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at1rest wrote: ↑Fri May 31, 2019 2:57 pm Single disk.
But what about the part number look up at
https://www.shopbmwmotorcycles.com/p/BM ... 02357.html

???

That is generic advice. The R65 could come with one or two front disks. A single disc would come with a 13mm master. A double disc with a 16mm master... but... it's not that easy. For various reasons, the fitment varied. A PO might have fitted a 16mm master to a single disc or on the other hand, might have fitted a second disc without changing the master leaving it at 13mm. The only thing to do is to dosmantle and check the existing master.

You also have to face the possiblility that the master might be beyond salvage and you may have to source a replacement.

Sorry to be a Jonah but I'm just saying it like it is!

Rob

If it turns out you have a single disk with a 16mm master cylinder then the brakes will be truly awful and you will need a grip of iron to make them work at all. They are not great with the 13mm and BMW recognised that by dropping to a 12mm for the 81 model year onwards. If you are going to replace the master cylinder I recommend you go for a 12mm rather than a 13mm. Some have gone smaller still but it does increase brake lever travel.

If the master cylinder is original i.e. it has not been sleeved then the size is printed on it. Look underneath and on the rear face you should see the number cast into the master cylinder body.

Rob Frankham wrote: ↑Sat Jun 01, 2019 6:15 am

at1rest wrote: ↑Fri May 31, 2019 2:57 pm Single disk.
But what about the part number look up at
https://www.shopbmwmotorcycles.com/p/BM ... 02357.html

???

That is generic advice. The R65 could come with one or two front disks. A single disc would come with a 13mm master. A double disc with a 16mm master... but... it's not that easy. For various reasons, the fitment varied. A PO might have fitted a 16mm master to a single disc or on the other hand, might have fitted a second disc without changing the master leaving it at 13mm. The only thing to do is to dosmantle and check the existing master.

You also have to face the possiblility that the master might be beyond salvage and you may have to source a replacement.

Sorry to be a Jonah but I'm just saying it like it is!

Rob

Thanks Rob. No Jonah. Just good info. I appreciate your input.

barryh wrote: ↑Sat Jun 01, 2019 6:24 am If it turns out you have a single disk with a 16mm master cylinder then the brakes will be truly awful and you will need a grip of iron to make them work at all. They are not great with the 13mm and BMW recognised that by dropping to a 12mm for the 81 model year onwards. If you are going to replace the master cylinder I recommend you go for a 12mm rather than a 13mm. Some have gone smaller still but it does increase brake lever travel.

If the master cylinder is original i.e. it has not been sleeved then the size is printed on it. Look underneath and on the rear face you should see the number cast into the master cylinder body.

Thanks barry,

I'll see if I can find the number.

Your reference to the look up clearly says 16mm diameter right above the yellow warning triangle.

George Ryals wrote: ↑Sat Jun 01, 2019 11:36 am Your reference to the look up clearly says 16mm diameter right above the yellow warning triangle.

Yes George. My problem is not knowing anything about this and discovering what is currently in there, and wondering why the original owner bought that new 16 mm piston.

You really need to plan on removing and opening the caliper.
Unfortunately, replacement pistons can be hard to find. Perhaps you know someone with a lathe?
The rubber hose will be replaced. I replaced the metal lines as well, when I did my '79, simply because they were available OEM.
There is a small rubber o-ring that seals the fluid path between the two caliper halves. Last I heard, they are not listed on the fiche, but suppliers do have them.
There is no listed torque value for the caliper-half fasteners. Just tight as hell, then a little more. Steel fastener into female ALLOY threads, but they are large.

These pictures show why regular fluid changes are important.

This video was taken after the rebuild (along with rebuilding the forks and replacing the brake rotor).

https://youtu.be/961A4V371sc?t=69

Thanks Rob!