639 Vito with sinking pedal

[Kev555]

I have a 2011 vito 113, it was sitting about the yard doing nothing so I decided to mot and sell it. Brakes were perfect before I put it in the garage, I freed up the brakes and other work to make it ready and when I pulled it out I had a sinking pedal. It's hard when the engine is off so I thought master cylinder
Replaced it with a new one and bled all the brakes, I even done an abs bleed with a diagnostic tool. If I clamp the two front brake flexi,s at the caliper side I have a good pedal? The front caliper slides are all moving freely, I am stumped, never had this happen before, everything points to the front calipers being the culprits and they aren't leaking. Anyone ever had this issue?

 

[M80]

I've suffered similar, using a bleed tool at 2 1/2 bar cured it.
But for me getting a good flow of fluid at the rear was a problem. The fronts would bleed ok.

 

[Kev555]

I forgot to add I used a pressure bleeder at 20 psi M80 as I had no help. I don't get it at all, even put new pads in as old ones were caked a bit in rust on the piston side and I though the caliper piston was flexing a bit. Ruled out the flexi pipes bulging by clamping them were they join the caliper.

 

[Kev555]

Going to try manual bleeding as a last resort on Monday to see if it can push any air out M80.

 

[M80]

Going to try manual bleeding as a last resort on Monday to see if it can push any air out M80.

Good luck.
Personally I wouldn't expect a change.
It was the pressure that did it for me, you have used 1 1/2 bar if I understand.

But I'm not sure the symptoms are the same.

 

[curious]

My tortuous route after bleeding, replacing master cylinder, bleeding and bleeding again, turned out being expanded corrosion on the hangers that was squeezing the stainless abutment clips very slightly that was impeding the pad movement.
Scraping, filing, shot blasting, etc, etc, and then after reassembling, all good.

 

[Kev555]

I put a new set of pads in today Curious and they are nice and free as regards movement. The stainless clips are clean and fresh so I can't put it down to that unfortunately. It just seems like air in the calipers but I never opened any brake lines when I initially made sure the brakes were free at the start, I just pushed all the pistons on the calipers in a bit to make sure they hadn't seized.

 

[Kev555]

Good luck.
Personally I wouldn't expect a change.
It was the pressure that did it for me, you have used 1 1/2 bar if I understand.

But I'm not sure the symptoms are the same.

I had it at 20 psi which I think your right is 1.5 bar. It actually blew the small plastic pipe at the back of the fluid reservoir off at 20 psi at one point so I didn't want to go any higher with the pressure.

 

[Kev555]

Ended up replacing callipers as I couldn't see anything else wrong with it. Still had the same sinking pedal
I ruled out everything except the ABS module. It had to be the culprit. I took it around the local loop road a few times and the pedal started to feel better after a bit of heavy braking attempts.
I know its not up to MOT pass quality yet but I will take it a few more runs to see if it improves anymore. I guess it sitting about has possibly seized it up a bit or perished seals or solenoids in the module?

 

[mattkh]

Just occurred to me.
Did you replace the whole of the brake fluid or not.

 

[Kev555]

Bled it that many times I know there's none of the old stuff left lol

 

[curious]

I haven't tried, but is it possible to test/diagnose the ABS unit with Xentry?

 

[Kev555]

I have think diag which is very good as I can activate the abs unit to make sure there's no trapped air in it. As regards live values and testing any components, I don't think I can achieve anything else with it.