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Pedal to floor after bleeding - '79 245

B

Bricktothefuture

Member
Joined
Aug 11, 2015
Location
Central NH
Losing my patience with this. Had a seized front right caliper, have done the following.

Replaced both front calipers with remanned units. New pads, hardware, everything.

Tried pedal bleed, didn't work.

Replaced brake master cylinder after the pedal bleed didn't work and I figured it was worth replacing after reading about how that can kill an older BMC. Unit was bench bled.

Borrowed motive power bleeder, left at 15PSI for 30 min, no leaks in system.

I've bled this system three times with the motive at 25PSI, have gone through 3 12oz bottles of DOT4. No bubbles anywhere. Pedal will seem ok in driveway, but as soon as I test on a back road, it goes to the floor and will still allow the car to roll a bit. Needed to engage the parking brake to get it to stop completely.

I know even if the booster was shot I'd still have working brakes, just without the assist. This feels like there's still massive air somewhere, just don't know what else to do to get it out...
 
Bricktothefuture said:
Should I lift the rear of the car or does that not really matter?
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I almost always jack up the rear of the car. The nose-up MC orientation makes it really easy to get bubbles trapped.
Give the rear brake valves many many taps, and that's the best you can do.
 
Harlard said:
Get a Motive power bleeder. It won't matter then.
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It still matters. Pat was having a heck of a time bleeding the brakes on his rally car using a Motive. He lifted the rear up, lightly tapped the brake pedal a few times (gets bubbles to migrate into the reservoir), and it was good to go.
 
You may just have trapped air. I had the same problem on my 79 242 after replacing the flex lines and 2 front calipers with vented rotor brake calipers. I bled the brakes 4 times with a Motive bleeder and every time the pedal would drop when the car was started. I figured the master cylinder might be leaking internally. I replaced it with another used one that was good when I removed it. Same thing. I bought a new master cylinder, same thing. I finally opened up the brake bleeders one at a time and literally kicked the brake pedal when bleeding the brakes. I think it was the right front caliper that finally made a pop like noise and the pedal dropped quite a bit and....that was it. A huge air bubble had shot out of the bleeder and I had rock hard brakes all of a sudden. I figured the problem was with one of the proportioning valves. It turned out to be in one of the shortest paths the brake lines make. Air can get trapped with the fluid just moving right past the air bubble. That was the worst 240 brake experience I've had. $50 worth of brake fluid, a master cylinder I probably didn't need and at least 6-8 hours of my time.
 
Another thing you could try that has always worked for me is to use the caliper pistons to do the bleeding. I have never had a power bleeder so I worked this system out.

I put the old worn out pads (or a spacer) in the caliper and use the brake pedal to push the pistons out as far as possible without ejecting them. I use short pedal strokes to avoid damaging the seals in the MC. Then I open the bleed screws and push the pistons back in until only fluid comes out and close the screws. If the calipers are good they will be bled at this point. Pump the pistons out again and repeat to check to make sure no more air has come in from the brake lines. If only fluid comes out close the valves and push the pistons all the way back in. This should push any remaining air in the lines back through the master cylinder and you should be good to go.

If you block the brake pedal down about an inch before you start a brake job you will save yourself a lot of trouble. You will barely loose a drop of brake fluid and you can change lines right back to the junction block. Then 240s will gravity bleed. Just open the bleeder screws on the caliper, wait for brake fluid to start leaking out and you are done.
 
Problem solved. Well, identified. Defective caliper. One half from a drivers side, one from passenger. Wasted a whole day and waaaay too much brake fluid.
 
Bricktothefuture said:
Problem solved. Well, identified. Defective caliper. One half from a drivers side, one from passenger. Wasted a whole day and waaaay too much brake fluid.
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Don't have enough fingers and toes to count the times I've heard this story.


brake50.jpg
 
Not really embarrassed - first time working on brakes and it was a defective unit. Half passenger side, half driver's side. Lousy way to learn my way around the system but I learned! Picking up the new caliper tonight...
 
Bricktothefuture said:
Not really embarrassed - first time working on brakes and it was a defective unit. Half passenger side, half driver's side. Lousy way to learn my way around the system but I learned! Picking up the new caliper tonight...
Click to expand...

You mean it was rebuilt incorrectly as hiperfauto guessed, right? Nothing for embarrassment in that regardless of how many times it has come up on the forums. But putting the bleeders at the bottom? That might be embarrassing to admit.
 
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