It would also be leaking down somewhere so the pump would have to keep it up almost constantly. It would also take the motor more time to pump it up. It's not happening here based on the description given. It's the basic physics of the unit.

In his situation, the only thing that would "technically" cause the light to flash is a sudden rush of the acc pressure to overcome air somewhere in the system. Depending on how the OP bled the system, and if he feels confident there is no more air left, there isn't anything else left.

If the flash is being caused by the prop valve, there is still air in the system. It's easy enought to figure out with a basic DMM on either the prop valve or the pressure switch.


Well, OK. But in my experience with my 2 GN's over the last 20+ years, everytime my brake light started acting as described, it has always been the accumulator that needed to be replaced and solved the issue.
I've only had one pressure switch fail in all those years, and it's failure was obvious.

[zeus87gn]

Well, OK. But in my experience with my 2 GN's over the last 20+ years, everytime my brake light started acting as described, it has always been the accumulator that needed to be replaced and solved the issue.
I've only had one pressure switch fail in all those years, and it's failure was obvious.

I understand your point. The flashing light is a classic symptom. But in this situation the OP has a pump up time that is in line with a new acc ball. I'm not saying that isn't the problem, but I would be stumped if it is. I would have to go back and read up some on my fluid dynamics and re-check my manual to refresh my memory.

I really think the OP should do more testing before he spends his money.
I know I would.
Just some advice, that's all.

[turbodave38]

One would think so, but I'll just add, the bad accumulators that I have, I changed out when the light started flashing and didn't let them get more than a few days into their death nell. My pump times were not out of the ordinary at that point. I'll assume that if the acc goes REAL bad that the pump times, etc. would reflect the difference.

Just an option. Unfortunately neither will be a cheap replacement any longer.

[zeus87gn]

I'll assume that if the acc goes REAL bad that the pump times, etc. would reflect the difference.
To my knowledge, yes.

Unfortunately neither will be a cheap replacement any longer.
You got that right!

[IL KIM]

Sounds exactly like the issue I had. And it exhibited these symptons for months till I changed the accumulator ball.

[Supercomp729l]

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[IL KIM]

:stooges:Glad you got her fixed.

[Keller]

Scott thanks for your straight forward advise and the best GN web site.
Glad to help.

The site is the effort of many people over the last 16, almost 17, years. I'm not going to take all the credit. Please just chip in, and help us keep working to help others and keep this the kind of resource it has been for you. Everyone knows something that someone else would like to know.

[Supercomp729l]

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[Keller]

Probably just need to drive it a bit to break things in. I bet you installed new shoes, too. Did you use all large pads on the rear?

Might need to readjust the rear brakes as well. (i.e. Close the pads a bit, insure the adjusters are going the right way, etc.)