Poor brakes on Defender 110

Need some ideas about 110 brakes please.

The effort required to stop is like there's no servo. It's ok but I couldn't lock the wheels so I'd rather not ignore it. Here's what I do know;

Pads are nearly new all round

Problem has developed progressively rather than suddenly

The servo is getting vacuum from the air pump but barely measures on a vac guage. Does anyone know what kind of vac reading might be reasonable at idle / when revved ? It's definately a lot less than a conventional manifold vac on a petrol engine.

Revving the engine produces more vac but not huge amounts.

When I start the engine with the brake pedal pressed it stays in the same position - ie doesn't drop a bit as you might expect.

The non-return valve to servo works correctly.

The car doesn't have a front/ rear pressure proportioning valve.

So - any ideas on where to look next or is it just a weak vac pump ?

hi nush

i'd suspect perishing somewhere on vacuum hoses, as you mention was a gradual deteriation. Given that pedal doesnt sink, then you can rule out leaky/contaminated fluid, or air in the system (double check that pedal doesnt 'pump up')
A slight increase in vac when revving also suggests a hole somewhere. If you have no problems with binding, then i think you can forget about sticky brake pistons (chances are one wheel would suffer, so you would notice serious pulling under heavy braking)

I had a similar problem to this with my 110. The poor brake performance was down to brake fluid which had leaked out of the master cylinder on to the servo stripping the paint off. This causing rusting and a small split appeared in the servo unit which was made worse by the action of pushing the pedal to stop ,therefore no vacuum could build up .

Rich

Thanks for thoughts on this. Forgot to say new fluid 6 months ago...

Had a look at all of it and in the end I figured it could only be the pump. A lot of money later (but less than LR - thank you paddocks) and brakes are fixed - also the oil leak that the dealer claimed was oil cooler hoses.

I have heard that vanes can break in the pump and am planning to disect the old one at some point out of curiosity... doesn't explain gradual deterioration but it was the answer.

I know I'm resurrecting a pretty old thread here, but just wondered how common this problem is ? My 97 Hicap has dismal braking performance,even though superficially all is OK. Passes the MOT, but certainly won't lock the wheels in the real world and with a load on requires some stopping.
I am getting some servo assistance as it does dip the pedal if the servo is exhausted and then the engine started while keeping pressure on the pedal. Does anyone have the figure I should expect if I put a vac gauge on the servo hose ?

I have no fluid loss, a good pedal feel and no spurious hissing or sucking noises when the engine is turned off.


All thoughts / info welcome.

Thanks, Mike.

Have you checked the servo for cracks ?

Look very carefully at where the master cylinder is attatched to the servo. You could find cracks there. Servos don't last very long before they crack.

mike