New Front Master Cylinder for 79 GS1000L

[Guest]

I will be replacing the front master cylinder with a universal, I was wondering if you guys think either of the following would work? I've never replaced one of these so I don't know which things to look into for compatability.

http://www.amazon.com/gp/product/B00QYS69E8/ref=ox_sc_imb_mini_detail?ie=UTF8&psc=1&smid=A2GZD2Z67ZDSVI

https://www.denniskirk.com/shindy/master-cylinder-brake-kit-5-8-in-piston-diameter-17-651.p193153.prd/193153.sku

As far as installation goes, tell me if this sounds correct. Detach current master cylinder and remove the lines. Attach the new one, install the lines, bleed the air out with DOT4 brake fluid.

[Nessism]

You need a master with 5/8" bore. Lots of cheaper choices on ebay these days.

[crash7863]

Thank you. Found some 5/8" ones.

[tkent02]

A smaller bore will give you more braking for less finger pressure, IF your calipers and lines are in good shape.

[Nessism]

A smaller bore will give you more braking for less finger pressure, IF your calipers and lines are in good shape.

True, but at the cost of more spongy feel at the lever.

[crash7863]

Changing from 5/8 to 14mm (Which are way cheaper) would require some sort of conversion kit wouldn't it?

[tkent02]

Changing from 5/8 to 14mm (Which are way cheaper) would require some sort of conversion kit wouldn't it?

No, nothing different at all.

True, but at the cost of more spongy feel at the lever.

Not if the lines and calipers are tight.

[Nessism]

Not if the lines and calipers are tight.

Don't mean to go against you here but...

It's simple physics that a smaller bore master will require more stroke distance to move the same amount of fluid as compared to a larger bore master. Even if the parts are in good working order the level feel will never be as firm with a small bore master compared to a larger bore master.

[hannibal]

Make sure you get a MC that uses a 10mm banjo bolt. If you're changing to stainless lines, just make sure your new fittings match the new MC.

[tkent02]

Don't mean to go against you here but...

It's simple physics that a smaller bore master will require more stroke distance to move the same amount of fluid as compared to a larger bore master. Even if the parts are in good working order the level feel will never be as firm with a small bore master compared to a larger bore master.

Which do you want, firm lever or firm braking? I have done this on a few GSes, it's a noticeable difference. I think you don't really have to move much fluid if the lines and calipers are good. The lever doesn't feel any worse, it just stops better.

[crash7863]

I don't know how well the calipers are. Would I want to replace the calipers and rotors with something more modern if they're all beat up? My bike before this was a 600RR, I would like to recreate the feel that bike had.

[Grimly]

Which do you want, firm lever or firm braking? I have done this on a few GSes, it's a noticeable difference. I think you don't really have to move much fluid if the lines and calipers are good. The lever doesn't feel any worse, it just stops better.

I've been finding out about exactly this issue. After rebuilding the GS calipers to nil play, the XJ900 5/8 master cyl is a very effective tool, and I just don't need a smaller one on there. It was always a better m/c than the Suzuki one.
Otoh, I fitted a Kwack 14mm m/c to the XS, and the tiny amounts of play in the calipers are causing some lost motion at the lever - it's a cracking stopper now, but just slightly too much travel before it bites. I'm going back to 5/8 on that, with a Deauville master cylinder.