sen2two

iTrader: (10)

I know theres plenty of aftermarket choices with large single and dual masters. but im looking for a junkyard/eBay choice for a master cylinder. Kinda like upgrading to a 929 master on a FC. the 929 master is 15/16" wich is pretty large. but since im going to be using it with no booster, i'll need a little bigger. anyone know of a car/truck/van that came stock with a 1" or larger mastercylinder?



*this will be used on an Rx2 wich is also far lighter than Rx7's. A MC with a 1" bore or larger will plenty strong with no booster for a car that will only weigh in the 2300-2400lb area. for heavier cars with bigger or upgraded brakes, this is not reccomended...

sen2two

iTrader: (10)

well, im going to stick with a 929 master since i did a little readin about pressure Vs. volume in braking.

heres a little exlpantion i found thats easiest to understand.

"One of the most common misconceptions is that a larger master cylinder will create more pressure. While a larger master cylinder creates a larger displacement, it takes more force to create the same pressure as a smaller bore. While a larger master cylinder will take up system slack with less pedal stroke, it will take more force to create the same system pressure. The result after adding the larger master cylinder is a harder pedal which needs much more pedal pressure to create the same amount of braking force. For instance, moving from a 3/4" master cylinder to a 1" requires 77.7% more force on the push rod."


So a larger MC equals you pushing much harder. I believe a 929 master is a good medium between pressure needed by your foot and stopping power.

Josh18_2k

iTrader: (3)

the larger the master the harder its gonna be to push. ever tried stopping with your engine off? i would think you'd want smaller than stock.

clokker

iTrader: (2)

That's a completely fallacious analogy.
A boosted system without a vacuum source feels nothing like a true non-boosted system, pretty much like a power steering rack with the belt removed isn't anything like a manual rack.

@the OP:
The MC I removed from a 929 was a 1" bore, not 15/16".
Perhaps different years came with different part, I'm not sure.
At any rate, RX-7s that came with 4-piston calipers also came with 15/16" MCs, so if your 929 part is in fact a 15/16" bore, there would be no point in using it.

While it's true that a larger MC requires more effort- albeit over a shorter distance, much, if not all, of the difference can be reclaimed by changing the leverage ratio at the pedal. In other words, raise the point on the pedal where the MC pushrod connects.

This summer I spend considerable time in junkyards and experimented with several MC/booster combos.
I'm now toying with the idea of swapping to a non-boosted setup, just to see what it feels like.

There are several potential donor cars...some Subaru Legacies use a 1 1/16" MC with four ports (2 front & 2 rear) that is quite easily adapted and several Nissan/Infinity models use a 1" MC that features an integrated proportioning valve that really simplifies installation (fewer hardlines to fab).
Both units work quite well with the RX-7 brake calipers but I don't know what your RX-2 has, so I can't say how they would work for your application.

No matter what, you're probably in for some "try it and see" experimentation.
I'd recommend that you start by redoing your stock hardlines so they terminated conveniently close to the master cylinder using splice ends.
Several Toyotas use double ended female splices with the correct thread (10 x 1.0) and handy mounting flanges set up for 6mm bolts...these make spiffy line ends and look OEM.

Once you've done this, swapping out a MC for another with different port locations is easy since all you need is to configure short hardlines to mate with your system.
While at the junkyard snag lots of brake lines, some of which are cleverly shaped and can be used with little tweaking.
When testing, I spent little time making the short lines look good and just waited till I decided on a final setup before making nice lines.

It's actually kinda fun to play around with.

sen2two

iTrader: (10)

thanks...

but after i posted that, i did a lot of reading about braking. pretty interesting stuff. and i found Wilwood products arnt as exspensive as i thought. im looking at a Wilwood master and pedal set up. And as long as your pedal ratio is correct, you dont have to press that hard. same as using a small ratchet Vs. a long breaker bar.

im just having trouble with one thing. the wilwood master i found only has one outlet on it for brake lines. theres usually 3 outlets on a MC, front, front, and rear. am i supposed to somehow split this one opening into a 3 way T?

clokker

iTrader: (2)

Really depends on how you set up the system.
In a perfect world you run two cylinders- split front/rear- each sized for the calipers they operate.
More commonly for a street car you'd have but one cylinder and it's outlet would be split in two with one side going to the proportioning valve for the rear and the other split again for the two front calipers.

The only downside to the Wilwood/Tilton parts is they don't use a metric thread so you'll have to make custom lines instead of the cheap, generic ones.

Far cheaper to use a OEM junkyard part which will have multiple ports and use standard metric threads.
The only thing you'll have to modify is the input shaft (since the OEM cylinders really don't have one...).

Black91n/a

According the FSM it's only true of the S5 TII's, the rest got the same MC, a 7/8" one.

clokker

iTrader: (2)

I stand corrected.

Anyway, IMO the 4-piston calipers work best with a 1" master cylinder.

sen2two

iTrader: (10)

i did a lot of looking around cause its hard to find the correct year 929 in junk yards here. and the 89-93 240sx has a very similar master cylinder. and theres probley 7-8 of them in the junk yard down the street from me right now.

clokker

iTrader: (2)

Have you thought about how you're going to deal with the pushrod?

sen2two

iTrader: (10)

i was just going to cut a section out of it and reweld it. that should take car of it.