Vintage Dirt Bike Q & A

Hi all,

I have a perplexing one here.

A buddy of mine has a '73 CR-250. He put a '75 MT tranny in it and it continues to drop out of second gear down to first when he puts any load on it. It holds in first, third, fourth and fifth.

I've taken it apart and can't see anything wrong. Dogs aren't rounded and it looks to fully engage. I don't know that all of the parts came from a '75 MT though. He may have a mix of CR and MT parts in there.

I don't have an MT parts book so I'd like to know if the shift drum and forks are the same between the two? Any other differences that could lead to this problem?

He does have the original '73 tranny and I may just drop that one back in. And I told him that for the short AHRMA style tracks he'd probably be better with it anyway.

Any ideas?

Thanks,

Loren

_________________
Those who can make you believe absurdities can make you commit atrocities.

Loren Davis
51y

The MT 250 tranny will not go into the CR cases unmolested. The MT250 output shaft bearing has a bigger opening than the CR so there is a high spot on the MT250 output shaft for the bigger opening. In desperation I ground down that spot to fix the tranny in my CR250 so I could race. The ratios are a little different but useable in the CR. The only gear that will swap is the second gear (female) which are identical with both trannies. All others will not work since they will bind if you try to swap em. You must put the entire MT250 tranny in the CR cases to make it work. My guess is the second gear dawgs are a little worn so it is slipping out. Use the best second from either tranny to make it work. The shift drums should be the same.