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JulieG

Member Since: 25 Jul 2024
Location: Scotland
Posts: 3

Brakes need pumping all the time

So this is a struggle.

I fixed the three amigos around 10 years ago with the bypass mod, but it went wrong again, this time the error was a pump fault, and sending the ABS modulator away confirmed it was faulty and non-repairable.

So I got a fully reconditioned unit, fitted that - sorted the problem, but I now found the brake pedal would slowly go to the floor.

So replaced the master cylinder with a new one, which has sort of fixed it.

However there is a new problem, press the brake pedal and it goes almost to the floor, pump it once or twice and it goes solid (well defender solid anyhow).

Sit there several seconds to a minute and again the cycle repeats - pedal goes to the floor, one or two pumps and back solid.

Importantly, the vehicle is not moving, just stationary whilst we find the problem. A few years back it had stainless braided hoses fitted all round, it had the front pipes replaced and new pipes all around at the calipers.

It has been pressure blead (several times now) including power blead through the modulator, no leaks anywhere.

I can't find how to solve this at all, the master cylinder has been changed, no driving, so not wheel bearings, when it goes solid, it's more solid than ever before, all new brake fluid, no air bubbles and the fluid isn't going down .

Totally stuck

Any ideas guys?

25th Jul 2024 7:11am

JulieG

Member Since: 25 Jul 2024
Location: Scotland
Posts: 3

OK, found the problem!

In the brake servo, there is the plunger/rod that goes into the master cylinder - it is this that drives the piston.

It's held in place by a star washer/clip - turns out this was loose - so as the engine runs, the vibration causes the plunger/rod to shift about pushing the master cylinder piston down a little, leaving a gap between the plunger/rod and piston or diaphragm - thus after a bit when you press the brake, it has to take up this gap before it starts pushing the piston.

I used a bit of tube, pushed the washer/clip hard into place, with the plunger/rod now fixed to the diaphragm it doesn't produce any gap.

Took some finding!

1st Aug 2024 1:14pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5642

2006 Defender 110 Td5 USW Zermatt Silver

Great work

Did you disconnect and remove the master cylinder to do this.

1st Aug 2024 1:31pm

JulieG

Member Since: 25 Jul 2024
Location: Scotland
Posts: 3

Yes, it's a bit of a pain, because with the ABS modulator there isn't enough flex in the pipes, so it has to be removed completely (Inc bleeding the brakes etc).

You have to adjust the length of the plunger/rod to match the new master cylinder anyhow.

So you end up removing and replacing it several times too long and the brakes lock on - unable to release, too short and there is excessive travel in the brake pedal.

1st Aug 2024 3:18pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5642

Thanks for that info.

1st Aug 2024 6:13pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 7981

2011 Defender 110 Puma 2.4 USW Stornoway Grey

You can adjust the servo rod without completely removing the master cylinder. Undo the bolts from mc to servo and ease it forward. Depress the brake pedal so plunger/rod is protruding and then adjust. Its tight but doable, at least on the defensersninhave had. Cheers

James
110 2012 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

2nd Aug 2024 5:17am

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