how to on Powermaster motor replacement?

[Evans Ward]

Need to swap motors on my Powermaster. What is the proper procedure? Can it be done on the car with master cylinder attached so not to have to bleed brakes? Hoping someone can provide tips here to aid me in this. Thanks!

 

[gofstbuick]

IMHO, the PM motor can be replaced with the master cylinder still installed. You'll need to split the feed hose from the junction or at the mastercylinder body. Then remove the bolts and rubber grommets that hold the motor to the master cylinder. Being you'll be working from underneath the master cylinder, I think this will be the toughest part, not to mention the exhaust, electrical and other parts being in close proximaty (sp?) will make for tight quarters. Once the new motor and lines are installed, fill the PM reservoir and turn the ignition on. the motor should run for no more than 20 seconds. If it does, turn ignition off and loosen the PM feed hose (on the master cylinder body), until fluid flows from the hose. DO NOT COMPLETELY REMOVE THE HOSE IT IS STILL UNDER 700PSI OF PRESSURE!!!!!!!!!! . Tighten the hose and turn ignition on, PM motor should not run for more than 20 seconds. If the front port on the floor of the largest reservoir (PM reservoir) becomes uncovered in brake fluid during the ignition on process, add just enough brake fluid to cover the port.

 

[Evans Ward]

Thanks for that description- that really helps. Should I keep the fluid filled in the PM resorvoir during this or pull it out by siphon (turkey baster)? Main concern is not having to bleed brakes during PM motor change. I would need to depressurize unit, right?

What do you mean by splitting the feed hose from the junction or at master cylinder? I can't disconnect that hose from mc to PM motor and block it off during PM motor change? Thanks for helping out! Want to make sure I've got detailed instructions before doing this.

 

[gofstbuick]

I haven't look in a while, but the feed line should separate (un-screw) where the metal line meets the rubber line or where the rubber line meets the master cylinder. Easiest is to remove the line at the master cylinder body. Remove as much fluid (using a turkey baster) from the reservoir. Less of a chance of it getting on the paint. Double the fender covers. I use a inpenatrable (sp?) cover on the car and add a clothe cover over the one on the car.

 

[Evans Ward]

Thank you. That was clear for me to understand. I have the donor used PM in hand today (thanks Black Demon/ Mike Waters in N Augusta SC!) so I'll take off the motor from that one to know exactly how to attach. Will take on this project this weekend.

 

[Evans Ward]

couple more questions....

I'd like for someone to address a couple of more questions I have before I perform this motor/ pump replacement tomorrow. First, should I pump brake fluid back into main powermaster body after hoses are off for a good prime? Secondly, how about same concern on fitting where pressure hose attaches to electro hydrolic powermaster motor/ pump? Does that pump need and circulate brake fluid through itself? Last question I have is what exactly is the relationship between the coolant fan delay relay and the powermaster brake system? I keep seeing this relay mentioned in the Factory Service Manual and don't and can't understand how it interfaces with the braking system? I do know it's the large relay on the driver's side inner fender closest to driver. (PN 25527402)

My plan is to replace motor/ pump, pressure and sump hoses, pressure switch and this coolant fan delay relay if it is needed too. I have parts taken off the donor powermaster unit, appropriately cleaned by service manual standards ready to go on car. I'll be doing this change over with unit still attached to car.

Again, any and all help fully appreciated!

 

[gofstbuick]

I can answer most of your questions, but not all. You need to pump the brakes to relieve the pressure from the power assist side. Here is a short description of how it works. The accumulator has a diaphram (that stretches across the center) one side is subject to hydraulic pressure and the other side is filled with nitrogen. The motor pumps pressure against the diaphram. When the pressure switch sees a specific amount of pressure it turns the motor off, below a specific pressure, it turns the motor on. When you press on the pedal, the a port is opened to allow fluid to flow back into the reservoir, but more importantly, the nitrogen filled side of the accumulator pushes the pressure to the power piston to provide power assist. Excess fluid (from accumulatator) is returned to reservoir and when the motor pumps, it applies against the accumulator to re-charge the pressure. The best way to test the system is to use brake pressure gauges. You'll have to make an adapter (ask me how if interested). The gauges allow you to monitor specific hydraulic pressure (created by the PM motor), bleed pressure off to allow the motor to pump up and know that the pressure switch is turning on/off at specific pressure.