Brake issues update

911Etarga · 07-02-2008, 08:41 PM

I just figured something out with my brakes,

Every time I open the bleed valves for my rear calipers and push the pedal, it goes right to the floor. When I close the valve, the pedal dead heads at about three quarters. By dead head, I mean, it goes from nothing to ROCK hard.....it feels like the master cylinder is bottoming out. I drove it down the street like this and it has NO brakes, until I pump them, then they grab, only to do the same thing over again. What could cause this???
I just bled them again....

This is the last time I will post the problems with my brakes. An update: New master cylinder, bled lines about a million times, after that I would pump brakes and get some pressure, just to loose it the second I let my foot off the brakes....

Eagledriver · 07-02-2008, 08:46 PM

sounds like stuck calipers.

-Andy

rnln · 07-02-2008, 08:52 PM

One of the posibility is you didn't bleed it right so it has air in the system, but when it was "rock hard" when you close the bleeder valve, is after you pump it too much so it's tight as it was working.
Just curious how did you bleed it?

911Etarga · 07-02-2008, 09:10 PM

I used pretty much every method. Two person pump, one way valve-one person pump, pressure, vacuum.....the thing is, the left rear caliper is new, so I would assume that it wouldn't be seized. If the right one(which is very old) is seized, would it feel rock hard with out pumping? I now the feeling of a well bled brake, and this feels like it is bottoming out with out deploying the calipers. BUT it is bottoming out way before it should (3/4 of the travel) and when I bleed the fronts, even with the bleeder valves open, it still bottoms out pre-mature.

911Etarga · 07-02-2008, 09:17 PM

How would you free up a seized caliper?

rnln · 07-02-2008, 10:54 PM

There might be something I don't understand, but I don't see why/how it's seized. You said when you open up the valve, the pedal went to the bottom. When you close the valve, it's tight. Then how can it's seized.
Did you:
1- fill up the solenoid
2- 1 person depress the brake pedal and hold
3- you open the valve. Fluid comes out. Pedal will go all the way down (keep holding it down, NEVER release the pedal)
4- Now you close the valve
5- the person can release the pedal.
Keep doing it untill you feel all the old fluid already came all the way out. Repeat all 4 corner. The furthest corner first.
Is it how you did it?

911Etarga · 07-03-2008, 07:55 AM

That is how I did it, several times. The thing is, with all four bleed valves closed the brake pedal only goes 3/4 the way down and feels bottomed out, not pressurised. When I open one of the rear valves, the pedal goes to the floor smoothly. If I open one of the front valves it still just goes 3/4....weird.
Some thing is causing the brake fluid to dead head when I close the rear calipers. But one is new(left rear) so the right rear would be the problem...?

rnln · 07-03-2008, 08:17 AM

when you are all done with the bleeding, close all valves, depress the pedal and test each wheel. Do they all bite, hard?

cole930 · 07-03-2008, 08:30 AM

911E,

You might try power bleeding the brakes. This will allow you to maintain constant pressuer at the master cylinder and eliminates the need to pump the pedal and fight getting air in the system I'm going to try to attach an artical on building a power bleeder for abour $25.00. Great artical from a felloe Pelican . Hope it helps !!! Couldn't load that file for you, go to search in the 911BBS forum and search for making brake bleeder.

COLE

Por_sha911 · Por_sha911's Garage

Couple of dumb questions:
Did you bleed all 4 wheels?
Did you bench bleed the MC? (I am told that it is really hard to bleed it on the car).

911Etarga · 07-03-2008, 02:20 PM

I just pressure bled the system and still not working....The new Master Cylinder is shot. I am taking it out and returnig it for a new one. What a pain in the ass, this took me a week and a half.

Thanks for your help though!
Brent

rnln · 07-04-2008, 12:32 AM

Keep us up with the result of another new MC.

djpateman · 05:39 AM

You should expect the pedal to go to the stop when any bleed valve is open. When a bleeder is open there is no way to build pressure in the circuit.
I can sort of understand it only going 3/4 when a front bleeder is open since there are front and rear circuits within the master cylinder. I suspect that this means the rear circuit is well bled, and the problem is in the front circuit.

Here are a couple of things to check out:
You replaced the master cylinder, so there are a few things to verify. Where the reservoir lines go into the MC there is a rubber boot. Is there a washer under the boot, and is the boot new, cracked, properly seated, and lastly are the lines properly seated? The washer acts as a stop for the lines, and they must seat on them correctly. Is there anything in the lines or the reservoir that may keep fluid from flowing freely? Is the reservoir vented properly? What I'm trying to establish here is if the MC is getting fluid from the reservoir properly or it it may be sucking air from the fittings. You MUST ensure that the reservoir has sufficient fluid at ALL times when bleeding; if you suck in air, then you have to bleed all over again.

It is a good idea to bleed the caliper nearest the MC first when installing a new MC to get as much air out of the front circuit as possible before doing the remainder of the bleeding procedure.

The proper bleeding procedure is to start at the caliper farthest from the MC. Pump the pedal until you get pressure, open the bleed valve until the pedal goes 3/4 to the floor, then close the bleed valve, and finally allow the pedal to return to normal position. The person opening the bleed valve has to instruct the person doing the pumping of the pedal to PUMP, HOLD and RELEASE at the appropriate time while opening and closing the valve. Using the pedal and MC to build pressure and move the fluid is important to compress any bubbles to a tiny size in order to get them to move though the system. Use a rubber mallet to rap on the calipers to dislodge bubbles while bleeding. You may want to use some grease or Never-Seize on the bleed valves to ensure the bleed valves don't seize over time and to keep air from leaking down the threads while bleeding. Use a plastic line on the bleeder to go to the collection container; this allows you to see the bubbles exiting the bleeder and should keep any air from going back, so loop it up to ensure the tubing has a few inches of fluid at the bleeder. You should not be able to turn the brake rotor when you have pressure in the system, and it should turn after the pedal returns to normal position. Never bleed a large amount of fluid from a caliper without checking the level in the reservoir.