Brake vacuum servo

Hello,
My defender td5 110 failed it's MOT for having underperforming brakes. The diagnosis was "probable bad vacuum servo". I've fitted a new one but now I've got very soft brakes - the pedal goes half way down before I get any braking and is slow to come back up again.
I've bled the system as per the HM instructions, but with no improvement.
Can anybody suggest what the issue might be, please?
Thanks

eprothe said:

Hello,
My defender td5 110 failed it's MOT for having underperforming brakes. The diagnosis was "probable bad vacuum servo". I've fitted a new one but now I've got very soft brakes - the pedal goes half way down before I get any braking and is slow to come back up again.
I've bled the system as per the HM instructions, but with no improvement.
Can anybody suggest what the issue might be, please?
Thanks

Click to expand...

Is the vacuum pump working correctly? Have you got good suction on the vacuum pipe?

Hi,
Thanks for that.
It was good before I fitted the new servo...I've not checked it since, though...I'll let you know.

...yep, vacuum seems good - I pumped the pedal a few times without the engine running to release any vacuum, started the engine with the pedal held down and felt it sink as the vacuum built up.

The brakes actually feel pretty sharp...the pedal just has a lot of movement and doesn't come back up as fast as it should...
Thanks for your help

Is the servo clevis rod adjustable for length? I've read a few posts for other vehicles which talk about screwing in/out the servo to pedal rod...it never occurred to me to check that...

...so I did...and it's not, as far as I can see...

I hate it when people leave threads hanging like this, so here's the solution in case anybody finds this in the future...

Yes, you can (in fact, you probably have to) adjust the new servo, but not the side I was looking at. You can adjust the master-cylinder side of the servo by screwing out the plunger and locking it off with a lock-nut. You need to get the plunger fully out to do this, by holding the brake-pedal down (which I did with a stick wedged against the drivers seat). Having asked around a bit, I was told a quarter turn of the plunger is a big adjustment - I turned mine out about 8 turns and the brakes are now good enough that I can't be bothered taking the master cylinder off to adjust the plunger again, but they're not perfect.

So there you go - all in all, very easy to do. 13mm socket to get the master cylinder off the servo, bend it back out of the way on the brake-lines, jam the brake pedal down, 2x 8mm spanners to adjust and lock the plunger, put it all together again, job's a good'un.