105 Dual Booster Brakes

["Mark Battley" <m.battley@domain.elided>]

>Hi I have a 1974 2000cc 105 GTV, RHD ( I live in Australia).After about 45
>minutes driving in suburbia, the brakes tend to stick for a few seconds after
>releasing the pedal.  For example, approaching a set of lights, once stopped
>the
>brakes will stay on for about 3-5 seconds, then the car may roll forwards or
>backwards, depending on road incline.Different "experts" have
>suggested different things.  At this point the front pads are new, all the
>callipers have been checked for sticking, brake hoses are new, fluid has been
>completely replaced with dot4, boosters were reconditioned by previous owner
>in
>1999, car has travelled little since then.  There is no change to brake pedal
>feel and stopping performance, just this sticking tendency.Does anyone in the
>group have any suggestions and what parts would I require to rectify the
>problem
>in your opinion?

Yes... very cheap, very easy, but it took me a long, long time to find it on
mine.

I had the basically same symptoms (although when they stuck the pedal felt
harder??). It was only the rears. The booster was leaking so I rebuilt that
- no change, new fluid, new brake hose, check calipers etc... no change..

Solution in my case:
On the outside of the boosters (underneath) there is a small 90 degree
rubber hose that connects the the pipe from the airvalve system (screwed on
the underside of the booster, it is what releases the vacuum) to a short
pipe that comes out of the base of the "vacuum chamber" (the large diameter
round chamber) at the end of the booster. What was happening was that this
hose had softened with age, and was collapsing when vacuum was applied (i.e.
when you brake). Once it had collapsed it could not release the vacuum
properly when you lifted off the brake. Replacing this hose took minutes and
solved the problem. 

If you can't find a suitable generic hose locally Tony Stevens at Alfastop
in the UK can probably help:
 
http://www.alfastop.co.uk
tony@domain.elided
ALFA STOP, POBox 50, Belper DE56 1AS, UK
Tel: +44 (0)177 382 2000
Fax: +44 (0)177 382 1900

In the short term stuffing a smaller diameter hose inside the main one
worked for me until I got the correct part.

I suspect that is also possible for a sticking valve/piston within the
airvalve system to cause similar symptoms, so if the hose is not the problem
I would consider checking the boosters again - there are different levels of
"reconditioning" for these boosters. If only the main piston seals were
replaced the airvalve system may be sticking.

Another possible cause is not enough free play in the brake pedal linkage,
preventing the master cylinder from retracting fully. That is easy to
adjust.

Presumably master cylinder faults could also cause similar behaviour.

As an aside, I have found "speedbleeders" (bleed nipples with one way valve
to be excellent), and it also seems to help to bleed the brakes a second
time with the engine running, so that the boosters work as you bleed the
system.

Mark Battley
Auckland, New Zealand.

1973 Alfa Romeo 2000 GT Veloce

Which recently lost most of its brake boost, following a steep downhill,
seemed to "swallow" a gulp of brake fluid presumably from a leaking booster,
and hasn't felt the same since. The brakes work, but are much heavier, yet
it still seems to be holding vacuum. Haven't had a chance to pull the
boosters out and see what is going on yet. Any ideas?

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