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Single Rotor brake Master (F)

Bought. Put it on and it stops pretty good. Has some play, but i suspect some more bubbles i couldn't get out. Gonna bleed it to death tomorrow.
 
Stock caliper is actually pretty good. Rebuild it if it leaks, slap on some modern pads and resurface the rotor.
A good upgrade would be larger slotted/drilled rotor with a bracket to reposition the caliper. Now, gotta figure out which rotors to use, and make a bracket.
 
A tip I picked up from the ZRX guys. For twin brakes a master with a 14mm bore will actually give you more stopping power. I did it to Simons 750 (retrofitted dual disc but used the single disc master) and that thing will stop your face off. Best brakes on any GS I've ever rode. Ridden. Whatever.

Guys over there will use the mono caliper master from a ninja 250 and in combo with the six piston calipers the Rex already has it will stoppie that 500 lb monster. Winning!
 
TheCafeKid said:
A tip I picked up from the ZRX guys. For twin brakes a master with a 14mm bore will actually give you more stopping power. I did it to Simons 750 (retrofitted dual disc but used the single disc master) and that thing will stop your face off. Best brakes on any GS I've ever rode. Ridden. Whatever.

Guys over there will use the mono caliper master from a ninja 250 and in combo with the six piston calipers the Rex already has it will stoppie that 500 lb monster. Winning!
Click to expand...

Truf.

Pressure = Force / Area
The smaller the bore, the more pressure is generated within the system.

An issue one may run into is that the stroke of the smaller master cylinder may not displace enough fluid to move four pistons their full travel, but these bike calipers have no return springs to take up distance between the disc's and pads so it shouldn't be a big issue.

I have a '78 GS with the single disc front, single piston caliper so i'm thinking about doing salty_monk's fireblade disc / twinpot upgrade.:cool:
Just need brackets and a twinpot caliper.
 
The smaller bore will take a longer lever travel for the same amount of caliper piston movement - not an issue for most moving from 5/8" to 14mm but should be considered for anyone looking into downsizing their master cylinder....

There is no direct fit caliper for the 550's etc that use the larger rotor. If you swap to a fork lower from a twin rotor bike (650 in the case of the 550) you can then fit a Kawi twin pot with one of the brackets I have. :)
 
I started up another thread before finding this one, and seems it's somewhat of a duplicate thing...

http://www.thegsresources.com/_forum/showthread.php?t=174735

Anyways, just seeing if there's any other train of thought on a couple of options that are so far available to me:

A CBR250R MC19 master cylinder which has a 1/2 inch piston bore, or a Yamaha R1 master cylinder that has a 14mm piston bore, but will need a new lever.

Apparently both are in good working order (except the R1 lever end).

I expect with the CBR cylinder and a braided steel line, I should get nice firm brake action with the stock caliper and possibly a bit more "feel" from the slightly longer lever travel.

Does that sound about right? Any other opinions/thoughts?
 
pete said:
I expect with the CBR cylinder and a braided steel line, I should get nice firm brake action with the stock caliper and possibly a bit more "feel" from the slightly longer lever travel.
Click to expand...

Yup, sounds about right. It won't be as stiff of a lever but you can apply a good bit more force through the system resulting in a lever that has a little more play after the pads touch the rotor.

Attached is a table of MC/Caliper final ratios. For a single piston caliper ideally you'd want a 12:1 - 14:1 ratio.
Numerically higher ratios/mechanically lower ratios will have more "feel", while numerically lower ratios/mechanically higher ratios will be more stiff/wooden.

I have a stock single 43mm? front caliper, stock disc, 1/2" MC (down from the stock which i believe is 14mm), and it is a world of difference. The 14mm lever was rather stiff and didn't afford me much power to the caliper. With the 1/2" I can come close to locking the front up with 1 finger running the the stock (1977) rubber lines and stock (1977) brake fluid drenched pads. I have EBC pads and stainless lines on the way and i can't friggin' wait to see how it stops after those go on:cool:
 
Cool, thanks for the confirmation.

However, I just had ChicagoBob let me know on my other thread that Mikes XS has a few different master cylinders, and all the suitable ones are less than $80 AUD. The CBR one on eBay is $50 AUD and I'll probably have to pay a similar amount of postage for it and it's second hand.

So, depending on shipping costs (trying to find that out now), the Mikes XS 13mm is what I'm eyeing off now.
 
Gonna be around $US110 shipped to Aus, not too bad... CBR will probably be $10 - $20 shipping interstate so $60 - $70 total, but it's second hand.

I think the Mikes XS option is better, but I'll need to be patient now as I have some budgetry constraints at present...
 
Good stuff. You will be pleased with the 13mm if that's the route you go. Just be sure you bleed the snot out of it.
 
As it turns out, my budgetry concerns were unfounded, that's only stopping my exhaust...

Ordered a 13mm from Mikes XS last night :)
 
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