Wanted Dunlop P90 Brake booster

Description: Looking for the P90 brake booster as used on 4.2 mk10’s, except for very late models, and some early 420Gs. Condition not important as I am rebuilding from scratch.
If the original Dunlop MC is still attached then all the better.

Asking price (if selling):

Location: MA, USA

Willing to ship worldwide? Wiling to pay for shipping from overseas.

Thank you.

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I’m thinking @Jeff_Schroeder may have one.

Thanks Wiggs will check my stash today.

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Did you ever find one, I have one that I took out of my 1964 MKII 3.8 it ‘may’ be the same


In the end I did.
Always looking however.
I’m not sure the Mk2 was the same. The P90 was specific to the 4.2 mk10s.
I’ll check out the part numbers to be sure.


OK no sweat I know a lot of parts interchange, but of course the MKX is a monster.

The Mk2 appears to be a Lockheed unit. This was from checking part numbers.
Wiggles had suggested you may have one?

No: that may be @Jeff_Schroeder .

Yes, that’s who I meant.
Jeff, do you happen to have one?


I don’t believe I do / just MK2 units presently, but I’ll go “shopping” in the barn in the morning to verify.

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Read through this thread, Nick, it goes into great detail on substitutions.

AFAIK, the P90 is still effectively un-rebuildible due to parts being NLA. EDIT - obviously not the case, as you indicated that you rebuilt yours!

Hi Jeff,
What thread are you referring to?

Well so far I’ve managed to rebuild 2 units to the point where they are ready for testing.
The reaction plate and diaphragm assembly at the rear often splits due to age and the actuation valve seizes up.
There are limited parts available, and they are Midland Ross items as used on specific. early to mid 60’s Ford and Mopar cars.
The research continues…

To follow up, I do not have any P90’s. Sorry.

did you ever find out if the Dunlop P90 booster was possibly used in certain Aston Martins, and whether a kit was available via Martin Robey?

A possibility…

Thanks for looking.

I stand to be corrected as need be:

My research of the original Dunlop and Girling application catalogues suggest that the P90,
which is a dual diaphragm unit, was unique to the 4.2 mk10s and early 420Gs prior to stock being used up and then being supplemented by the Girling Supervac 100 unit.

This is backed up by different part numbers shown for the Astons and Jensens and Ferraris for that matter.
The Jensen, Aston and Ferrari 275 and possibly 330GT units were supposedly single diaphragm only.

In conversation with the guys at Contract Auto in the UK, they said, if I understand correctly, that the Astons and Jensen servos at least, had a steel plate in place instead of the second diaphragm, the reason maybe as a result of brake pedal position, MC cylinder bore diameter etc.

They were known apparently for being quite heavy as a result.

As for the Ferrarris, the servo was known as a C48 which was a 9-12 inch unit.
Not Sure what that means but:

Midland Ross in the USA also made a 9-1/2 inch unit which was used on certain American cars in the 60s and may have shared components with the Dunlop C48.

Back to the P90 unit.
It seems as if the, manifold valve rubber seal, the front bellows, the reaction levers and gasket assembly , the front diaphragm, the control valve assembly, the valve housing, the MC actuator rod, the rear cover adaptor and various seals and O-rings were also common to the Midland Ross servo used in 64 to 65 Chrysler Dodge Coronet, Plymouth Fury and the Ford Thunderbird and Fairlane from 63 to 65.
There maybe others, but that’s as far as I’ve got for now with research on this.
So far I have laid hands on the reaction finger gaskets and the rear adaptor as American parts and they are SPOT ON a dead match for the Dunlop items

Very specifically the rear diaphragm reaction plate assembly, at 10 inch OD, is unique to the Dunlop as far as I can tell due to the 4 point screw attachment to the sleeve connecting to the front diaphragm.

Also note that the manifold take off right angle port is NOT a check valve in this case as that is further down the line as a Tee-piece to the vacuum reservoir.

I spoke to PowerTrack and they suggested that the Ferrari units that are being remade at significant cost by an outfit in Germany may work but as noted above, they are apparently single diaphragm units.