Crazy brakes

B

Beagle 1

Well-known member
Joined
Mar 25, 2008
Messages
332
Location
Orange Co. Ca
My 69 power brakes work fine, but something is a little screwey. With the motor off, I can pump the pedal a few times and it will hold steady and is hard as a rock. But once it's started and I pump the pedal, the pedal is soft and will bleed down in about 5 seconds. Not all the way to the floor, but about 2/3 of the way.
I've bled the system, replaced the master cylinder, and bled the brakes 2 more times. There are no leaks and they seem to work fine.
My concern is, what would happen if I made a hard stop from 80-90 mph?
Would the system bleed down and lose pressure?
 
How did you bleed the brakes? The only way I could get the air out of mine was using a Motive Power Bleeder. Once you use one, your hooked!
 
Beagle 1 said:
I use a little hand vac pump and suck the fluid through.
Click to expand...


I tried that will no luck. The air seems to get trapped in the calipers. After many attempts to get the air out, I broke down and bought a Motive Bleeder. I'm not cheap, just hard headed. :banghead: Best money I have ever spent!
 
Since the only commonality with your symptoms is engine on/engine off, it just may be a bad booster. Pretty rare, but not unheard of.
I have a Motive Power bleeder if you wish to come by and borrow it.
If that doesn't do it, I would change the booster. Do be sure your getting vacuum, and the check valve is good first.
 
Thanks all. Thanks for the offer Bird.
The booster is a 5 yr old new, not rebuilt unit. Actually, I'm thinking that the booster must be working, because the it seems like the extra pressure at boost may be compressing the air in the lines. Maybe I'll try the old fashioned way with the wife pumping the pedal and me underneath yelling at her. She really likes doing this. HaHa.
I'll check the check valve also.
 
Beagle 1 said:
Thanks all. Thanks for the offer Bird.
The booster is a 5 yr old new, not rebuilt unit. Actually, I'm thinking that the booster must be working, because the it seems like the extra pressure at boost may be compressing the air in the lines. Maybe I'll try the old fashioned way with the wife pumping the pedal and me underneath yelling at her. She really likes doing this. HaHa.
I'll check the check valve also.
Click to expand...

Okay. But once you use one of these bleeders, you won't go back. It's like a cell phone. We were fine without it, but now can't imagine not having one.:wink:
 
Okay. But once you use one of these bleeders, you won't go back. It's like a cell phone. We were fine without it, but now can't imagine not having one.:wink:[/QUOTE]

Yea, but you know, old fashioned, hard headed. And thems my good points. :suicide:
I'll keep your offer in mind. Thanks again.
 
It can't be the booster, there's still a mech. linkage. A bad booster gives the feeling of no brake assist, or even intermittent no brake assist (the booster in my truck is displaying those very symptoms since yesterday)
If the pedal goes to the floor you have a leak somewhere. If the pedal goes to the floor partially you most likely have an internal leaking MC. With the motor off you said you pump it a few times? If not it's not rock hard with the 1st push? if so, that's definitely an internal leaking MC. Pumping will make the pedal feel harder with each pump if you have an internal leak. If you push the pedal slowly it will still bleed off pressure.
 
Twin_Turbo said:
It can't be the booster, there's still a mech. linkage. A bad booster gives the feeling of no brake assist, or even intermittent no brake assist (the booster in my truck is displaying those very symptoms since yesterday)
If the pedal goes to the floor you have a leak somewhere. If the pedal goes to the floor partially you most likely have an internal leaking MC. With the motor off you said you pump it a few times? If not it's not rock hard with the 1st push? if so, that's definitely an internal leaking MC. Pumping will make the pedal feel harder with each pump if you have an internal leak. If you push the pedal slowly it will still bleed off pressure.
Click to expand...

TT, common sense, and logic dictates I have to agree with you and bird above....which is why I never went after my sucky vac booster and tolerated bad brakes with the exact same symptom he shows above....same shit, close as words can describe.....I finally got pissed a few years ago and all I did was take the m/cyl off the booster, never touched the lines one bit, put it back on the new HBOOST setup, and planted my nose into the steering wheel....pedal is hard as a teen age dick since then....

actually I had a iron truck m/cyl on there with larger bore, another last ditch effort to get more pedal....it was way too much with the HB......so I stuck a aftermarket aluminum m/cyl on there.....stock bore....everything works fine.....out of 15 years with this car it has had brakes for maybe 4 years now.....

:smash::sos::fishing:
 
Beagle 1 said:
Okay. But once you use one of these bleeders, you won't go back. It's like a cell phone. We were fine without it, but now can't imagine not having one.:wink:
Click to expand...

Yea, but you know, old fashioned, hard headed. And thems my good points. :suicide:
I'll keep your offer in mind. Thanks again.[/QUOTE]

Take Bird up on his offer! You have nothing to loose!
 
Beagle 1 said:
My 69 power brakes work fine, but something is a little screwey. With the motor off, I can pump the pedal a few times and it will hold steady and is hard as a rock. But once it's started and I pump the pedal, the pedal is soft and will bleed down in about 5 seconds. Not all the way to the floor, but about 2/3 of the way.
I've bled the system, replaced the master cylinder, and bled the brakes 2 more times. There are no leaks and they seem to work fine.
My concern is, what would happen if I made a hard stop from 80-90 mph?
Would the system bleed down and lose pressure?
Click to expand...


This a normal characteristic of a functioning vaccum-assist power system. It takes a few pumps to completely bleed off the vacuum when the engine is not running, and the pedal gets very stiff (assuming no air in system, which it sounds like you're good). When the engine is started, it pulls a vacuum into the booster providing the assist, and the pedal drops. The power system was designed so that it takes very little leg effort to stop the car, even though it feels like crap. I for one wouldn't mind having to push a little harder; but my car has stock calipers (save for o-rings not lip seals), stock vacuum assist (NO hydroboost), and it stops like crazy with very little leg effort. Like I said, I wouldn't mind having to push a little harder to get the car to stop.

If you want to know what happens in an emergency stop, find an empty parking lot and try it from about 45-50mph.
 
Last edited:
OK, quick update here. I ran the car about 90 miles this morning, and the brakes worked with a very low pedal. Alot of travel. No real hard braking on this trip. So I get home and jack the beast up and get the little woman to start pumping the brakes while I work the bleeders. The rear bleed fine, very little or no air in the system.
Then I go to the front and I can't get any fluid to pump out. I know the system is full because I vacume bled all 4 wheels last Sat.
Ok, so I'm thinking that the mc is shot.
But the mc is brand new from Napa. Chinese from Napa by a Americal Co.!! WTF!! Anyway, I didn't notice till I got home, so I put it on about 2 months ago and it seemed to work fine for 2 mos. So what are the odds that a brand new mc is shot?
Sounds like 100%.
Thanks for the help everyone.
 
It sounds like your rubber hoses have swollen shut. Take them loose & try and blow air through them. It's typical on older hoses. If that's the case, go ahead and change all four.
 
Dirtbuster1 said:
It sounds like your rubber hoses have swollen shut. Take them loose & try and blow air through them. It's typical on older hoses. If that's the case, go ahead and change all four.
Click to expand...

The hoses are 5 yr old aftermarket ss braided hoses. Could be, but I don't think so. The rear are the same and they seem to be OK. I got the mc off tonight and I'll exchange it tomorrow. I'll try to get a American one, but Napa didn't list any other new ones then the one I have. Most places will only do at exchange on warrantee, not a refund.
Thanks again all.
 
Beagle 1 said:
Dirtbuster1 said:
It sounds like your rubber hoses have swollen shut. Take them loose & try and blow air through them. It's typical on older hoses. If that's the case, go ahead and change all four.
Click to expand...

The hoses are 5 yr old aftermarket ss braided hoses. Could be, but I don't think so. The rear are the same and they seem to be OK. I got the mc off tonight and I'll exchange it tomorrow. I'll try to get a American one, but Napa didn't list any other new ones then the one I have. Most places will only do at exchange on warrantee, not a refund.
Thanks again all.
Click to expand...

Rock Auto, New, not rebuilt Delco. $40. (China)
 
Beagle 1 said:
OK, quick update here. I ran the car about 90 miles this morning, and the brakes worked with a very low pedal. Alot of travel. No real hard braking on this trip. So I get home and jack the beast up and get the little woman to start pumping the brakes while I work the bleeders. The rear bleed fine, very little or no air in the system.
Then I go to the front and I can't get any fluid to pump out. I know the system is full because I vacume bled all 4 wheels last Sat.
Ok, so I'm thinking that the mc is shot.
But the mc is brand new from Napa. Chinese from Napa by a Americal Co.!! WTF!! Anyway, I didn't notice till I got home, so I put it on about 2 months ago and it seemed to work fine for 2 mos. So what are the odds that a brand new mc is shot?
Sounds like 100%.
Thanks for the help everyone.
Click to expand...

Does that car have that block with the switch? Those things can jam shut one way.
 
Does that car have that block with the switch? Those things can jam shut one way.[/QUOTE]

Yes, it does. But when that switch upsets, wouldn't the pedel be hard because 1 circuit is blocked? And why would the switch upset? Every thing worked fine for 2 mos. with no external leaks.
Anyway, I took it back to Napa and they ordered me a identical replacement. I could not upgrade to a American one, they don't carry one.
Thanks again.
 
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