Master cylinders

Post by **phil63** » Tue Feb 13, 2007 12:52 pm

I am just changing my master cylinder and I noticed that the new one ( that I have had for a couple of years) is marked 13/16 . I read that the earlier ones were that and the later is 7/8 . all the ones I have seen are 13/16 so why don't the spares suppliers have the later type .

Post by **rayofleamington** » Tue Feb 13, 2007 1:20 pm

They were all made from the same casting - therefore the number on the outside of the casting is irrelevant on the recent parts.

The number was used 30 or 40 years ago when they made 2 different types, however that's no longer the case. I would guess the supplier/s didn't care what number was shown on the casting anymore as long as it works.

As far as I'm aware, nobody is supplying the early m/c - as it makes vry little difference anyway and the later one can be used on all cars.

Post by **Willie** » Tue Feb 13, 2007 1:48 pm

This is a common error. the early Master cylinders had a 7/8" bore, the later type were reduced to 13/16" bore because it gives more pressure to operate the 8" front brakes.

Post by **rayofleamington** » Tue Feb 13, 2007 2:35 pm

the later type were reduced to 13/16" bore because it gives more pressure to operate the 8" front brakes.

I thought the m/c changed at the same time they changed wheel cylinder diameters. I'm pretty sure the rears ones got smaller. i'm guessing, but i think this was to give the same braking effort at the rear and increased braking at the front - which in conjuction with the 8" drums gave extra improvement.
I've never checked the changes against dates but it would seem logical if they changed at the same time, although maybe the rear cyclinders changed between series 2 and 3

Post by **Willie** » Tue Feb 13, 2007 5:15 pm

Yes. at the same time the rear wheel cylinders were reduced from 7/8"
to 3/4".

Post by **Onne** » Tue Feb 13, 2007 5:45 pm

A trader is selling both sizes again. I'll PM you

Post by **phil63** » Wed Feb 14, 2007 1:05 pm

I just assumed that bigger would be better .seems not
Phil

Post by **IslipMinor** » Wed Feb 14, 2007 2:50 pm

I believe all the brake changes were made at the same time.

Increased to 8" front brakes to give more powerful brakes for the faster 1098 engine, reduced the m/c bore to make the pedal pressure slightly lower, and reduced the rear cylinder bore to reduce the rear braking power to compensate for greater front weight transfer under braking.