Hey All

Thanks to those of you who helped me originally.

I've found that I have fluid leaking out of the rear of the Master Cylinder, between the MC and the brake booster. What next? Do I just replace the seal between the two or does this call for a total rebuild of the MC?

As Always, Thanks in Advance,

Rob K
Raleigh, NC

What year?

Most 200 masters are only $55 new. Something in my recollection says the seals alone aren't much cheaper, but yes, if it leaks there, it needs to be fixed before you drive it.
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Art Benstein near Baltimore

It is an '87 245. Yeah, I was driving the other day and the pedal hit the floor at a stoplight. Had to use the E-Brake the whole way home, I'll be replacing those shoes soon too now that I had that experience.

You might be surprised about the parking brake shoes. More likely you just cleaned the rust off of the drums on the ride home. But once you get the drums off to look it would be a shame not to have the shoes if it turns out you need them. The master is easy to change on the 87. Only special device you'll need is a bench bleeding kit, that can be made from a new or old piece of brake line and a bit of plastic hose.

Art,

What is the purpose of bench bleeding the master cylinder? I've never had to do this before, but I've never put a new MC in, I've always rebuilt them (old triumphs and MG's). Is this 100% necessary?

Rob K.
Raleigh, NC

If you don't you will force air into the lines and need to bleed the entire system. Doing this on the bench clears the air out first, so as you are reconnecting the two lines the fluid dribbles out a bit and only tiny bits of air are forced out at the top of the connection.

If locating the brake line to do this seems difficult, ask at your auto parts store; I've heard of, but not seen, bench bleeding kits already packaged ready to use. Or purchase a short brake line (about $4) when you buy the master.

The idea is to force the liquid through both ports back into the reservoir by pushing on the piston with a blunt tool, like a phillips screwdriver or punch. It doesn't take that much force, so you don't need a vise to hold it.

I'm very happy these are available new and at competitive prices. I don't have much faith in the reman industry, so I'd do as you did with the smaller production cars if the new masters were not so reasonably had.
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Art Benstein near Baltimore

In my shop I always bench bleed the m/cyl, NEVER use a rebuilt and always bleed the system until there is no air and clean fluid. Don't mess around with brakes.

Art:

I haven't found a need to bench bleed.

1. Install the MC and fill with fluid. Wait till bubbling stops.
2. Pump the brake pedal. Probably drops to floor indicating air trapped.
3. Crack open lines. Depress pedal and block in down position with something eg.2X4
4. Tighten lines. Release pedal.
5. Repeat from 2. until pedal firms up. Then proceed to 6.
6. Bleed brakes if you want to.

I park facing up-slope, so that air moves to MC exits. There is some brake fluid spill that's easily wiped/washed away.

"If you don't you will force air into the lines and need to bleed the entire system."
Since the bleeder screws are kept closed, air will be forced out the end of the MC exits (air rises to the highest point which will be MC).
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1980 245 Canadian B21A with SU carb and M46 trans

Trev,

I guess you are right. It is not like you would be forcing the air far down the lines. I do wonder though, how much air is trapped at a level higher than the master line connections, inside the unit. While bench bleeding, I see air forced into the lines even after a dozen full strokes and tapping on the casting. In fact, I usually spend some time holding the cylinder at 1/2 stroke while allowing the streams of leetle teeny weeny bubbles slowly merge into one large enough to send out the tubing with the remaining stroke. Couple that with my fear of stripping the paint with Dot-4, I suppose.
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Art Benstein near Baltimore

There are times when somebody has bench bled their MC, removed the bleed lines, installed the MC, only to find that the pedal drops to the floor. They're told to bench bleed again. It's a hassle.

Leaving the MC installed, they'd probably only need to crack open the line(s) once and depress the pedal to clear out the air (and of course close off the line before pedal release else air will get sucked back in).

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1980 245 Canadian B21A with SU carb and M46 trans

Trev, I think your method is very much like bench bleeding, only on the car. But IMO, doing it on the bench is easier if you have the 2 feedback lines to the reservoir.

I always use your Step 3 whenever I pull calipers or open a line for any reason, because no fluid will escape the MC with the pedal depressed.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.