My latest (other) project is a White LT-12 Cruise-matic ride-on mower. I'm in the strip-down stage and I'm struggling to understand how the speed selector works. The gearbox/transmission has only one lever attached which control forward/neutral/reverse. The speed selector is on the right hand side at the back and has stop/brake and 6 speeds. Looking underneath that lever connects the the brake and to pulley brackets through elongated holes and pins. The main drive pulley has a very wide pulley which I assume is a variable speed pulley, but I can't see how it works or what makes it work. The machine is obviously old and has some rust and maybe some parts missing. Can anyone tell me how it works or how it should work? I have some parts diagrams but they are fairly congested and difficult to see detail. Does anyone have better pictures?
If the LT-12 IPL that I am looking at is the correct one it would be the MTD variable speed belt system with a single speed transaxle. This system uses a sliding sheave pulley to variable drive and driven pulleys diameter.IE: The center divider slides up and down). As the belt tension from PTO is increase it cause pulley diameter for that belt to decrease thus increasing the driven diameter (Sliding sheave to transaxle). This change results in an increase in the speed that belt moves that drives the transaxle input pulley. As tension is released the reverse happens; slowing the transaxle.
This should be the mid point pulley as shown in gallery view.
Personally this is a much more liable system than the hydro static especially went towing a small loaded trailer as there is no hydro slippage. The belt sizes are critical though on this system and not just any close enough sizes will work properly. Otherwords if the spec is .7 x 44.2" you can't simply throw in a 43" or 44" and expect it to properly. Now in a standard 5/8" the size would be 43.94". When in doubt about the size use OEM belts.
Last edited by Bruce; 01/02/1808:47 AM. Reason: Image was not secure
Thanks AVB, you are correct, it the MTD variable speed belt system with the sheave as you described. What I don't understand is how my selection of speed alters that sheave. The speed selector on the rear RHS has "brake/ 6 speeds", but I cannot see any connection with the drive system. I have ordered OEM belts, but I was thinking about removing the deck completely and just using it as a "paddock basher" and to increase the ground speed I intended to increase the size of the engine pulley, and maybe slot the engine mounting bolt holes, move the motor back a little to maintain the correct tension on the belt. Your comments on the correct length of belt for proper operation now has thrown some doubt in my mind as to whether this would be satisfactory. Any suggestions?
The sheave is spring loaded just like most idlers that automatically keeps belts tensioned. As shifter is moved to higher speeds it allows the Brake/Clutch to rotate more from the depress position. This in turn via linkages from the brake/clutch pedal allows the very large spring to pull the sheave assembly rearwards along its rotating axis thus applying more tension on the engine to sheave belt which forces the sheave to slide closing the gap that the rear belt has to ride in. This forces to belt outwards effectively acting like a larger pulley is now there. The idler on the rear belt gives. As you brake/clutch or shift to a lower speed the idler takes up the slack as the sheave returns to normal position.
The slots are there so as you depress the brake/clutch you don't need move the shifter everytime you stop. The shifter just provides a positive stop to the pedal when you release it.
Hopefully I haven't confused you too much here as I don't have manual that details this particular setup which is I believe the MTD 600 series. Even in that series there several variations of the system.
If your planning changing the engine pulley to a different all bets are off as which size belt you need. It would take experimentation from there.
Forgot to mention the spring tension on the sliding sheave pulley is why you must lock down the brake/clutch pedal to change the front belt and even then it can be a pain to change out on some mower versions.
Thanks again, AVB. I certainly have a lot better understanding of the whole operation now. Yes, changing the front belt is not without its challenges. I found I have to remove several unrelated pieces to get the old one off. I hope I can remember how to get the new one on....LOL. Thanks again, you have been a big help.
