I'm about to install the third master cylinder this month in my '66. I've bought two of them from Mid American Motorworks, and I'm on the verge of finding another supplier.
I wonder whether or not I've done something wrong here. I've tried to use the "old school" brake bleeding method of using a helper to pump the brake pedal. Maybe I didn't explain the process very well, but I couldn't get any of the people helping me to press the pedal gently--they stomped the pedal to the floor, which seems to have drawn quite a bit of air back into the system.
I gave up on using an assistant and bought a powerbleeder, which worked very well. BUT--the master cylinder leaks now, and has apparently failed.
My question is whether the master cylinder can be damaged by applying too heavy a foot pressure while the cylinder is empty or partly filled with fluid.
Is it me, or is it the quality of the parts? I'd be grateful for any help or advice.
single circuit master cylinder headache
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fatalifeaten
- Senior Member
- Posts: 512
- Joined: Sun Feb 03, 2008 12:05 am
- Location: The 480
This is one case where quality absolutely counts. Give up on the 30 dollar masters and get the German one. It's a hundred bucks or more, but you won't have to exchange it 6 times. The Brazilian and Mexican sourced masters just don't seem to be good quality at all.
I've seen many cases where the rubber grommet will fail (or get badly chewed up) and swapping that will fix your issue. It's a 2 dollar fix, I usually buy 3 or 4 and keep them on hand in my tool box.
I'd also strongly suggest bench bleeding the master. Are you familiar with that process? If not, you can search the samba forums for a procedure, or just holler back here and I can run you through it.
If you bench bleed before you install, you will eliminate 99% of the air beforehand and have a much easier time.
Did you adjust the pedal pushrod at all? You shouldn't have to, but sometimes it's needed to get the 1/4" pedal play.
I supposed it's possible that you can damage the master by mashing the pushrod down into it too hard, but my 6 year old is my brake monkey and he's not managed to break one yet slamming it down...
I've seen many cases where the rubber grommet will fail (or get badly chewed up) and swapping that will fix your issue. It's a 2 dollar fix, I usually buy 3 or 4 and keep them on hand in my tool box.
I'd also strongly suggest bench bleeding the master. Are you familiar with that process? If not, you can search the samba forums for a procedure, or just holler back here and I can run you through it.
If you bench bleed before you install, you will eliminate 99% of the air beforehand and have a much easier time.
Did you adjust the pedal pushrod at all? You shouldn't have to, but sometimes it's needed to get the 1/4" pedal play.
I supposed it's possible that you can damage the master by mashing the pushrod down into it too hard, but my 6 year old is my brake monkey and he's not managed to break one yet slamming it down...
Well, that answer kills two birds with one stone.
I suspected that German parts were the way to go; I'll definitely go that route from now on.
I've heard of the bench bleeding procedure; guess I ought to learn it, huh?
Could you walk me through it?
I also assume that you're referring to the rubber grommet on the top of the cylinder, on the line from the reservoir. I used my last one today; I'll have to get some more.
I suspected that German parts were the way to go; I'll definitely go that route from now on.
I've heard of the bench bleeding procedure; guess I ought to learn it, huh?
Could you walk me through it?
I also assume that you're referring to the rubber grommet on the top of the cylinder, on the line from the reservoir. I used my last one today; I'll have to get some more.
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fatalifeaten
- Senior Member
- Posts: 512
- Joined: Sun Feb 03, 2008 12:05 am
- Location: The 480
Bench bleeding's pretty simple, albeit messy.
Mount the M/C on a sturdy workbench vise - by the flange - not the cylinder body!
Install flanged brake lines onto each outlet port. If you don't have these, skip down to the alternate method. not as effective but still works well enough to get you almost there when you install.
Install clear vinyl hoses onto each end of the short steel brake lines and use hose clamps to insure a good seal. run the ends of the hoses into a container with brake fluid in it
Fill the M/C reservoir with fluid. (take it off the car of course)
Manually push the M/C piston all the way home - and hold it in. A big slotted screwdriver works well for this. You aren't going to hurt the M/C and it gives you something to use as leverage.
Slowly release the M/C piston, allowing fluid to be drawn into the cylinder.
Repeat until all the bubbles are gone. Occasionally tap the M/C lightly to help dislodge any trapped bubbles. Be sure to keep the reservoir filled.
The alternate method is to fill a coffee can with fluid, drop the cylinder in, and pump it that way. You might get more air trapped at the end of it (because it will be vertical in the can), but you will still prime it enough to get a good bleed going when you install. Make sure all openings are completely covered with fluid.
Yes. I do mean the rubber inlet grommet
Mount the M/C on a sturdy workbench vise - by the flange - not the cylinder body!
Install flanged brake lines onto each outlet port. If you don't have these, skip down to the alternate method. not as effective but still works well enough to get you almost there when you install.
Install clear vinyl hoses onto each end of the short steel brake lines and use hose clamps to insure a good seal. run the ends of the hoses into a container with brake fluid in it
Fill the M/C reservoir with fluid. (take it off the car of course)
Manually push the M/C piston all the way home - and hold it in. A big slotted screwdriver works well for this. You aren't going to hurt the M/C and it gives you something to use as leverage.
Slowly release the M/C piston, allowing fluid to be drawn into the cylinder.
Repeat until all the bubbles are gone. Occasionally tap the M/C lightly to help dislodge any trapped bubbles. Be sure to keep the reservoir filled.
The alternate method is to fill a coffee can with fluid, drop the cylinder in, and pump it that way. You might get more air trapped at the end of it (because it will be vertical in the can), but you will still prime it enough to get a good bleed going when you install. Make sure all openings are completely covered with fluid.
Yes. I do mean the rubber inlet grommet