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83 r80rt front master cylinder
Posted: Thu Nov 20, 2025 4:13 pm
by Basher
The seals are away on the front master cylinder on the r80, it’s leaking out the back, I’ve stripped it and it’s a 15mm cylinder, no real corrosion on the cylinder and it may clean up but I think it’s better to replace it. There seems a few different sizes from 13mm to 16mm and read some comments saying the smaller ones have better feel, anyone got any experience with this or just replace like for like? It’s a twin disc set up
Re: 83 r80rt front master cylinder
Posted: Thu Nov 20, 2025 5:27 pm
by SteveD
My bike is a twin R100RS that came with a 15mm MC. Very wooden feel. I replaced it with a 13mm. That gave longer lever travel but a more progressive feel. It took a short ride only to acclimmatize to the change. 14mm would work too!
But, if your brake was working fine and you were happy with it before the leak, then a new o-ring might be all that's required. Consider doing that anyhow whilst looking for the alternative 
Re: 83 r80rt front master cylinder
Posted: Fri Nov 21, 2025 5:03 am
by Basher
Sound like a 14 would be a good middle ground, the problem is the seal kit is around £80 and no guarantee it will sort it and the new cylinder is around £180, the reservoir leaked as well which i bodged up as I don’t have an o-ring the correct size to sort it so I’m thinking just fit and forget a new one!
Re: 83 r80rt front master cylinder
Posted: Fri Nov 21, 2025 5:04 am
by Basher
Was the twin disks standard on an 83?
Re: 83 r80rt front master cylinder
Posted: Fri Nov 21, 2025 12:00 pm
by Rob Frankham
Basher wrote: ↑Fri Nov 21, 2025 5:04 am
Was the twin disks standard on an 83?
The 1983 R80RT was specified with twin front discs in the US and the 1982 model was specified with them in Europe. I don't have a copy of the Europe brochure to see 83 'Euro' models were so equipped but I would asssume they are, certainly the BMW parts ordering system shows two discs.
Re: 83 r80rt front master cylinder
Posted: Sat Nov 22, 2025 12:34 am
by SteveD
Rob Frankham wrote: ↑Fri Nov 21, 2025 12:00 pm
Basher wrote: ↑Fri Nov 21, 2025 5:04 am
Was the twin disks standard on an 83?
The 1983 R80RT was specified with twin front discs in the US and the 1982 model was specified with them in Europe. I don't have a copy of the Europe brochure to see 83 'Euro' models were so equipped but I would asssume they are, certainly the BMW parts ordering system shows two discs.
I also expect they were dual discs. Partly because they were marketed as an affordable "copy" of the R100RT, (except for the engine size o'course) Fwiw, a quick search via google images only showed twin discs.
Re: 83 r80rt front master cylinder
Posted: Sat Nov 22, 2025 12:43 pm
by Basher
Thanks all, it’s my brothers father in laws bike so I’m not hugely familiar with them, just sort bits and pieces for him to keep it going