Advice please on Front master cylinder conversion

[Darryl Flynn]

Hi, i have a 1980 BMW R100RS which is fitted with the standard 40mm ATE calipers and cable operated under tank master cylinder.

All is working but i have been offered this Master cylinder assembly of a later R100




and would like to know what else is involved in converting to this handlebar mounted set up.

Can i retain my existing starter button kill switch assembly and integrate it into the unit off the photo or do i need a complete assembly including switch gear from a later bike. Will my existing throttle assembly work with this later set up or do i need that as well?

The main reason for considering the change apart from hopefully improved braking is that this master cylinder is fully working and VERY cheap.

A breakdown of what is needed or involved ( or links ) using later BMW parts would be greatly appreciated.

Cheers Darryl

[Motorhead]

you didn't mention piston size

my point of view says switch gear should fit

BMW bits have decent model to model ratio of working out


a 13mm piston will make that 40 nice

[chasbmw]

13mm is good.

Is the mc twin throttle cable or is it set up for single cable with splitter?

You will need top hydraulic brake hose, plus splitter that fits where existing undertank MC is.

One of the wires that goes to undertank level warning light will needed to go to earth, or your other warning lights won't work

[Darryl Flynn]

13mm is good.

Is the mc twin throttle cable or is it set up for single cable with splitter?

You will need top hydraulic brake hose, plus splitter that fits where existing undertank MC is.

One of the wires that goes to undertank level warning light will needed to go to earth, or your other warning lights won't work

Hi Chas, not sure re twin or single cables yet as it has not arrived from Ebay but for £20 it seemed a good starting point.

Obviously as yet i am not certain of bore size but am aware that i will need hydraulic splitter amd brake light switch.

My main concern is whether my existing starter / kill switch assembly will marry up ok with what i have bought.

Time will tell but for £20 it's worth a punt.

Darryl

[chasbmw]

My 1975 switches fit on my late 80s/90s 13mm twin pull MC

[moosehead]

Your switches should fit....both LH and RH.

This is twin disc ATE set up on your 80 RS? 13mm MC should be good (oops chasBMW just mentioned). Undertank splitter and ss brake lines available from motobins at reasonable cost.

I just did the reverse...I put MC and LH/RH switchs from an 83 RT junker (along with twin Brembos brakes and forks) onto a 78 R100/7. The switchs just bolted on but I had to redo wiring in the headlight shell as the turn signal switch on the left switch on the transplanted 83 switch gear whereas the older 78 turn signal switch gear on the right side. Just a plug and play thanks to the colour coded wiring and board. I did put new ss brake lines from the MC to undertank splitter (also from the RT) and then ss lines from splitter to Brembos...greatly improved braking...like a new bike!

The throttle cable was single pull with splitter from the 83RT so just moved this to the 78 which was a dual cable pull...easy conversion.

[Darryl Flynn]

Thanks Moosehead, sounds like i may be able to sort this quite cheaply then. The guy that i am buying the MC from is checking for other bits that will help out for the switch over.

Cheers Darryl

[bbelk]

You will probably need a mirror with a longer stud on the bottom at least that was the case for me when converting a 1975 R90.

[Darryl Flynn]

You will probably need a mirror with a longer stud on the bottom at least that was the case for me when converting a 1975 R90.

Hi, thanks but my bike is an RS so the mirrors ( JOKE ) are on the fairing.

Cheers Darryl