Disco 2 Brake Pedal drops to floor at idle

Jamiegreen · Nov 10, 2018

Heeey, so quick question, if anyone wants to jump in their d2 and hold the brake pedal hard with the engine idling... does it slowly creep until it hits the floor? Cause mine does, Its stiff as can be without the engine on, but when fired up it will hit the floor, one pump and it will go back up, but again gradually go back down.
It does brake fine, but feels somewhat late to respond, like theres a little spongy bit and then it will "lock" the wheels fine, I don't like the fact theres not much sharpness to the braking though. All new calipers/pads/discs/flexi's/lines. But I ran the system dry for a good couple weeks and pressed the brake a good few times on accident. Thinking Ive fooked the seals in the brake master cylinder?
Oh and, first maybe 2 brakes in the morning are real sharp.. then back to not that great.

neilly · Nov 10, 2018

Jamiegreen said:
. does it slowly creep until it hits the floor?

Not that I am aware of...reckon I would have noticed that and soiled myself if it did.

Cheers

dieseldog69 · Nov 10, 2018

Jamiegreen said:
Heeey, so quick question, if anyone wants to jump in their d2 and hold the brake pedal hard with the engine idling... does it slowly creep until it hits the floor? Cause mine does, Its stiff as can be without the engine on, but when fired up it will hit the floor, one pump and it will go back up, but again gradually go back down.
It does brake fine, but feels somewhat late to respond, like theres a little spongy bit and then it will "lock" the wheels fine, I don't like the fact theres not much sharpness to the braking though. All new calipers/pads/discs/flexi's/lines. But I ran the system dry for a good couple weeks and pressed the brake a good few times on accident. Thinking Ive fooked the seals in the brake master cylinder?
Oh and, first maybe 2 brakes in the morning are real sharp.. then back to not that great.

Fit a new master cylinder ASAP.

You will get a drop in the pedal as the servo boost kicks in but dropping to the floor is very bad.

Jamiegreen · Nov 10, 2018

dieseldog69 said:
Fit a new master cylinder ASAP.

You will get a drop in the pedal as the servo boost kicks in but dropping to the floor is very bad.

I don't want to exaggerate things too much, it takes a good force and 5 secs or so for it to sink all the way.
And braking is still acceptable, atleast better than others Ive driven! Can lock the wheels easy enough etc.
But er.. yeah probably shouldn't make excuses.. was thinking of getting a complete brake booster and cylinder from a scrap d2.
Those new cylinders sure ain't cheap..

dieseldog69 · Nov 10, 2018

Jamiegreen said:
I don't want to exaggerate things too much, it takes a good force and 5 secs or so for it to sink all the way.

Those new cylinders sure ain't cheap..

I don't want to sound alarmist, but it shouldn't do that, not ever, if it does then the MC has sealing issues and all I can say is you obviously feel that your life and the lives of your passengers are very cheap if you begrudge replacing a brake master cylinder that is obviously faulty.

God forbid someone dies cause you're a cheap bastid.

Jamiegreen · Nov 10, 2018

dieseldog69 said:
I don't want to sound alarmist, but it shouldn't do that, not ever, if it does then the MC has sealing issues and all I can say is you obviously feel that your life and the lives of your passengers are very cheap if you begrudge replacing a brake master cylinder that is obviously faulty.

God forbid someone dies cause you're a cheap bastid.

I assure you I ain't questioning changing the thing knowing it's not normal, not exactly being able to afford a new one right now is why I mentioned using a spare one, which I can't imagine being a problem? Obviously if the problem persists after that then I'll have to get a new one.

dieseldog69 · Nov 10, 2018

Jamiegreen said:
I assure you I ain't questioning changing the thing knowing it's not normal, not exactly being able to afford a new one right now is why I mentioned using a spare one, which I can't imagine being a problem? Obviously if the problem persists after that then I'll have to get a new one.

Second hand isn't usually a problem unless it exhibits symptoms of failure on fitting but as far as MCs go I always fit new out of preference.

Although I will add that most reputable breakers I've been in trash MCs as they don't want any liability from a failure, not sure if it's changed in the world of eBay etc.

brian47 · Nov 10, 2018

Immaterial of whether there's a servo or no servo, once the brake pedal is pressed to the point of the brakes being fully applied, the pedal should not continue moving down any further. If it does then that suggests that fluid is being forced passsed one or more cylinder seals. If it happens at a wheel then that's usually fairly obvious to detect. The place where it's not so easy to spot is the Master cylinder.
Another problem which can arise from fluid passing the seal is that if fluid can go one way, air can be sucked into the system in the opposite direction.

Like @dieseldog69, I would prefer to bite the bullet and fit new for brake parts.

sierrafery · Nov 11, 2018

brian47 said:
Immaterial of whether there's a servo or no servo, once the brake pedal is pressed to the point of the brakes being fully applied, the pedal should not continue moving down any further.

+1, if there's no leak and the system is air free you have to replace the master cylinder

Jamiegreen · Nov 11, 2018

I'll try and source a new one asap.. Just curious, I've seen quite a few brand new ones on Ebay for around the £100 mark, I'm guessing they aren't OEM but seem to have sold a lot of them. Would you steer clear of these or reckon they'd be alright?
>Here

Disco 2 Brake Pedal drops to floor at idle

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