The Girling servo, now part of Lockheed-Girling, is unlike almost all
other vacuum boosters in a number of ways.
1) It is remote, and not part of the master cylinder assembly. This is
not a "fatal" difference, as it gives greater flexibility for location,
but also requires an additional connection tube. Ford used a similar
Bendix system, that was fairly good, on an old mid-50's T-Bird. These
mount differently, but have been adapted to Tigers, and some are still
available. There is also a Lockheed design that has all cast iron
cylinders and has been used successfully, although it does not have the
boost ratio of the Girling (which varies between Alpine and Tiger versions).
2) This system operates with a large, full diameter, steel plate in the
large housing. It is sealed against the inner cylinder wall with a
synthetic flexible seal. With vacuum on one side, and a long rod
connecting the plate to the hydraulic servo pistons, movement of the
plate moves the rod and energizes the cylinders attached. Diameter
differences multiply pressure levels in the next section, ending up with
greater pressure in the brake line.
Pictures of this are located on TigersUnited.com in both the Workshop
Manual http://www.tigersunited.com/resources/wsm/wsmk21.asp
(the illustration isn't coming up, so I'll have to look into it.) I
have attached one to Tony's copy, but it will not show on the list.
and the parts list http://www.tigersunited.com/resources/wsm/wsm1.asp
(Brakes and Controls) with part numbers, but no illustration. Sorry,
that is the way Rootes did it.
3) The main reason for failure, and these seem to occur frequently do
either to poor design, or simply old age. The major issue is actually
very minor. The rubber "donut" seal around the shaft wears too quickly,
and allows internal pressurized brake fluid into the canister. From
there it quickly gets by the large piston disc seal and into the intake
manifold vacuum tap. From there - out the exhaust.
Many have had their hydraulic cylinders in the servo body sleeved with
brass of stainless. This is not cheap, and not needed unless the bores
are bad. Brass has been used a long time. Although stainless sounds
more modern, the thermal coefficient of expansion of brass is closer to
the aluminum than the steel sleeve. When things heat up, the brass
stays more firmly in contact with the bores. Can't say if this has ever
been a problem, but users of brass are convinced of it's superiority.
My own opinion is to leave the walls alone, unless scored or worn. They
are multi-diameter stepped cylinders in two rows. Most shops can't do
all the co-axial cylinders, anyway.
There IS a "trick" solution to this design, and it involves adding a
washer in the final rod seal compartment before pressing in the new
seal. This causes greater compression, and squeezes the excess material
into the worn areas that would otherwise leak earlier. It is not an
amateur fix, and should be done by someone who has successfully found
the correct material and size of this "shim", and knows how to install
it on reassemble. Those that do this professionally probably will not
reveal their secret of successful reputation, though many know of the
principle.
<http://www.tigersunited.com/resources/wsm/wsm1.asp>
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Steve Laifman
Editor
http://www.TigersUnited.com
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