HI BLACKSHEEP, Here is how I modified my 840rpm rear pto to 1754rpm. this mod will allow you to use the 2000rpm equipment like the 318/420 etc. no longer will you be confined to ''400 specific'' implements that use the original 840rpm pto.
before we get started here, let me say this, you DONT have to do everything I did to my unit. basicly, all you have to do is replace the top sprocket. I just saw ways to improve on the original design and built to my own taste and for my own needs.
I used sprocket dia., not tooth count to figure the gear ratio.
bottom sprocket from jd is 12T or 2.71'' dia. we will stay with a 12T here.
top sprocket from jd is 30T. we will replace that with a 14T. that measures 3.11''.
3.11 divided by 2.71 = a ratio of 1.14 to 1.
so with a 2000 rpm input speed, you will net 1754rpm out-put speed.
at this point you are asking why did I not use a 12T on top and get the full 2000rpm, the 1 to 1 ratio? here is where you run into problems that involve MORE time, money, machine work, parts availability, fitment, etc. this will be shown later. It CAN be done however. but the 14T upper sprocket avoids a lot of problems. and with only a 12.5% drop in performance at WOT I believe us 400 owners can live with that. Keep it simple!
all work was performed with basic tools, a welder and 5 1/2'' hand grinder, and small phneumatic die grinder. the exception being to key ways were cut at machine shop. the key ways only apply if you go to the extent that I did.
So lets get started.
on the left are the original sprockets and shafts. NOTICE; that they are welded to the shaft on one side only. the weld is lathe turned also. the sprockets are oriented like they go. why they weld is on the back side of top sprocket, I don't know. at this point, if you replace the top sprocket your done. on the right is the new set-up. NOTICE; the spacers on top of each sprocket, installed. there are corresponding spacers on the underside also. each shaft pair is identical except there is a relief cut to clear the weld on the one that fits on that welded side. NOTICE; the upper shaft. you see how close the chain comes near the spacers outer shoulder? this is where you run into problems if you go with a smaller sprocket. CONTACT. 13T. same results, CONTACT. Turn them down in a lathe? these things are as hard as automotive lifters. make your own? yes, if you want to. Get a set like on the bottom shaft from JD, which are a smaller outer dia.? your stumped again; one side is n/a.
so go with a 14 on top and be happy!
new 1'' shafts are made from cold drawn shafting rod obtained from Mcmaster Carr.
NOTICE; the amount of free play in shortened chain. this chain is used. but good as new. I could not find a reason to replace it. I used a half link to obtain this amount. you can see it located in the lower rt. corner. a master link in place of a half link will yield slightly more play. you will have to find your on SWEET SPOT in your unit as chain condition warrants. the original jd chain has no master or half link. so get you one of each to ease the build. this is 50 PITCH standard duty.
here is an upper and lower spacer. sorry I have no photo showing the inside where the relief area is to clear the weld. all 4 spacers are the same thickness. where the spacer meets the weld is a non contact surface between the weld and spacer. if you don't have a lathe like me also, just grind down your weld at a 45 degree till spacer sits flat on sprocket. that's all there is to that.
here is a new sprocket. these are the keyed, collar mount type. I cut the collar off and ground flush. they are from SUPPLY CENTER. 6 OR 7 bucks each. they will still press on good on to a new shaft and self a line for a square fit. if you can find some from a different supplier without the collar, you can save yourself some extra work. I didn't bother, unfortunately.
view of original lower shaft assy. minus spacers. this shows outer cap needle bearing, sprocket, front caged needle bearing, jd seal, woodruth key. NOTICE the factory weld I spoke of. this shaft has wear at the bearing surface and seal contact area. this is where weeds, etc., get twisted up on the drive shaft input connection and destroy the seal resulting in 90w fluid loss. then excessive wear. unit holds only a few ounces, 6 or so. it aint much. I will build an entire new assy. NOTE, that is a new $11 JD seal in the photo. I will use a better seal here shown later. I will replace old key style with plain key stock. that will allow me 1/4'' longer contact area with the yoke. yoke has the space available.
here is a view of the old top showing the outer cap bearing, and weld surface. if you need a new 15 spline shaft, SC has 2 versions I believe that could be made to fit, for $22 or so. check with them. I will build a new shaft with a standard 6 spline 1 3/8'' dia. for my preference. NOTE, if you get all new bearings for your unit, pay attention to the one at the 15 spline output. it contains a small seal that faces to the outside. don't confuse it with lower shaft input bearing. the upper and lower cap bearings are the same.
this shows that bearing, near spline end.
this is the new lower shaft and seal.my seal selection protrudes un like the jd seal. but it has no clearance issues.
left my seal, right jd seal. both are double lipped with a spring. NOTICE, the larger contact area of the one on left. the one on left is for the axle of a troy-bilt horse tiller, if your interested. cost about half.
here is a mod I came up with. I cut a slot in each case half on top, at upper output shaft to help with bearing lubrication. a feeder channel of sorts. cant hurt.
here is new 6 spline shaft from SC, FOR $30. It comes with 2'' long inside hole. I cut it down to 1 1/4'' long inside. relocated set screw. also installed a second set screw 180 degree opposite. the reason I cut this is so equipments drive shaft does not get to short, causing yoke bindage in raised position. every little bit helps. so modify this now.
here is the tensioner installed. a new jd is $14 or so. mine had some wear. not real bad. I filled it with JB weld after routhing the surface. use original formula, not the KWIK SET, original is more than twice the tensile strength.
here is unit installed. NOTICE, I cut a second grove of notches for lock pin, they are 3/4'' inbound from original. again, better safe than sorry. keeps the drive shaft longer, and gives full contact to the yoke. I used a air grinder with double helix carbide bit, 3/8'' to do this. mark a straight line with tape around the shaft on both sides of cut. no lathe, no problem. just test fit each slot with your yoke.
another view, NOTICE, full yoke.
NOTE; I used all new bearings from JD, lube added, job COMPLETE. Only thing left is to go and kick some earth worm ass!!!
in closing, I would like to say this. I don't want to hear any whining or BLEATING about the 400s rear pto limitations. if I can up-grade mine, anyone can if they so choose. it was more aggravating doing this post than the rebuild and conversion!!! I have done so many modifications and up-grades to this 400, I call it PROJECT-X. Like the yellow 57 chevy Popular Hotrodding was always testing out equip. on back in the 70s. later, J.Z.M.