1981

Trying to bleed my brakes, my brake light comes on after long road trips at about 75 mph.
This could be rotor run out, but I do not think so since I have tried and tried to bleed this caliper (inside then outside) and can not get anything but air and brake fluid. The other rear caliper bleeds perfect. It is driving me nuts. I use the MityVac and I use the pumping of the brake pedal. Nothing works.

But my mechanic bleeds them fine, What can he be doing that is different? Ahhhh! I hate bringing the car to have the brakes bled until I can solve this problem. Because they will fail again the next time I take a road trip, about once a month. I should be able to do this my self!

Any ideas what could be stopping me from bleeding this caliper? I feel this is the failure that causes the brake problem with aire getting into my system. Should I change out this caliper?

I want to trade this caliper in for one of the new piston style calipers from Van Steel or whoever supplys them.
AHHHHHHH! I am losing my hair over this.

1981

1979toy

That was exactly the problem that I was having. I'd run down the road at 70 MPH and have to bleed the brakes again. I had just replaced the calipers and still had the problem. When my buddy said that it was a rotor runout problem and I needed to have the discs turned I didn't beleive him since I didn't have a pulsing pedal, but I did it since I didn't have any other ideas so I had the rotors turned. Sure enough, my brakes were rock hard after bleeding and have stayed that way.

1981

Could you explain the process of how you made sure they were turned correctly, I here they should be turned on the car? Are most shops equipped with any special tools to do this, if they have to be turned on the car?

Should I then turn all four rotors?

I am at a loss of remedies and will try anything.
1981

GTR1999

Welcome to the forum. This has been discussed here a lot so check the archives by doing a search. The only way to tell is by usinig an indicator to check the runout. You should try to get them under .003" anythingover .005" and you'll start to have pumping problems. New rotors have runout too. I inistalled a new front rotor today and it had .009" out of the box,USA made.
I was able to shim it down to .0025-.003".
Your garagfe is probably using a power bleeder but if you have runout then you'll soon have a soft pedal.
gary

Van Steel

1981-
I don't think your calipers are the problem. Your run out on your rotors are bad and that why you are getting air in the system. You can pull the rotors off and have them turned. Now it seems to me that this problem has been a reoccuring one. I think you have more problems than you think. I think your caliper mounting bracket is bent also. With this being bent your problem will never be solved. Period. You can cut your rotors and make them as straight as possible and they are still going to let air into your system w/that bracket being bent. It may not be right away but it will happen again. This is a very common problem.

Wrecked82

Same problem for several months - I drive about 1,750 miles a month.

Finally gave up and ordered new rear wheel bearing assy's (which came today! Hooray!).

I wanted to believe it was everything but rotor runout.

I was wrong.

Big Fish

Certainly has to be a run-out problem. If the spindle is bent, turning the rotors won't correct the problem unless they are done on the car. I know my car was broadsided when the previous owner had it and the spindle was good and bent. Works just fine now with a new spindle and (rebuilt) caliper.

1979toy

I only had the rears done. Took them to the local auto parts place and waited on them. No special shimming was done when they were reinstalled.

1981

Thanks to everyone who has replied,
Van Steel,
How do I straighten the caliper braket, can it be straightened?
Right now the Left rear brake pads (problem side) are sitting closer to the rotor than the right rear are. In fact the pads can not be forced away from the rotor like I can do on the right side. I can move the right rear pads away from the rotor with my hands, but not the left rear pads. Does this tell you anything?

I have read all of the previous discussions on this subject, and understand how rotor run out happens, but why can I not bleed this caliper? Even though I have a rotor run out problem shouldn't I be able to vaccum bleed this caliper without the continuous air? Where is the air coming from, it just keeps pumping out of the caliper when I bleed the brakes. This is what is really bothering me. I can not seem to bleed my own brakes while troubleshooting this problem, and I hate having to go to a mechanic to do it for me. And then a week later have failed rear brakes again.

If I buy a rebuilt bearing assembly, what will this get me in the form of a solution? I 4-pointed the car today and put one hand on top of the left wheel and the other on the bottom, I tried to whoble the wheel and it whobled about 1/8 inch, not a huge whoble, but is this a problem? I know I should have NO whoble, but the right side whobles just as much and I have had NO problems from that side.

Thanks for helping out, all of you have really taken me in and your knowledge is priceless,
1981

1979toy

Given the price of a new spindle, or a caliper bracket, or a caliper, why not just have the rotor turned and if that doesn't solve your problem then you can move on to more expensive solutions?

Tom454

s discussions on this subject, and understand how rotor run out happens, but why can I not bleed this caliper? Even though I have a rotor run out problem shouldn't I be able to vaccum bleed this caliper without the continuous air? Where is the air coming from, it just keeps pumping out of the caliper when I bleed the brakes.


.... you're drawing in air past the outer dust boot and then past the inner o-ring seal between the pistons & caliper bore. This is why I never bothered to buy a MityVac... too easy to mis-use.

When you use the "pumping" method, if you're not using "one-man-bleaders", this method requires 2 people.

Let's call them John & Sue.

John sits at the caliper and Sue sits in the drivers seat.
John tells Sue to press the pedal to the floor slowly.
John opens the bleeder just a little when Sue begins to press the pedal.
When Sue's foot reaches the floor, she tells John "Down"... and she holds the pedal at the floor.
John immediately closes the bleeder to stop air from re-entering the system when Sue lets the pedal come back up.
John then tells Sue to let the pedal come back up.
Sue says "Up" when the pedal is all the way up.

Repeat until the fluid has no air in it... about 1 cup of fluid is more than enough.
Using the "Lisle" brake bleeder cup/hose kit... 1 plastic container is enough for 1 caliper.
Make sure you monitor the fluid level in the master cylinder during this process... keep it topped off. If it runs dry, you'll have to start all over again, including "bench bleeding" of the master cyliner.

General rule is to bleed from the farthest to the nearest caliper.... RR. LR, RF, LF. Some service manuals give a different order. But I tested this theory recently and found absolutely no difference in job quality based on order of bleeding, as long as you bleed each line/caliper properly.

This is just the bleeding process.... you probably have other issues.

Hoses could be bad (collapsed on the inside, invisible to the eye)

"Proportioning Valve" (switch) could be messing you up.... it has sliding pistons inside which close off one half of the lines if there is a massive fluid leak. Getting it to re-center can be tricky. You cannot bleed the system if the valve is off-center.

If the calipers are not stainless sleeved, internal rust/corrosion could be a problem
Piston seals could be worn out... leaking etc

Also... when you press the pedal to the floor during bleeding, you are forcing the master cylinder piston beyond its average/normal braking travel. This may be pushing the internal seals across rust pits or contamination (or both) in the bore, and this causes failure of the master cylinder. That may be your next problem. Depends on how old the master cylinder is.

1981

Thanks for all of the replies,

I toke a trip to New Orleans yesterday with the vette and about 30 miles into the trip the brake light came on! My front brakes work great when this happens, so I kept my plans. The proportioning valve must not have a problem, I guess.

So I arrive home last night after the trip. Park the car, and this morning notice a good 1 inch line of Brake Fluid coming from the left rear tire. Never had a brake leak before. Checked the master cylinder and it was empty in the rear about 1/4 inch from where it should be, so I filled it to full (1/4 inch from top). I use DOT 3.

Is it possible that the rotor run-out has damaged the seals in the caliper? If so, I guess I need to replace the caliper, and turn the rotor. I was going to turn the rotor from the advice on this forum, but now the caliper is probably shot. If I do have to replace it, I will replace it with the newer piston style, and the hell with this old technology junk. Now I know some like the old stuff, but I am so fed up with no mechanics around here being able to properly work on this brake system. I have to "conveince them what the problem really is", and now after I tell bubba how to do his job, how great of a job will it be. And does he really want to prove himself wrong with my solutions? It is a NO WIN situation over here!

I live in Lafayette, LA, if enyone knows of a reputable mechainc in my area please tell me about them. I am going nuts over here with these guys, and do not know what to do first.

This is what I want to do, is it a good choice of action?
1. turn rotors
2. Fix leak, hopefully it is the caliper because I really want to get away from the old style brakes. If it is the caliper I will replace it with the piston type (without springs? right) The caliper was replaced about 7 months ago with a stock AC-Delco.
3. check to see if caliper bracket is bent, but then who will do it and how is that done? If need be I will just have my bearing assy. re-built, and forget about it.

If you have anything else to add to my fix please help me out with your knowledge.

Thanks,
1981

Van Steel

1981-
I know of a great shop in your area. Delkin Motorsports. I can give you their address if you would like it. They work on a lot of vettes and topflight every car they build. Talk to Mark, the number is 337-233-9179. excellent service. I know he can fix any problem you have and you can tell him I sent you

Fevre

Personaly I would check the rotor run out on the car or take it somewhere to have it done. Just ask them to check it, no sense telling them what the problem is since it might be an invite to all kinds of unnecessary work. Proceed from there.

1981

Gave them a call, now I don't feel so alone over here. :grouphug:

I dropped my car off with the usual mechanic, they will tell me what is leaking, and I told them to turn my rotors to .002. If this does not fix the problem, I will go to Delkin and try to get some sleep. Will let ya'll know what happens when I here back from the mechanic.

There is a yearly corvette show coning up on the 18th that I was going to enter for the first time! I hope I can make it.

1981

Van Steel

:cool: Hope everything works out for you.