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Remote vacume servo unit GT6 mk 3


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Hi, I would like some advice on fitting a replacement remote servo unit. I have bought and fitted a powertune aftermarket unit and it has made no difference at all to the feel of the pedal. The instructions say it must be connected via a vacuum hose to a suitable vacuum source e.g. the engine induction manifold or vacuum pump. It says on some vehicles the manifold is already tapped and fitted with a removable plug, otherwise it will be necessary to drill and tap the manifold.

   I would need to order the relevant adaptor, pipe and in line non-return valve, the adaptors come in three different sizes 1/8 BSP, taper. 5/8X16 Whitworth, and 5/8 UNF thread.

   Where would the connection go and what size adaptor will I need. I would presume the inlet manifold is what the carbs are attached to, this is referenced as Stanpart 311749 although it looks to me that the front of the manifold has a tube connected to the bottom of the water pump and the back of the manifold is connected to what I think is the heater unit and off the bottom of that is another tube returning under the exhaust manifold to the water pump.

    Is the manifold a duel unit, having water running through the top of it and the underneath section the inlet, separated in the casting. If this is the case where would be the best place to drill and tap it. Any help would be appreciated, photos or advice on other peoples experience with these, as you may gather I am not a mechanic and this is my first project.

    Thanks Ken

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there should be a blank plug,or its oready been used by engine breather

it wa fitted to a llate mod GT i had,

totally useless, binned it v v soon

brakes ed nee feel, pedal was spongey,

and it took alot of room up on bulkhead,

just where me Cuppa  now sits wen workin on engine


The cars fitted wid a servo, had bigger MCs t,try an get pedal movement lower

it did,nt wuk v well,

So, if ye got the smaller MC   5/8th  as opposed t,the 3/4 MC, then yer pedals gonna move even further.

esp if yer on bigger rear cyls too. as 5/8th had smaller rear cyls too,if i can recall


Note, all servos will mek pedal spongey, lots of travel,

just like all moderns pedals move a country mile


Can meb,e try a 2 PSI  RPV on frunt  brakes, and a  10 PSI ont rears

as it,ll help wid pedal travel

most,if not all moderns ev em already fitted into their MCs noo




not wot yer wantin to hear, but, me self, Bin it.



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Here is a picture of the GT6 inlet manifold from the Canley Classics web site.




This manifold has the vacuum connector part 149487 and was fitted from when the Servo became standard on the GT6 in February 1973.


You have to follow the fitting instructions carefully for the servo to work correctly, for instance the servo slave cylinder at the correct angle, the U trap in the vacuum line. Most servos have an internal one-way valve but I don't know your one. My own replacement servo had a poorly fitted one-way valve so I added an external valve, nice chrome job from a Jaguar!

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Nope, no a MOT fail, 





  1. I want to fail a particular item on a modified vehicle. Is there any allowance for this?

Where a vehicle has been extensively modified or converted, Reasons for Rejection for components missing where fitted as standard should not be applied. For example:

  a car converted for rally use (i.e. rear seats removed and fitted with a roll cage and full harness seat belts  etc.) may have been converted so as not to require a brake servo or power steering

   a car converted to a stretch limousine may no longer be fitted with curtain airbags


AND, it only applies to AT time of test for other things too.


Butt, yes yer correct, they totally useless brakes, or moer to the point,

pedal feel an feed back



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You are talking about an "Extensively modified vehicle" On a standard car, like mine is and I suspect Ken's, If the servo was  fitted as standard and you've taken it off, that's an MOT fail.


I've had this discussion before and some say how would the MOT man know you've removed it? Well, mine spotted that I'd changed my knackered old Girling servo for a new Lockheed type. So they know.


He also told me that the servo doesn't actually have to work, it just has to be there! I didn't quite believe it so checked it out and section 3.6 says, check servo for presence, condition of vacuum pipe and leaks. Fail if servo absent, pipes deteriorated, leaks. But, no mention of it actually having to work!


My pedal feel and feedback are fine, I suspect you had the original Girling which aren't very good even when new.

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