Air in the Brake System!!

[Paddy]

I have had a problem with my brakes over the past few weeks. When braking the brake pedal is at the bottom and struggles to stop. There are no leaks and I am not loosing any brake fluid. The first thing I did was change the Master Cylinder but this did not make any difference. When I bleed the brakes up the pedal comes back to the top and the brakes work great for a few days, after a while it slowly get worse. Has anybody experienced this or have any ideas what it could be? I have a bravo 1.4 98, if this makes any difference.

Cheers Paddy

 

[Tipo16v]

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leak in the slave cylinder then?

 

[Paddy]

Re: .

I had thought about this but wouldnt I be loosing brake fluid in this case?

 

[Paddy]

Re: Re: .

Would the slave cylinder be linked to the brakes or would it just be linked with the clutch?

 

[Schumaniac]

Re: Re: Re: .

Are you using the correct dot rating?

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.......ONE SPORT ONE LEGEND ONE SCHUEY.....

............X....X....X....X.....X....X....(X)..................

.............6 TIMES....going on to 7 times..............

 

[Deckchair]

Re: Re: Re: Re: .

It still sounds like you're getting air into the system and losing fluid. The fact that it is fine after you have bled the system points to fluid with air getting in.(you are using new fluid aren't you!) The fact it's OK for a few days afterwards means you could have a very slow leak and may not notice it at the master cylinder reservoir. Check around the back of the wheels for leaks first but it may be such a slow leak that the only way is to inspect the slave cylinders.
As you put a new master cylinder in then check for leaks there too of course

Do your brakes "pump up" ie improve with quick on/off applications of brake? (Sure sign of air in the system) Do the brakes pull to one side? (side it's pulling towards will be the good brakes)
Is your handbrake holding as well as it used to? Try moving off with the handbrake on, see if one wheel stays and one rotates
Might help you to guess which is the wheel with the problem

 

[Paddy]

Re: Re: Re: Re: Re: .

Thanks for the reply.

Deckchair I am using new fluid each time I have bled them. The brakes do pump up this is why I figured there is air in the system. The handbrake does appear to be ok. Had not tried moving with handbrake on which sounds like a good idea. When trying to stop quickley I have noticed that the nearside rear is locking up.

 

[Pete]

Re: Re: Re: Re: Re: Re: .

So if there is a leak, it'll be in the offside wheel cylinder as the fluid contaminates the shoes and they lose friction. Does the m/cylinder need frequent topping up?

 

[Pete (again)]

I re-read your post and realised you have no leaks. Did you bleed them as in Haynes? If not, do l/h rear 1st, then r/h front, then r/h rear, then l/h front. If your car has load-proportioning valves (they balance the front to rear pressure according to the load in the car), the weight must be on the rear wheels to keep the valves open whilst bleeding.

 

[Paddy]

Re: Re: Air in the Brake System!!

Yeah Pete did in that order and its fine for a bit but then it gets a bit scary.

 

[Pete]

Re: Re: Re: Air in the Brake System!!

The brakes are dual circuit, r/front with l/rear, l/front with r/rear, so if there is a problem on one circuit, the other circuit should prevent the pedal going to the floor. I can only surmise, without seeing the car, that the problem can only be in the servo or m/cylinder and you've ruled the m/cylinder out!

 

[Tom]

When you bleed it again do you get bubbles out?

 

[Paddy]

Re: Re: Air in the Brake System!!

If the servo was at fault then I wouldn't get any assitance even when I had bled the brakes up. Not sure or not if I am getting bubbles Tom as it is my mate who has bled them up while I press the pedal. Why do you ask?

 

[Pete]

Re: Re: Re: Air in the Brake System!!

The servo can be faulty hydraulically and still give servo-assistance. You only lose servo help if there's a fault on the vacuum side.

 

[Tom]

Re: Re: Re: Re: Air in the Brake System!!

Paddy, if its going spongy then I'd expect bubbles to come out.

Pete, the servo is integrated into the master cyl on the bravo. No seperate hydraulics as it aids the brake pedal directly.

 

[Paddy]

Re: Re: Re: Re: Re: Air in the Brake System!!

When bleeding the brakes my mate said he can hear the air coming out and as this is done the pedal gets higher and much more firm.

 

[Pete]

Re: Re: Re: Re: Re: Air in the Brake System!!

Tom, it's many, many years since I saw a servo that was NOT integrated with the m/cylinder, and you can still have faulty hydraulics AND servo-assistance. The servo actually magnifies the amount of play in the system.

 

[Tom]

Re: Re: Re: Re: Re: Re: Air in the Brake System!!

Pete, he said he changed the master cyl and that contains all the hydraulics. The servo acts on the pushrod. If his servo was faulty if would not give any assistance.

Not like the crap old lockheed seperate servos

Its VERY odd that the level is not going down, maybe the bias valve is shafted.