Girling MK2a vacuum servos?

I thought I would post this in "others" since quite a few cars use(d) these brake boosters. I think MGC,Alpine/tigers some rovers and Lotus models and possibly AH/AM too (as well as the Volvo I am working on).
Does anyone have any experience with owning - maintaining - and rebuilding these? Any thoughts on parts sources also appreciated.


TIA
Dave G.

Hello Dave,

I rebuilt a pair of those many years ago (Aston Martin DB5 has two of these) and then I had terrible troubles with the brakes sticking on.
After many tries I rang Girling and spoke to an engineer. The problem he said was that the vacuum piston seal in the rebuild kits is the wrong material and causes the piston to stick. He suggested I use the old seals and this cured the problem. Other than that it was an easy rebuild job.

As I am in the U.K. I don't suppose the supplier is of any use to you unless you have difficulty finding someone over there?

Alec

Moss sells a special coating to recondition the inside of the big piston. I've never used it, but it's supposed to cure the sticking problem. I've done one on an AH 3000. Had problems with sticking afterwards. I would send it out in the future.
they're basic units. there's not much to them, but they seem to be trickey.

Thanks for the replies. I was beginning to think that no one else was having any problems with these things. I have managed to get three of these units (one off the car, 2 from e-bay) and have taken them apart. One was apparently rebuilt and then shelved, large piston stuck! Heh, this unit also had some bad dents in the vacuum pot, wonder why.
Currently I am trying to source a 5.5" PTFE or vitron wiper seal to replace the leather on the large piston. I have also replaced the seals in the 'hi pressure' bore (.75") with industrial vitron seals and made an additional new wiper seal that replaces the plastic spacer that is next to the vacuum pot in this bore(attachemnt). I think that this is a problematic area and a primary source of the fluid leakage that plagues these things.
BTW - The seals in the control bore (.625/.437" ) appear to be the same as the seals in the big healey clutch master cylinder!
I have found a Swedish source for these - https://www.cvi-automotive.se/resdela/5_bromsar/1_p1800brakes.htm
That should work on any of the 5/8" Girling units with the 5.5" piston.

Cheers!
Dave G.

Here are the results of my MK2a servo experiment (attached). The dual MC is an ATE unit off a Volvo 164 the Girling servo has the best parts of several that I had gathered. As I outlined earlier the internals have changed a bit and I machined a new seal for the vacuum piston out of PTFE (I did source a vitron that would have worked but I wanted the NON-STICK option after hearing the horror stories) PTFE is also very inert so it won't be bothered by brake fluid, or anything else...much.
Ultimate stopping power is not really improved, but brake effort and feel are, very much so. IIRC there was always a little hesitation between the application of peddle and braking results with the old servo, that is gone now.
Note the small green UNI filter on the servo air intake, I am sure that's what the improvement is due to!
Cheers!
Dave G.
P.S. Disclaimer - Do Not try this at home! - your milage may vary - contents may settle due to shipping - If you try this on a girling servo, you do so at your own risk!

hmmmmm - & I have a pair in one of my MGC's that need rebuilding....

Early MGC kits can be sourced thru a company called NOS Locators (or that may be late...they can tell you). They are in RI IIRC. If the bores are not pitted and the leather not shot, then that is the easy way to go. I did mine the way I did because I had some PTFE, and did some seal design work on waterjets in the mid 80's, plus I am old and retired (mostly). They (the waterjets) work with pressures that are suprising, to say the least!
Attached is the flip side of the installation.

Cheers!
Dave G.

Hi Dave,
I’m not an expert so this is a question, not a statement. In the photo, it looks like the vacuum line from the manifold to the booster T’s off to the crankcase. Would that T rob the booster of vacuum, making it less effective? My Healey has the crankcase and valve cover venting to the air cleaner.

If you look at the photo you will see that there is a hose to the air cleaner from the filler cap on the valve cover. Also in the 'T' connection you will see a PCV type valve at the bottom of the T. As I understand it, in this vintage Volvo the line to vacuum is only active if there is enough crankcase pressure to activate the valve in the T and let manifold vacuum normalize the pressure. On an engine in good shape, I doubt this would happen very often. A year or two later Volvo went to another system and the hose to the air cleaner became an 'intake' for a valved draw to manifold vacuum.
I am thinking about adding a reservoir to this system but I am going to wait and see if it really needs it.

Cheers!
Dave G.

Ahhh, PCV.

I thought the booster had to physically/mechanically interact with the master cylinder... Thats the first one I've ever seen seperated from it. Interesting!

KP wrote:
"I thought the booster had to physically/mechanically interact with the master cylinder."
It does - but it is physically/hydraulicaly interacting - in my set up, the front half of the MC supplies pressure to a 'control cylinder' that valves the supply of vacuum/ambient air pressure to the front end of the vacuum pot thru the line seen on the 'flip side' photo in my post above. this moves the pneumatic piston rod into the hi-pressure bore where it shuts off the lower pressure side and pushes the plunger at a 2:1 ratio for the power part of power brakes. This, in turn, acts on the small end of the control bore (also at 2:1) to modulate brake pressure by pushing back the control piston regulating the supply of vacuum/ambient air pressure to the vacuum pot, a typical analog control loop.
There was a photo of a 69 duetto alfa somewhere here that uses the very same concept only it has ATE components and had two of these 'remote' boosters valved for the right front/rear brake balance, much like the 007-ish AMs, IIRC there were some cars (lambos?) that varied the balance by sensing suspension position (nosedive) to regulate the two boosters!
These units are beginning to remind me of the way SU carbs used to be viewed, impossible to keep in tune! Heh, if you can't keep SUs in tune, best to leave Webbers alone! The more I research the Girling servos the better I think they are, just a little "hidebound" in their choice of seals.

Cheers!
Dave G.

Kenny - on the MGC, one is separated from the booster - on the other side of the engine bay.

Interesting... Like I said though, I guess I either never saw one like that before, or didn't pay attention to it if I did. All my cars have the booster between the firewall and the M/C. And I've owned one old enough to not have a booster at all (46 willys).

Boosters ???? Real men don't drive cars with boosters !!!

/ubbthreads/images/graemlins/devilgrin.gif

Er, should'nt that be - Boosters? We ain't got no boosters. We don't need no boosters. I don't have to show you any stinking boosters!?

Cheers!
Dave G.

I've got two sets of the bloody things out corroding inna shed... Lotus used 'em in pairs on the +2 and the Cortina... I suffer the need for added pedal effort so's to leave them onna shelf. Silly things.

Yeah! they suck all right(literally-brake fluid-right out)! Why don't you stick em in a box and send em to me? I can always use a few more to dissect, and when I'm done, I'll see they get a good Christian burial (kindly specify C of E or Papist...shoot, I'll even plant the consarned things out in the Sierra Madres next time ah'm out thataway - iffin ya want).

Cheers!
Dave G.

Thanks, but they're buried sooo deep inna shed it ain't worth the effort to mount an expedition to hunt the 'orribol things down. They'll die a rather ignimonious death, certes. Anonymous grave, so to speak. /ubbthreads/images/graemlins/jester.gif

Well, the '79 I bought y'day need the booster rebuilt - Joe a kit in the trunk so all I've gotta do is work up the steam to disassemble the sucker...good brakes as it is but I can tell a difference in vacuum when I pinch off the hose to the booster.