Bulging master cylinder repair

[kdxdazz]

This came up on my Facebook memory and thought I would share, kdx's are known for the bulging rear master cylinder reservoir problem, mine was so bad that when I would do a river crossing the rear brake would fail
I own 4 bikes and all had the bulging master cylinder problem caused by heat from the exhaust, this is the reason later model bikes went to an integrated reservoir system but some such as later klx250's mounted the reservoir higher up.
Just pop it in the oven for 10 minutes, job done

[Chuck78]

This has always troubled me that they bulge out in the middle like that... I was looking at converting to at a later integrated reservoir type rear master cylinder, but each manufacturer uses their own bore size on the rear masters, meanwhile nearly all fronts are 11 mm across manufacturers.... The integrated KX masters have a slightly different mounting tab location placing them at the wrong angle, and many or all of them put the banjo bolt right up against the frame which causes additional trouble if trying to align things with the caliper guard intended for your bike frame model.

I believe the Yamaha YZ/WR & Honda CRF/later CR style might be a good fit, or better than the Suzuki and Kawasaki versions with their rectangular reservoirs, but that would mean changing for a caliper from those bikes also, in order to keep the same hydraulic leverage ratio. Some older CR models use the same rear brake pads as the KDX so I'm fairly confident those calipers would swap onto the KDX caliper hanger bracket.


This warping of the rectangular plastic reservoir is likely also why Kawasaki KX models use a round screw cap on the remote reservoir versions.

It's a shame that Kawasaki did not modify the cap so that it protrudes below the outside top edge of the rectangular remote reservoir, in order to hold it captive, but likely it took a good 10 years for these reservoirs to start bowing outward, so it was not an on the fly change during the middle of the KDX model production era.

Starting I believe in 2024, Kawasaki did change to the Yamaha / Honda (2004-ish+) reservoir shape, perhaps those would still have the correct half inch bore and fit better than the rectangular Kawasaki versions? I purchased one of the 2019-2023 Kawasaki versions which is just slightly modified from the earlier version 2003-2019 (different sight glass location), but it was not such a good swap candidate due to ill fitment with the stock aluminum master cylinder guard or the Works Connection versions.

[billie_morini]

Learned something new today. Didn't know about the reservoir deformation or its remedy. Will look at mine and add reflective heat shield to it.