PM III problems - accumulator or pressure switch?

[GnatGoSplat]

The pump on my PM III runs EVERY TIME I step on the brakes. It runs for about 2-3 seconds every single time.

I've heard this is NOT normal.

 

Neither the yellow "ANTI-LOCK" or red "BRAKE" lights are lit. Occasionally, when I start the car, the yellow "ANTI-LOCK" light is lit, but it goes out after a few minutes.

 

Is this more likely a bad Accumulator, or pressure switch?

[Guest Anonymous]

I would guess accumulator. This question is best left for Chris A. though. You could check his site and look under PM III. Explains pretty much everything.

[eclipse5302]

I met a guy through work who had a PMIII that NO ONE in town would touch. I said, no problem...I'll fix it. After replacing the accumulator (yellow/red lights on...only complaint) the pump still ran whenever the pedal was pushed. I replaced the pressure sensor, and all was well.

 

Just make sure to depressurize (you know that), and don't worry about brake fluid leaking out or any left over pressure, because there is a schrader valve in the fitting that the pressure sensor screws in to.

 

If the accumulator was bad, the light would go on...or a scan tool can tell you that you are low on accumulator pressure. Also, the pedal will change and feel very different when the accumultor loses pressure. It will stay the same if it's only the pressure switch.

 

Usually the only stuff that goes wrong with these units is:

 

1.Accumulator charge

2.Pressure switch

3.Pump relay

4.Cracked housing...leaking fluid

 

Nothing else really gives a problem...that I've seen.

 

Jason

[GnatGoSplat]

Thanks Jason.

I'll look into the pressure switch. Do you have any pics of it? I'm just curious if there's any aftermarket source for it. It's an expensive little bugger.

The brakes on this car already feels very different than my Cutty, but it could be the pads for all I know. It's hard to tell.

I feel like I really want to be right on this one, because both items are pretty damn pricey.

[Chris A]

The pump on my PM III runs EVERY TIME I step on the brakes. It runs for about 2-3 seconds every single time.

I've heard this is NOT normal.

 

Neither the yellow "ANTI-LOCK" or red "BRAKE" lights are lit. Occasionally, when I start the car, the yellow "ANTI-LOCK" light is lit, but it goes out after a few minutes.

 

Is this more likely a bad Accumulator, or pressure switch?

 

If you fully depressurize the system, how long does it take to charge? If the accumulator is dead, it won't take very long as the accumulator isn't displacing the volume it normally would for the pump to fill. If the pressure switch is bad, its kinda hard to tell. The only REAL way to be sure is to use a pressure tap on the accumulator port to see when it is coming on and going off. If the pump portion of the switch is bad, you should be able to get a 5-7 rapid presses of the pedal before the red light comes on. This will suck down the accumulator pressure and trip the pressure warning light portion of the switch. Or you can try unplugging the motor power fuse and turn the ignition on and see if you can get a normal 4 to 5 presses of the pedal before the light comes on. If you can get at least a few presses in any situation before the light comes on then it is probably the switch. If you like I can send you a switch I know is good for you to try and see if it makes a difference. Unfortunately I sold my last good accumulator, its a little easier to change.

 

Chris

[GnatGoSplat]

Chris, thanks for the offer.

I'll have more answers after Wednesday - I left the car in the garage of the old house, and we don't plan to go out there and do more work on the house till Wednesday. Although the accumulator costs more, I was kind of hoping that was it because it seems like quite a bit less work.