Here’s what I do to 700 series trannies, I find them in Junkers and pay as little as possible for them generally horse trade or whatever, Anyways here goes... I first off clean all the benonite grease out of them that’s that black muck that you find when you open them. Clean them thoroughly. Do not put the brass bushings in degreaser or spray them with carb cleaner, they are impregnated with oil and yes I use them. I do not put needle bearings on the shafts. Once everything is clean I inspect all parts, The shift keys get a good look at the engagement tips, if they are chipped or show signs of much wear REPLACE them. Everyone has their own opinion on how many shift keys to use, some like the 4 key shafts, which only come in the newer trannies, and if you order one for the older that’s what you will get they don't make the two keys anymore. I use what’s in them. I have run a two key shaft every since I started running the 700 series Tranny. I have never broken a key. Only had one dnf for a tranny and it wasn't a key I bounced real hard never lifting and ripped the input out but it was two years old. (Race wise). Now look at the inside of all gears off the shift shaft make sure all the corners are square and not chipped or rounded. If everything is in good shape great. If not you will need to replace the damaged gear. Now check the input shaft for wear and the needle bearings, if all is good then I put some automotive grade bearing grease in the input shaft keeping a finger over one end I put the shaft back in which presses the grease into the bearings packing them well. I do not put the O-ring back in I replace it with an oil seal which can be gotten from Tecumseh or even a Napa store. I sometimes put an extra flat washer on before I put the snap ring back on to remove all the play. If you have to replace the input shaft bearings I use an old bearing and grind the ends down to make a spacer between the two bearings to keep them from walking towards each other. They have been known to do this on some cases once bearings have been replaced. Now I do replace the input and bevel gear with steel gears, if the rest are not steel no biggie, that’s what I use, I use what is in it, and have never broke but one gear and it was 5th gear the 19 tooth 5th gear counting the one on the shift key shaft. I also remove the reverse chain and sprockets. I do not put spacers back in their place. Everything will work fine without them. Now I gear to race in third, which both gear’s in most trannies especially a 5 speed will count 25 teeth each. If you forget which gear matches what, no worries the two from each shaft will always add up to 50 teeth. Now I add a touch of the bearing grease on the ends of the shafts before I put the brass bushings on. This gives a little lube before the oil gets to them. Once everything is assembled and before you put the top case on put some perma-gasket of your choice on the bottom case to seal the top to it. I also lift each shaft and put a little under each bushing and then a film on top of each, only if it’s an open case type end though, this is one less place the oil can leak out. While that’s setting up add app. 8 ounces of gear lube, type and weight is your choice, I use 80/90 Wal-Mart brand. If you have no way of measuring the amount of oil, with the case level, simply add enough oil to cover the input gear. Now I use all 6-mount holes to bolt it down and the whole I cut for the input shaft is a very snug fit. I only use 1/4-inch thick plate for a tranny plate. Now for the do it yourselfer E.C. Distributing has a cnc precision cut trans plate that will fit most anyone’s application in building their race mower. They sell for 55.00. They also have an idler sprocket bracket assy. Bolts to the bottom of the trans plate and can bolt a idler of your choice to it. They have two plates specific dimensions are 10.5 wx8 and 13wx8. The first being designed to be an exact fit for a Murray wide body and the second being a direct fit for the box frame MTD chassis. Both are universal and usable in many chassis setups. They come with a bushing that once you bolt the tranny in place it slides over the input shaft centering itself on it and supports it all the way to the base of case. You weld it in place and end result you have one heck of a tranny plate. That pretty much sums what I do to them simple, cost efficient except the two gears that you replace, and works very well. I don't hot rod my mowers nor run them on pavement very much. And if the motor is running, and I am not moving, the clutch is in. Look at it this way its less wear and tear on the tranny pulleys and belts, basically the whole drive train. Now below is all the part numbers for everything I use in or on the tranny from Tecumseh.
700 series parts and no.
7 tooth sprocket 786077
8 tooth sprocket 786047
10 tooth sprocket 786076
12 tooth sprocket 786095
15 tooth sprocket 786111
Steel bevel gear 778154
Steel input gear 778153
Shifter key 792089A
Flanged Bushing 780105A
Input oil seal 788083
Input Needle Bearings 780086A
Input Shaft 776135
These are all Tecumseh part no. There is an after market oil seal also it is a Federal Mogul no. 340387 you can obtain at most car parts stores i.e. Napa etc and CR number is 6106