Almost Couldn't Stop Yesterday!!!

[6=8]

I have reviewed several Powermaster threads, and have also taken a look at the gnttype.org Powermaster diagnostics, but I still have symptoms that seem unique.

The brake light "Flashes" at me when I apply the brakes very quickly. (Listed as normal operation.) Now, this has slowly progressed to the point that it flashes EVERY time I tap the brakes. I can hear the PM motor cycle, and shut off (3-4 seconds run time, max).

And yesterday, I had a very close call. Had someone pull out in front of me without looking, and I hit the brakes... Pedal went HARD and then the pump "Caught up". If it didn't, I would have ran into the person! I had a nasty front end/body repair bill flash before my eyes!

So, sitting in the safety of my driveway last night, I listened to the PM unit while I pushed on the brakes. With a "Panic" application, the pedal goes hard at first, then "Pumps up" giving you that "Oh Sh t!" feeling when you hit the brakes and they aren't there. With a "Normal" gradual application, the PM cycles for 1-3 seconds and the power assist feels OK. Each time I press a little harder, the pump turns on for less than a second. When new, this unit gave me at least 1 pedal application before it ran. Now, any brake application turns the pump on.

Are these symtoms of a bad brake pressure switch, as in turning the pressure/pump off too soon? Or is it an Accumulator problem bleeding off too much pressure during a brake application? Combo?

I have a few old units from previous replacements, so I am planning on swapping a few parts before I go to AutoZone and replace the whole unit. Anyone have some ideas for me?

 

[Black Car]

It sounds like the accumulator to me.
The pressure switch is turning the pump on & off so that isn't it.

Gary

 

[Micah]

I had a similar if not the same exact problem. I got a new accumulator and they've worked super ever since. From what I understand the bladder goes about every 6(?) years or so. They're kinda hard to find though. The only place I could find it was Kirban's and they run about $70 or so if I recall

:enter everyone who's gonna tell you to convert over to vaccum brakes:

 

[granitestategn]

Sounds like the accumulator to me, too. I replaced mine last year. My pump would start running as soon as I hit the brakes. I bought my accumulator from a Buick dealer. $110.00! Ouch! Put it in and all worked great until I drove half-way accross the country with a bad battery (late at night) and popped the brake fuse about 20 times . Low volts. New battery fixed the problem. Fast forward one year. Good battery and I keep blowing fuses now and then. The pump sounds like it's laboring just before it shuts off. Scanmaster says I've got 13.6 volts. Any ideas? Bad pressure switch? Buick dealer wants $119.00! Seems like last year I checked and that switch was about $60.00?! Does anyone know if anybody sells it for less? I don't mind spending the money if it fixes the problem. I just don't like throwing money at a problem until it goes away. I don't really want to convert to vacuum, either.

 

[granitestategn]

I must be nuts!

Did I say in a previous reply that I don't want to convert to vacuum brakes? I must be nuts! After reading a few threads on this site and checking out gnttype.org for the procedure, it looks like the way to go! It sounds easy enough and it will cost a lot less in the short and long run. Anybody need a 1 year old accumulator ball?

 

[6=8]

Sounds like I do! But....

I have 3 complete Powermaster units in my garage. Yep, previous replacements, 1 the OEM unit, 2 GM factory rebuild units that I purchased from ATR. I don't think all 3 were due to bad accumulators, so I have 3 to try out!

These replacements were made before I knew of this site, and all the nice folks pulling together to help each other out. Thanks for everyone's replies. I'll give the old swap a try and let you know how it all turns out.

Granitestategn:
By the way, the only time I had a brake fuse popping was when an internal pump seal let go, causing brake fluid to enter the electric motor itself. Unit seemed to work fine brake wise, but after the car had been driven for a couple of miles, the fuses started popping (Brake light would come on, and I would have about 3 stops before the power assist was gone.) Check for a strong smell of brake fluid or signs of leaking out the back of the powermaster motor itself. Maybe this is your problem? Good luck to us all!

 

[6=8]

Brake Fluid INSIDE?

Swapped the accumulator last night. That was the problem. Brakes work much better!

I have another question: Should there be any brake fluid inside it?

 

[GNICETRY]

VACUUM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[TurboDave]

Re: Brake Fluid INSIDE?

Originally posted by 6=8
Swapped the accumulator last night. That was the problem. Brakes work much better!

I have another question: Should there be any brake fluid inside it?

If you're talking about the one you took off. Of course, it's attached to the master cylinder, and must apply the pressure directly to the fluid. There are no air reservoirs like vacuum brakes. Everything is done with high pressure exerted directly to the fluids in the master cylinder.

 

[6=8]

Thanks TurboDave... The old one I took off the car had some fluid in it, but the one I took off an old unit didn't. I was a little worried, but thanks to you, I feel better now!

GNICETRY: I have added a vacuum block with the extra port for a possible vacuum brake upgrade, but I've been given another thing to consider lately: The vacuum cap I put on the unused port has blown off due to boost 2 times. The first was without a hose clamp. The second was one with!

So, if I can drive more than a couple of days without the cap blowing off, THEN I might go ahead and convert to a vacuum system. Right now though, I'm kind of in a test mode. If the cap can stay on for a month without any attention from me, that might push me over the edge when this unit finally dies (So far, it has lasted 2 years longer than the previous units!)

 

[granitestategn]

I finally did it!

I took the plunge! Converted to vac brakes yesterday. I'm not done yet, though. I got my pedal off a mid-80's Monte SS ($10 including the underbody front braces). Bought a re-man master cylinder w/reservoir for about $26 + $5 core, re-man tandem vac booster for $95 + $10 core. Misc other stuff, ~ $10. Bench bled MC per instructions (put in vise, slowly pushed on plunger until I had no more bubbles), installed on car, connected vac line. Checked pushrod length. About 3/8" travel before fluid moves in reservoir. Started engine to see how bad the rest of the brakes needed to be bled. Noticed A LOT of bubbling in the rear reservoir with a really soft pedal when the engine is running. Do I need to take out the MC and do the bench bleed over again? Can I re-bleed the MC in the car? As soon as I get these brakes fixed I goin to the track and see what she'll do!

 

[Johnboy]

I also had the same exact problems with my slugmaster as you did. I'm also in the process of changing mine out. Got mine out of a cutlass supreme that I bought awhile ago. I assumed that I would eventually have problems and I did. As far as the air in the system, sounds like you have air in the lines. Maybe try and bleed through bleeder screws?