1966 Manual brakes - Air in brake system after M/C replacement and highway driving

[William L.]

I had the m/c rebuilt and system bled and filled with DOT3. I had a firm brake pedal for days running town on surface roads. The first time I took on the highway(15 miles) the brakes went to the floor on the exit ramp. I'm able to stop the car using a lot of runway and the last inch or two of pedal prior to hitting the floor. If I pump the brake rapidly the pedal firms up for a second then quickly loses firmness.

This the 3 time this has occurred: First time I lost the pedal, the fluid was a little low after a firm stop. I filled it up, but never got the pedal back. So I had the system bled and filled. Firm pedal until I drove on the highway and lost my pedal on the exit ramp. Since the bleeding did not fix the issue, I had a new m/c installed. Same thing... Firm pedal until freeway drive. Lost the brakes on freeway exit ramp. I've done a lot of research on this site and sounds like rotor runout, but I haven't changed the rotors or calipers or anything in quite awhile. The car has Repo KOs. Does this impact anything? The gentleman who has done the last two m/c installatons is dubious about the rotor runout, but now will not return my calls. Am I on the right track? Any other possible solutions? No leaking has been seen at the M/C, calipers or brake hoses.

[Joe L.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

I had the m/c rebuilt and system bled and filled with DOT3. I had a firm brake pedal for days running town on surface roads. The first time I took on the highway(15 miles) the brakes went to the floor on the exit ramp. I'm able to stop the car using a lot of runway and the last inch or two of pedal prior to hitting the floor. If I pump the brake rapidly the pedal firms up for a second then quickly loses firmness.

This the 3 time this has occurred: First time I lost the pedal, the fluid was a little low after a firm stop. I filled it up, but never got the pedal back. So I had the system bled and filled. Firm pedal until I drove on the highway and lost my pedal on the exit ramp. Since the bleeding did not fix the issue, I had a new m/c installed. Same thing... Firm pedal until freeway drive. Lost the brakes on freeway exit ramp. I've done a lot of research on this site and sounds like rotor runout, but I haven't changed the rotors or calipers or anything in quite awhile. The car has Repo KOs. Does this impact anything? The gentleman who has done the last two m/c installatons is dubious about the rotor runout, but now will not return my calls. Am I on the right track? Any other possible solutions? No leaking has been seen at the M/C, calipers or brake hoses.

William------

The first thing I would do is to measure the rotor runout, front and rear. This is not very difficult to do.

[William L.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Thanks, I'll get a dial indicator and give it a whirl.

[Guest]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

i would open all bleeders and let it gravity bleed for a while to make sure all the air is out and no trap air anywhere at the same time check the rotor run out

[Duke W.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

I had the m/c rebuilt...

Pedal goes to the floor with no evidence of leakage can be an internal leak/failure of the master cylinder. Check under the IP for fluid leakage from the end of the m/c, and discuss the situation with whoever rebuilt it.

Duke

[Mel S.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Check the pads for wear. I had a problem years ago with loosing the brake pedal like you. Putting new pad on did the trick for me.
Mel

[William L.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Thanks for responding. I'm trying to learn and do not mean any disrespect when I ask why would having the bleeders open impact the measurement the rotor runout? Thanks for your patience.

i would open all bleeders and let it gravity bleed for a while to make sure all the air is out and no trap air anywhere at the same time check the rotor run out

[William L.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Duke,

I could not see any evidence of leaking outside. I will follow your direction, but am unsure what the 'IP' is that you are referring. I'm sure its very simple, but I don't know what you're referring to. Thanks.

Pedal goes to the floor with no evidence of leakage can be an internal leak/failure of the master cylinder. Check under the IP for fluid leakage from the end of the m/c, and discuss the situation with whoever rebuilt it.

Duke

[William L.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Interesting. I will take a look. Thanks for your reply.

[Mark E.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Instrument Panel

[Mark E.]

Re: 1966 Manual brakes - Air in brake system after M/C replacement and highway drivin

Thanks for responding. I'm trying to learn and do not mean any disrespect when I ask why would having the bleeders open impact the measurement the rotor runout? Thanks for your patience.

They don't. I believe Danny is merely suggesting you do both- not necessarily at the same time.