Brake issues

Hi,I have a problem with the brakes on my disco,when I put the brakes on the truck stops as it should but then the pedal gradually goes to the floor if you keep the pressure on.I have searched the brake lines and looked at the cylinders for signs of a leak but no joy,also the fluid doesnt seem to be going down in the reservoir,could it be a problem with the ABS unit,any help would be appreciated

Truck!!:nothingtoadd:

It's symptomatic of an iffy master-cylinder or air in the system.

Yes there is air in the system which is compressable hence the pedal travel, whereas liquid or brake fluid in this instance is not, so you need to bleed the system and see if that sorts it

discool said:

It's symptomatic of an iffy master-cylinder or air in the system.

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The pedal gradually going down while under pressure sounds to me more like the brake fluid being forced back around the master cylinder piston due to a worn/perished seal rather than just air in the system, which can give the pedal a spongey feel.
I would say a rebuild of the master cylinder is called for.

I agree 100% with this.....the place to start is the master cylinder.

brian47 said:

The pedal gradually going down while under pressure sounds to me more like the brake fluid being forced back around the master cylinder piston due to a worn/perished seal rather than just air in the system, which can give the pedal a spongey feel.
I would say a rebuild of the master cylinder is called for.

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Thanks for the replys I will look at the master cylinder seals and obviously a full bleed will be required so hopefully the problem will be cured

I had the same issue The brakes were grabbing too. It was sorted after I service the master cylinder. I also changed the flexi pipes as they were 21 years old. Old working servo was shoved on as well to save me doing it later.

It solved the problem.