Very late to this thread.
I’m currently attempting to rebuild a P90 and searching for the rear larger reaction plate diaphragm assembly with a good rubber.
Supposedly it’s also a Midland Ross item or at least they made a version of it.
I’m not so sure. Does anyone know more about this?
Also, (Marek maybe you’re the one to answer this one), it appears that the valve body can’t be dismantled, as there are four tangs which hold the inner flute against the outer body and was presumably pressed in by the factory against spring pressure up to the larger receiving boss. Is that right?
I was able to free mine up by rotating gently back and forth and once done there is approx 1’8" 3mm of free movement which seems to be enough to allow the vacuum to exhaust from the rear chamber during brake application.
I recently read something I thought would useful to MKX owners with the rare Dunlop P90 booster, and that is that it is also fitted to some other vehicles, and that as I recall, one was some Aston Martins, and that I think it was Martin Robey supplied parts
Its possible I have some confusion, but the clues are there to be investigated
As far as I know P90 was only fitted to 64-67 MKX and that the parts became NLA, which seems to have led to many MKX being upgraded to the later Girling system
Unless one is really a stickler for originality, I don’t know why anyone would want to mess with the P90 rebuild. The series 1 XJ6 master and booster is a direct bolt up in the 4.2 MK10 except for drilling a 1" access hole on the left side of the pedal box. The xj6 booster pin is retained and the P90 is not, so it’s pretty much impossible to get the clevis and cotter in the pedal shaft from the driver’s compartment on the xj6 part without the access hole. Better yet, pull the pedal box out of the car to do the job. 1 hour round trip. You can make the series 2 xj6 work (I did), but your rebuilder has to change the the bolt plate on the booster can to the series 1. The series 2 has plastic fittings on the master for supply from the reservoir, while the series 1 are brass.
Ron, yes, I am trying to keep it original if at all possible and noted that actually the Girling MCs and Supervac servos were gradually installed in these cars during servicing, so it could well be considered to be quasi original.
Also the P90 is a very simple unit to rebuild it seems.
What did you end up doing with your old Dunlop unit?
Of the possible diaphragm alternatives, the Ferrari 246, 275 and 330GTs used a Dunlop C48 unit as did the Jensen CV8s and early Interceptors, but I think that’s a single diaphragm unit as opposed to the P90 which is dual diaphragm.
Supposedly the C48 is a 9-1/2" unit. Not sure if the diaphragms are interchangeable.
Tony, I do have a Girling Dunlop cross reference and will check out the Aston Martins.
Thank you.
I’m not sure whether I still have it. I’ll take a look. It was cobbed together with a GM master, and there was no boost when I got the car, so definitely not functional.
Thanks Ron
I’ll wait to hear from you.
Nick
Thanks
Will send PM
Nick
Can I add a question. Reading through this discussion, the XJ S1 booster/master was noted. I have a good S3 (1982) unit still on a former running now parts car. What is involved (if possible) to install the S3 booster and or booster/master on a 65 MkX 4.2?
If you want a strange one, 20 years ago the master went out. As a quick repair, we installed a master from a 2001 Cadillac Seville. It was a bolt on to the booster and worked like a champ till the booster gave up a few years ago. If I swap out to the S3 (or other) booster/master, I’ll obviously be back to “original”. But even now, the brakes work fine, just takes both feet to stop the big girl without vacuum assist.
That doesn’t have metric threads?
If you have both parts, measure the bolt patterns front and back and if the drum fits physically… maybe there’s something in the forum already. The S3 has a separate one way valve on the intake manifold, don’t forget that.
It may
Things to check…is the bolt pattern on the booster compatible with the pedal box ?
If so, you should be good to go
You may have to make some new brake pipes
I have what is believed to be an XJS MC, mounted to a Girling booster,
it is bolted to a pedal box, and came out of a '66 MKX
I don’t know about the S3, but the bolt pattern on the S2 booster can is wrong so I presume the S3 is also wrong. What you need, and I posted this here before, is a S1 booster (An S2 will work, but you have to change the half of the can with the bolts to S1) to which you can bolt either the S1 or S2 master cylinder. The S2 master has plastic reservoir fittings, the S1 brass, otherwise the same. If you do this, you add a 1" access hole to the side of the pedal box so that you can get the the clevis pin in - some late cars already have the hole. Since the MkX had a loose actuating rod and the XJ6 a retained actuating rod you must do this. You will never get the clevis in from the footwell.
So, it’s an easy job with the right parts. No need to reinvent the wheel. Do just pull the pedal box off the car (very easy) and do this work on the bench. The results are magnificent, with a modern feeling brake system.
I’m including this a response to Tony and Paul in the classifieds posting.
Thought it maybe more useful here.
Tony,
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.
Paul.
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.
Nick
Thanks, Nick. Everything one wants to know about the P90.
Ron