Bad Master Cylinder?

[NVRL8]

Did a few searches and think I have a bad master cylinder. Hope you guys can tell me for sure.

My brake pedal goes to the floor every time I apply it. The Powermaster motor runs with each application as well. I have brake fluid leaking from the passenger side reservoir and looks like its leaking around the pressure switch as well.

 

[Swt_86]

I believe you are correct. Here is what you need: Zip Code Entry at PartsAmerica.com I have just installed the Cardone unit and it works great.

 

[NVRL8]

That's going to put a dent in my wallet! Does the Cardone one look original? The pics in the link make it look so.

 

[mario987]

How about the wagner ? Is it the same?

 

[Swt_86]

The Cardone looks original - because it is. It is a remanufactured unit. The accumulator is a new unit but looks very similar to the original. I don't know about the Wagner unit. At the price of these puppies, I didn't want to pay for more than one. That is why I went with the lifetime warranty Cardone unit. Kirban Welcome to Kirban Performance Products also carries the Cardone unit - their part number 7021. The other options are to go with a vacuum conversion or a hydroboost. Either way, it is not cheap - but what is on these cars?

 

[NVRL8]

Does it make sense that with the key off and the acc. discharged I have firm pedal pressure, and it does not go to the floor?

 

[POWERBRAKEBOB]

Hydroboost Conversion

The Powermaster Has A 1.250" Master Piston. It Is Really Hard To Push The Pedal Without The Motor Running To Build Pressure. You Only Have About 250-300 Psi Manually. Usually The Motor/pump Wears Out, And The Motor Windings Fill With Brake Fluid, Shorting It Out. If The Pedal Drops Much Lower Under High Pressure, There May Be A Caliper/pad Problem, Or Rear Brakes Out Of Adjustment

 

[NVRL8]

Powermaster kicking my a**

Swt 86 sent me the service bulletin for Powermaster. (Actually same one I had in Peter Hoffman book).

I have bled the entire system including master (using Zues method). Rear brakes adjusted properly (S-10 wheel cylinders if that matters). No apparent problems with calipers. System pressurizes in about 7 sec, and time from motor start to light off is about 6 sec. Brake light does not come on during normal braking. Pump does not cycle within 5 min period of brakes not being applied (internal leak test).

Suggestions or input?

 

[zeus87gn]

With those times, the high pressure side of your P/M sounds to be in good shape. The acc ball may be a little old (only 1 second after light off). If you plan on keeping the P/M, I suggest getting a spare acc for backup. The motor should not run every time you apply the brake. Maybe every other time at the most. I think mine runs every 3rd or 4th time.

Are you saying your pedal still goes to the floor, under power, even with these times? Bob is correct in that the pedal is very hard to push without the power assist so it will not go as far as you would expect without it.

Have you blown the fuse yet?
Has the bowl stopped spewing fluid? The P/M will spew only when it is overfilled and the acc begins to discharge.
Is there any resistance as you push the pedal down under power or does the pedal travel and then stop?
Will the car stop with the brakes as they are?
What are the condition of your flex brake lines to the wheels and axle?
What does the fluid in the d/s of the bowl do when you apply the brakes under power?

Some GM brakes just take more pedal travel than others. I have noticed this over the years. But if your pedal is going to the floor, and your car is not stopping, then further investigation will certainly be necessary. I have never heard of a P/M loosing the orings on the low pressure side....but I suppose it could happen.

 

[NVRL8]

I was not clear in my last post. With the acc depressurized, I turn key on and brake light goes off in about 7 sec. The pump continues to run for about 6-7 seconds more (pump running a total of 13-14 sec). The motor does not then self cycle without brake applies.

Yes, pedal still goes to the floor under power. There is slight resistance when pushing the pedal under power, but goes to the floor easily. The resistance is the same throughout the entire pedal stroke.

No blown fuse yet.

Bowl still spews fluid (I'm positive it is filled properly). When the brakes are applied under power, fluid comes up stongly through the port in the drivers side rear reservoir. I think it is this burst of fluid that is causing the leak around the lid.

Car will stop with the brakes as they are, but haven't taken it out since these problems began.

Flex brake lines: no significant cracking, no leaks, no bulging.

 

[POWERBRAKEBOB]

Hydroboost Conversion

It Sounds Like The Master Cyl Piston Seals Are Not Sealing. When You Push The Piston Cups Forward, They Must First Pass The Compensation Port, ( The Tiny Hole In The Casting) And Then After The Cup Seal Passes That Port, Fluid Starts To Push Out Of The Outlet Port To The Brakes. Normally You Will See A Momentary "geyser" Of Fluid Until The Cup Goes Past The Comp. Port. Then Pressure Starts To Build Up To The Wheels. "if" The Cup Does Not Seal, All Fluid Being Pushed Out To The Wheels Will Be Forced Back Up Into The Reservoir, With A Huge "geyser" Of Fluid Shoved Back Into The Reservoir. At That Time You Will Only Have Front, Or Rear, Brakes.

 

[zeus87gn]

I'll have to agree with Bob on this one. You seals in the low pressure side (the typical mastercylinder side) are gone. Time for a rebuild P/M or one of Bobs hydroboost units.

Strange that happened. Usually the high pressure side goes first.

 

[NVRL8]

Thanks guys for all the help. I have a rebuilt on the way.

 

[NVRL8]

New unit is in, and I'm back in action. I wish diagnosing this thing was as easy as replacing it! Thanks again everbody.