Dave the tram Posted September 27 Report Share Posted September 27 My late Mk 3 GT6 suffers from very slow leakage of fluid (silicon) from the master cylinder (0.75 bore) and always seems to have a little bit of air in the system - pedal comes up a little after a quick extra jab. I was going to replace the seals, but as I’m unsure of the condition of the bore I thought it might be best to fit a new cylinder, especially when I spotted these for about £35. I know from experience that a lot of aftermarket parts are substandard, and this might still be the case if I spent more on one from the big suppliers. Has anyone got experience of using these? https://www.ebay.co.uk/itm/143425077356?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&_trkparms=ispr=1&amdata=enc:13J8ZrbDsQBi2XHBVC7F4kQ1&customid=Cj0KCQjwr9m3BhDHARIsANut04aKbTzf7GmL02Hsl9PAGguEWZHMoSi2bvm4s73oLDYlb-kHSWbM1BoaAo-zEALw_wcB Link to comment Share on other sites More sharing options...
dougbgt6 Posted September 27 Report Share Posted September 27 Dave, I have a late GT6, I thought my master cylinder had a problem, I tried to find a new one, they are hen's teeth! If you have found one buy it! Doug Link to comment Share on other sites More sharing options...
trigolf Posted September 27 Report Share Posted September 27 Hmm... I'm not totally convinced that it's genuine Girling new old stock- if they are that rare. Demon Tweeks, for one, advertise very similar looking Master Cyls for a whole range of fitments.🤔 Link to comment Share on other sites More sharing options...
johny Posted September 27 Report Share Posted September 27 2 hours ago, Dave the tram said: My late Mk 3 GT6 suffers from very slow leakage of fluid (silicon) from the master cylinder (0.75 bore) and always seems to have a little bit of air in the system - pedal comes up a little after a quick extra jab. I was going to replace the seals, but as I’m unsure of the condition of the bore I thought it might be best to fit a new cylinder, especially when I spotted these for about £35. I know from experience that a lot of aftermarket parts are substandard, and this might still be the case if I spent more on one from the big suppliers. Has anyone got experience of using these? https://www.ebay.co.uk/itm/143425077356?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&_trkparms=ispr=1&amdata=enc:13J8ZrbDsQBi2XHBVC7F4kQ1&customid=Cj0KCQjwr9m3BhDHARIsANut04aKbTzf7GmL02Hsl9PAGguEWZHMoSi2bvm4s73oLDYlb-kHSWbM1BoaAo-zEALw_wcB but thats got a tiny little reservoir much smaller than the your original Dave which is not good on brakes and says nothing about being 'Girling new old stock'. They are from early Land Rover clutch use (search part number STC500100) and come quite a bit cheaper than that but are sometimes advertised as being uprated for Triumphs with a corresponding increase in price. Ive got a cheapy one (12 pounds delivered) installed on my Vitesse brakes and it works very well but I have added a reservoir extender to give extra capacity.... Link to comment Share on other sites More sharing options...
Pete Lewis Posted September 28 Report Share Posted September 28 (edited) the only change is using a 3/4 bore to replace the orig 11/16" bore will raise pedal pressures but reduce travel the 5/8 bore was used on type 14s calipers the 11/16 intro for bigger capacity type 16s or there abouts using a 5/8 bore on type 16s will lower pedal effort but can increase pedal travel travel and output is a balancing act in general fitment of a servo will often increase the m cyl bore to reduce sensitivity Pete Edited September 28 by Pete Lewis Link to comment Share on other sites More sharing options...
johny Posted September 28 Report Share Posted September 28 Yes I suppose Triumph used 3/4 in the last GT6 to counter the extra pedal travel introduced by the servo and bigger slaves... Link to comment Share on other sites More sharing options...
Josef Posted September 28 Report Share Posted September 28 https://www.pastparts.co.uk/ I had these guys rebuild my Spitfire master cylinder. Certainly was more than £32 but it’s worked away happily for some years unlike the series of repros my Herald has gone through in the past… Link to comment Share on other sites More sharing options...
johny Posted September 28 Report Share Posted September 28 Another alternative for Dave is a 3/4 master cylinder without reservoir from somewhere like Demon Tweaks and then use an appropriate large capacity plastic reservoir that screws into it. Plenty of different known brands to choose from and has the big advantage of a visible fluid level.... Link to comment Share on other sites More sharing options...
DanMi Posted September 29 Report Share Posted September 29 I believe they are a land rover defender master cylinder and would need the push rod swopped as they are different Link to comment Share on other sites More sharing options...
dougbgt6 Posted September 29 Report Share Posted September 29 When I thought I had trouble with my 3/4" and couldn't find another, I borrowed an 11/16" from one of the East Berks Massive. The additional pedal travel was surprising, 3-4". I bled and bled it, couldn't get it any better. I re-installed the 3/4", one bled and back to normal. The fault turned out to be the dodgy new servo, assembled in China with precision machined cheese components. Doug Link to comment Share on other sites More sharing options...
johny Posted September 29 Report Share Posted September 29 oh dear but not sure I understand: a 3/4" master was ok with the dodgy servo and 11/16" not or the first was used without the servo? Link to comment Share on other sites More sharing options...
Dave the tram Posted September 29 Author Report Share Posted September 29 Thanks for all the useful info. Mine’s a late swing spring GT6 -1973, so my understand was, as some of you say, that it had the 3/4 master cylinder to go with bigger rear brake cylinders - and a servo. I’ll steer clear of the cheap one I mentioned and hadn’t noticed the smaller reservoir. Sounds like the Demon Tweaks one plus a screw on reservoir might be the way to go. Meanwhile, I think I’ll live with it and keep an eye on it as I think it’s been leaking very slightly for quite some time and nor getting any worse. Then first try rebuilding it with the new seals I got from Rimmers when I get a window of opportunity and see what the bore looks like. I guess if I’m really lucky the bore will be ok and just the seals gone off a bit. Cheers, Dave Link to comment Share on other sites More sharing options...
johny Posted September 29 Report Share Posted September 29 I agree with rebuilding it and using silicone the bore should be good as it doesnt absorb water like conventional fluid so reducing the likelyhood of corrosion. However I would do this asap because its your brakes and they havent even got the back up of a dual circuit system... Link to comment Share on other sites More sharing options...
Dave the tram Posted September 29 Author Report Share Posted September 29 And finally, how can I tell which cylinders are on the rear and that it really has got the larger ones - like many cars, mine has been messed with quite a bit over the years. It feels a bit weak on rear braking and on a loose surface, it’s the front that locks up easily. Might just be that the rear needs an another overhaul and adjustment. I think the auto adjusters stopped working long ago. Link to comment Share on other sites More sharing options...
Dave the tram Posted September 29 Author Report Share Posted September 29 Guess I know that you are right johny. I’m always mindful that the 1500 Spitfire I had many years ago was better in this area, with dual circuit. Brakes are pretty useful and I well remember the day when a drum shattered on my old moggy traveller and all the fluid was lost. It was our family car back then, my wife was driving, downhill, but at low speed so she steered it into the wall with only a bit of damage. That was the start of persuading me to swap it for ‘a proper car’! Happy days. Link to comment Share on other sites More sharing options...
johny Posted September 29 Report Share Posted September 29 The slaves usually have their bore marked on them but of course you have to take the drum off to see. On yours I believe wider drums were used with the bigger cylinders and they were also self adjusting so theyre shouldnt be an adjuster on the back of the drum. Unfortunately that set up is notorious for not taking up shoe wear very well... Link to comment Share on other sites More sharing options...
dougbgt6 Posted September 29 Report Share Posted September 29 7 hours ago, johny said: oh dear but not sure I understand: a 3/4" master was ok with the dodgy servo and 11/16" not or the first was used without the servo? The fault was the servo would no let go, press the pedal, the brakes stayed on. Swapping to 11/16" changed nothing except 3-4" more travel on the pedal. Doug Link to comment Share on other sites More sharing options...
Andrew Posted September 29 Report Share Posted September 29 If you want my input just buy from a reputable supplier after all we are taking brakes Link to comment Share on other sites More sharing options...
Dave the tram Posted September 30 Author Report Share Posted September 30 15 hours ago, Andrew said: If you want my input just buy from a reputable supplier after all we are taking brakes Yes, thanks for that additional input of common sense - quite right. Funny how one can be a professional specialist at risk assessment at work, then leave all that behind when you start doing jobs on the house or in the garage! Will try harder haha! Dave Link to comment Share on other sites More sharing options...
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