Brakes....Part 2
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 803
Likes: 0
From: South San Francisco CA
Brakes....Part 2
I had a very soggy brake pedal two weeks ago. The pedal would go almost all the way to the floor, which of course isn't normal. There was absolutely no brake fluid loss and the car would stop....but it was scary. I took the car to my mechanic and he replaced the brake fluid, which was dirty and bled the brakes. He said he found the left front calipers were leaking but his machine that tests brakes was on the fritz and being repaired. He suggested driving the car and see if just the fluid change might remedy the problem. The brakes felt perfect when I got the car back and they worked well for about three days. Now the pedal goes to the floor (almost) again. My question is....how can calipers leak without losing brake fluid? If there is some sort of air leak....can't the fluid get out....if the air can get in? Any ideas....suggestions.....whatever? I thought it might be some kind of vacuum problem but I'm certainly no brake expert. Any help or ideas would be appreciated.
If I pump and push on the pedal hard, the pedal goes down. If I drive the car around, the pedal is better....but I know it's not quite right.
If I pump and push on the pedal hard, the pedal goes down. If I drive the car around, the pedal is better....but I know it's not quite right.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Brakes....Part 2 (fontking1a)
Think you are getting the air sucked into the calipers. Had the same thing in my rears. Bleed em they would work great but slowly lose pressure until pedal to the floor. I think the theory is the rotor has some run out (not sure if that is the correct tech term) so it pumps the piston in and out ever so slightly but enough to create a vaccum that sucks air in through the seal. I had my rear calipers replaced and rotors turned. Not a problem since.
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 803
Likes: 0
From: South San Francisco CA
Re: Brakes....Part 2 (fontking1a)
Fevre, I talked to my mechanic and that's pretty much what he said. His machine that turns the rotors is arriving Wednesday. It's brand new and I'll be the first set to get turned. He already tested the calipers and they're fine. He's convinced it's the rotors and said it's a simple fix. Thanks...
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Brakes....Part 2 (fontking1a)
The guy that did my rear brakes had just blew his engine in his racing car so I think the rotors helped pay for his rebuild since I know he ordered them through the muffler shop he worked at and did not pay for them. :mad Live and learn. Glad you got a honest guy doing your work.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,987
From: Connecticut, USA
Re: Brakes....Part 2 (fontking1a)
I was wondering how you made out with the brakes. Sounds like rotor runout. Be careful if he turns the rears. The fronts can be turned because they "chuck" them on the inner bearing races to spin true. The rears can only held by the ID of the rotor which isn't concentric with the spindle & bearings. Make sure he checks them with an indicator to get the runout under .003".
Gary
Gary
Melting Slicks
Joined: Oct 2000
Posts: 2,143
Likes: 195
From: Englewood FL
Re: Brakes....Part 2 (gtr1999)
Have read in a number of posts not to turn the rear rotors off the car.
They should only be turned on the car (hard to find a shop that has
this type of machine). If turned off the car should be turned with
the spindle mounted (requires disassembly of wheel bearings).
If fronts are the problem, new rotors riveted to the hubs can still be
purchased from GM.
They should only be turned on the car (hard to find a shop that has
this type of machine). If turned off the car should be turned with
the spindle mounted (requires disassembly of wheel bearings).
If fronts are the problem, new rotors riveted to the hubs can still be
purchased from GM.
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 803
Likes: 0
From: South San Francisco CA
Re: Brakes....Part 2 (gtr1999)
Gary, thanks.....he knows which rotor it is. It's the left front and I'm not sure if he's going to do both fronts....or just the left. He didn't mention the rears at all, but I will ask him and let him know about the rear concentricity problem. We'll find out Wednesday or Thursday.....
Melting Slicks
Joined: Oct 1999
Posts: 2,581
Likes: 14
From: Tolar Texas
Re: Brakes....Part 2 (fontking1a)
I've read it many times here on the forum that the rear calipers are very susceptible to sucking air if the rotor runout is excessive.
I was able to go from .010 to .002 runout using aluminum shims that I cut from a soft drink can. Just takes a little trial and error time while placing the aluminum between the spindle flange and rotor hub until you get results that you can live with.
My brakes have remained consistent.
Check out Terry Rudy's FAQ website http://corvettefaq.com/ You might find some good information on the Brake System page.
I was able to go from .010 to .002 runout using aluminum shims that I cut from a soft drink can. Just takes a little trial and error time while placing the aluminum between the spindle flange and rotor hub until you get results that you can live with.
My brakes have remained consistent.
Check out Terry Rudy's FAQ website http://corvettefaq.com/ You might find some good information on the Brake System page.
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Drifting
Joined: Feb 2001
Posts: 1,603
Likes: 0
From: San Francisco, CA
Re: Brakes....Part 2 (fontking1a)
So for the :conehead 's among us, are rotors sometimes turned on the car? man I must be living in the 70's or something. I thought they still had to take them off!!
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 803
Likes: 0
From: South San Francisco CA
Re: Brakes....Part 2 (R. Bruno)
Update on the brake situation. After having new fluid installed and the brakes bled...they worked great for about two days. Then, sort of suddenly...I noticed I could pump the brakes while idling and the pedal would go down. I pushed hard several times while idling in driveway and the pedal went all the way to the floor. I phoned my mechanic and he thought for sure it was a warped rotor and informed his new "rotor" machine would be in a couple of days. Deciding to drive the car to work the next day before the brakes got worse only confused me more. The brakes worked perfectly all the way to work. My mechanic is just down the street from my shop so I called him to let him know. He says it sounds like the master cylinder. At this point...right now....the brakes are working just fine and I'm waiting for his new machine to arrive so I can bring the car to him. Anybody got any theories? Are the brakes OK? Is it the master cylinder....or is it the rotors? No matter what, I'm going to have the mechanic go over the whole system just to make sure everything is working correctly. Brakes are one thing you want to be 100% reliable....
Melting Slicks
Joined: Oct 2001
Posts: 2,065
Likes: 1,395
From: Halifax, Nova Scotia, Canada
Re: Brakes....Part 2 (fontking1a)
Sure sounds like a bad master cylinder.
When the rubbers/bore gets bad, the fluid leaks past the rubbers. Pedal goes to the floor.
Most likely rust in the MC. Sometimes it seals, sometimes it doesn't.
I have read on the forrum that it could be difficult to find a good rebuilt MC. Many have experienced bad ones right out of the box.
I had similar problems about 12 years ago. Fluid like mud, and calipers leaking. I replaced all the calipers with SS.
Also rebuilt the MC with a Delco rebuild kit. (New rubbers and piston)
Also went with Silicone fluid.
No problems since.
Barry
When the rubbers/bore gets bad, the fluid leaks past the rubbers. Pedal goes to the floor.
Most likely rust in the MC. Sometimes it seals, sometimes it doesn't.
I have read on the forrum that it could be difficult to find a good rebuilt MC. Many have experienced bad ones right out of the box.
I had similar problems about 12 years ago. Fluid like mud, and calipers leaking. I replaced all the calipers with SS.
Also rebuilt the MC with a Delco rebuild kit. (New rubbers and piston)
Also went with Silicone fluid.
No problems since.
Barry