Vintage Dirt Bike Q & A

Recently acquired a '77 MR175. The rear brake sticks badly. I have taken it apart, cleaned and greased the pivot point, still sticks. Any ideas on what I am missing?

Try popping the cable off the rear brake actuator arm, then pressing down on the pedal and releasing it. If the pedal immediately returns to the up position, the problem's in the backing plate assembly (at least 4 possible things). If it doesn't return, the cable and/or pedal system is at fault (another 4 or so items).

I completely disassemble and clean everything in the backing plate assembly during every brake service, grease everything that needs greasing with the absolute minimum amount of hi-temp grease, then wipe off every bit of excess I can find. I also lube the cable once or twice a year. My brakes still fade a bit when hot, but they work every time.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thank you sir, I'll give that a try.

Look for a groove on the shoe assembly where the actuator cam presses against it. If that surface wears too much, the brake cam can stick in the groove and refuse to return. I have only had this happen with aftermarket shoes, never OEM. A new set of oem shoes is the cure if that is the problem.

Ideally you want an unworn brake drum surface with fresh shoes so the shoe surface doesn't have to travel out too far to make contact. Too much wear in all the pieces and the brake cam has to rotate really far to actuate the brake. At a nearly 90 degree angle between the brake cam and the pivot pad on the shoe and you'll get a groove worn in there too quickly to last at all. If your hub is too worn, you can either get a replacement wheel or have your relined at a good moto machine shop.

If that's not the trouble, then maybe your return springs are tight enough - worn or just not even there.

Good luck,
Jon