CR vs XC & WR rear wheels

I found that out when I got a rear wheel with an 83 250CR frame. One has a grooved backing plate while the other has a flat backing plate. The grooved backing plate was tighten enough to wear the groove thru the backing plate. I got a replacement on eBay but found it to be almost as bad

the grooved backing plate is from the mx models and it floats with the suspension action. the xc and wr have the flat plate and it get attached fast to the swing arm or brake stay depending on the year. i found this out the hard way. bought a $180.00 CR backing plate thinking it would work on my wr or xc. WRONG!!!

That is rather intresting I used the rear wheel from one of those silver streak 500 bikes for a car stud tire on my xc 500 1983 The shoes were a bit narrower on the cr version if I recall. From what I have the dual shock water cooled 400 and an early monoshock bike used a backing plate and hub design like the later mono shock but have a bolt to the swingarm stay rod instead of a prong and socket like most of the mono shock. I am just guessing that set up or at least the hub/plate interlock design went a year or so earlier on the 83 cr. Good part to have might have to tamper with the way the brake arm goes but it allows you to use more modern wheels on the earlier bike. I hoarded at least one off ebay years ago. If you go to the races and bring the wrong wheels you can run mis matched, one way there is a gap dirt will get in the other way you have to stick a washer somehow inside the brake drum area and spreead the swingarm a bit probably a gap then as well.

I can't say about cr stuff but for the other stuff the 83 has a wider brake shoe and no stepped inter fit between hub and plate. The mono shock stuff has the thinner shoes and the interlock design. I don't like the prong and socket of most of the aluminum swingarms strange things can happen when you use the rear brake stalled out on a hill going up at last on the worn stuff I generally have. I know I made it work one time, like you say at least one of the little washers I crammed in there was the opposite of a fender washer. I don't think you can see much detail in the picture but just for fun. That looks like the stepped drum which would fit the plates at three and nine o'clock with thinner shoes but not the wider shoe one at eight o'clock. How applicable it is to an 83 cr can't say.

Don't feel bad cause I did the same thing till I figured out the differences in the rear hubs/backing plates.

Now I have a collection of XC hubs.

Ymmv, your mileage may vary.
I found the backing plate from that cr 500 1982.5 one of the three hundred sent to the states, and it seems to interchange in the hubs of that era fine for me. It doesn't like the more modern like on the aluminum swingarm. The one with the tab for the brake stay rod is in a 17 inch wheel, non conical hub with the date Jan 82 on the rim and has no wear from the springs of the brake plate. The cr brake plate has the springs farther back. The other hub has a date of late in 82 and is an 18 inch rim and though the fresh scratches in it are odd the normal spring rub marks are there. I guess it is possible someone laced up hubs and wheels along the way but these two brake plates seem useable in the same hubs.

fran