Peter Truman Posted June 1, 2023 Report Share Posted June 1, 2023 I'm in the process of upgrading my daughters Mk2 Spitfire from Type 12 brake calipers to Type 14, which require a master Cylinder of larger capacity. Today I got a new Mk3 Brake Master Cylinder (Coventry GMC224), which came with a very long pushrod (150mm), I have several other push rods in my spares box, 63mm long, 88mm long, the existing Mk2 push rod & also an adjustable rod. The current Mk2 small reservoir master cylinder fitted appears to be around 95mm from the face of the master cylinder mounting flange to the centre of the clevis pin, the actual length of the push rod to get this distance hasn't been measured yet, but can anyone confirm what this measurement from the mounting flange to the clevis pin should be, &/or the actual push rod length used in the Mk3 Spit Master Cylinder? Link to comment Share on other sites More sharing options...
johny Posted June 1, 2023 Report Share Posted June 1, 2023 I like the adjustable type as you can minimise any play in the linkage, ensuring its still free of course... Link to comment Share on other sites More sharing options...
dannyb Posted June 1, 2023 Report Share Posted June 1, 2023 I bought a mc for my 1500 spit a couple of years ago. The push rod that came with it was much too long. Ended up fitting an adjustable one. Danny Link to comment Share on other sites More sharing options...
Peter Truman Posted June 2, 2023 Author Report Share Posted June 2, 2023 (edited) Just fitted the new Coventry Master cylinder and transferred the push rod over to the new master cylinder, now as suggested elsewhere the reservoir just sticks up a little high, I don't like the recommended solution of raising the bonnet rubber cones, it must affect the bonnet door bulkhead alignment, o I'll have to think about that? I could remove the plastic reservoir and mount it remotely and use a SS braided hose between the remote reservoir and the Mast cylinder body. As long as the reservoir is higher than the master body is there an issue if the suction hose drops lower than the master cylinder inlet? Edited June 2, 2023 by Peter Truman Link to comment Share on other sites More sharing options...
johny Posted June 2, 2023 Report Share Posted June 2, 2023 Only problem I can see is you might get an air pocket where the hose connects to the MC which might impeed the flow of fluid. However you could clear this by lifting the MC up when its filled to clear any air before fixing in its position... 1 Link to comment Share on other sites More sharing options...
Peter Truman Posted June 2, 2023 Author Report Share Posted June 2, 2023 (edited) Just cut 1/4 inch off the top thread off the plastic reservoir body and it just touches the bonnet a little with the cap on. So ok a little more sanding off the top reservoir body say 1/8 in minus and it’ll be ok shouldn’t affect the res usable capacity. there’s still just enough external thread for the cap to hold. Edited June 2, 2023 by Peter Truman 1 Link to comment Share on other sites More sharing options...
Peter Truman Posted June 20, 2023 Author Report Share Posted June 20, 2023 You know there's just some jobs you wished you hadn't started, well I fitted and filled the new Coventry brand Spit Mk3 brake master cylinder BUT was very concerned re the loss of volume in the reservoir due to its slope caused by the bulkhead mounting bracket, see attached pic's. Now to put the new res volume into perspective, as shown it's holding twice the original Mk2 backward sloping reservoir (vertical), and approx 1.5 times the original Mk2 volume from the new Coventry sloping res outlet hole. The Mk2 & Mk3 master cylinders bore are the same at 5/8in, but the Mk2 Type 12SP caliper has a smaller piston at approx 42.8mm dia vs the Type 14 piston at 48mm dia, over the 4 pistons this equates to 1.26 times increased area and hence volume, assuming the piston movement is the same. As I said sometimes it's better not start these projects, to assure me the set up as shown is usable can anyone show me a picture of a Mk3 Spit with the plastic style integral reservoir showing the fluid level? I'm trying to avoid the extra work of separating the plastic res from the master cylinder and mounting it so the fluid level is horizontal so as to gain the full capacity of the reservoir, not impossible but extra work in making a mounting bracket and cost for two banjo's and 7/16in UNF Banjo bolts around $110, must be gold plated! Link to comment Share on other sites More sharing options...
Peter Truman Posted June 26, 2023 Author Report Share Posted June 26, 2023 It appears my local supplier had & sold me the incorrectly labeled master cylinder the one shown above is GMC224 for the earlier Type 12 calipers not Type 14 which should be GMC220 which has a taller centrally mounted and narrower reservoir, I found the suitable GMC220 in NZ and gave up messing around with the above shallow and off center mounted big dia unit. When the replacement arrives I'll clean the above incorrect one up and try to return it or get a credit, it was fitted but not used? If that doesn't work I might try and sell the rebuilt Type 12 Calipers (great condition no rust in bores, new pistons and seals), mounting brackets, S/S braided hoses and above Master Cylinder to one of the local drum braked Herald crew! Interestingly whilst the incorrect GMC224 unit was a Coventry brand the reservoir was stamped Girling! Link to comment Share on other sites More sharing options...
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