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Bleeding brakes

I changed both front calipers, I have bled them over and over (can’t get pedal) check for leaks no leaks…do I need to bleed the backs also when I do this type work. What could be wrong !!!

Thanks Chris

Will the pedal get firm after you pump it a bunch of times? If its only air then the pedal should eventually firm up. If not then maybe you’re looking at a bad master cylinder. What was the problem that led you to replace the calipers?

Did you keep the master cylinder full at all times while bleeding?

What is your bleeding method?

Here’s an easy one: put a tube on the bleeders, open them up and just let them gravity bleed. Its very slow but easy and it works very well. It is still imperative to keep an eye on the fluid level.

Its not the Master, just had it changed about a yr ago and it all worked fine until I changed Calipers, I just need to know if I need to bleed the backs also, or are the front and back separate. I always keep my eye on the fluid… never heard of gravity bleed.

Thanks Chris

I’ll repeat the question, why did you change the calipers?

You asked what could be wrong. The master cylinder could be the problem. If a caliper failed and the master cylinder went dry it very well could have caused it to fail. There are many reasons for brake failures and you can waste a great deal of time and money looking for a convenient reason, overlooking the obvious.

If you never opened the back then you shouldn’t have to do anything. The only air you would have gotten in would be there at the front calipers.

My Master cylinder did not go dry…I changed the calipers because one of them was sticking and I have 150,000 so I thought I should just change both.


I would probably do a 4-wheel gravity bleed - just to be sure about it all. If you’re brake fluid hasn’t been changed in a long time its a good idea anyway.

If that doesn’t do it then I would actually wonder about the master and here is why - presumably when you removed the old calipers you did force the piston back into the bore of the old calipers. This forces brake fluid back through the system.

It is not at all uncommon for this to cause problems and it isn’t all uncommon to get “new” MCs that are bad right off the shelf.

I’m not saying that getting the bleeding straight might not be it - but don’t be surprised if it turns out that the new MC is now leaking - partly from its own initial quality + the back pressure when you put those old pistons back in.

Let me ask you something…to gravity feed just open the bleeding screw and let it leak until you see no air coming out…am I correct to say that.

Thanks for your help

also can I do one at a time

Yes and yes. But it is a slow process. So all 4 is easy to manage and faster.

Same set-up - clear hose on the bleeder and wait for no bubbles.

Thank you for your advice.I will try that…

Thank you

You were right it was the MC I don’t know how it went bad just because I changed Calipers,
Still doesn’t make sense to me because I never ran it dry…but anyway Thank you very much for your help…Appreciate it


MC’s can be finicky. It’s not unlikely that when you bled the brakes, you pressed the pedal down farther than it usually goes down. That made the MC’s piston pick up gunk that’s been accumulating on the cylinder wall since it was installed. Now that gunk is between the piston and the cylinder wall, creating an opening, through which fluid can leak.

Another possibility is as cigroller said - when you compressed the piston on the caliper, that forced fluid to backflow into the MC, which can damage the MC’s piston seals, either by forcing gunk in them, or if the seals are already somewhat weak, just by pushing them the wrong way - - think of how you destroy a credit card by pushing it back and forth until it breaks.

Many thanks for taking the time to report back. Normally reports of problems come and go with no word about resolutions.

I have actually stopped just mashing the pistons back into the calipers when doing brakes. I now open the wheel’s bleeder and send the piston back in that way - to avoid basically back flushing the brake system.

The other thing is the possibility of having sent the piston into the “gunk zone” as shadowfax mentioned.

Then, on top of that, there are lots and lots and lots of rebuilt parts out there with very questionable quality. MCs are among them.