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Update 4/12/2023 - problem solved, parts replaced. Weak side had a broken inner E-clip lying in pieces inside the clutch mechanism. PDF showing photos and details of repair. Kudos to Rivets for helping out.

PDF showing photos and details of repair
http://kentcomputer.com/toro/torocr.pdf

Original post:
2006 or so 21" rear wheel drive super recycler. Replaced the belt and lubed the bearings thru the zerk fittings last week. Really takes off now when the traction bar is pushed forwards but the mower torques left as it takes off. Never noticed it as the old belt was growing tired. I put the mower on concrete and gently lifted the wheels evenly as I pushed the traction bar forwards, and while both wheels have good spin and traction, the right rear one takes a lot more friction to stop. It appears to be getting the bulk of the power, and the left rear gives up much earlier. Does the transmission have friction clutches in it or something like that, or is this by design? The wheel spins evenly and does not skip, so it is not like wheel drive gear is stripped, it just gives up easier than the right one does, which I suppose is why it is torqueing left when we take off to mow, It is significant enough that it could be dangerous to someone not anticipating it.

I would be checking the condition of the friction ring and clutch washer first. Clutch washer may be worn or ring may be dirty. This manual may help you out. https://www.toro.com/getpub/22446

So to start, I greased it using a malfunctioning hand grease gun and likely one side got more grease which is causing a friction difference. I found the section in the manual you posted that shows how it comes apart but I am still not confident I understand the mechanism. Here are links that may help much better than my attached images at the bottom. There are two pages at Toro. I have not had one of these apart so I do not have the pieces stored in my head yet.

Central Transmission

Outbound Section

Central part of transmission link above (or Toro.jpg at bottom).
#17 is the pinion gear. That is where power comes in
#16 is the spur and Bevel gear. It looks like it relays power from the pinion to gear #18.
#18 is a 30 tooth gear. It looks like this gear transfers power to #19, the output shaft thru the "Type A groove pins" (#6)

I reviewed the wheel drive which is the outer section and the pages on it in the manual you linked. I am having trouble understanding how the clutch & washers balance power from side to side. How does power transfer from the output shaft to the thrust washer(s)? Does the one with internal tabs lock into the output shaft and then the other parts rotate/slip against it thru the friction ring and clutch?

If the parts most commonly worn can be ordered in advance then it will be easier to take it apart and put it back together - rather than take it apart, order parts, wait three weeks and try to put things back together after memory fades, even with photos. It may not even need parts, just a cleaning. Open to suggestions.

That said, don't really want to take it apart without sort of understanding how it works first. I am no stranger to mechanical things although not as dexterous and adventuresome as 30 years ago. Taking it to the shop here is almost out of the question. We have a wonderfully competent shop here a mile from the house that is busy all day long with commercial accounts. Maybe a staff of six or 8 people work there. The problem is they don't want jobs like this. The cost of labor (wages, taxes, insurance, overhead) in California is about $150 - $175 an hour, and going up. When one adds up time, including book keeping and counter time, anything that takes 3 hours of work total and a couple parts is as much as a new mower. They spend most of their time selling new equipment, doing warranty work, and servicing commercial equipment. I asked them last week if they were interesting in adjusting the valves since I had other things to get done this month and they declined. They said that it was too much work for the gain I might get even though the valves might need it after 700 hours use. On top of it in 8 months small gasoline engine equipment is outlawed in the state as to being sold or resold.

From you description the transmission is not the problem. First, you need to reread the section #7 of the manual which talks about the ”Wheel Pinion Clutch” which does describe how this drive system works. I’ve worked on these drive systems since they were introduced and 99% of the time that cause is with the pinion clutch, due to wear and over lubrication attracting dirt. If I’ve repaired one of these I’ve done about 25 every year for the last forty years. The manual does an excellent job showing how to do it. The replacement parts can be easily be ordered beforehand and if you do it right I would replace the ring, washer, gear and both keys, which are different depending on the side.

Rivets said:

From you description the transmission is not the problem. First, you need to reread the section #7 of the manual which talks about the ”Wheel Pinion Clutch” which does describe how this drive system works. I’ve worked on these drive systems since they were introduced and 99% of the time that cause is with the pinion clutch, due to wear and over lubrication attracting dirt. If I’ve repaired one of these I’ve done about 25 every year for the last forty years. The manual does an excellent job showing how to do it. The replacement parts can be easily be ordered beforehand and if you do it right I would replace the ring, washer, gear and both keys, which are different depending on the side.

Click to expand...

ring = Friction ring 65-4710 ?
washer = Keyed Thrust Washer 65-4740 AND/OR Clutch Washer 65-4760 ?
gear - #16 pinion gear 65-4750 ?
Keys - rocking keys left and right? 139-6643 and 139-6644 ?

Can’t tell you if those are the right part numbers because you don’t supply us with the units serial number. Unit was built over a number of years and it may make a difference. I’m not going to go through the different years to see if there are any changes.

thanks. I already posted a link to the service page at Toro with the part numbers, unit and serial range. I'll figure it out.

one thing that does puzzle me is that all the videos of the assembly on the rear wheel Toro show a small spring under the rocking key. The link I posted for mine does not show such a spring but one can see the hole for it in the photos of this type assembly. The only spring the pictorials show is the compression spring. Do all the models with a rocking key have a spring under them or does it vary? The manual you provided states, (which may imply there is not a spring on this model):

... Rocking Key – causes the wheel pinion to turn with the output shaft when up. Allows the wheel pinion to “free-wheel” when down. Clutch washer brings key up. Wheel pinion turning forward “wipes” key down.

Click to expand...

Drive friction assembly:

Toro uses a ratcheting key and a spring loaded key, depending on the year of manufacture. If you look at the website you posted you will see that there are two ratcheting keys, one for the left side and one for the right side. I can tell you that if you have a friction ring and clutch washer you will the using ratcheting keys. I can’t tell you if that is correct for your unit as it seems too hard for you to post the serial number. This will be my last post in this thread, as it seems to me that even with the drive service manual you can’t understand what type you have or how it works.
PS: The teacher in me says I do have tell you that all washers in the drive system need to be installed correctly or the unit will not work properly. You’ll have to figure that out.

I plan to take photos as they come out and lay them in an order on a shop towel. Sometimes when in doubt I will use an engraver on parts and mark them in a non-destructive way. Where I was having difficulty is that I've rebuilt standard differentials, locking differentials, clutch pack differentials, and even welded a few to make cheap lockers out of them for the track, but I did not really grasp how this worked until I picked up some parts and saw that the friction ring was a flat neoprene O-ring. The service manual is one size fits all, and it will say things like replace the shaft O-ring then a half paragraph later it will say some models don't have an O-ring. Then I have to go look at the blow up to see if mine has it. The model is 20055 and the serial is 260015175 if that makes it easier for others to help. The link shows that the blow up was for the 20055 model, 260000001 - 260999999 serial range.

The manual describes removing the bearing and bushings from the Pivot assembly as part of the process to rebuild the mechanism. While I have a press, unless that bearing and bushing are bad, is there any reason to remove them just to clean and re-grease them as the manual specifies? Can I not just spray it with some Berrymans, blow it out and regrease?

got all the parts I need. Really surprised with as many as was stated get serviced, there were no other members who have done this repair.

25 x 40 = 1000 repairs of this nature just for one shop. Both the local Toro shops had parts, although I had to hit two shops as one had only one clutch left in the pack of 5. That tells me the other 4 went to two mowers.

25 every year for the last forty years

Click to expand...

As a follow up. Rebuilt. Goes like a rocket and will leave tire tracks on the concrete if you hold it back while pushing the personal pace lever forwards. The Inner snap ring fell out in pieces on the side that lacked torque. Putting it back together was a challenge because even with the adjuster spring arms hanging so there was no pressure on them, I had to hold one hand on the far wheel, push against the near adjuster block with my side to expose the e-clip groove. While holding that pressure, load the E-clip and squeeze it on with one hand and a pair of pliers. I suspect that the deck is slightly bowed out a little and that puts pressure on the clip that wore it out.

PDF showing photos and details of repair