23mm master cylinder, out of what??? Options

[Mueller]

RX7=36mm (ea)

Big Reds=36/40

Boxster(F)=35

M-Caliper (early rear)=38

[Brett W]

Everybody follow alonge here:

The 23mm master cylinder is not going in anything stock. I am well aware of the problem with upgrading the master on stock system.

I will get the Volvo piston sizes later tonight.

[ArtechnikA]

QUOTE (Brett W @ Feb 15 2005, 05:28 PM)

Everybody follow along here: The 23mm master cylinder is not going in anything stock. I am well aware of the problem with upgrading the master on stock system.

i'm not worried about you; you know what you're doing.

but you are not the only one asking questions in this thread...

and you are not the only one reading the answers.

[Mueller]

QUOTE (Brett W @ Feb 15 2005, 03:28 PM)

Everybody follow alonge here: The 23mm master cylinder is not going in anything stock. I am well aware of the problem with upgrading the master on stock system. I will get the Volvo piston sizes later tonight.

i knew that (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

problem is, people see those eBay ads and get excited...."oh, it's a racing part, it'll make my car better"...

is your rotor hat off the shelf with no mods except the thru holes for the lug bolts?

how is the alignment with the caliper? is your pricing good? best pricing I found was with Pit Stop USA for the rotors..........still undecided which direction I'm going with mine....

[Aaron Cox]

got a volvo caliper question....

they bolt up fine. they can be centered on the rotor with a washer.... how much of the pad over hangs the edge of a rotor?

[Mueller]

QUOTE (Aaron Cox @ Feb 15 2005, 03:40 PM)

how much of the pad over hangs the edge of a rotor?

something like 1/8" or a tad bit more...nothing to worry about unless you put on new pads and wear them down enough for the overhanging material to touch each other when you hit the brakes...you can always add a bevel to the edge to help minimize/eliminate the overhang

[Aaron Cox]

QUOTE (Mueller @ Feb 15 2005, 03:45 PM)

QUOTE (Aaron Cox @ Feb 15 2005, 03:40 PM) how much of the pad over hangs the edge of a rotor? something like 1/8" or a tad bit more...nothing to worry about unless you put on new pads and wear them down enough for the overhanging material to touch each other when you hit the brakes...you can always add a bevel to the edge to help minimize/eliminate the overhang

1/8th thats it???? i thought something like a quarter or something.....

hmmm..... maybe front and rear volvo calipers.... (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) that could probably use a 23mm MC....

[lapuwali]

CODE

914/4 & A rear  320i/M front   RX-7 4piston  Boxster front  M rear                                   42x4                 48x4              36x8               35x8               36x4 stock 914/4       17      24                    32                   36                  34                  18 stock early 911 19       20                    26                  29                  27                  14 mercedes          23       13                    17                  20                  19                 10

If the table above looks all messed up, it's Andy's fault. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)
I could attach the spreadsheet, too, I suppose.

Down the left are the three most commonly used MCs. Across the top are the brake calipers I have data for.

The numbers in the table are the ratios of the MC piston area to the total caliper piston area for the front or rear half of the circuit. Note the stock 914/4 ratio of 24:1. With a smaller number, pedal effort increases for a given braking force, but pedal travel decreases. If the number gets too small, you need more pressure than you can physically exert on the pedal to lock the tires. If the number gets too big, the pedal hits the stop before you're generating max braking power (actually, before it gets there, the pedal will usually feel all mushy, like it needs bleeding). So, you're trying to strike a balance between pedal effort and feel. Most people like a harder pedal (smaller number), but most people don't have the leg muscles of a Mr. Universe qualifier (number too small). For non-servo'd brakes, the range 19-26:1 seems to be a good one, with personal choice determining where along that line you want to be.

See that the 19mm with stock 914/4 calipers requires more pedal effort, but less travel. Some people like this setup, with a 20:1 ratio, and I can say it's adequate but not ideal (PO fitted this to my car). I can just barely lock the tires with big effort, but day to day the brakes feel OK.

Note that with with the 320i/M fronts/A fronts (the 48x2 calipers), you get more braking force with slightly longer travel using a 19mm MC. This is why so many people like this setup. Less pedal effort than stock, but not so little you have to practically push the pedal through the floor to get full braking.

The RX-7 or Boxster calipers require a 23mm MC just to get down to the 19mm/stock setup. With a 17mm MC, I'd expect this setup to be very touchy and feel awful, requiring a looong pedal to get braking effort. The Boxster fronts with the 19mm MC will feel a bit more powerful than the 320i/M caliper w/ the 19mm setup. I would think a 21mm MC (if such a beast exists or could be made) would be about ideal for these calipers.

Some rear calipers are also included, and you'll note how small the numbers are. This indicates much less braking force for those calipers, which is how you get front/rear brake balance w/o a prop valve. Also note that adding a bigger MC with bigger front calipers REDUCES rear braking even more, moving the brake bias forward. This is why removing the prop valve is usually helpful in such cases. To keep brake balance, you need to increase the size of the rears as well as the fronts when upgrading.

[nsyr]

QUOTE (ArtechnikA @ Feb 15 2005, 03:24 PM)

you are going to need to change the hard lines to the front and possibly to the first junction to the back.

why would you need to do this?

[ein 6er]

caliper spec sheet

[ein 6er]

and brake bias sheet

[Mueller]

QUOTE (ein 6er @ Feb 15 2005, 04:34 PM)

and brake bias sheet

here is a great link with tons of Porsche caliper and brake information

Porsche Brake page

[ArtechnikA]

QUOTE (nsyr @ Feb 15 2005, 05:55 PM)

QUOTE (ArtechnikA @ Feb 15 2005, 03:24 PM) you are going to need to change the hard lines to the front and possibly to the first junction to the back. why would you need to do this?

you would need to do it because the lines exit on the opposite side of the MC vs the OEM, and it is longer, so the hardline might not be long enough to reach the outlet port in the MC.

[Mueller]

second pdf file screen shot:

[slivel]

I installed a 23mm M/C this winter and have one test day at Willow to evaluate the difference. Previously I was running a 19mm and always had too much pedal travel when the pads wore anything beyond about 75%. I would only have a good firm pedal after a new pad change. Calipers are Carrera front and SC rears so I was on that margin between the 19 being too smalll and the 23mm too large. After a couple of hours testing, I can modulate this combination of the 23mm and the Carrera/SC calipers OK, but its probably not for everyone. Pedal pressure is significantly higher. I plan to upgrade to Boxster fronts so this should bring the overall ratio into a more optimal range. My first race with this setup (23mm, Carrera/SC) is this coming weekend in Phoenix (if we don't get rained out). I let you know how it went.

BTW, I did install with the steel crossmember, but had to take off about 1/8 inch dimple with my grinder and and another 1/8 inch off the casting bump on the M/C. It fit but had me exercising my four letter word vocabulary. Not a fun job - the fluid supply lines were tricky to insert into the M/C. I loosened the crossmember and dropped it and the front suspension arms about 2 inches to get the M/C in.

Steve

[ArtechnikA]

QUOTE (lapuwali @ Feb 15 2005, 05:54 PM)

...I would think a 21mm MC (if such a beast exists or could be made) would be about ideal for these calipers. ...

there *used to be* a 20,5mm MC used with the early 911E and 911S with aluminum calipers front but the rear brakes unchanged. those have been NLA for years.

BTW - we call these MC sizes by their nearest metric equivalents, but they're *actually* English-system measurements. 19mm is really 3/4", that 20,5 is really 13/16", and the 17mm is really 11/16" (11, 12, and 13/16")

[davep]

Just a note here, the master cylinder sizes are actually in increments of 1/16 of an inch, they are not metric. The '19' mm is actually 3/4 inch. Moreover, the 911S used a 20 mm master with the aluminum 'S' calipers. It would be really nice if it was still available.

17.46=11/16
19.05=3/4
20.46=13/16
23.81=15/16

[ArtechnikA]

QUOTE (slivel @ Feb 15 2005, 06:43 PM)

...the fluid supply lines were tricky to insert into the M/C....

here is the trick on that that i learned only after having struggled with it - once.

put the reservoir lines in the MC while it's still sitting on your bench and you have good leverage from the top. some brake assembly grease helps, but mostly it's just a matter of being on top of the problem rather than it being on top of you.

then snake the lines up to the reservoir as you install the MC onto the studs ...

[lapuwali]

QUOTE (ArtechnikA @ Feb 15 2005, 03:47 PM)

QUOTE (lapuwali @ Feb 15 2005, 05:54 PM) ...I would think a 21mm MC (if such a beast exists or could be made) would be about ideal for these calipers. ... there *used to be* a 20,5mm MC used with the early 911E and 911S with aluminum calipers front but the rear brakes unchanged. those have been NLA for years. BTW - we call these MC sizes by their nearest metric equivalents, but they're *actually* English-system measurements. 19mm is really 3/4", that 20,5 is really 13/16", and the 17mm is really 11/16" (11, 12, and 13/16")

Something handy to know.

On Honda motorcycles (using Nissin brake parts, Nissin is owned by Honda), they cast the size of the MC into the body of the MC. However, some are shown as metric (11mm for a particular 400), some are English (0.5 for a popular 600). I'll bet the 11mm isn't really metric, either, but 7/16" (only 4 thou different: 0.433" v 0.437").

Wilwood makes a "21mm" (13/16") and a "22mm" (7/8") MC with a remote setup. They're only single circuit, though. They make some dual circuit MCs, but they're big (smallest is "25mm" or 1").

[Britain Smith]

I have Carrera (wide-A) calipers all around and according to that link above the stock set-up was a 20.64mm MC vaccum assisted. Do you think that a 23mm MC would be too large for this set-up when not using vaccum assist? Also, should a proportioning valve be used?

-Britain