Brake pedal sinking to the floor

Hello from Lisbon, Portugal.

I have a '88 XJ 2.1 TD 144K miles, that I bought recently.

It came with a brake problem that no one seems to know what it is.
The dealer that sold me the car said that he tried everything... he said he replaced the master cylinder and other parts, but I'm finding it hard to believe, as he couldn't solve the problem.

What happens is that the pedal has a spongy felling and it sinks to the floor, but it still has some brake power at the end, enough to sometimes block the wheels. When I push the pedal quickly I hear a issing noise. When I push it repeatedly, I feel some pressure building up, but it goes away when I stop to push it, sinking again to the floor.
If I push it to the floor and then try to move foward in 1st gear, the car is well braked and it doesn't move.
The brakes are well bleeded and the fluid in the master cylinder remains between the recommended levels.

I read some posts here in the forum that talk about the proportioning valve... could it be that ?

Any help would be great, because it's getting very scary to drive the Jeep like that, specially with wet roads.

(Sorry for the bad english )

Bom dia ...

(more than likely it has something to do with the power booster/vacuum leak ???)

Someone, here, who actually knows what they are talking about should be able to answer your question .... soon.

Bad english ? You should hear my Portuguese

The problem you describe is exactly what my friend in Philadelphia experienced. The brakes worked, but the peddle was always soft and close to the floor, and the rear brakes were not helping to stop the vehicle.

The problem was the proportioning/combination valve.

The Factory Service Manual (FSM) specifically states that this valve is NOT serviceable and must be replaced if bad. It is expensive. I think if it were my Jeep I would remove it, clean it, and reassemble it. If that fixes the problem, great. If not -- you can then buy a new one.

Yes, I also think that the rear brakes aren't doing much.

My pedal isn't close to the floor, it hits the floor with barely no feeling of pressure.

One thing that helped a little bit was adjusting the rear brakes, but the improvement was almost not noticeable.

So, Eagle, your Philadelphia friend solved it by replacing the proportioning valve with a new one ??
Like you say, I'll try to clean it, here in Portugal it costs nearly 180$, so if cleaning solves it, the best !!

Thanks

P.S. - Lou, it's "Boa Noite" here in Portugal... 11 P.M.

Kurika --

The proportioning valve is very expensive here, also.

My friend decided to eliminate the factory proportioning valve. He replaced ALL the metal brake lines, and instead of the factory proportioning valve he installed a Wilwood adjustable proportioning valve. This allows him to set how much or how little the valve reduces pressure to the rear wheels.

However, he eliminated the pressure switch that warns of a brake system failure. This was not a problem for him ,because he has been around cars all his life and he doesn't need an idiot light to tell him if he has lost half his brake system.

Chrysler also sells an adjustable proportioning valve in the Mopar Performance Catalog. Neither the Mopar nor the Wilwood is a direct replacement for the factory unit -- some plumbing will be required to use it.