Ok Lawnboy M series experts.

streamlight2 said:

I'm somewhat new to this forum, need some advice on switching transmissions on M series mowers. I have a 1992 680523 (says C21ZMR on the recoil).On the 680523 I'm putting a complete axle and transmission from a 1991 M21EMRB. The only difference is the 680523 has a belt guide on top on each side of the pulley, where the M21EMRB does not. I can switch the belt guide over no problem,but was wondering if the belt guide was causing the drag when pulling backwards on the mower. The 680523 being a 1992 with the belt guide seems to be an update or an improved version from the 1991 M21EMRB. But that might not be the case ,any advice would be appreciated.

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I think what you have in the 680523 is the best available components of the "original M-style" drive. From that I mean that the rear height adjuster bodies have roller bearings (parts 36 & 41) instead of bushings that are on the base model. You also have the updated engagment system (parts 4-14 in the figure) that bolts to the transmission case instead of a bushing riding on the axle as the M21BMR had.

I haven't ever used a 680523 style system, but I have experience with the original M21BMR style. If you want to eliminate the high-effort pull-back, I think the best option is to swap out the complete drive system from a 10590 or 10591 M series. You would need the rear wheels, the wheel clutches, dust covers, drive gears and the rear height adjustment plates from the donor mower. One note here is the color of the wheels. I'm guessing that your 680523 wheels are orange. LB makes wheels that will fit the 10590/10591 that are orange also, but stock wheels from a 10590/10591 will be white plastic.

If you want to make the best of what you have, lubricate the rear height adjusters often, make sure the transmission (inside the case) has a good supply of grease, and make sure the clutch on the transmission is disengaging when the drive bail is not depressed (part 16 in the figure is the clutch arm, and the spring is part 8). The spring should pull the clutch arm forward enough to disengage the clutch when there is no tension on the drive bail.

Lovemysan was offering a complete drive setup from a 10590/10591 a few days ago. It sounds like he may still have one available if you choose that route.