Rebuilding a Master Cylinder

[West Coast GT]

Pulled off both front calipers today and blew out the ports, freed up the pistons, cleaned and reassembled them.

Removed the master cylinder (MC) and blew my lines clear, from the flex hoses back to the disconnected MC to make sure I've got no blockages.

I've disassembled the MC. Remember old threads where folks wanted to know how to get stuck guts out of a MC? Block off all ports but one, then apply compressed air. Best to have a bag over it to catch the projectiles. Mine hit the ceiling, then just missed my wife's Miata on the way down.

Same thing when removing pistons from calipers. Plug ports, then apply compressed air. Point it away, keep your hands out of the way, and do not point it at your face.

I plan on using a vacumn bleeder. Anyone have problems using this method? I figure it's best to keep vacumn in the 10 inch range, but no more than 20 inches. Also, I just replaced my flex lines, so they should be able to stand up to the vacumn, right?

[namba209]

I tried to use a vacuum pump on the monza and was sucking air in through the wheel cylinders. Best bet I've found is to use a short piece of hose over the brake bleeder and a zerk fitting on the other end in a container. The zerk fitting has a small check valve (ball and spring) in the end and allows flow only one-way. Use slow action on the brake pedal, checking the MC for low brake fluid often and you're done. It helps to have someone hold the hose in the container and check for no more air bubbles.

[opelwasp]

I Hate Vacuum Bleeders!!!

[BQS4]

Originally Posted by namba209 I tried to use a vacuum pump on the monza and was sucking air in through the wheel cylinders. Best bet I've found is to use a short piece of hose over the brake bleeder and a zerk fitting on the other end in a container. The zerk fitting has a small check valve (ball and spring) in the end and allows flow only one-way. Use slow action on the brake pedal, checking the MC for low brake fluid often and you're done. It helps to have someone hold the hose in the container and check for no more air bubbles.

Ron;
This is exactly how "speed bleeders" work, and they work great. I put a set on the calipers I rebuilt for the wife's Sportwagon, and it worked like a charm.!

[West Coast GT]

I just spoke with a friend at the local Morgan club, and they recommend I thrash the vacuum bleed equipment and use the method Namba209 described. Looks like I'm out to pick up zerk fittings today!

Thanks

[namba209]

Originally Posted by BQS4 Ron; This is exactly how "speed bleeders" work, and they work great. I put a set on the calipers I rebuilt for the wife's Sportwagon, and it worked like a charm.!

I bought one of those things and it didn't work, so I tore apart to find out why, and saw it had a check valve for each direction of flow. That didn't make sense so I made my own with what I had laying around. Oh well.

[West Coast GT]

My vacuum bleeder didn't work out so well either:

1. The O-ring Seal on the reservoir was too small and would only work if I pulled it out and re-set it each time I opened the reservoir. Major PITA.

2. I found I was pulling air in through the bleeder valve threads.

So I ran out and picked up some zerk fittings to try the "speed bleeder" method. Meanwhile, I have high confidence in my front brake calipers, pads, flex lines, and lines from the MC.

Just need to get the MC squared away.

[sawdust]

Originally Posted by West Coast GT Removed the master cylinder (MC) ........ I've disassembled the MC.......

Just curious, did you remove the booster? If not, how are you going to get the "O" ring seal in/on between the MC and booster. I am at the point and stumped.

[West Coast GT]

Originally Posted by sawdust Just curious, did you remove the booster? If not, how are you going to get the "O" ring seal in/on between the MC and booster. I am at the point and stumped.

I did not remove the booster as I replaced it this spring. But it's a really good question. I just went and looked at the MC and I do not see the O-ring seal. So either:
a. I'm missing it,
b. It fell off when I removed it,
c. It's still in the booster.

When I find the answer I'll get back to you.

[sawdust]

Originally Posted by West Coast GT When I find the answer I'll get back to you.

I can still see mine by looking thru the grill. It's not a beautiful site.

[West Coast GT]

Just rebuilt the MC. Can't find the missing O-ring seal. I even shined a light in the booster and inspected via a mirror. Still don't see it. Slapped on the new one from OGTS and installed it.
_______________
But the bad news. Last week when the local Midas shop tried unsuccessfully to pressure bleed my system they blew the reservoir off the MC and sprayed hydraulic fluid all over my new paint job. They hosed it down, but didn't mention it to me. Today I flipped my lights over and it looks like paint stripper attacked the paint. It's gooey and peeling.

I just called the shop, but of course they are acting cautious on the issue.
Wish me luck.

[namba209]

Well, now we all know that you cannot pressurize an MC reservoir that is just a slip fit onto the MC. You may want to ask them how much pressure they tried to use. Be firm with them, their screw-up is gonna cost you a paint job, and probably somebody lost their job too.. Lotsa luck.

[opelwasp]

Originally Posted by namba209 Well, now we all know that you cannot pressurize an MC reservoir that is just a slip fit onto the MC. You may want to ask them how much pressure they tried to use. Be firm with them, their screw-up is gonna cost you a paint job, and probably somebody lost their job too.. Lotsa luck.

I power bled my MC with no problems, they either had the pressure too high, or were just sloppy.

The fact remains though, you cam into the shop with good paint, and left with screwed paint. It doesn't take a rocket scientist.

[sawdust]

Originally Posted by West Coast GT Just rebuilt the MC. Can't find the missing O-ring seal. I even shined a light in the booster and inspected via a mirror. Still don't see it. Slapped on the new one from OGTS and installed it.

Sorry about that. I know that sick feeling.

Back to the seal, did you find someway to get it into the booster or did you stick it on the the MC before you re-assembled the two.

I sure hope you feel like talking.

SUE the bsartds.

[West Coast GT]

Ron, I need your advice & experience.

I've installed the MC and connected my lines.
Filled the brake reservoir.
Loosened one bleed valve, attached hose, and inserted a new zerk fitting (ball-end into the hose / threads facing out.

As I pushed my brake pedal slowly, I suddenly wondered if I need to loosen those two set screws on the MC. Last time I touched them was this afternoon when I assembled the MC. Both screws are screwed down tight, which is where they were originally when I dissembled the MC.

I'm worrying my seals may be getting hung up on those set screws and tearing seals.

Am I just second guessing myself?

Thanks in advance.

[namba209]

I don't remember setscrews in my MC but there was a bolt going into the upper chamber that keeps the front piston from comiing too far back, and doesn't interfere with the seals.

[West Coast GT]

Originally Posted by namba209 I don't remember setscrews in my MC but there was a bolt going into the upper chamber that keeps the front piston from comiing too far back, and doesn't interfere with the seals.

Yes, the 10 mm bolt. I have another one up in the front of the MC (front facing forward towards the nose of the car) in addition to the one that keeps the front piston from coming too far back.

Thanks for the info.

________________

But now I've gone and cross-threaded the most remote brake line as it enters the MC. I'm so pissed at myself. And I'm screwed now. I should have removed the MC and re-tapped it, then cut new threads on the brake line, but noooooooooo, I was tired and frustrated so I just tightened it down. Of course it leaks. So I've left it for tonight and will tackle it again tomorrow night. Hell, brakes aren't all they're cracked up to be - sorta over-rated. Right? Maybe?

[namba209]

Originally Posted by West Coast GT But now I've gone and cross-threaded the most remote brake line as it enters the MC. I'm so pissed at myself. And I'm screwed now. I should have removed the MC and re-tapped it, then cut new threads on the brake line, but noooooooooo, I was tired and frustrated so I just tightened it down. Of course it leaks. So I've left it for tonight and will tackle it again tomorrow night. Hell, brakes aren't all they're cracked up to be - sorta over-rated. Right? Maybe?

I sure hope the fitting is just screwed up and not the MC internal threads. If it's the fitting, you may be in luck. Just slide the fitting back on the line, and cut it real close to the flare. Get a new real short metric fitting brake line, take one of the fittings off the line, same as the original. Slide the new fitting on the line and double flare the line. You might lose an inch or less off the original line, but it should work out o.k. If the internal threads on the MC are bad, maybe you can get a machine shop to retap it with a bottoming tap, make sure it is really clean, use some teflon tape on the fitting and hope it won't leak. If it does, you'll need another MC.

[West Coast GT]

Good News!
Midas said they'll accept responsibility for damage to the headlight cover and to have them invoiced from the paint shop. I expected more of a hassle.

[West Coast GT]

Question:
What diameter brake line and what size fitting do I ask for? It goes on a 1972 GT.

Well, I took last night off from the frustration.

Removed the MC tonight, and sure enough, the MC's threads were crossed, not the fitting. I've spent so much time on this MC it's ridiculous.

Of course, had I followed Ron's advice the 1st time around (which was to rebuild the NOS Master Cylinder from the get-go) I would have saved myself two weeks of evenings, not to mention I could have spared my paint job from the damage done by the brake shop - WHO STILL DIDN'T FIX THE DAMN THING.

Tomorrow I'll see if a local machine shop will re-thread the MC, or locate another. Plus, to be safe, I'll cut off the end of the brake line, and add a new short section.