Brake pedal pushes back !!!

[swiftcruiser]

Where do we go to from here !!
Now sorting brakes, replaced seals and pistons in front calipers, replaced various brake pipes fitted new Brake master cylinder,checked out rear calipers,set handbrake and all we think is as should be; even sent the Girling Mk2A servo away to be overhauled and now refitted.
The problem is; we have now bled and bled and still push the pedal after leaving for a few moments, drops nearly to floor, pump up and goodish pedal . However with engine running do the same pedal drops pump up goodish pedal but now pedal starts to push back !!! and pedal comes up !!! Has anyone experienced the same, could we have fitted the pipes the wrong way round on the servo, did make up new pipes whilst servo away being overhauled, but did check on an illustration we had so fairly certain on correctly.
Any feedback will be appreciated
Thank you

[oldelanman]

According to the Workshop Manual ... who reads that thing anyway ? .... pedal push back is caused by either incorrect connection of hydraulic input and output pipes or major fault within the servo. Sounds like you may have the connections reversed on the servo. Inlet from the master cylinder should go to the connection nearest the booster can, the other end is the outlet to the brakes. If that doesn't fix your problem the Manual also has a full page section on testing the servo unit itself which may help.

[bill griffiths]

I have discovered, with completely new components, the same 'push back" of the pedal.
I believe all connections are correct and while contemplating dismantling the booster I have been troubled about not knowing what to look for when it is apart!
More recently I have noticed that when the engine is not decelerating the push back is not present.
So I wonder if there is some component within the booster designed to limit the amount of vacuum, and by not doing so provides to the booster excessive enthusiasm!
Any thoughts appreciated.
Regards,
Bill

[Hawksfield]

Bill
The control piston is a source of push back problems also it cam lock the brakes on embarrassingly
Check that it is not sticking it can be checked via the air valve chamber
Good luck

[bill griffiths]

Thanks, John.
Ive been reading that some of the seals for Mk 11B Girling boosters are not available because the relevant part was sold only as a complete unit!
So looking now for an available replacement.
However would you please add some words of wisdom as to the method of checking or attacking via the air valve chamber.
So far having no luck in locating in the exploded diagram the air valve chamber.
I have however identified the Control Piston!
Hopefully it is not the control piston for which there is no seal!
Regards,
Bill

[Hawksfield]

Bill
You can get seals but sometimes quality of size is an issue. Try ebay.
Today will put together some images for you

[bill griffiths]

I spent a good deal of time searching the world for a replacement for my Girling Mk 11B booster.
Then I discovered a company just up the road (in Australia that means less than 500 miles) who can provide a new or rebuild PBR 44 which will suit.
I have ordered one and will report back.
Regards
Bill

[2cams70]

There's supposed to be a one way check valve in the vacuum line to the booster. Did you confirm that it's fitted and functional?

[bill griffiths]

Thanks - there is a one way valve at the manifold and the original plastic variety at the booster.
I have tried several combinations of these, all to no avail.
Yesterday the car lost power...quickly diagnosed as the brakes coming on by themselves. Nothing too dramatic, but I suspect booster related!
Now I wait for the replacement even more eagerly!
Regards,
Bill

[bill griffiths]

I decided to replace the Girling with a PBR vh44e from an Australian company called Hydroboost.
From enquiries they have a good reputation and know what they are about although I had previously not heard of them.
They provided the above replacement in a timely fashion and it works in a progressive and satisfying manner.
I say that having previously had a Plus 2 for 39 years.
Fitting was easy; I shall attach a photo.
What is not easy to see is the brace from the stud on the inboard face of the unit running back and down to the engine bay. Each can just be made out.
Regards,
Bill