Still got a brake problem

[KERRSURF]

the garage pressure bled my brakes (twice) and it passed MOT ok, brakes are good but it seems to dive at the front a bit, the problem is the massive amount of travel on the pedal.
I replaced the master cylinder and both front calipers, rear shoes are adjusted and no leaks in system, mechanic said system held good pressure but because I have braided lines he couldn't clamp and isolate the problem.
I'm now suspecting the proportioning valve has seized with the truck being laid up for months, what do you guys think?
Could the valve not working properly cause this problem with the pedal?

Am I looking at £90 for a new one or would one from a breaker be ok?

[yoshie]

MOT, thank fec mate, thats been a long 11 months. Bet your glad to be back rolling in what now is almost new 2nd gen lol

[KERRSURF]

Aye but still not happy with the pedal travel, really do suspect the valve is sticking.

[davec170]

Yup, from your description it's the load proportioning valve. Try disconnecting the link rod and "exercising" the input arm. Give it a good soaking in WD40 Too. With rod off and tied out of the way, move the lever into arse heavy position and take it for a gentle drive. Gentle mind, as if internal valving is working the rear brakes will lock easily! If it still dives under braking the sliding piston inside proportioner is seized. If so, change whole assembly. Internal valving usually only seizes due to corrosion due to irregular fluid changes of brake fluid.

[KERRSURF]

Thanks for that I'll try it asap. Would this account for the pedal travel then?

[Albannach]

Thanks for that I'll try it asap. Would this account for the pedal travel then?

I would say no. The valve only proportions how much of the braking effort is allowed to go to the back brakes, less when it's light, more when it's heavy.

[BUSHWHACKER]

Was all the fluid replaced or just bled?
It's either the old fluid causing the problem or there's still air present.

[KERRSURF]

Litres of new fluid have been put through the system by myself in my bleeding efforts.

[yoshie]

Litres of new fluid have been put through the system by myself in my bleeding efforts.

Aye at least 10 ltrs here prior to the garage having a play.

[KERRSURF]

I'm tempted now to try bleeding with the engine on and using the finger method.

[BUSHWHACKER]

Seeing as you all like submerging your trucks in wet mud up there, are the hard brake lines behind the fuel tank sound?

(There's an inspection plate under the rear seat)

[KERRSURF]

Seeing as you all like submerging your trucks in wet mud up there, are the hard brake lines behind the fuel tank sound?

(There's an inspection plate under the rear seat)

The mechanic checked the system for leaks and told me during the pressure bleed that the system held pressure when nipples were locked. There is no fluid loss at anytime and all calipers/cylinders are dry and in good order, the brake lines are all in good condition (most parts still with black/grey paint on them) and the braided lines are sound.

[Lyndasbottom]

No help on this I'm afraid but this is exactly the same problem I had on my Disco. The brake pedal was perfect until you started the engine and then it would go almost to the floor before any braking. I did all you have done (5 litres of brake fluid in all), servo, master cylinder etc. and even changed the vacuum pump cos there was the slight chance that it was causing the problem. All to no avail. The only thing I didn't change was the proportioning valve but by that time I'd been at it for several weeks and had enough. That was what shifted me onto Surf ownership and I have to say I don't miss the constant fixes/repairs. Hope changing the valve sorts it for you.

[davec170]

It's the load proportioning valve.

No Smilie added.

[Albannach]

I suppose, as it's about the only not new thing in the system, it has to be that. But why?