Can't get front brakes to bleed

[Dallas K.]

All new calipers, lines, and master cylinder on a '70 Corvette. Ready to bleed the brakes.

Bench blead the master cylinder.

Using vacuum bleeder, I can suck fluid at all bleeder valves except the left front.

The rear (left and right) bleeds fine out both valves when pumping the brakes.

The front right bleeds using vacuum, but can't get to bleed when pumping brakes.

Can't get the left front to bleed by vacuum or pumping brakes.

Does anyone know what could be causing this? I have blead many brakes, but have never run into this problem.

[Gary S.]

Re: Can't get front brakes to bleed

Had the same type of problem a few months ago on my 67 when I had the master cylinder resleeved and put on new calipers and lines. I was getting nothing at the bleeders using pedal pump, vacuum suction and several bench bleedings. Even put on another freshly sleeved never used master cylinder. Never had the problem before. Bought a Motive pressure bleeder and had all working in 15 minutes after mounting the bleeder on the master cylinder. There is lots on the web from others frustrated with the same problem. Many said pressure bleeding was their answer....thus why I bought one.

[Joe L.]

Re: Can't get front brakes to bleed

All new calipers, lines, and master cylinder on a '70 Corvette. Ready to bleed the brakes.

Bench blead the master cylinder.

Using vacuum bleeder, I can suck fluid at all bleeder valves except the left front.

The rear (left and right) bleeds fine out both valves when pumping the brakes.

The front right bleeds using vacuum, but can't get to bleed when pumping brakes.

Can't get the left front to bleed by vacuum or pumping brakes.

Does anyone know what could be causing this? I have blead many brakes, but have never run into this problem.

Dallas-----


There are very few service operations on a C2-C3 Corvette that I fear more than bleeding the brakes.

[Wayne W.]

Re: Can't get front brakes to bleed

Adjust the push rod on the MC so it doesn't block the port.

[Edward J.]

Re: Can't get front brakes to bleed

Dallas, I have done many corvette brake bleeds over the years and they are a bear with out a pressure bleeder. Heres how I do it, its a one man operation.

The vacuum pump doen't work well on the corvette system. The way I do its is smiple gravity bleeding.Start with the master cylinder and crack bleeders or lines til you see the air bubbles stop and straight fluid come out. then crack the closest bleeder which is the left front, right front, left rear, r.rear.I know what the shop manuel says on the order but this will work it takes alittle time because you are letting gravity do the work. don't forget the rear bleeders there are two, start with the inner then outter. Also you'll want a flash light or drop light because you have to keep and I on the bleeders to watch the air bubbles rise to the top and when they stop close the bleeder and work on the next.

Buy the way Wayne post is correct the push rod on corvette brake system is a problem, the way I get around this is to just unbolt the master cylinder from booster or firewall and let hang.Or just pull away enough so the push rod is not a factor.The piston is positioned between the m/cyl. port and hinders bleeding and the gravity process. so maybe after you bleed the m/cyl. just unbolt.

[Terry M.]

[Clem Z.]

Re: Can't get front brakes to bleed

when we pressure bled race car brakes to make sure no moisture got in we used a pump up garden sprayer filled with a desiccant to absorb the moisture to supply the pressure to the master cylinder. later when we used dry nitrogen to fill the tires to prevent presuure build up from heat we used the dry nitrogen to pressurize the MC

[Bill C.]

Re: Can't get front brakes to bleed

My dad taught me this one man bleed operation years ago - work really well...

get a second bottle of brake fluid. Run a hose from the bleeding valve to the bottle of fluid - just only have it half full.

have the master filled correctly, put cap back on.

Pump the brake pedal. do this slowly, it will push fluid from the master through the line into the bottle and then it will suck fluild from the bottle back in when you release the pedal (return stroke).
You still have to do the calipers in the correct order (as stated above).

Next to gravity bleeding (which I always do on a Vette), this is a great way. No need for expensive vacuum bleeder etc..

Bill

[Larry M.]

Re: Can't get front brakes to bleed

Terry:

For what its worth..............some guys use the Motive Brake Bleeder simply as a pressure source, and do not fill it with fluid. Fluid refills are all done directly into the master cylinder. This is obviously more work in removing and reattaching the master cylinder top cover plate, but it does eliminate the issue(s) you mentioned.

I think Clem Z basically stated the same thing, using a garden sprayer with desssicant inside to hookup to the master cylinder top as a pressure source. Obviously one needs to make a special MC cap for this procedure. But that isn't too hard to do.

I have always used a Mighty-Vac to pull some fluid through each caliper, and then get my (very unhappy) wife of 42 years to work the brake pedal. We have been doing this procedure for more than 42 years, and she knows better than me how to do it correctly. But she still hates to do it. Maybe it's time I buy a Motive Bleeder.....

Larry

[Patrick H.]

Re: Can't get front brakes to bleed

Terry:

For what its worth..............some guys use the Motive Brake Bleeder simply as a pressure source, and do not fill it with fluid. Fluid refills are all done directly into the master cylinder. This is obviously more work in removing and reattaching the master cylinder top cover plate, but it does eliminate the issue(s) you mentioned.

I think Clem Z basically stated the same thing, using a garden sprayer with desssicant inside to hookup to the master cylinder top as a pressure source. Obviously one needs to make a special MC cap for this procedure. But that isn't too hard to do.

I have always used a Mighty-Vac to pull some fluid through each caliper, and then get my (very unhappy) wife of 42 years to work the brake pedal. We have been doing this procedure for more than 42 years, and she knows better than me how to do it correctly. But she still hates to do it. Maybe it's time I buy a Motive Bleeder.....

Larry

Larry,

Not only does my wife know how to do the procedure but so do my 17 and now 14 year old. You just have to keep training the other family members.

Patrick

[Terry M.]

Re: Can't get front brakes to bleed

Terry:

For what its worth..............some guys use the Motive Brake Bleeder simply as a pressure source, and do not fill it with fluid. Fluid refills are all done directly into the master cylinder. This is obviously more work in removing and reattaching the master cylinder top cover plate, but it does eliminate the issue(s) you mentioned.

I think Clem Z basically stated the same thing, using a garden sprayer with desssicant inside to hookup to the master cylinder top as a pressure source. Obviously one needs to make a special MC cap for this procedure. But that isn't too hard to do.

I have always used a Mighty-Vac to pull some fluid through each caliper, and then get my (very unhappy) wife of 42 years to work the brake pedal. We have been doing this procedure for more than 42 years, and she knows better than me how to do it correctly. But she still hates to do it. Maybe it's time I buy a Motive Bleeder.....

Larry

Larry,
See the second #2 bullet point in my post.

I haven't bit the bullet for the Motive yet, but I continually think about it. John Hinckley's post with the huge C-clamp holding the adapter to the master kind of scares me each time I see it. Fortunately the hybrid vacuum system I use works very well for all the daily drivers, so no problem yet. I last changed the DOT 5 in the 1970 when it had been in there for about 25 years, and I doubt I will live long enough to see the next 25 year mark. However it is time for the 2008, and I am not sure what I am going to do about that with all the electronic brake parts on it. The Motive seems to be the answer for that at this time, but Clem's nitrogen message has a lot of appeal as well.

[Michael W.]

Re: Can't get front brakes to bleed

Make sure that the piston in the distribution block/differential switch assembly (not a 'proportioning valve' as incorrectly identified) is centered and not blocking the port to the front brake.

[William L.]

Re: Can't get front brakes to bleed

Recently helped a friend bleed the brakes on his 66. Bought the calipers from a well known supplier. The hole for the bleeder had been drilled out with a larger plug put in it and then the correct size bleeder put in the plug! When we went to open the bleeder the plug backed out and the bleeder stayed closed, no fluid would come out. Had to send the caliper back for a replacement?

[Richard F.]

Re: Can't get front brakes to bleed

I had all of the aforementioned fear of the Motive bleeder til I used it. I did find that I could not get a seal on the master usind a c-clamp. But I found that 2 pistol-grip wood-working clamps that I bought at Sears did the job perfectly. They have rubber on the feet, so they don't mar the master. Keep the tank pressure low. I only used 5 lbs; it was sufficient. As a last step, I released the pressure, left the cap and hose on the master, and bleed a little more fluid from one front and one rear caliper. That way, when I removed the cap, the level was low enough in the master that there was no spillage.

I had bled my 68 before, but this last time I went thru a couple of quarts of fluid with no success. 15 minutes with the Motive was all it took.

[John H.]

Re: Can't get front brakes to bleed

Spend the sixty bucks for the Motive pressure bleeder, and never have a problem bleeding Corvette disc brakes again; it takes longer to remove the wheels than it does to bleed the whole system, and 5-10 psi is all it takes.