Outer Limits 4x4 Board

Hi everyone,

Every since I changed my front pads and bled the brakes, the pedal feel has been ordinary. Its been bled correctly and there is no air in the system as far as I know.

The problem I have is the car pulls up ok, althogh if Im stopped and I put pressure on the pedal, it sinks to the floor slowly with some resistance.

I had a look at the brakes tonight and one of the wheel cylinders seems to be weeping a little. Its not pouring out, but there is some slight wetness around the bleeder / brake line. At first, I thought I might have damaged the deals on my master cylinder during the bleeding process, although would a weeping rear cylinder cause the pedal to sink right to the floor?

Here is a pic of it. I was going to change the drums, shoes and cylinders anyhow, just means I need to do it tomorrow now

still sounds like master cylinder. the wheel cylinder leak doesnt look so bad, air in the system would give a spongy feel, but when the pedal slowly sinks all the way to the floor, its the seals in the master that are bypassing. (as long as you arnt obviously loosing heaps of fluid with every press.

Doesnt seem to be loosing alot of fluid each time the brake is pressed. The pedal only sinks to the floor if I apply pressure to it. If I hold it there, the ute will hold and the pedal will not drop.

I guess if the wheel cylinder is changed and it still sinks to the floor, then I'd be up for a new master cylinder as well.

Last time I go and flush out the fluid

What year is your vehicle? it's quite common for an older vehicle to destroy the brake master cylinder when bleeding because you can push the pedal down further than it has ever gone in its life.

I doubt it would be the wheel cyl, you may have only noticed it because you started looking.

You possibly could still have air in the system, have you tried gravity bleeding? You shouldn't need to bleed the brakes when changing pads unless you crack the bleed niplple when pushing the pads back.

Its a 1992 so it could still be the master cylinder. I'll change the rear cylinders etc and see how it is.

If it still sinks to the floor, I'll put a new master cylinder in it.

I bled it the normal way. Gravity bleeding as in just cracking open the bleeder and letting it flow out?

Did the rear wheel cylinders, shoes and drums today. Still the same problem with the pedal and brakes though.

I also took apart the master cylinder and it wasnt leaking from the back. The seals and bore looked fine although its probably hard to determine if the bore is out of shape.

Might have to get a new master cylinder fitted to see if it fixes the problem.

The bore wont be out of shape, it probably just had a tiny bit of corrosion which cut the piston seal a bit. The brake fluid can then bypass the seal and ends up back in the reservoir, so doesnt actually need to leak out the back of the master to be stuffed inside. Its not hard putting a new master on. When you do, it makes bleeding easier if you fill the master with new brake fluid before you bolt it in, means you can pump most of the air out without trying to push it all the way through your brake lines. Though shoudnt cost much more to get a brake place to do it do you either.

When I had my master cylinder off the car, I tried to bend bleed it and it didnt really bleed. I blocked up one outlet and tried to get the other to bleed with a constant flow of fluid and I wasnt really successful in doing so. I assume it means the fluid is weeping past the seals as you state?

Also, do you know what lines the front and rear piston on the master cylinder operate?

bleeding wont show up problems with master seals as there just isnt enough pressure created without the lines hooked up. Bench bleeding can be a real mongrel of a job because there isnt a 1 way valve where the lines screw into (for obvious reasons) which means you are likely to get some drainage which might suck air in at the same time. Try both pistons at the same time and something like blu-tack to plug the holes lightly when the cyclinders are pretty full. If you cant get all the air out dont worry about trying too hard.

Front and rear lines on the cylinder are for front and rear brakes respectively, but you should be able to trace a line through to make sure.

Sam

we would install the cylinder then have a mate in the car without putting the lines on gently bleed the cylinder. you need to hold your finger over the master outlets so the fluid can squeeze out but it doesnt suck the air back in when you release the pedal out. If you are having a major pain in the ass getting it to bleed you need to look at the brake pedal to brake booster adjustment.

once theres no or very little bubbles screw the lines back on and drip bleed.