Disco 3 sinking brake pedal - normal or not?

[reb78]

I've done a search on this but the replies are all quite contradictory with some saying all normal, others saying not.

2007 D3 TDV6

Just replaced a section of the rear left brake pipe as it was corroded and leaking.

I also did the rear pads and discs and have just bedded in the handbrake shoes.

Did a manual bleed (two man) then used my hawkeye to do a power bleed as the passenger side of the brake fluid reservoir was empty by the time I'd changed the corroded pipe. Hawkeye only powered the ABS module when doing the FR and RR calipers (not sure if that's normal).

Engine off press the pedal and it's firm and doesn't sink. Engine on, the pedal will gradually sink until.it feels like it's hitting something at the end of it's travel. This is with pretty firm foot pressure. Probably more than you'd use in normal driving.

Is this normal? Of course, I'm looking for problems now and can't remember how it acted before the leak as I never sat there with my foot hard on the pedal and thought about it!

There's no external leaks and no air was coming out from the calipers.

On a test drive it seems to drive fine and as above the pressure needed to make the pedal.sink isn't used in normal driving, even hard braking will lock the wheels and stop before it comes to the end of travel.

I compared it to my 5 series BM and the pedal on that gradually sinks to 'the bottom' too when running so assume this is all normal?

 

[tom2207]

yes , expect a bit of sink , but it should stop long before you hit the floor... I had bother with this on a disco and I mean a lot of bother ,,,, long story short ,,, in the end a master cylinder and servo swap out of a similar car sorted it , but it was also binding up brakes and messing up a few other things ,,, it led me some merry dance.

 

[reb78]

Thanks Tom. It doesn't reach the floor but definitely seems to reach a stop point (presume in the master cylinder?) where it won't go any further down.

 

[tom2207]

Thanks Tom. It doesn't reach the floor but definitely seems to reach a stop point (presume in the master cylinder?) where it won't go any further down.

as long as its not going further , and theres no heating or binding on the discs ,,, never worry ... Ive seen it on lots of them and they have no issues, its odd if your not expecting it or if your actually looking for it.

 

[Ubique]

As above, it's 'usual' but doesn't feel normal.... If you're worried or want some reassurance, take it to whoever does your MoT and get them to put it in the brake rollers (without the engine running but with the brake booster at full vacuum - and in neutral), no need to check the park brake, just service brakes.
Doing the test with engine & ignition off will stop the transfer box trying to throw you out of the rollers....

 

[reb78]

Thanks both. I'd never normally look for that type of behaviour but because I was trying harder to pressurise the system to check my joins I sat there with more pressure on the pedal than I'd normally use/maintain I think. It's braking fine.

I think there was a recall on this for the brake servo lines but I've checked before and it's had that done.

 

[Ubique]

The brake servo pipe recall was to cure oil in the servo, which would give you a hard pedal, you can easily tell if it's been done as there will be two vacuum lines connected to the vacuum pump rather than one.

 

[reb78]

The brake servo pipe recall was to cure oil in the servo, which would give you a hard pedal, you can easily tell if it's been done as there will be two vacuum lines connected to the vacuum pump rather than one.

Yep. There's two. I thought that was the case. I think I was just looking for brake faults!

 

[doubleboost]

Normal as long as no leak is present .
This is common on most diesels.

 

[BrokenBiker]

Same on my Freelander of similar age, didn't notice it before I changed a caliper then when bleeding thought I was going nuts