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Brake issues- soft pedal

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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 5:26 pm

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
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Brake issues- soft pedal

Post by enuff_zed » 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?
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Brake issues- soft pedal

Post by j3nks79 » 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.
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 6:08 pm

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?
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 6:08 pm

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
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Brake issues- soft pedal

Post by enuff_zed » Wed May 15, 2024 6:14 pm

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.
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 6:22 pm

Cheers Martin
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Brake issues- soft pedal

Post by Zedebee » Wed May 15, 2024 7:38 pm

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.
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Brake issues- soft pedal

Post by Zedebee » Wed May 15, 2024 7:40 pm

In fact I didn’t run the ABS, just did the manual bleed cycle twice.
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 7:42 pm

Thanks Ben

I’ll give it a good pump (fnarr fnarr)
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Brake issues- soft pedal

Post by enuff_zed » Wed May 15, 2024 7:56 pm

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.
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Brake issues- soft pedal

Post by enuff_zed » 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:
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 8:22 pm

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
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Brake issues- soft pedal

Post by john-e89 » Wed May 15, 2024 9:15 pm

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.
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Brake issues- soft pedal

Post by bigwinn » Wed May 15, 2024 9:19 pm

Bearing in mind one calliper and all lines are new too

Cheers John
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