Brake bleeding poor results

[Ted K.]

I have bled the brakes three different ways, wife pumping pedal, gravity, and suction. I continue to have very little pedal. With all that bleeding I should have a very firm brake pedal at least half way (power brakes). I have about 3/4 inch and if I push hard it almost goes to the floor.
Any suggestions would be helpful.

[Patrick C.]

Re: Brake bleeding poor results

If its a dual reservoir master you need to make sure you have the air out of the master cylinder. This can be tough when the car is level. Did you bench bleed it? I always raise the back of the car when bleeding to level the master cylinder to insure air is not trapped in the front of the master cylinder. Its easier with a single reservoir master.

[Mark E.]

Re: Brake bleeding poor results

Patrick is right- begin by making sure the master cylinder is properly bled. See manual for process.

Also remember rear calipers have two bleeders- inside and outside. Check manual for sequence of bleeders, but general order is furthest to closest from the master cylinder.

After all that, I've had mixed results bleeding by pumping the pedal. Sometimes it seems air just stays trapped. The gravity method works better but is slow. I prefer using a pressure bleeder. They're not expensive and save a lot of time and frustration.

[Ted K.]

Re: Brake bleeding poor results

I think I will have to try the pressure bleeder. Any suggestions for a good one but not too expensive.

[Duke W.]

Re: Brake bleeding poor results

I disagree with the traditional advice that bleeding should start from the furthest wheel cylinder/caliper. On a single cylinder system the shortest path for air between the m/c and junction block pipe is the LF, and the LF and LR on a dual system.

...agreed that one must insure that the m/c bore(s) and full of fluid by bench bleeding, or you will not be able to purge the air.

Duke

[Leif A.]

Re: Brake bleeding poor results

Ted,
When was the last time you changed out the rubber brake lines? They can look good from the outside but be bad on the inside. If they're bad, you'll never get a good pedal.

[Gary R.]

Re: Brake bleeding poor results

As mentioned check the age of the rubber lines and if over 10 years old I would replace them and don't forget the copper washers for the fronts.

If there is any doubt about the MC remove it and bench bleed it for going further. I would go to NAPA and get the metric brake lines that screw into the MC, yes they were metric. Cut and bend them up into the chambers so you can slowly press the piston on the MC in the vise and see if you have bubbles. I found this works the best.

For bleeding I have used the 2 man or woman method for 40 years but really like the Motive bleeder the best. With it you fill it with a clean qt of BF and attach it to one chamber at a time. Pump it up to 10-13 psi and watch the gauge- it should stay firm where you pumped it to. If not there is a leak in that circuit. If good go and bleed that circuit and use a clear tube on the bleeder into a clear qt jar with clean BF in the bottom, keep the hose submerged in the clean BF, open valve and watch for bubbled until you get a clear path. Do the other bleeders and move to the next wheel. I do the rear first and then the front. Well worth the $60-75 they cost if you own a c2 or c3.

[Daniel S.]

Re: Brake bleeding poor results

I think I will have to try the pressure bleeder. Any suggestions for a good one but not too expensive.

Motive Products Bleeder. About $75.

https://www.motiveproducts.com/collections/domestic-bleeder-kits/products/power-bleeders-single-adapter-bleeder-kit-domestic-adapter-bleeder-kits-power-bleeders-single-adapter-bleeder-kit-classic-car-and-marine-kits-power-bleeders-domestic-bleeder-kits-power-bleeders-classic-car-and-marine-kits

[Bob H.]

Re: Brake bleeding poor results

Don't know if you changed calipers or not and this may sound silly but I have seen calipers come with plugs on the high side which caught a friend off guard until the plug was replaced with a bleeder valve and bled properly

[Patrick C.]

Re: Brake bleeding poor results

I have also had good luck with the Motive bleeder and I replace the standard bleed screws with speed bleeders. I have the speed bleeders on both Corvettes. They work great. You can get them at most autoparts stores.

[Ted K.]

Re: Brake bleeding poor results

The master cylinder has been on the car for at least 7 years. I guess it is possible that with a leaking caliper, in the car's history, the fluid level in the MC could have gone below zero and let air into the MC??? Can a MC be bleed while still on the car?? It is a power brake car.
Would a pressure bleeder get the air out of the Master Cylinder if there was air in it while bleeding the calipers??
Thanks
Ted

[Richard S.]

Re: Brake bleeding poor results

I recently purchased a Motive bleeder worked great. Took longer to set up than bleed the brakes on my 1965.

[Richard M.]

Re: Brake bleeding poor results

Another possibility is that during the pedal bleed process, the MC piston seal hit a corrosive spot in the bore and tore. I had that come up on a working brake system on a 70 once.

After replacing old brake hoses, a pedal bleed caused it. When the pedal went towards the floor the piston seal must have hit a bore restriction and tore. We lost pedal in the middle of the pedal bleeding process. Replaced MC and all was good.

Rich

[Mark E.]

Re: Brake bleeding poor results

The master cylinder has been on the car for at least 7 years. I guess it is possible that with a leaking caliper, in the car's history, the fluid level in the MC could have gone below zero and let air into the MC??? Can a MC be bleed while still on the car?? It is a power brake car.
Would a pressure bleeder get the air out of the Master Cylinder if there was air in it while bleeding the calipers??
Thanks
Ted

In this case, I would bench bleed the MC to make sure it's solid. They're not difficult to R/R.

Then methodically pressure bleed the complete system. You should have good result unless the MC is bad or there's a leak somewhere.

Visually check all fittings for any signs of a leak.

A MC with a slow internal leak can be hard to detect. You can press and hold the pedal for a couple of minutes to check that it maintains its height. However I've experienced a MC that held against pedal pressure yet had a slow internal leak. So as a last resort, if the entire brake system shows no leakage anywhere yet will not maintain a firm pedal after pressure bleeding, go ahead and replace the MC.

[Ted K.]

Re: Brake bleeding poor results

I have done all of the above including a new master cylinder and new pressure bleeder. The brakes have not improved, low pedal, they will stop the car but no emergency stop. Pedal goes to the floor.
I have not replaced any of the brake lines or hoses. QUESTION IS HOW WOULD THEY AFFECT THE AMOUNT OF BRAKE PEDAL?? Trying to avoid changing rubber hoses, they can be a real pain.
Is there any other adjustment to get more pedal?