here is an example of how confusing things are…says SP2484 (which I ordered) fits S1 XJ6
(and eslewhere 420G, Ferrari, Jensen)…the rear port wouldnt bleed when fitted on my '69 420G
The brake booster/master combo for a S1 XJ6 (68-71) isstandardised with 420G (68-70)…according to Thorley, various vendors…and me
The 3.8 MKX had an earlier system…forget them
The 4.2 MKX (65-67_, has an entirely different brake booster and master cyl from the other two
It has a separate master cyl & kit part nums (SP???)
It might be this one, even though once again, the years seem wrong
when I get a chance, I will try to confirm the SP number for the kit i suggest…or try Barratts catalogue etc
According to my brake expert, its the rear seal…so look at the pics attached in the ads
follow up…this Ebay Seller has some good additional info, which I have copied and pasted.
I think this helps clarify things a bit more.
what year is your 420G ? (they had changes made every year!)
I would order this kit …evidently part num SP9021
" 7/8" bore (0.875" inch) Brake Master Cylinder Kit (National ES9021) as shown in picture. Original Dunlop part number VB60097, but when Girling took over this became SP9021. Subsequently Girling replaced the Dunlop designed master cylinder with their own product. This kit is for the Dunlop type, NOT for the later Girling design.
Kit rubber parts as shown, in excellent visual and material condition, packed in sealed 500g polybags. Previously supplied to parts specialists ready for their own brand/part number label to be attached. UK manufacturer established since the 1960’s.
Rubber grease can be used for ease of assembly. If Girling Red Rubber Grease is not available the alternative product must be for use with ordinary brake/clutch cylinder rubber seals (not nitrile).
Application details derived from more than one parts catalogue:-
My opologies regard stating XjXs1 meant to be XJ6s1
420G is 1967… I do agree that the misinformation from the suppliers is worrying! Thanks so much for the details, this will be very helpful to many who emcounter this issue. ALso thanks to all regard jacking detail.
Now in my confused state, I repeated the removal and checked over the existing MC. It appears to have a perfect and smooth interior. I cleaned it all again and added the large gland seal to the primary plunger ( this was quite an ordeal!) I just bled the MC on teh car and was able to get both lines bled… The pedal quite stiff and drove around the yard. Brakes were active and suspect will need to bleed fully the lines next?
I learned something new (maybe) that the master cyl maker changed from Dunlop to Girling in the years they said…the Dunlop master that goes with the below booster has the actuator poking 2 inches out of it, the Girling one is flush, retained by a circlip
The BOOSTER changed, and they are easy to tell apart, the earlier Dunlop 90 can be easily taken apart by removing a central band that hols two clamshells together.
The later Girling Supervac 100 is pressed together with overlapping fingers
I think I mentioned all seals should be photographed and measured with calipers
its a devil of a job bleeding the rears on a 420G, I had to encourage them by bleeding each union leading to them by gravity, fronts are dead easy
ensure yours rears are active by a chalk mark on the disc, it should get wiped right off
the area that is swept by the pad should be shiny…rear pistons have a tendency to stick in the caliper
.vacuum leak (because you forgot to properly reconnect a hose, brake booster to resevoir would be my No1 guess ? )
at least one carb butterfly is not closing all the way, make sure the linkage is free, and depress the external lever that controls each one right down
If you have a vacuum gauge, that is very easy to use and should show a major vacuum leak
Thats the only place I can think of that would allow such a large vacuum leak that the engine could race as high as you said…3000rpm just doesnt even sound like a vacuum leak, more like open throttle plates.
Go over everything carefully, there is only the dizzy and vacuum for running the plenum and heating valves and flaps…all attached and not cracked…would not cause 3000rpm ??
THe open throttle plates/ perhaps dirty throttle plates might be more plausable? There is limited hissing and also I wonder regard the actual carb settings. I just looked at a log book and remember that we tampered with the slow and misture screws … I believe we tightened them and then opened but can’t remember exactly what was executed!! (such a good log!)
Anyway, I thought I might screw them all down a gain and look for the standard adjusting suggestions… Also, perhaps clean the throttle pates?? Is the latter invasive or reasonably accessible?
The only disconnect I made during brake work were the lines from the brake fluid reservoir to the MC and Brake lines out of MC …
Set the Jet height, using the FSM, and/or Vernier to ensure depth is correct on all 3
Set slow running screws as per FSM
(The idle can also be very high if the ASC needle is fully adjusted the wrong way, adjust it if neccessary thru its range)
high idle on start with ASC can be as high as 1200rpm.
(Its worth owning an accurate tachometer, among others, I have one that reads a reflected IR off a little piece of silver tape (glued onto my crank pulley)
It was cheap on Ebay, and can easily measure the RPM of most rotating objects
OK looking at getting started with the removal of bells and pistons from teh carbs…ill I need to remove the air intake to achieve this? It looks as if it might be somewhat tricky, but if it is a necessary evil then will do it?
That is all that is needed to setup the carbs for correct operation, but you will not be able to verify the butterflies are closed with the plenum in place
Just to verify as the manual is very detailed with regard the removal of teh air intake and associated attachments etc.
Would you be able to detail exactly what I need to remove,check and replace? I will then refer to the FSM for adjustments etc
I assume it idled normally before you worked on it
I do not believe a small vacuum leak could cause 3000rpm unloaded idle… your engine would roaring like a jet on take off…nevertheless, verify the main vacuum hose to booster resevoir is totally intact
If so, I would suspect your throttle mechanism is somehow jammed…check it carefully
If none of the above work, verify all vacuum lines are intact, next, tune all 3 carbs as per FSM.
This can be done by removing 4 each screws that hold the carb bells, remove carb and piston, set screws
The advantage of removing the plenum, is you can peer up the carb throats and verify the butterflies are fully shut at idle…even one open a tiny amount will cause high RPM
There is an external clamp bolt that can be lose and allow the butterfly to slip
To remove the plenum is 6 x 1/2" nuts, the outer 2 are easy, the middle 4, you will need small 1/4" drive sockets…and a 1/2" slim open end spanner…lube the studs and use the spanner jaws head on to work the tricky nuts one flat at a time!..undo each nut a bit at a time and work the plenum back…its not impossible, just time consuming
Appreciate the detail, it will help me along this task for sure. The high idle is actually more likely 1500 or thereabouts, certainy higher than regular start with choke… I suspect the effect of being higher as inside the garage. Yes, I agree at 3000 it would sound like a plane taking off! It is nothing like that but cerainly higher than normal.
I will try the vacuum check, make sure the throttle mechanism is not jammed and then if no change, proceed.
So I conducted a full investigation of all hoses and finally, there it was, a bracket had broken and back of hose was exposed… This was great news. Mosty back to normal although I wonder regard the throttle plates as the idle still quite high and drops if I tap on the throttle???
Anyway, all way better than before.
