HELP! Need M813 Brake Master Cylinder

[Scout]

I have a job to do with my truck tomorrow. Brakes have been kind of spongy lately so I pulled the cap on the MC - empty. Tried to suction bleed the brakes with strange results. Built a pressure bleeder from a weed sprayer and was able to bleed at wheel cylinders, but have fluid leaking/spraying out of the front and rear of the MC. I have a good hard pedal while the weed sprayer is connected and under pressure, but when I disconnect the system and put the cap back on with the bleeder - pedal goes to floor.

Is there any chance this master cylinder is anything I will find locally (Fleetpride?) Was it common to any civilian vehicle?

Is there any chance I can rebuild it myself? I assume internal seals are shot and the MC is just recycling fluid within itself. Are the seals anything typical?

 

[gimpyrobb]

Yup, time for a rebuild, no its not a regular rebuild kit at napa. Look for a mil-surplus dealer. If you search, the seals might be listed in a thread here somewhere.

 

[Scout]

Thank you. i just e-mailed Dave at Eastern Surplus hoping he can overnight one to me. Going to go pull it from the truck now and asess the damage.

 

[Scout]

I just pulled the MC and took it apart on the bench. There isn't much to those things! About 2 pieces of rubber, a spring, and a plunger. Bore looks/feels smooth. If I can get the rubber parts am I good to go, or am I missing something - what else is there to rebuilding these?

 

[R Racing]

No there isn't much to them but there is a check valve thats critical.

 

[Scout]

I didn't see a check valve anywhere. I pulled the clip off the back and the following parts came out in the following order: clip, thick washer, aluminum plunger, rubber cap, and spring. The plunger had a rubber seal on it which I expect was leaking because I had fluid spraying out the boot. Is the check valve somewhere in the casting between the reservior and the bore?

 

[R Racing]

It should be a disc in the bore if I remember right. it has a small spring in it. I thought Eriks had a kit that included it.

 

[Scout]

On the end of what I'm calling the "plunger" (part rod pushes on) there was a disk with holes in it that looked like a revolver cylinder. It was flat against the end of the plunger and pressed on the rubber cap. Couldn't figure out what it did.

 

[gimpyrobb]

I have had a master that leaked till I honed it and put everything back together, its a long shot, but might work while your waiting for parts. Then rebuild it right when they show up.

 

[R Racing]

That sounds like it . it does have a few holes in it.

 

[R Racing]

Hone it and put some Gimpy love on it !! lol

 

[Scout]

What would make the fluid "recycle" within the master cylinder? I did notice when the cap was off and I pumped the brakes fluid was returning into the reservoir. There was a stream that lined up with the reservoir cap. Is there some kind of check valve between the reservoir and bore that is shot? Also noticed the fluid was filthy after it "recycled"

 

[gimpyrobb]

There are 2 holes in the reservoir that go to the bore the piston moves in. I think one is the "compensation port" Filthy fluid is a bad sign, might need airpack work too.

 

[Scout]

Awesome - I'll bet airpacks are even cheaper AND easier to find than MC's! Any words of widsom on assesing the condition of the booster? As far as I know it does not leak, and this whole problem started with a mushy pedal and empty MC. What are the signs of a failed booster. The brakes were working even with the empty MC - not sure how.

 

[gimpyrobb]

Your reservoir was empty, maybe not the bore which is what does the work. As long as it works, I'd let it go. I would certainly flush the system with new BFS though.

 

[R Racing]

The 5 ton Airpacs are gold plated compared to the master cylinder.

 

[gimpyrobb]

PM sent to both of you.