Time for a new brake drum?

Im going to put a drum brake setup on my 77 kz1000. The drum Im planning to use is from a 76 kz900 parts bike that had 18k on the clock. Inside the drum is marked max dia. 200.75 mm and it now measures 200.025. That seems really close,but it looks good otherwise. Should I use it or find a better one? I dont know what those measured new.

Most automotive drums give .060 from new to max diameter. I always convert to inches (mm x .03937) But you have 200.025mm (7.87 in) and 200.75mm (7.90 in) which leaves .030in which should be within specs.

ujmrider wrote:

Im going to put a drum brake setup on my 77 kz1000. The drum Im planning to use is from a 76 kz900 parts bike that had 18k on the clock. Inside the drum is marked max dia. 200.75 mm and it now measures 200.025. That seems really close,but it looks good otherwise. Should I use it or find a better one? I dont know what those measured new.

Per FSM, new was 200.00mm-200.185mm. Whereby existing 200.025mm is still new.

FSM also confirms service limit @ 200.75mm

If helpful, inch conversion is 7.784"-7.881" with 7.904" service limit

Good Luck!

Before reading Patton's reply, I was going to ask "why would you replace a new brake drum?"

better yet:why would you replace a disc brake with a drum?

Thanks Patton thats the info I was looking for. Based on this it seems I have a long service life ahead for my drum. I just didnt want to relace my wheel now,and then again next season.

I'm curious, mechanics like bluemeanie can probably answer. What does it really hurt if the drums are majorly worn. I'd bet my old KZ650 is worn way beyond the limit, but brakes still work just fine?

I like the vintage look of a drum. My bike is a commuter any way,and I travel 2 miles of gravel road to get to the state route. Im hoping the little bits of grit wont get in the drum cuz they were chewin up my disc & squealin last season.:huh:

are you adding a 2nd disc up front i hope?

I probably will. I have the parts to add a side,just need a caliper rebuild kit. My wife "approved" $400 for this seasons get ready. Im spendin every penny! swingarm bearing kit,tires,airbox ducts,various rebuild kits.......

RonKZ650 wrote:

I'm curious, mechanics like bluemeanie can probably answer. What does it really hurt if the drums are majorly worn. I'd bet my old KZ650 is worn way beyond the limit, but brakes still work just fine?

Getting thinner reduces the strength of the drum and the amount of heat it can handle before it saturates (and fades out). A thinner drum is also more easily warped, but your point is valid: they do more or less draw a line and say it's gone at point X when in fact, it still has most of it's capability left.