I just bought what was advertised as a 19mm master cylinder off EBay. I got it last night in the mail and I believe it is a 17mm. Thing is, there is a 17 stamped (cast) onto the neck and a smaller 19 cast onto the underside of the body. So, which is it? I need to contact the seller and let them know they sent me the wrong one. But first I want to make sure I know what I am talking about.

Also, out of curiosity, is possible to convert a 17mm to 19mm by having a machine shop bore out the inside 2mm. I know a 19mm piston would need to be procured. Just wondering.

Thanks!

That would be a 17mm master Cyl.

I have never heard of anyone boring out an MC but I don't see how that would be impossible, I wouldn't do it though.

check out this thread

http://www.914world.com/bbs2/index.php?showtopic=62171

I could use a 17mm MC! Is it gud? How much did you pay for it?

Usually, if it says "17" on the master cylinder, it's a 17 mm part. On the other hand, if it says "19" on it, it usually is a 19 mm part.



























and if you want to know where this is coming from, check the following thread:
http://www.914world.com/bbs2/index.php?showtopic=65307

(tongue in cheek, of course)

The MC's may be marked in mm, but they are most definitely an inch part. You would want to bore it out 1/16". On the other hand, I don't know if the bore is exactly the inch size, the piston is the inch size, or the average is the inch size.

The size marking is on the neck that fits inside the pedal cluster. All other marks are just casting info, and must be ignored. You definitely got a 17mm part.

I'm having trouble finding a 19mm for my 911 upgrade. I thought it should be a 19mm from 1970-1973 911S but some of them seem to indicate there's a power booster. I'm also not fussy about an ATE instead of a Rabestos.
Anyone got a source for the right one?

I'm pretty sure the power booster versions did not come as early as 1973. Pelican and others sell the correct one. They are easy to find, just not cheap anymore.
Rabestos? OMG

Thanks for all the feedback. I am quite certain this is a 17mm part as has been confirmed here. I am sure the seller is a stand up guy so I have requested a refund.




Borderline, this unit really needs a rebuild and I paid as much for it as I would have paid for a rebuilt 17mm. So, no economy here.

Thanks!

James

The power boost did not come on line until the 74 911. The pedal assembly changed at the same time.

I believe the MC size is on the neck.

When I took out my old busted MC it had 19 stamped on the bottom middle.

But on the neck was the 17. I guess the 19 was a number/code for something else?