I don't see how it could since he said the pedal goes to the floor.
Another wierd brake problem
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Another wierd brake problem
I installed a set of VBP O-ring calipers on my 68, and re-bench bled the MC while I was at it. After two bottles of fluid, the pedal seemed OK, but when I applied vacuum to the booster(electric pump brought the booster down to about 20 inches) the pedal goes right to the floor. Pumping the pedal helped, but it would then slowly sink right back to the floor. Sounded like a master cylinder problem, so I went to Corvette Clinic in San Jose and picked up a new(not rebuilt) one, did the bench-bleed, and installed it. Same problem!
A couple things I noticed, I am pressure bleeding with 10 lbs. of air, and saw that fluid is being pushed into the adjacent reservoir(if applying pressure to the rears, the front fills up, vice-versa). I also tried vacuum bleeding, and noticed the level in both reservoirs dropping
Does this sound like I got another bad MC? Still more air in the system? Would a bad distribution block have anything to do with it? There are no leaks anywhere that I can see, and everything else is still fairly new.
Anyone know whats going on here? Thanx
A couple things I noticed, I am pressure bleeding with 10 lbs. of air, and saw that fluid is being pushed into the adjacent reservoir(if applying pressure to the rears, the front fills up, vice-versa). I also tried vacuum bleeding, and noticed the level in both reservoirs dropping
Does this sound like I got another bad MC? Still more air in the system? Would a bad distribution block have anything to do with it? There are no leaks anywhere that I can see, and everything else is still fairly new.
Anyone know whats going on here? Thanx
Melting Slicks
Joined: Aug 2004
Posts: 2,063
Likes: 1
From: Beverly Massachusetts
the only thing that comes to mind is maybe with the new master cylinder you dont have the pushrod adjusted corectly. i would check that first. the adjustment on those can be thrown off very easily since it just screws on and is very easy to turn. well at least that is the case on my 76 which i spent more time then i care to admit trying to figure out my problem before i figured out that it was the pushrod that comes out of the booster. i hope that helps.
i hope that helps.
Race Director
Joined: Oct 2000
Posts: 15,017
Likes: 79
From: central FL, near the beach.
does the car stop ok?
http://community.webtv.net/MATTGRU/bubba
http://community.webtv.net/MATTGRU/bubba
Last edited by Matt Gruber; Sep 17, 2007 at 02:54 PM.
Racer
Joined: Mar 2005
Posts: 473
Likes: 2
From: Champlin Minnesota
The way it sounds to me is that your distribution block/proportioning valve/warning switch might need to be reset, when the system has low pressure in one line it moves a piston inside of it to prevent anymore fluid being lost and closing off the nonfunctioning brakes. That might explain why fluid goes into the other reservoir...See what some of the experts have to say
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Thanks for the replies eveyone!
About the pushrod, I had to make one as my booster did not come with one. It's very possible it could be a shade too long
Haven't had the car on the road yet since replacing the calipers, so I don't know if it'll stop, would like to get these issues done before I try it
I had the dist block apart a few years ago, cleaned it up, ran a reamer through to clean up the bore and replaced the O-rings. I noticed some minor pitting on the bore, never occurred to me at the time it might cause any big problems. May have to get a new one
Keep the suggestions coming!
About the pushrod, I had to make one as my booster did not come with one. It's very possible it could be a shade too long
Haven't had the car on the road yet since replacing the calipers, so I don't know if it'll stop, would like to get these issues done before I try it
I had the dist block apart a few years ago, cleaned it up, ran a reamer through to clean up the bore and replaced the O-rings. I noticed some minor pitting on the bore, never occurred to me at the time it might cause any big problems. May have to get a new one
Keep the suggestions coming!
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
OK, I removed the distribution block and disassembled it, both O-rings on the piston are thrashed, and it looks like a small leak at the pin for the brake wire. I'm not going to screw with trying to rebuild it again, so it looks like I'll be buying a new one, see if that cures the problem
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Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Booster leak?
Sounds like the booster is bad/leaking. Pedal dropping to the floor shouldn't have much to do with the fluid.
Maybe a vac hose or fitting leak on the booster also.
Good luck Randy,
cardo0
Maybe a vac hose or fitting leak on the booster also.
Good luck Randy,
cardo0
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
OK, here's the latest. I installed a new distribution block, re-bench bled the MC, and got all the air out of the system. The pedal is as firm as one could expect, but when I turn on the vacuum pump, the pedal still sinks
I noticed when I look at the vacuum gauge, that 20 in of vacuum, the pedal goes right to the floor. As I pump it, it looses vacuum, and the pedal becomes firmer. As I hold the pedal down, I can feel it sink as the vacuum gauge reaches 20 in.
I think cardo0 might be right, the booster is bad. I had always thought there was a direct link between the pedal and MC with the booster providing the assist, and it still makes no sense that the pedal sinks the way it does when vacuum is applied
This is weird. Really weird
Anyone care to enlighten one on how a booster works?
I noticed when I look at the vacuum gauge, that 20 in of vacuum, the pedal goes right to the floor. As I pump it, it looses vacuum, and the pedal becomes firmer. As I hold the pedal down, I can feel it sink as the vacuum gauge reaches 20 in.
I think cardo0 might be right, the booster is bad. I had always thought there was a direct link between the pedal and MC with the booster providing the assist, and it still makes no sense that the pedal sinks the way it does when vacuum is applied
This is weird. Really weird
Anyone care to enlighten one on how a booster works?
Race Director
Joined: Oct 2000
Posts: 15,017
Likes: 79
From: central FL, near the beach.
does the car stop ok?
http://community.webtv.net/MATTGRU/bubba
http://community.webtv.net/MATTGRU/bubba
car has to be moving to test PB.
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
OK, here's the latest. I installed a new distribution block, re-bench bled the MC, and got all the air out of the system. The pedal is as firm as one could expect, but when I turn on the vacuum pump, the pedal still sinks
I noticed when I look at the vacuum gauge, that 20 in of vacuum, the pedal goes right to the floor. As I pump it, it looses vacuum, and the pedal becomes firmer. As I hold the pedal down, I can feel it sink as the vacuum gauge reaches 20 in.
I noticed when I look at the vacuum gauge, that 20 in of vacuum, the pedal goes right to the floor. As I pump it, it looses vacuum, and the pedal becomes firmer. As I hold the pedal down, I can feel it sink as the vacuum gauge reaches 20 in.
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Z-man-The vacuum pump is being used to try the brakes while the booster is under vacuum. I'm not vacuum-bleeding, is that what you meant? The system has already been pressure bled
Matt-I'm a little leary about taking a car out on the road with a brake pedal that won't stay off the floor. Of course, I could be going about this wrong. Instead of using a vacuum pump, I should be using engine vacuum. I'll give it a go tonight
Matt-I'm a little leary about taking a car out on the road with a brake pedal that won't stay off the floor. Of course, I could be going about this wrong. Instead of using a vacuum pump, I should be using engine vacuum. I'll give it a go tonight
Racer
Joined: Jan 2005
Posts: 365
Likes: 1
From: Glenview IL
~Rich
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Update-Pressure-bled the brakes one more time, then got the car back on all fours and took it for a cruise. Pedal is about the same as it was before I started all this(about 1 1/2 off the floor), car stops on a dime, plus now I know there aren't any leaks!
I'll check for a blown booster(it's only two years old), otherwise I think the brakes will be alright.
Thanks to everyone that responded
I'll check for a blown booster(it's only two years old), otherwise I think the brakes will be alright.
Thanks to everyone that responded