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Joey Fri Nov 13, 2009 3:52 am

I just replaced the master cylinder on my '79 panel. I bled the master cylinder and all four wheels but still the pedal goes half way to the floor before I get any brakes. The brakes are not spongy and pumping the pedal doesn't make it any better. When I push the pedal down all the way sometimes an air bubble comes up out of the brake reservoir. When I let go of the brake pedal I'm get two or three air bubbles coming up out of the brake reservoir. I'm not loosing any fluid so I can't figure out where the air is coming from.

VDubTech Fri Nov 13, 2009 5:34 am

Are your rear brakes properly adjusted? Rear brake adjustment plays a HUGE role in your brake pedal.

Joey Fri Nov 13, 2009 5:46 am

Yep. Shoes adjusted up against drum and then backed of two teeth on each star adjuster.

Tom Powell Fri Nov 13, 2009 11:39 am

does the brake rod coming out of the master cylinder have an adjusting nut?

Aloha
tp

Joey Fri Nov 13, 2009 1:58 pm

No adjusting nut. There's 1-2mm of play between the brake pedal rod and the master cylinder rod.

1975 Kombi Fri Nov 13, 2009 2:40 pm

Do you have the 2 bleeder calipers up front. I think you have to go from the top on each side. If you have them.

Joey Fri Nov 13, 2009 2:53 pm

I have two bleeders per caliper. I don't think it's a bleeding issue as the pedal is firm and not spongy.

1975 Kombi Fri Nov 13, 2009 3:16 pm

Reservoir seal to master leak. Master to lines leak. It must be pulling air from somewhere.

SGKent Fri Nov 13, 2009 3:22 pm

often a master cylinder gets rust or electrolysis inside it if the brake fluid is not changed once a year because brake fluid is hygroscopic. The area that gets pitted is most commonly the areas that are outside the normal sweep of the seal. When the MC is pushed to the floor it gets into this area and leaks. You may be seeing the first stages of a leak because it is easier to suck in air than expel fluid until the leak gets worse. I think I would replace the MC. Years ago you could hone them and replace just the seals but there are so many variants out there today on MC production that it is near to impossible to find identical parts to what will come out of it if you take it apart.

Joey Fri Nov 13, 2009 6:16 pm

SGKent wrote: I think I would replace the MC.

56ovalbug wrote: I just replaced the master cylinder...

I though I was bad for not reading the whole topic. :P

VDubTech Fri Nov 13, 2009 6:26 pm

56ovalbug wrote: SGKent wrote: I think I would replace the MC.

56ovalbug wrote: I just replaced the master cylinder...

I though I was bad for not reading the whole topic. :P

Nobody does, then they wanna play "expert" on your problem. READ THE POSTS PEOPLE. :roll:

1975 Kombi Fri Nov 13, 2009 6:33 pm

Maybe one of the rubber cups in the master has flipped. It sounds like one bank is working in reverse if it isn't pulling air from a bad reservoir seal.

Desertbusman Fri Nov 13, 2009 7:28 pm

1975 Kombi wrote: Reservoir seal to master leak. Master to lines leak. It must be pulling air from somewhere.
It could suck in air after all the fluid has leaked out.

SGKent Fri Nov 13, 2009 10:22 pm

I don't need to read a manual to know the differences between a dog and a cat but I apologize for not spending more time studying the thread if it makes you feel better. That said, I stand by my answer. Then replace it again.

If it is sucking air over and over and has been bled many times then there is a good chance it is bad unless one of the the brake lines or a switch is bad or loose. He says the brakes are hard and not spongy.

You can't assume just because it is new that it is good. I've actually had it happen to me with a MC where someone cleaned up their old one and took it back to a store as "bought the wrong one" and the clerk took it back and resold it - to me. We actually had to get a new shipment in because the store had trouble with several when we looked closely at them. Apparently someone did the trick more than once.

Joey Sat Nov 14, 2009 6:07 am

Not sure what dogs & cats has to do with fixing my brakes but I have six cats if that helps..... :P

I got the master cylinder at CIP1, trust me, it was NEW. It's the ATE brand.

I'm going to disconnect the lines one at a time and plug the outlet on the master cylinder to see if I can narrow it down to the front or the rear brakes.

The two rear wheel cylinders are new (two weeks ago), the rubber and metal line are only two years old and the front calipers are ancient but the pistons move freely and they work great - no leaks. The only things I didn't replace are the brake light switches. I'm not loosing any fluid and the fluid is all new & clean.

1975 Kombi Sat Nov 14, 2009 7:30 am

My guess is the front brake part of the master is the issue. Half the pedal travel to me is the backs working.

rockerbus Sat Nov 14, 2009 11:27 am

Don't rule out a bad new MC.... I got a bad MC for my Toyota from my FLAPS once - the lines just wouldn't bleed, and finally diagnosed it by swapping back in the old bad one, which would bleed, but wouldn't hold pedal. But the replacement was a chinese mfg unit, and I thought ATE was pretty good. But everyone is "globalizing" their production now ... CIP1 was easy to work with on a warranty Brazilian item I bought this year. They were surprised to see it was Brazilian, because it had been German the year before...

SGKent Sat Nov 14, 2009 11:34 am

Quote: Not sure what dogs & cats has to do with fixing my brakes but I have six cats if that helps.....

that does make it easier - hairballs in the brake fluid............

Rusty O'Toole Sat Nov 14, 2009 11:40 am

Your master cylinder is still full of air. It can take a long time to get the air out if you don't bench bleed the master cylinder. You can't develop any pressure.

Try working the pedal to make the bubbles come up. If you can work all the air out of the master cylinder you should start to feel some pressure on the pedal. Then bleed the brakes again. They should bleed quickly when you have pressure in the master cylinder. The difference will be marked.

I like to bleed the brakes, let the vehicle stand overnight, then bleed them again. Air can dissolve in the fluid but overnight it comes out and can be bled out.

Joey Sat Nov 14, 2009 1:28 pm

The air bubbles are gone - I think it may have been the switches not being tight enough. Guess I was a little paranoid of over tightening them when I first put the new master cylinder on. I tightened them both up along with one of the connections on the pressure regulator.

There's a problem with the right front caliper. If I put a line clamp on the rubber hose that goes to that caliper the pedal is firm and high. Take it off and the pedal goes down further and isn't quite as firm. I'll have to dig out one of my spare calipers and see if that solves the problem.



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