Fraggle Posted February 15, 2012 Report Share Posted February 15, 2012 Hello, Does anyone know the bore size of a standard clutch master cylinder? Many thanks! Quote Link to post Share on other sites
sarajitTR6 Posted February 15, 2012 Report Share Posted February 15, 2012 The bore size is 0.75. Originally this was fitted to the TR5/6 1967 - 1970. Sometime after that Triumph changed it to the 0.70 bore to create a lighter pedal. I understand it required all the clutch components to be within very fine tolerances. Im in the process of overhauling my own clutch, and am fitting the 0.75. The question I myself have asked the experts is how i can identify an OE master cylinder and slave. There are so many **** repros at 20quid which are a total waste of time. PS: there are lots of comments on this topic in the forum if you search under clutch. Sarajit Quote Link to post Share on other sites
Fraggle Posted February 16, 2012 Author Report Share Posted February 16, 2012 Thanks for reply. The cylinder I have just removed is 0.625 or 15.8mm. Don't know if it's standard. The pedal is heavy, was thinking if changing it to get a lighter pedal. Any ideas? Quote Link to post Share on other sites
johnny250 Posted February 17, 2012 Report Share Posted February 17, 2012 Surely the smaller the cylinder the greater the force needed to move it (but the travel is also greater of course). I have a 1" diameter slave cylinder and about 1" alloy spacers fitted to the mounts....works fine and gives a light pedal. It's no problem to fit spacers and different cylinders if required to get the travel and feel that you need. john Quote Link to post Share on other sites
alanprice Posted February 21, 2012 Report Share Posted February 21, 2012 I think it works like this - the smaller the MASTER cylinder, the less pressure required, but the more pedal movement. In theory halve the piston bore and you need to move the pedal twice as far, but at half the pressure. The relationship reverses at the SLAVE cylinder end. Of course the leverage effect of the pedal determines the exact changes in the movement/pressure relationship but it will always go in the same way for that one change. Without trying to crunch too many numbers, if I need a certain volume of fluid to travel down the line at 100lb/sq in, then I can get this by applying 100lb pressure to a 1sq in bore master cylinder (100lb/1sq in = 100lb/sq in), or by applying 50lb to a 0.5" cylinder (50lb/0.5sq in = 100lb/sq in). But the smaller (by half) master cylinder will equally only move half the volume of fluid for a set piston displacement and therefore will need to travel twice as far. So dropping the clutch master cylinder bore from .75" to .70" will achieve a small reduction in pressure required (hopefully noticeable) and small increase in pedal travel (hopefully not too noticeable or enough to prevent full clutch disengagement). There's a lot of use of the word bore here, so I'll shut up now Quote Link to post Share on other sites
alanprice Posted February 26, 2012 Report Share Posted February 26, 2012 Fraggle still waiting for an answer on the TR7? My TR7 was originally bog standard, bought from 8 years old and it had a .625" (5/8" or 15.9mm) Girling master cylinder. My previous post said halve the bore size and you get the twice the line pressure, but double the piston movement, that's cobblers I realise now because of pi rsquared of course, I meant halve the area size of the piston, not quite the same thing but the relationship of smaller bore = less pedal effort (due to more line pressure generated) but more pedal movement ('cos it's smaller!), still stands. Alan Quote Link to post Share on other sites
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