master cylinder size

[poo slinger]

i currently have a 0.75 master cylinder in the pedal box and have a rover sd1 slave cylinder at the clutch.

the 0.75 does not move enough fluid,

any1 know what size i need or what the sd1 had as standard???

Ross

[unstable load]

You can basically go up to any size you want, but it will involve higher pedal forces and similar compromises. Another alternative could be a longer stroke instead of a bigger cylinder.
Here's a site that could help you calculate those and let you decide what is acceptable to you.

http://www.wallaceracing.com/brake-master-cyl-calc1.php

I'm sure there are more out there, but this will give you an idea.

[gelmonkey]

0.625 was the standard size I think

Cheers
P

[marcjagman]

I build kit cars a lot and am a member of locostbuilders forum, this problem crops up a lot. We generally use a Fiat 124 master cylinder, not the sport, and move the pivot hole a little higher giving a bit more leverage and travel.

[richardpope50]

I had a problem as I needed my M/c to pump more fluid but my space was limited and the standard Girling type was not big enough. I eventually found a Willwood one (available from Rally Design, Kent) and works fine. However note they have a tapered thread but I drilled and re-cut mine to use standard (and much cheaper) connectors.

[poo slinger]

well how much fluid will i have to move for an sd1 clutch??

[unstable load]

A rummage in Google tells me the SD1 slave is 7/8" and the master is 5/8"(0.625 from Gelmonkey). You have a 3/4" in your pedal box so you should have adequate volume to move the slave further than the original for a given stroke, but at higher pedal weight.

It's too early for my brain to crunch the numbers, but pi rsquared times stroke will give you the volume of fluid moved by the master and by juggling the formula you can calculate how much you need to achieve a required length from the slave.

[Ian Anderson]

Ok some "General" informationI found during my build

Most slave cylinders seem to be required to move th lever in the region of 3/4 inch or 19mm. Sure someone on here will say thier slave ylinder moves 10mm and others will say 30mm but a good starting point is 19mm

Obviously if you have inmatched parts you may not be getting the movement required so I'd suggest get someone into the drivers seat and measure what movement yu are getting at the slave. You many need to take up some "slack" by lengthening the pushrod - avoiding too much slack before the arm starts moving.

Is you are not getting 19mmmovement I would suggest your have air in the system and need to bleed it some more

One last thing - if you end up using a bog master and big slave you need to move a lot more fluid along the pipe - this can cause the clutch to slip on clutch dumps as there is a finate length of time required for the pressure plate to forse the fluid back to the master cylinder (Ask me how I know! 3/16 pope mid engines car and a Renault slave cylinder of about 26mm!)
Ian

[Denis247]

i currently have a 0.75 master cylinder in the pedal box and have a rover sd1 slave cylinder at the clutch.

the 0.75 does not move enough fluid,

any1 know what size i need or what the sd1 had as standard???

Ross

Standard is 5/8" bore master and 7/8" for the slave.

I use a 0.7" master and a standard slave, BUT, I also use the long release bearing carrier and long pivot post with this.

Don't know if the poster is just replacing a working system or is building from scratch, in which case the bearing carrier/pivot post sizes may be his problem.