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TJsBeer

aka LuckysDad
Joined
Jan 26, 2015
Yes, I know another PM question.
But I have searched here, read Richard Clark's book and all the docs on gnttype.org and haven't found my particular issue.
So I beg of your help please...

I’m having intermittent brake failure.
At start up all brake functions show normal.
Light and PM motor run normally.
Fluid levels pressurized and unpressurized are correct.
No leaks
30 AMP fuse is good.
5 minutes into drive brake light comes on and off for a few seconds, brakes are operating normally.
10 minutes into drive, brake light comes on, stays on, still have brakes
A couple minutes later no brakes,
Pull over, re-start procedure, still no brakes.
Turn around, head home.
Brakes come back on a couple minutes on the way home.
Arrive at home a couple minutes later and light comes on and no brakes.
I do live in a VERY hilly area if that makes any difference.


From the diagnostic flow chart:
Start, light comes on, yes
Disconnect pressure switch, light comes on, no
Reconnect pressure switch
Depressurize accumulator
Check correct fluid level on passenger side, level ok
Turn on ignition, determine time, light off in 5 seconds, motor off in 7 seconds
Replace the accumulator
Retest
Depressurize accumulator, same results, but still having intermittent brake failure.
 
Your going to get a lot feedback to dump the powermaster for a vacuum brake swap. In truth, that is probably the best advice for most owners with flaky powermaster systems. That being said, I’m still running a powermaster and had a similar experience as you described. In my case, the motor was not able to build enough pressure. I had a rebuilt motor in my supply of extra parts which once installed corrected the problem.
 
Your going to get a lot feedback to dump the powermaster for a vacuum brake swap. In truth, that is probably the best advice for most owners with flaky powermaster systems. That being said, I’m still running a powermaster and had a similar experience as you described. In my case, the motor was not able to build enough pressure. I had a rebuilt motor in my supply of extra parts which once installed corrected the problem.

Agreed. Mine was doing the exact same thing. I didn't have any spare parts laying around so switched it over to vacuum and put the powermaster in a box for the next guy. It it helps your decision, I liked the braking with the powermaster better and only decided on the change for simplicity and price.
 
I'm leaning that way. These things are just too complicated with too many parts that could go wrong.
The vacuum swap almost seems like a no brainer at this point.
 
I was having some issues with my PM and I replaced the switch and accumulator bowl and it fixed my problem , Mine was doing what yours was doing so this is a good starting point . Good luck and let us know how things go .
 
Thanks Keith. I replaced the accumulator and the proportioning valve. The switch and check valve tests as operating correctly. Maybe I should just go ahead and replace the switch too and see if it makes a difference.
 
Thanks Keith. I replaced the accumulator and the proportioning valve. The switch and check valve tests as operating correctly. Maybe I should just go ahead and replace the switch too and see if it makes a difference.
I would do that , Good Luck
 
Update: I brought Rosey to my mechanic for a second opinion before we do the vacuum brake conversion. He double checked over everything according to RC's book. While checking over the electric connections were clean, tight and grounded he noticed that if he wiggled the PM switch it would trip the light. We agreed to first replace the switch and re-bleed the system. We took it for a 20 mile test loop using the brakes in varying conditions and they didn't fail nor did the light come on. All seems good for now.
 
If you intend on making more power in the future I would recommend hydroboost.
If you are going to keep it a driver go vacuum. Definitely replace that system before it kills you
 
Do not play Russian roullete with a 32 year old power disaster. It will not end well. Evenually you will loose.
 
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