76' R90/6 Dual front ATE brake conversion

[achart17]

Hey Guys,
Looking to convert the 76' 90/6 to dual ATE brakes up front. I have a right fork slider that matches to the tube and axel nice but I just cant seem to find much information on the calipers and if the ATEs are left/right specific. I did some research on snowbums site but couldn't find much concerning a conversion for keeping the ATE's. My questions are if the calipers are left/right specific. The difference between silver and blue 40mm calipers. Can the stock fork clamp and top yoke be used or would a triple clamp conversion be necessary. Lots of questions here, thanks in advance. Any other advise for this conversion would be greatly appreciated.

 

[20774]

There are a few older threads in the Similar Threads pane below for some info. RealOEM shows the part number for the R90S caliper...says you need two of them. Sounds like they can be switched...would have to rotate it though.

https://www.realoem.com/bmw/enUS/showparts?id=0294-USA-03-1976-2476-BMW-R90S&diagId=34_0604

 

[69zeff65]

38mm and 40mm calipers

Make sure you have either 2 38mm calipers or 2 40mm calipers to do your conversion. You will also have to upgrade your master cylinder to a dual outlet so make sure it matches up to what ever size caliper you use. I believe the black calipers are the 38mm ones, silver are the 40's (they have the size on them somewhere) and the blue ones may be the Motosport ones but its just a cosmetic difference but I don't know for sure.

Top clamp and all that other stuff is the same so no need to change. I think the calipers can be used on either side, not right or left specific. You just have to switch the bleeder and brake line to keep the bleedr fitting on the top and the brake line on the bottom.

Zeff

 

[RPGR90s]

brakes

Hey Guys,
Looking to convert the 76' 90/6 to dual ATE brakes up front. I have a right fork slider that matches to the tube and axel nice but I just cant seem to find much information on the calipers and if the ATEs are left/right specific. I did some research on snowbums site but couldn't find much concerning a conversion for keeping the ATE's. My questions are if the calipers are left/right specific. The difference between silver and blue 40mm calipers. Can the stock fork clamp and top yoke be used or would a triple clamp conversion be necessary. Lots of questions here, thanks in advance. Any other advise for this conversion would be greatly appreciated.

I have an R90s so it has the stock dual ATE 38mm setup. The calipers are black. Somtime in '75 or '76, the calipers were enlarged to 40mm but were still black. Blue 40mm calipers were exclusive to later r100RS models, but would work with your conversion.

And yes, there are specific left and right calipers in regards to how they plumb. I think you could switch one from left to right by simply turning it over, but your brake line plumbing might be inconsistent.

And if I recall, the dual disc master cylinder found on the R90s has a different bore size than the single disc setup.

FWIW, I've owned R90/6's with the single disc setup and they stopped fine, once the caliper is aligned, with correct brake pads and brake lines either in stainless or with stock lines that don't expand.

I also owned a R75/5 with stock front drums and I would swear that setup worked as good as the dual discs on my R90s.

No matter what you do, you're not going to transform your braking into modern Superbike class, so if it's aesthetics you're after, then I would say go for it.

just my $.02

RPGR90s

 

[pglaves]

FWIW, I've owned R90/6's with the single disc setup and they stopped fine, once the caliper is aligned, with correct brake pads and brake lines either in stainless or with stock lines that don't expand.

Oh sure. Those were BMW's first anti-lock brakes, even with the slippery tires of the time.