Regarding this page that everyone seems to reference:
http://www.rx7.org/Robinette/mastercylinder929.htm

This write-up (as well as this one: https://www.rx7club.com/showthread.p...&highlight=929) tell you that you have to create a new line with a new fitting because the banjo won't work. Then look at the last photo on that web page, and you'll see he has the 929 MC installed using the old banjo bolt! Notice the line clamped to the shock tower, that's how you can tell it's the same car as in all of the other pics.




This is how I did mine, and I'm not getting any leaks. Has anyone else done this to retain both banjo bolts? It seems to make sense that it would work.

Thanks in advance.

 

Do you have stock calipers?

 

The port on the 929 master cylinder closest to the firewall isn't machined flat to offer a good sealing surface for a crush washer, it's just cut out and tapped for a regular tube nut. I had a nice pretty stainless line with banjo on mine, it literally SPRAYED brake fluid when I tried to bleed it out. I noticed this soon afterwards and put a hard line with tube nut into it.

If there is a banjo in the one closest to the firewall and it isn't leaking, probably just lucky. It's not designed to use a banjo.

 

Yes, but not sure what difference that makes.
Aah, makes sense. Mine dripped a bit when I was bleeding, I just tightened it and the leak was gone, but I may have to replace the MC, so I'll do it properly next time. His pictures still baffle me, though. :\

 

It seems the 929 brake master will reduce pedal travel, increase pedal pressure (more pressure required by your foot) and reduce pressure at the calipers.

The 929 master increases the area of the master which effectively decreases the pressure at the calipers.

Is it an upgrade?

 

Yes, it's an upgrade. Seems to me that it would give the same output pressure for greater input pressure. I don't see how it could produce less line pressure unless you're comparing them with equal pedal pressure.

 

the 929 master cylinder will have a volume larger than stock so it will take less pressure(pedal length) to displace that much brake fluid to brake.

 

I think you guys have it backwards. The bigger master cylinder will require more pedal pressure for the same line pressure than stock. More volume yes, less pressure at the caliper.

If you had a tiny master cylinder you would have to push the pedal a long distance but you would develop more pressure (pounds per square inch). Decrease the square inches and the PSI increases.

Force on master cyl piston/ area of master cyl piston = pressure in the line

For example:

20lbs/1 sq in = 20psi

20 lbs/.75 sq in = 26.7psi


The math is simple, you want a force at the brake caliper pushing on the pad. Force divided by area. Figure out the line pressure the master cylinder generates, then multiply that by the area of the pistons at the caliper to get the pounds force. Since you have stock calipers we don't need to do that part of the math since it is constant. The larger master will generate less line pressure for the same pedal pressure.

 

This mod increases pedal feel, reduces pedal travel. Firmer pedal. More control.

At least that's the hype. I've got one on a shelf. Will report after install.

 

Hate to bump this, but what was the final verdict on this "upgrade"

Yay or nay?

I'm installing a BBK and need to change my master anyways because it has gone bad.

 

I just did it a few weeks ago and I give it a yay! Pedal feel is much better (harder) and it is easier to modulate the breaks without locking them up. it also took out the slop at the top of the brake pedal.

The write ups for this mod make it out to be much harder then it actually is. The hardline that uses the banjo fitting can be reused after being slightly bent and a 12" line is the perfect length to fabricate the new line. I bought a 12" line with the metric fittings already on it from autozone and it was the perfect length. I didn't have to cut the line and re flare it as described in the write up. I just bent it to fit and I was done.

I see this mod becoming more common as the RX7 master cylinders are getting harder to find. They were on back order last time I looked into it.

 

For those thinking about doing this mod, I found Atkins Rotary's Ebay store where they sell the 929 MCs (HG31-43-400R-0G) new for $99.95 shipped. Mazda 929 New Brake Master 1992 To 1995 | eBay

Mine should be here sometime next week and I'll post my impressions.