booster motor when brake pedal pushed

[GNX261]

Good Morning,

I have read the various technical articles that have been published about problems/solutions with the powermaster III brake system. This includes reproduction of the GM service bulletins. However, I cannot seem to find the problem I am having which is my booster motor runs every time I apply the brake pedal.

the brakes work fine,
there is no hard pedal,
there are no external leaks,
the red dashboard light does not come on,
the motor does shut off after discharge and ignition then on,
the motor does not run all the time,
the motor does not run erratically (just whenever I push the brake pedal),
there is power assist,
the motor does not run when the ignition is off

So what have I missed? I would rather replace a faulty part (e.g., accumulator, pressure switch, motor relay, motor, etc) as opposed to the complete system - but how do I determine what is not working?

Also, what is the "pump section of the reservoir?" Is it the passenger side or the drivers side?

 

[GNocide]

the pump runs to refill the ball after the brake pedal is applied.
pump side is the the one towards the passinger side

 

[gsgns4me]

I'm no expert, but it sounds like the accumulator is loosing it's charge. Powermaster Diagnostics

 

[zeus87gn]

Yes, it does sound like an accumulator.
But, you need to run the testing for internal leaks to rule that out.
The diagnostic procedure will have the acc test as well.
Have a good timepiece handy to run the diagnostics.

If you have trouble, or don't understand the results, post up and we can figure it out.

 

[GNX261]

zeus87gn, thanks for your advice. I did begin with the diagonostic tree, however I did not get very far. The first item on the tree notes that if my red light is not on then the system is ok. My red light is not on, but of course I do have a problem. Any help would be much appreciated. Thansk, again. Doug:

 

[zeus87gn]

The brake light in your dash only comes on when the pressure inside the acc ball drops below a certain point...or you have the parking brake engaged. From experience, the light in the dash doesn't always come on. My accumulator (and consequently the entire P/M) went out on me and my light never came on.

It may be possible that you do have a bad switch. But without the proper tooling, you will only be able to rule that out by replacing it with a new one. The accumulator seems to be a common failure item. It takes all the abuse.

Run the accumulator test and let us know what you find out.

 

[GNX261]

Zeus, what is the accumulator test. By the way, I do have a GNX dash and the brake light comes on when the emergency brake is engaged and the ignition is on. Thanks, again

 

[GNocide]

which ball do you have=there are 3

 

[GNRick]

I followed the troubleshoot manual on my PM. Problem pointed to the ball. I replaced it and that didn't fix it. I replaced the pump and that fixed it. As I recall, my dash light was on though. It didn't go off when it was supposed to.

 

[GNocide]

try the check valve fix-its free

 

[zeus87gn]

Rick,
Been offline for the weekend solving other problems.
Did you get your P/M working?
Zeus

 

[GNRick]

I may be sending one back to Cardone. Pump runs too much. Thanks.

 

[zeus87gn]

Is it priming?
You will see it begin to drop the fluid level in the p/s of the bowl as it pumps up the acc ball.

 

[GNRick]

My pump was running each time that I pressed the brake pedal. Only ran for a second or two. This was happening on both of my GN's. On GN#1, I replaced the accumulator and now the pump only runs every third time I hit the brakes. So I emailed Cardone to see what was up. They said the pump should only run every third time that I hit the brakes. They said bring it back to Autozone and they will send me a new unit. Gotta love that life time warranty! :smile: So I dropped it off today, and I will have a new PM tomorrow! FWIW, I paid $216 for it 3 years ago, and they now cost $407.

 

[zeus87gn]

D@mn, you got a deal. Take care of that new P/M. Keep fresh fluid in it, the air out of it and it will serve you well for many years.

 

[superjaay]

Hi guys I'm having a similar problem with my PM brakes. Every time I apply the brakes They work but the pedal slowly sinks to the floor. No drop in fluid level or leaks.....any ideas!

 

[GNRick]

If you have a spare accumulator, I would just try swapping it and see if that fixes your problem. Easier than going through the flowchart and buying the wrong part. Where are you located?

 

[zeus87gn]

Every time I apply the brakes They work but the pedal slowly sinks to the floor. No drop in fluid level or leaks.....any ideas!

Don't bother with the flow chart.
I hate to be the bearer of bad news, but the pedal slowly sinking to the floor is a classic tell tale sign of the seals in the m/c going bad. Same as in any typical m/c. A new Acc will not help it.
You need a ew P/M.

 

[superjaay]

I'm in Augusta, GA. A new accumulator is about $180.00 right?

 

[superjaay]

Don't bother with the flow chart.
I hate to be the bearer of bad news, but the pedal slowly sinking to the floor is a classic tell tale sign of the seals in the m/c going bad. Same as in any typical m/c. A new Acc will not help it.
You need a ew P/M.

The only problem is that no one has Pm's for a decent price. Autozone and Advance both told me that Cardone and Bendix are both out of supply at the factories. These units run about $300-$400. Know any other reliable sources, or should I just scrap the PM and do the vacum conversion for $200.00?