Does the brake master self bleed at all ?

[T.Hanson]

Fully assembled, up on stands, car running. Brake pedal working. Responded to pumping as if bleeding the last few air bubbles itself,... but not great, firm at the top with very little travel as hoped.

Bled the calipers one more time. No large bubbles. Pedal felt firm, solid.

Car on the ground, something changed. Pedal reasonable but not as solid, firm at the top. I've not gone on a neighborhood test drive. Is there a chance driving it, using the brakes will return the firm feel with self bleeding ?

[Lenny D.]

I've not gone on a neighborhood test drive. Is there a chance driving it, using the brakes will return the firm feel with self bleeding ?

Maybe.

Ideally, there shall be NO air bubbles, even tiny ones absorb the force produced by the master to drive the pistons hydraulically in the caliper.

Go for your neighborhood drive, carefully, and USE the brakes. I have heard and witnessed that a slight front end elevation during overnight parking can firm a pedal after a brake bleeding. But you might have to rebleed the calipers one more time, but use the brakes, then evaluate.

Don't forget to bleed the slave cylinder, you necessarily upset the entire system with a master replacement.

[RonDwyer]

Nothing beats the power bleeder for this job. I bought one 25 years ago for $19.00 and have used it to do brakes all alone with outstanding results. Don't forget to start at the RR first and work furthest to nearest to the master.

It's noting more than a bug sprayer bottle with a hose and a nipple fitted to an ATE reservoir cap. For home-builts the need for a pressure gauge is nil. 3-5 PSIg is going to push fluid right through the system. Use a clear hose to see the fluid. Don't just let it go all over the place.

Did you know the front calipers have 2 bleed screws? They are on top.

Remove as much of the old fluid from the reservoir as possible first, that way you aren't mixing old with new. I use a giant medical syringe. An old turkey baster works well too, just don't ever use it for food ever again.

[Lenny D.]

Did you know the front calipers have 2 bleed screws? They are on top.

Agreed on any power bleeder device.

Correction on the front caliper bleed nipples.

There are three and must be bled in this sequence:

1) uppermost (outer),
2) middle (inner),
3) lowest (outer).

An over engineered late '70s way of ensuring that either half of the two part braking system will operate one half of the front caliper for stopping power in the event of brake system failure.

[RonDwyer]

Hmmm, I'll have to go look at one again. LOL, might as well have another beer.

[Lock]

I'm slowly working on fixing my neglected brakes. For bleeding purposes I'm curious - for the twin circuit fronts, does anyone know - is each circuit the left side and right side of the caliper, or the two lower pistons and two upper pistons?

Also my MB cyl is leaking internally, and has possibly similar behaviour. The pedal is firm most of the time but randomly will go soft (esp after hard braking). Maybe something to consider if after multiple bleeds is still acting weird?

[T.Hanson]

Pressure bleeder, standard operation, (left hand drive) begin with right rear caliper, then left, to right front, then left front as directed by Lenny D., no bubbles, or very very few tiny ones.

My question came from somehow imagining the new master pedal would be very firm from the top. I don't know why. After driving, the pedal and the system works, feels the same as my '79, comparison, no problems.

I have the air in my bubbles.

[RonDwyer]

When you get hinky brake operation, no obvious leaks, possible fluid consumption, your booster is likely full of fluid. No way around it, you need a master cylinder and might as well see the place in San Jose for a booster rebuild.

I have rebuilt many calipers over the years and yes, i split them. Don't lose the seals. I use a brake hone and when available I have chucked the pistons in a lathe to spin them against some crocus cloth. Be careful, you can get your arm sucked in to a lathe if you are not paying attention. Brakes operate like new after a thorough cleaning this way. If pitted, oh well. buy new or get them sleeved with new pistons.

[CBradio]

+1 my brakes were actually okay, and it still turned out my booster was full of fluid

[Lock]

Replaced my brake master cyl. No fluid in booster, just an internally leaking MB. Stops great now, & I can drive it in commute traffic without fear of causing a pileup.

[RonDwyer]

Just because the brakes were still good masks the fact that your rear seal on the master cylinder has failed. The booster now full of water absorbing brake fluid residue is going to rust from the inside out. Those seals will fail soon.