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Brake issues- soft pedal ***updated with video***

Posted: Wed May 15, 2024 5:26 pm
by bigwinn
Hi all

So a new issue with the project to sort

The brake pedal is very soft. Will go to the floor with minimal resistance. However with a few pumps it tightens up to how you’d expect.

New fluid and full bleed including ABS bleed
New hoses
No leaks
New master cylinder

Any thoughts what to check next?

I would say vacuum leak but I took the master cylinder off today after the car sitting overnight and there was a good amount of residual pressure in the system.

Thanks in advance chaps

Stuart

Brake issues- soft pedal

Posted: Wed May 15, 2024 5:31 pm
by enuff_zed
Well now you mention residual pressure I am leaning back towards an air lock.

Forgive me for the daft question but have you definitely got the pipes on the abs unit in the right order. I know there are two different sizes so can't really go that wrong.

Do you have any ABS/DSC codes?

Brake issues- soft pedal

Posted: Wed May 15, 2024 6:04 pm
by j3nks79
If it’s not leaking and you have check the vacuum. Then it must have air in the system.

Brake issues- soft pedal

Posted: Wed May 15, 2024 6:08 pm
by bigwinn
enuff_zed wrote: Wed May 15, 2024 5:31 pm Well now you mention residual pressure I am leaning back towards an air lock.

Forgive me for the daft question but have you definitely got the pipes on the abs unit in the right order. I know there are two different sizes so can't really go that wrong.

Do you have any ABS/DSC codes?
No codes

And yes I did originally get the pipes the wrong way around

But at least I’m fessing up to that

So a damn good bleed needed we think?

Brake issues- soft pedal

Posted: Wed May 15, 2024 6:08 pm
by bigwinn
j3nks79 wrote: Wed May 15, 2024 6:04 pm If it’s not leaking and you have check the vacuum. Then it must have air in the system.
Roger that

Brake issues- soft pedal

Posted: Wed May 15, 2024 6:14 pm
by enuff_zed
bigwinn, to confirm, when I did mine I started rear right, then clockwise round the car to the front right last. That was a conventional bleed, with the pressure bleeder, but not activating the ABS.
Then did the ABS part repeating the four corners in the same order.
For each corner I ran the abs pump twice.

If it helps, I counted ten pulses of the pump in eight seconds every time.

Brake issues- soft pedal

Posted: Wed May 15, 2024 6:22 pm
by bigwinn
Cheers Martin

Brake issues- soft pedal

Posted: Wed May 15, 2024 7:38 pm
by Zedebee
I had a similar problem with OBY after changing the brake pressure sensors. Not much fluid came out, but I must have let some air in nevertheless. I followed Martin’s bleeding guide, but with an extra hand topping up the reservoir, rather than a pump. It worked a treat.

Brake issues- soft pedal

Posted: Wed May 15, 2024 7:40 pm
by Zedebee
In fact I didn’t run the ABS, just did the manual bleed cycle twice.

Brake issues- soft pedal

Posted: Wed May 15, 2024 7:42 pm
by bigwinn
Thanks Ben

I’ll give it a good pump (fnarr fnarr)

Brake issues- soft pedal

Posted: Wed May 15, 2024 7:56 pm
by enuff_zed
Zedebee wrote: Wed May 15, 2024 7:40 pm In fact I didn’t run the ABS, just did the manual bleed cycle twice.
If you don't disturb the ABS unit you can just do a normal bleed.

Brake issues- soft pedal

Posted: Wed May 15, 2024 7:57 pm
by enuff_zed
Stuart, if it turns out to be air I shall tell everyone you are 'bleeding' useless. :poke: :rofl:

Brake issues- soft pedal

Posted: Wed May 15, 2024 8:22 pm
by bigwinn
enuff_zed wrote: Wed May 15, 2024 7:57 pm Stuart, if it turns out to be air I shall tell everyone you are 'bleeding' useless. :poke: :rofl:
I’ve been called a lot worse

Brake issues- soft pedal

Posted: Wed May 15, 2024 9:15 pm
by john-e89
It’s possible to get air stuck in the calipers, even a thorough bleed doesn’t always shift it. Bleed while clouting the calipers with a rubber hammer has been known to shift an air lock.

Brake issues- soft pedal

Posted: Wed May 15, 2024 9:19 pm
by bigwinn
Bearing in mind one calliper and all lines are new too

Cheers John