RS2 - rock hard brake pedal after refurbishing PAS pump

[JonRS2]

Hello.

The PAS pump on my RS2 was weeping / leaking hydraulic fluid such that the red (!) came on when the hydraulic fluid level dropped below the minimum.

I drove the RS2 to a mechanic. He has removed and rebuilt the same PAS pump using new seals and a new X-plug. Apparently one other plug on the PAS pump was seized tight and could not be removed. The rebuilt PAS pump was then reattached and old green hydraulic fluid replaced with new green hydraulic fluid.

The front brake discs, pads and shims were replaced. The brake fluid was changed.

The RS2 is still with the mechanic. Apparently the power steering is fine and the PAS pump no longer leaks. The red (!) does not come on at all (it only came on before when the hydraulic fluid level was too low).

Unfortunately, however, the brake pedal (which was fine) is now rock hard. There is apparently no power to the braking system. The brakes have been bled at the front, then at the rear and with the handbrake off.

The mechanic is unsure what the problem is and will go through everything again. From what I have read, it seems to me like there is a blockage somewhere between the high pressure brake side of the PAS pump and the brake bomb (accumulator). Or air trapped somewhere.

It would be a bad coincidence if another part had failed (brake bomb or brake servo). There was no hint of a problem before the work described was carried out.

Has anyone here encountered a similar problem in similar circumstances?

Any ideas?

Many thanks.

[Rusty]

Try a secondhand, working pump to rule out the rebuild as the source of the issue.

[John.]

Try a secondhand, working pump to rule out the rebuild as the source of the issue.

Rusty, are you thinking there's pressure for the steering but not enough for the brake assistance ?

[Error404]

There is probably a problem with the rebuilt pump, has he forgotten to put the piston back in it behind the X plug?

[Rusty]

They're separate systems.

The fact that the pump had been rebuilt and that's the only difference says to me that it would be the first place to start. Rusty nut has had a few issues with rebuilt pumps... 2 have gone pretty wrong.

[John.]

There is probably a problem with the rebuilt pump, has he forgotten to put the piston back in it behind the X plug?

Yes, system should purge itself of any air...yes/no?

[Error404]

Yes it is self bleeding.

[UrS4boy]

Tandem PS/PB pump info

Rusty, are you thinking there's pressure for the steering but not enough for the brake assistance ?

The pump is a tandem pump. Vane pump for the power steering system and a piston pump for the power brake system. Your mechanic has F'd up the piston pump side somehow. Perhaps missing a piston or two.

Here is GrahamT's pump rebuild DIY in case you want to have a look at it:

http://12v.org/urs/GrahamTsPSPBPumpStripDownDIY.pdf

Some general 20VT PS/PB pump info: http://forums.quattroworld.com/s4s6/msgs/38240.phtml

[JonRS2]

Thank you all. I had provided a copy of Graham T's PAS pump rebuild DIY information with photographs before the PAS pump rebuild commenced so hopefully the DIY information was complete and followed correctly. I will post again when this has been resolved. In the meantime, if there are any other conceivable sources of the problem (other than the recent rebuilding of the front, high-pressure brake half of the tandem vane pump), please post the possibilities. Cheers.

[Mr G]

The brakes have been bled at the front, then at the rear and with the handbrake off.

Haven't experienced the same thing and I'm taking a chance with this comment - isn't there a specific procedure when bleeding the brakes - starting at the furthest point from the master cylinder and working your way to the closest (on my RHD RS2 - start RL, RR, FL then FR).

[VagOrBust]

Haven't experienced the same thing and I'm taking a chance with this comment - isn't there a specific procedure when bleeding the brakes - starting at the furthest point from the master cylinder and working your way to the closest (on my RHD RS2 - start RL, RR, FL then FR).

This is correct. Longest brake line to shortest brake line.
However since the problem is a rock hard pedal and not a spongy pedal I don't think air in the system is a factor.

[Rusty]

I would say ditch the hydraulics and go vacuum but jiving just done it, it's a bit of a pig on an ABY/ADU...

[Error404]

Vacuum conversion involves cutting metal out of a RHD car, so probably not desirable on an RS2

[JonRS2]

How does the hydraulic fluid system self bleed? Will it self bleed over time while the car is just sitting there, engine switched off? Does the engine need to be idling? Does the car need to be driven? Where does the air go to? To the accumulator / bomb? Thank you.

[Rusty]

The engine needs to be running so the pump circulates fluid in the citcuits and forces the air out. It's not uncommon for the PAS pump to make a little chattering noise when first turned on. The air makes it way to the reservoir, so the level will drop fractionally.