SRX600 vs 400 master cylinder bore sizes

[Ram427]

Hi all

Hopefully someone can help me on my first post.

I have a 1jk srx 600 but it looks like a previous owner has swapped the wheels for the 2nx version which has the single 320mm disc and four piston caliper.

The front brakes take a Herculean effort to get the bike to stop.

My master cylinder size is 5/8 . Is this the m/cylinder for the twin disc set up? Do I need a 14mm m/cylinder which would lessen the force needed.

Thanks in advance

Roger

[Ian]

Hi Roger, I will stand corrected but Im sure the standard master cylinder on the Mk1 SRX600 is 5/8" as you say (nearest metric equivalent 16m/m)
From the Mk11 (2NY 400 and 2NX 600) onwards throughout the range (both 400 and 600) is a master cylinder diameter of 14 m/m. If you have the 320 disc I would certainly say you need a 14m/m master cylinder. The 320 floating disc setup, in my opinion, is a far superior brake than the rigid twin disc setup of the earlier models. In fact Im almost sure the single 320 disc lasted till the end of production.

In true Yamaha tradition Im sure you will find a similar master cylinder on different models of a similar year

HTH Ian

[iansoady]

I have to say I know nothing about the specifics. However, in general, the optimum master / caliper ratio (area) is reckoned to be around 20. The bigger the ratio, the less lever pressure but of course greater travel and vice versa.

Obviously, if you have twin discs and multiple piston calipers for each you need to multiply up the areas.

My Guzzi V50 with linked brakes had a really wooden front brake till I changed the 15mm master cylinder for a 12mm one. It's still hard work but does at least do something without rupturing my forearm muscles every time I use it!

Most master cylinders can be adapted to fit most bikes without too much trouble and it's just a matter of research to find out what's what. The master cylinder I used actually came from a Honda Silverwing apparently.

[Ram427]

Thanks Ian(s)

Great help from both, as luck would have it, I bought a 2nd hand m/cyl 14mm from a 400 some time ago so i’ll Overhaul it and put it to good use.

Does anyone know the diameter of the pistons in the 400 4 pot calipers. All the searches i’ve done with parts suppliers doesn’t list the diameters.

Thanks again

Roger

[themoudie]

Aye Roger,

Welcome to the forum. 

Just been out to the workshop for a measure up and a look-see at the front brake on Sally (1986 SRX600 1JK with 1988 SRX400 wheels). I am about to add to the mayhem rather than clarify, as the front master cylinders that I have on both Sally and an SRX400 Mono are both ⅝" (16mm) bore and I find it works fine on Sally, with a stainless, braided brake hose, stainless steel pistons and Vesrah organic pads works fine for me. SteveL uses an organic pad and a sintered pad in the caliper, as it suits him.

Diameter of the stainless pistons I have in both Sally and the Mono's caliper are 32mm O.D. and the last ones I bought, were from Yambits. Their quality is fine and the seals supplied are fine as well. Use a good quality red rubber grease when installing and maintanence amounts to taking the pads out, pumping the pistons forward and then giving the whole caliper a good scrub with a detergent (AutoGlym) (NOT BRAKE CLEANER) and rinse off with hot water. Push the pistons back in, refit the pads and pins with a touch of copper grease (applied with an artists's paint brush!  ) torque up the mounting bolts to 25ft/lbs and pump the pads back to the disc.

It appears from the Fowler, Yamaha parts lists that these calipers are shared with 1988-1992 FJ1200 & FJ1200A, FZ750 Genisis 1989-1991, FZR1000 1987-1988, FZR750R 1988, SRX400 1988 and TDM850 1991-1995. However, OEM parts are eyewateringly priced!

Link to the Yambits SRX400 brake piston page: 1988-89_SRX400_stainless_pistons

Speak to Yambits if you require specific information before ordering.

Images of my bits for reference, attached.

Also, if you haven't found it yet, I would recommend a view of SteveH' website: SRX600_website

My regards, Bill

[attachment deleted by admin]

[Ram427]

Aye Bill

thanks for the info, yes, I've been through SteveH website. It was that which lead me to the conclusion of my bike/ wheel combo.

In terms of the m/cyl size, I had assumed that the previous owner had swapped wheels but didn't bother with the m/cylinder for whatever reason. If the single disc versions had 5/8 bore then the ratio of calliper:m/cyl would be 16:1. With a 14mm, the ratio becomes 21:1 which is more in line with Ians stated ideal of 20:1, neither are out by a million miles and I guess usage of either is down to preference.

working back with a 5/8 m/cyl, the "ideal"piston size should be 35.5mm. I don't suppose you know if that's what the twin disc calliper piston diameters come out at? all the tinerweb searches I get don't list the diameter.

the bike is current SORN but the recent weather has started me dreaming again.

I think I'll take the pads out and check that all the pistons are free, it currently feels like it needs a servo added 

thanks again

Roger

[Ian]

Hello again Roger, you haven't said if you have stainless braided hoses or the original type rubber ones. If the latter then  I would seriously suggest you fit the braided type which will improve the performance of what ever setup you have.
Regards Ian

[themoudie]

Aye Roger,

Welcome to the forum. 

Diameter of the stainless pistons I have in both Sally and the Mono's caliper are 32mm O.D. and the last ones I bought, were from Yambits. Their quality is fine and the seals supplied are fine as well. Use a good quality red rubber grease when installing and maintanence amounts to taking the pads out, pumping the pistons forward and then giving the whole caliper a good scrub with a detergent (AutoGlym) (NOT BRAKE CLEANER) and rinse off with hot water. Push the pistons back in, refit the pads and pins with a touch of copper grease (applied with an artists's paint brush!  ) torque up the mounting bolts to 25ft/lbs and pump the pads back to the disc.

It appears from the Fowler, Yamaha parts lists that these calipers are shared with 1988-1992 FJ1200 & FJ1200A, FZ750 Genisis 1989-1991, FZR1000 1987-1988, FZR750R 1988, SRX400 1988 and TDM850 1991-1995. However, OEM parts are eyewateringly priced!

Link to the Yambits SRX400 brake piston page: 1988-89_SRX400_stainless_pistons

Speak to Yambits if you require specific information before ordering.

My regards, Bill

Aye Roger, I wrote the piston diameter in my previous post, so have just quoted it and then made it bold for clarity. 

I hope this is what you are looking for?

My regards, Bill

[Ram427]

Hi Ian
good call, my lever pull is rock hard, so I don't think the rubber pipe (which I do have) is expanding otherwise the pull would be easy but no braking effort. but definitely an upgrade in the future.

Aye Bill

I had assumed that both your bikes had the 4 pot single calliper brakes @32 mm.  What I was trying to find out was the diameter of the pistons in the twin disc 2 pot callipers so I could see the ratio against the 5/8 master cylinder.
A bit more googling has yielded a piston size of 38mm in the 2 pot calliper, so

a 400 m/cyl @14mm with 4 pot single calliper @32mm dia has a ratio of 21
a 400/600 m/cyl @ 5/8 (16mm) with a 2 pot calliper x 2  has a ratio of 23
a 600 m/cyl @5/8 (16mm) with a 4 pot single calliper @32 mm diameter has a ratio of 16

so on the face of it, you could think that the single disc 4 pot should use a 14mm M/cyl, and the twin disc 2 pot callipers should use the 5/8 but that isn't borne out by real life on both yours and my bike.

I'm going to give the 14mm master cylinder a go, if there is too much travel I'll think again.

thanks all

Roger

[themoudie]

Aye Roger, nae bother. I'll be interestd to read how it goes.

Good health and my regards, Bill

[Steve H]

I run a 14mm Mcyl in conjunction with a FZR1000 caliper which has equal size pistons. I have tried 12mm and whilst it had a light feel the travel was a little too much for my liking.