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

B

bigwinn

Lifer
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
 
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?
 
enuff_zed said:
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?
Click to expand...

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?
 
[ref]bigwinn[/ref], 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.
 
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.
 
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.
 
New caliper, i’d suggest that’s where the air is then bigwinn, if you do rubber mallet it the air is usually at the top of the caliper in the ‘corners’ so to speak. Hope you get it shifted.
 
john-e89 said:
New caliper, i’d suggest that’s where the air is then bigwinn, if you do rubber mallet it the air is usually at the top of the caliper in the ‘corners’ so to speak. Hope you get it shifted.
Click to expand...
Just a thought. You could hang the calliper with the pads out and use a wind back tool to push the piston back in. That may help shift the air?
 
enuff_zed said:
john-e89 said:
New caliper, i’d suggest that’s where the air is then bigwinn, if you do rubber mallet it the air is usually at the top of the caliper in the ‘corners’ so to speak. Hope you get it shifted.
Click to expand...
Just a thought. You could hang the calliper with the pads out and use a wind back tool to push the piston back in. That may help shift the air?
Click to expand...

Absolutely enuff, just have to watch the fluid doesn’t get pushed out of the filler reservoir, plus you’d need to remove the caliper again as you know, not a huge job obvs. Worth the mallet first imho purely as it’s the easiest way, as I’ve done it myself and had others do it with success, but your suggestion is spot on.
 
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