Master cylinder question

So, the Wilwood dual master cylinder I'm using on the MG has clearly marked F and R ports. The F port is the one closest to the pushrod, so it's the "first" port.

I can't imagine why it would make a difference, as it's a 1" bore at both ends. But I do remember reading a mention in Hot Rod a while back about how getting these two ports mixed up could cause a soft pedal. I still can't figure out how.

Does this make any sort of difference? What am I missing?

Are you sure its a 1" bore on both ends? If thats the case the chamber cloest to the push rod will have larger bore. as there needs to be make up room for the push rods volume.

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Yes, it's a 1" master. Wilwood 260-7563, and the product description does mention 50/50 output. I'd never heard that it would have a stepped bore to make up for the pushrod volume. Have you actually seen this?

Yes, my Lotus Elan S4 has a stepped bore MC. However the bowl sizes are equal. The Elan has disc/disc arrangement. I'm guessing its sort of a self proportioning type of thing. Is your application a disc/drum? If so, the bowl sizes are most likely different, hence the marking of F and R.

"My application" is not one you're going to find in a normal parts catalog I'm running discs all around. Like I said the product description mentions 50/50 output so I would assume that means the two ports have the same output.

I'll have a spare one of these around soon, maybe I'll try pulling it apart. If it was a stepped bore, I'd expect the product description to specify the two bore sizes so I could figure out my pressures.

The reason a stepped bore M/C would have the larger size closest to the pushrod would likely simply be for ease of machining.

I think the reason for the F & R markings is not a stepped bore MC but the fact that there are two pistons in the MC and the back one (Closest to the push rod.) moves first, then takes the slack inside the MC and only then does the second piston starts to move. This way pressure goes to the front first before the rear.

jimbbski wrote: I think the reason for the F & R markings is not a stepped bore MC but the fact that there are two pistons in the MC and the back one (Closest to the push rod.) moves first, then takes the slack inside the MC and only then does the second piston starts to move. This way pressure goes to the front first before the rear.

yep.

Makes sense to me. Thanks!