So I'm laying on my back in the driveway, doing a bit of daydreaming and figuring out some oil cooler line issues. In a few weeks I plan on upgrading to a 19mm MC (thanks again Alberto!), BMW brakes, etc.

As I look at the MC that is in the car I see a large embossed "18" on the body of the cylinder. Truthfully, I always thought I knew my car well, but I just never had need to look at the master cylinder that closely before. So a stock master cylinder is a 17mm. Are they embossed with a "17" like I think they must be? I've never crawled that far under someone else's car to check.

I did a bit if searching on Pelican and a couple of other places and I can find no reference to an 18mm MC. Now, the PO was a notorious parts scavenger, so I'm thinking he may have come across an Audi or Fiat or who knows what that that could bolt right up.

Weird.

Anyone else heard of this? Am I on crack?

Many TIA!

QUOTE (hmeeder @ Jun 13 2005, 12:46 PM)

As I look at the MC that is in the car I see a large embossed "18" on the body of the cylinder.

if you realise that our "metric" sized master cylinders are actually just approximations of the real sizes, which are fractional inches, you'll find that an 18mm MC is kinda unlikely. (our "19mm" MC is *really* 3/4"...)

the casting number on the body of the MC has little if any relationship to the size of the bore. you may or may not find another number on the MC that has the 'real' size.

but i suppose there's some English fraction that's reasonably close to .7"

there was a posting recently (within the last 6 months) that showed a table of all the American inch fraction MC's made. i can't go search for it just now but i encourage someone to light up the search page and track it down...

Usually the master cylinder size is located on the portion inside the driver's compartment. It is on the underside of the pushrod cup. Can't see it from the outside of the car. It was probably a casting number of some sort.

No Herb, that 18 means it should actually be a m/c for 1.8 liter cars, they don't need much braking......

Cast Actual inch x/16"
17 17.46 0.6875 11
19 19.05 0.7500 12
20 20.64 0.8125 13
23 23.81 0.9375 15

The cast # is on that part of the M/C that resides within the pedal cluster.

Thanks for the brake lesson guys. I had no idea that the brakes were all in 1/16" increments and that the metric size was just a best guesstimate. Weird but a good thing to know. And, of course, Dave is right about where the size is cast on the body. Had I looked closer at the 19 on the tool bench I could see that the size is cast on the part that is on the pedal cluster side of the firewall.

As you can see from the attached photo the "18" is prominent on the the stock MC in the car. In fact it's the only marking I can find on it (I haven't pulled it from the car to see if the "17" is on the part inside the body. I'm going to assume it is.)



Thanks!

We don't believe you. Nice Photoshop job!

Jeez, Karl. I guess you caught me! You will also notice that I photoshop a little bit of rust into everyone of my undercarriage shots to give the appearnce of authenticity.

Yeah, yeah... easily applied with the Photoshop rust brush and pallette of rust colors?

That's NARP-colored rust, right?

Just messing with you?

Dunno about the 18? First I ever seen one.

Really? Looks like, in the picture later in the thread from this one, that the number is clearly visible on the barrel of the M/C, which is UNDER the car, NOT inside in the pedal cluster area. In fact, the very small portion of the M/C that resides inside the car is generally covered by the protective boot, and is machined.

The Cap'n

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Really!
Click to view attachment
On mine there is an 11 outside and the 17 inside. Maybe that outside number is not the size at all but some other record of the cast.
The nut on the side of MC seems to indicate the 17mm. On the 19 it is just a tit with no hole.