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Airhead master cylinders

Airhead handlebar-mounted master cylinders

Handlebar-mounted master cylinders started in the late '70s with the R65, but became ubiquitous in 1981. This article describes the types used until the K-type controls were introduced in 1991.

Prior to this, Airheads used the under-tank master cylinder with the cable control. The throttle housing resembled the ones mentioned here, but merely pulled a cable rather than providing for a hydraulic master cylinder and had no provision for a switch.

Application

Model* MC Housing Notes
Early R65 w/single ATE caliper 13mm 32 72 2 302 354 32 72 1 238 377 Round reservoir
Dual throttle cable
6x1 switch thread
Early R65 w/twin ATE calipers 16mm 32 72 2 302 355
'81-'84 single Brembo
All monolever G/S
12mm 32 72 2 302 369
13mm
32 72 2 310 784
32 72 1 242 563 Square reservoir
Single throttle cable
6x1 switch thread
'81-'84 twin Brembo

14mm  32 72 2 310 785
15mm 32 72 2 302 370
16mm 32 72 2 302 365

'88-'90 R100GS w/single Brembo 13mm (as above) 32 72 1 454 461 Square reservoir
Dual throttle cables
8x1 switch thread
'85-on** w/dual Brembo 13mm (as above)
14mm  (as above)

* Years are approximate. Brake systems often changed in the middle of a model run.
** excluding '91-on R100R/M/GS

Housings

The housings changed a few times:

The fiche shows the newer front brake switch as being used with new single-cable housings, but my experience is otherwise. The old switch has a 6mm thread while the newer one (with integrated cable) has an 8mm thread. The switch geometry is similar, so housings can be drilled and tapped for the newer switch if desired.