Chris A Posted April 10, 2023 Report Share Posted April 10, 2023 Good morning one and all. I'm going to replace the master cylinder and wondered if anyone has any tips as to how to reduce/stop air getting into the system while changing over the cylinders. As soon as the brake pipe is disconnected the end should be capped to stop air getting into the pipe, I assume. I also thought that putting some fluid into the new cylinder and pumping it through before connecting the brake pipe would help. clearly protecting the paintwork from spills is a must. I have done a pre check of the bolts holding the cylinder and they aren't siezed, the nut holding the pipe is also ok. I was surprised to find it needed a 10mm spanner, I assumed imperial like the bolts, is that standard? Thanks for any pointers. Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 10, 2023 Report Share Posted April 10, 2023 (edited) Hi Chris, The worst bit is getting the rubber boot to back into the hole in the bulkhead. Some boil 'em to soften 'em up, others oil 'em, some silicone sealant 'em back into place and some just give up saying "I'll do that later" But important to do to stop hot and nasty engine bay air getting into the cabin. Yes, I used cling film to cap the end of the pipe, not a lot of air gets in if you're quick and careful. Air can be bled out from the nearest slave, the passenger side front. This gives the least loss of fluid. 1 hour ago, Chris A said: I also thought that putting some fluid into the new cylinder and pumping it through before connecting the brake pipe would help. A nice idea, but you're gonna get fluid on the paint for sure! Is now the time for silicone brake fluid? It doesn't eat paint but does make it go a bit dull if you spill it. But who cares, it's out of sight under the bonnet. You just pour it in and bleed out until the fluid is a different colour. Bleeding in the regular way, furthest away first, driver's side rear. Doug Edited April 10, 2023 by dougbgt6 Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 10, 2023 Report Share Posted April 10, 2023 (edited) there metric and unf threaded cylinders with AF spanner sizes range to suit the type of sleeve nut used to match the cyl. if you can keep the pipe filled you canbleed the cyl from leaving the pie nut you speak of loose and give the pedal a light press then nip it up Pete Edited April 10, 2023 by Pete Lewis Link to comment Share on other sites More sharing options...
johny Posted April 10, 2023 Report Share Posted April 10, 2023 I wouldnt worry about the amount of air that gets in as youre going to have to bleed all the way from the new master cylinder to a slave anyway and to know its 100% I would do all four as well - normal brake fluid is cheap enough.... 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 10, 2023 Report Share Posted April 10, 2023 (edited) and thats right it only lasts for around 2 years as it absorbs moisture from the breather in the reservoir and is important to keep fluid changes with Dot 4 as a service job or when you really need the brakes the heat vaporises the moisture and you end up with no pedal and an expensive Bang some of us have simple and very cheap testers , use it at the pub meets and frighten the drivers with some awful results I was involved with testing brake fluid on trucks in storage often reservoirs were exposed (as chassis cabs) and the water content could be ridiculous Pete Edited April 10, 2023 by Pete Lewis Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 10, 2023 Report Share Posted April 10, 2023 1 litre of dot 4 £7.40 ! litre of dot5 £36.75 So silicone costs 5 times the price of dot4, but you should change dot4 every 2 years. Which means in 12 years silicone is saving you money! The only question to ask is will you still be driving in 12 years time? Doug Link to comment Share on other sites More sharing options...
johny Posted April 10, 2023 Report Share Posted April 10, 2023 Ah the conundrum of life eh! Of course you also have to ask yourself how many times youre going to spill brake fluid on paintwork in those 12 years😭 Link to comment Share on other sites More sharing options...
Chris A Posted April 10, 2023 Author Report Share Posted April 10, 2023 Thanks for the replies everyone, something to mull over. . . I won't be going over to silicone 21 minutes ago, dougbgt6 said: The only question to ask is will you still be driving in 12 years time? Doug 2 hours ago, Pete Lewis said: there metric and unf threaded cylinders with AF spanner sizes range to suit the type of sleeve nut used to match the cyl. Now I am a bit concerned about that. I am hoping that the new cylinder would have the same thread as the unit coming out so a straight swap. The unit fitted is a Girling 5/8 unit for the moment I haven't a make for the replacement but from Pete's comments the threads may not be the same? More work than I was hoping for. Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 10, 2023 Report Share Posted April 10, 2023 its the problems of alternative suppliers and 50yrs of that'l do mix not match repairs Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 10, 2023 Report Share Posted April 10, 2023 this remind me back in the 70s my Simca 1501 used to slice a groove through the maiin brake seal due to the recuperation port it would last a year and then you got the sinking pedal , you could pop the M cyl off easy turn it upwards remove circlip and flip the seal out , with a bit of submerging you fit the new seal , no bleeding , back on the road in 10minutes that was before progress crept in Pete Link to comment Share on other sites More sharing options...
Chris A Posted April 10, 2023 Author Report Share Posted April 10, 2023 1 hour ago, Pete Lewis said: its the problems of alternative suppliers and 50yrs of that'l do mix not match repairs Pete I've sent message to my supplier with details of the unit to be replaced and asked which of the 3 references they have in stock have the same thread as it has. I assume mine is imperial as it is a Girling Cambrian 6 unit. Knowing my luck the only one that is compatible will be the most expensive 🙄 Link to comment Share on other sites More sharing options...
Chris A Posted April 11, 2023 Author Report Share Posted April 11, 2023 Just got a reply from my supplier : GMC220 : imperial GMC205 : 0-3/8 UNF GMC205Z : 0-3/8 UNF So I guess any will do. The 220 is the larger capacity version which is the specified one for the 13/60 disc calipers. The 205/205Z is smaller capacity but I do have the extension piece, if it fits. Looking at the photos the 220 reservoir is vertical to the body, the others have a slight lean back - as does the one fitted to the car. Does the angle matter that much? Hey, ho. Easy answer - buy all 3 . . . I'd rather not though Come on guys help me out here before my brain explodes 🤯 Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 11, 2023 Report Share Posted April 11, 2023 Does straight up make it taller? Bonnet damage? What difference does "Z" make to the 205? I'd want to replace with as similar as possible Doug Link to comment Share on other sites More sharing options...
Chris A Posted April 11, 2023 Author Report Share Posted April 11, 2023 7 minutes ago, dougbgt6 said: Does straight up make it taller? Bonnet damage? What difference does "Z" make to the 205? I'd want to replace with as similar as possible Doug No problem with clearances. "Z" denotes it's a 'cheap' copy (64€), the 205 is original quality (104€) The 220 is 73€ The closest in appearance is the 205, with or without the 'Z', although strickly a 13/60 should have the 220 . . . Well, lunch calls then a meet with a mate over a glass or two. . . Link to comment Share on other sites More sharing options...
NonMember Posted April 11, 2023 Report Share Posted April 11, 2023 Heralds were originally fitted with the 205 type - reservoir angled from the cylinder to compensate for the slope of the cylinder on installation. Later Heralds (with disc brakes) had the plastic extension to increase the reservoir capacity. Spitfires used the larger capacity type - probably the 220 - where the reservoir was perpendicular to the cylinder. This means it leans forward when installed, so you don't get the full benefit of the size, but then it's a big enough reservoir that you dont care. Vitesse and GT6 used a larger bore version of the large reservoir type. There is no problem with clearance on a Herald, but the Spitfire/GT6 bonnet is lower, so the mounting bracket is subtly different on them. Link to comment Share on other sites More sharing options...
Chris A Posted April 11, 2023 Author Report Share Posted April 11, 2023 Thanks for the details Nonmember, some I knew some new to me. You caught me before I went for my drink with a mate, he is running late . . I think I'll go for the 205Z as that looks closest to what is fitted and hope the reservoir extension on the current unit fits 🤞 Link to comment Share on other sites More sharing options...
DanMi Posted April 11, 2023 Report Share Posted April 11, 2023 GMC205Z will be made by county and GMC205 TRW. The original metal cap certainly won't fit the TRW one so the extension won't. Though I have run with the brake master cylinder as a gmc205 for over 30 years with no extension and no problem, though mine is a MK2 spit so slightly smaller type 12 callipers Link to comment Share on other sites More sharing options...
Chris A Posted April 11, 2023 Author Report Share Posted April 11, 2023 15 minutes ago, DanMi said: GMC205Z will be made by county and GMC205 TRW Some sources actually stated that their GMC205 is TRW, but they didn't have the other bits I wanted as well. 16 minutes ago, DanMi said: Though I have run with the brake master cylinder as a gmc205 for over 30 years with no extension and no problem, though mine is a MK2 spit so slightly smaller type 12 callipers When I got my 13/60 in 2015 there was no extension and I've had no problems. I sourced an extension piece a few months ago for the sake of 'originality' rather than the need for extra capacity. Link to comment Share on other sites More sharing options...
johny Posted April 11, 2023 Report Share Posted April 11, 2023 Ive just fitted extensions to both my brake an clutch MC (both small reservoirs) and the big advantage is that I can see any change in level much more easily now👍 Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 12, 2023 Report Share Posted April 12, 2023 i puzzle at why so many caps are tightened by a gorilla corrosion doesnt help but of the many i get to check have been wrenched up never removed to check pete Link to comment Share on other sites More sharing options...
johny Posted April 12, 2023 Report Share Posted April 12, 2023 Yes thats why I like plastic caps and the extensions even more👍 Link to comment Share on other sites More sharing options...
Chris A Posted April 12, 2023 Author Report Share Posted April 12, 2023 48 minutes ago, johny said: Yes thats why I like plastic caps and the extensions even more👍 Same here, got fed up with having to fight the cap to get it off even though each time I refit it I do so very lightly . . Link to comment Share on other sites More sharing options...
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