Grimeca front calliper - which master cylinder ?

Hello
I am new on the commando 850.... (have 961 and wanted to go to the origin ...)
I got via a friend a Grimeca (2 pistons ) calliper and bracket to replace the original one.
I would need to replace the master cylinder bit which size/diameter would fit (the one installed is also not original and damaged (poor quality)
Thank you !!

Hi Chris, you need to measure the caliper pistons, or look on the caliper body where it may have the information. Then once you have the diameter go here to find the ideal M/cyl size.


Ideally you want 23 - 27:1 ratio.

Hope that helps,

cliffa.

The standard Grimeca caliper pistons are normally 41mm.

Chris CSTM said:

Hello
I am new on the commando 850.... (have 961 and wanted to go to the origin ...)
I got via a friend a Grimeca (2 pistons ) calliper and bracket to replace the original one.
I would need to replace the master cylinder bit which size/diameter would fit (the one installed is also not original and damaged (poor quality)
Thank you !!

Click to expand...

Options on the master cylinder...
1. Have your existing cylinder resleeved down to 13mm
2. Purchase a new or recon 13mm cylinder
3. Buy a new 13mm unit from Magura, Brembo etc

olympus said:

Options on the master cylinder...
1. Have your existing cylinder resleeved down to 13mm
2. Purchase a new or recon 13mm cylinder
3. Buy a new 13mm unit from Magura, Brembo etc

Click to expand...

And if you want to keep the standard look, Andover Norton now provide a 13mm M/cyl identical to the original. However 41mm pistons and 13mm M/cyl (of any make) may still feel wooden according to vintage brake, as the ratio will only be 19.89:1. Ideal would be a 12mm @ 23.35:1

Cheers,

cliffa.

Madass does a DIY resleeve for the original master cylinder at 1/2" to give you 20.84 ratio.

Lever ratio and disc diameter are equally important as master cylinder and caliper piston ratio imo.
Pls note that modified master cylinders have been unavailable from AN as well as RGM since some time. Possibly awaiting production of a new batch.

If you replace the caliper with a Grimeca then the best thing to do is replace the M/C with a Gremeca unit as well 12" floating disc and SS brake line, I went the full Gremeca set up over 7 years ago now after my stock brakes nearly killed me, best thing I ever done as now I have front brakes on my Norton which is as good as my modern Triumph brakes.
Norton stock disc will work great when all new but after a few hard years of riding they will let you down badly even after a few rebuilds, I rather spend the money on all new brakes system than trying to repair brakes that are over 40 years old and having modern brakes that will work great even with one finger on the lever, my life is more important that trying to fix a old problem with worn brake system, and it will let you down one day as mine did without any warning and put me out of action for 6 weeks, but it gave me time to order from RGM and new Grimica brake system and to have it all set up before I was out of plaster.

Ashley

Thank you all for your advices ... new parts seems indeed reasonable choice I will look for MC and will look at the disc. even if my Commando set up is « pretty Original »

Peter R said:

Lever ratio and disc diameter are equally important as master cylinder and caliper piston ratio imo.
Pls note that modified master cylinders have been unavailable from AN as well as RGM since some time. Possibly awaiting production of a new batch.

Click to expand...

Perhaps I had the last 2 from stock very recently, the first one was faulty, the second is fine.