Your tractor mower is equipped with a pretty complex transmission, it’s an integrated hydrostatic transaxle (IHT).
Hydrostatic transmissions are a type of CVT that uses an oil pump and oil motor for varying the gear ratio.
Your transmission has a differential, reduction gear set, oil motor, oil pump, swash plates, check IDS valves (that control backwards flaw for reverse), a brake disk, and brake shoes enclosed in one housing.
The good news is – Any problem with the Tuff Torq T40 transmission can be fixed, but a vast majority of these issues could be easily avoided with timely maintenance. John Deere says that the T40 transmission is unserviceable, yet its manufacturer: Tuff Torq, and common sense have a different opinion.
How to find the problem with your transmission, & Know if it’s a transmission problem at all?
Few obvious signs that your transmission has gone bad are –
- Wining and noise when in the move
- When the transmission works only in forward or only in reverse mode
- When it leaks oil
- When it performs well after a cold start and loses power as it gets warmed up
- When the problem was slowly building up over time (a sudden loss of power is usually a sign that the problem is not transmission related).
However, in a lot of cases, a bad transmission may not give as obvious and direct a symptom as those stated above, so you will have to remove it and take it apart for up-close inspection.
But first, let’s exclude other problems with a tractor that might cause similar symptoms to a transmission problem, like shutting off, losing power when under load and not being able to move the tractor on its own power.
Take a listen to how the engine is working when the transmission is not engaged. If it runs and responds to throttle input smoothly, if it doesn’t misfire and doesn’t choke under load; you don’t need to look for problems elsewhere
Otherwise, a thorough inspection of your engine and ignition as well as fuel systems is due.
John Deere D140 Shuts Off as Soon as you engage the Transmission
If your loan mower shuts off as soon as you engage your transmission, you may want to check the seat safety switch which may be broken and unable to detect a driver in the seat causing the engine to shut off.
To test your seat safety switch, lift up your seat, unplug the lead wire terminal from the safety switch and test the switch for continuity with an Ohmmeter in both off and on positions by testing corresponding switch pairs of contacts (there are four contacts that make two pairs, ON and OFF).
Change the switch if it’s bad.
Loses Power Under Load Or Fails to Move Forward Under Load
If your tractor mower fails to move when you engage the forward travel pedal or loses power when under load, you should check the drive belt.
To check the drive belt, start your engine up and put it on full throttle, then engage the electric PTO switch. If you hear your blades kick in (spin) immediately after engaging the PTO (in under half a second), your belts are fine.
Otherwise, when blades kick in with a delay or don’t kick in at all, you have a belt problem, but it can be just a deck belt problem. To check the drive belt, you’ll have to remove the mower deck first.
You need to check the tension (keep in mind that when the brake is engaged, the drive pulley is loose causing the belt to loosen a bit as well).
You should change the drive belt if it’s too old/slack and has visible wearing marks on it. Belt problems may also lie in bad or stuck pulleys. But to inspect all the pulleys, you’ll have to remove the drive belt altogether.
Also, this might be comical but check if the bypass valve lever at the back of your transmission (that’s meant to use when towing your tractor) is disengaged.
Otherwise, it’s probably your transmission.
How To Remove Transmission
To inspect your transmission, you’ll have to remove it first; but before that, make some preparations.
- Park your tractor on a flat surface but do not engage the parking brake as you will be disconnecting the brake linkage.
- Lower the mower deck on 1-2 inch wooden blocks, unhook the deck belt from the PTO drive pulley, disconnect 5 connecting arms by removing spring pins and take the deck out. More detailed instructions:
- Put some chocks before the front wheels of the tractor, place the jack underneath the tow hitch at the back of the tractor, and jack up the stern of the tractor. Then secure your mower with jack stands placed under its frame in front of the transmission housing to make sure that it won’t roll to the side or fall (be careful not to damage any linkages and wiring).
- Take the rear wheels off by prying E-ring clips off with a large Phillips-head screwdriver and taking off the spacers of the hubs (don’t lose them along the Woodruff Key, 2 washers, and the muff that sits on the inside). To remove the yellow plastic protective cap, you can use a heat gun.
- Take a pair of pliers (best if its side cut pliers or snap ring pliers) and press the circlip (1) that fixates the brake pedal linkage connection to the transmission brake lever (on the left side of the tractor) down and pull it out to disconnect and set it aside the linkage.
- Then push the bypass valve lever (2) at the back of your transmission fully inside and go to the right side of your transmission, locate where the bypass valve lever meets with the valve arm (3) itself (you can wiggle the bypass lever if you have trouble finding the joint), pry the connecting star lock-washer down, push the bypass lever out of the joint, and pull it out of the tractor entirely.
- Take a 15 mm wrench and unscrew the belt guard bolt (4) that sits on the right side of the transmission near the fan/input-shaft pulley assembly. Try to place the fan so that the bolt would go in between blades when unscrewed.
- locate your travel pedal linkage (5) and find where it meets with the transmission lever (of a variable swash plate), the joint is located on the right side of the tractor and must sit behind the right frame rail and above the transmission. Pry connecting starlock-washer out of the joint (be careful not to go too hard and lose it), disconnect the linkage and put it aside (if it’s hard to pry, you can use some metal stick to tap is out through the hole that sits on the outside side of the lever). It can be a little tricky due to the inconvenient location of this joint.
- Locate your forward/reverse safety switch sensor (6), it has to be positioned on the right side of the transmission and it is a copper brace-like piece of metal that sits near the frame. Once you’ve located the safety sensor body, disconnect its lead wiring terminal and put it away, then take a 14mm socket and unscrew the sensor body from the transmission case.
- Unscrew the bolts that hold black metal transmission bracings (7) to the frame on each side with a 10mm socket.
To remove your transmission, engage the parking brake so the belt tension loosens, place the jack under it and make it meet the (approximate) transmission center of mass. It would be great if you put some wooden board in between to have more stability.
Next, take a 13mm socket along with a 13mm wrench and unscrew 4 bolt-nut pairs (8) (two on each side) that are located on the drive axle and connect the transmission to the tractor body.
Now you can carefully begin leveling down the transmission. Level it down just a bit to loosen the drive belt of the pulley, then carefully remove the belt off of the fan-pulley assembly (be careful not to damage the fan).
Your transmission is free now, you can level it down some more and take it away. If you like, you can clean the transmission body with a degreaser to ensure a nice workflow and prevent dirt from entering the insides. Taking apart the transmission for a thorough inspection:
First, take a look at the exact transmission model on the barcode that’s located on the axle part of the transmission and use it when ordering any parts for it.
Take a pair of side cut pliers or snap ring pliers and take the snap ring out of the fan/pulley assembly.
Take your fan out and inspect the drive pump pulley, it should spin along with the input drive shaft and should sit tightly on the shaft.
If your pulley spins freely and wiggles on the shaft, it is worn out, has worn out splints and should be replaced (it might fix your problem all together).
Then place your transmission on an even surface and make it level with the help of some chocks.
Locate your oil fill plug (20), it’s a bigger flat plug that sits on the left side of the transmission (do not mistake it for a vent plug), and pry it off with a screwdriver (you can tap the screwdriver upwards around the plug with a mallet if you like to be more gentle).
Take out the filing catch magnet that sits inside, remove the metal base, notice the amount of metal filings stuck to the catch magnet and clean it thoroughly.
Measure your oil level with a metal ruler, it should be around 20~25 mm (3/4”~1”) below the lip of the (black cap) port when at room temperature.
If oil level is lower than that and your catch magnet has little to no fillings on it, you should consider replacing your drive axle and input drive/pump shaft seals (they could be the reason for low oil and bad transmission performance).
Take a look at seal replacement manual here
Before taking your transmission apart, prepare a big bucket or some other volume and drain the oil to it through the fill plug for about half an hour.
Then place your transmission securely (upside down) with lowercase facing upwards and input driveshaft facing the floor.
Unscrew all the bolts (9) that hold the lowercase to the transmission body with a 12mm socket. Keep in mind that two center bolts are longer (10) so make a mark on their respective crewholes to know their location for the future.
Once unscrewed, carefully pry lose the lowercase by leveraging specially casted pry points (11) located on the sides of the lowercase body with a large flat-headed screwdriver.
Remove the lowercase from the gearbox. Clean the lowercase and uppercase case foam sealant residue using a degreaser (like brake pad cleaner), a scrubber, Exacto knife, and a metal brush.
Be careful not to get any residual into the uppercase and thoroughly clean the channel around the lowercase mating service.
Inspecting the insides of your transmission: To understand what you are gonna be doing, take a look at this transmission diagram
Even though it is not about T40 transmission (it has a little different setup where the belt pulley sits underneath the fan and the gearing is a little different), the general layout is the same.
First, take a look at your oil filter (12) and a second filing catch magnet (13) located near the differential. If they are very dirty, it can be a bad sign.
Remove the oil filter and clean the magnet of filings. If the magnet was dirty, inspect your differential (19) and reduction gear set: (22) wiggle the gears around, they should have little to no play.
Then you can carefully remove your gear train for further visual inspection, noting the position and orientation of every gear and washer
If gears have visible damage to them or visible wearing, they should be replaced. A common symptom of a bad gear train is grinding noises when in motion (also a catch magnet near the differential is a good marker).
If the gear train is fine, the problem lies in your center block (14). One strong symptom that the problem is within your center block: a prominent wining nose and zero response when you press the travel pedal.
Your options are: to buy a brand new assembly; disassemble the center block and inspect the motor
and its pistons (23), oil pump within the main block and its pistons, IDS valves. motor output shaft (24) and swash plates (they all should fit tightly, have no play and no wearing) then change the parts that went bad; sending your center block for a rebuild to a professional.
I recommend the latter option as the brand-new assembly is pretty expensive and rebuilding it yourself will be extremely time-consuming.
In any case, you will have to remove your center block (14) by unscrewing three 14mm bolts (15) that hold it in place and prying it out.
Be very careful not to lose anything when lifting it out (springs, pins, washers bearings, or valves), note the position of the motor (static) swash plate (25), brake disk (16), brace calipers (17) and brake actuator (26), output shaft bearing and jerky plate (18).
If your transmission is damaged to the point where you have to replace components, if it has broken teeth, worn out center block, or metal debris in the oil; it is recommended to take everything out and thoroughly clean the case as well as the parts.
On the other hand, if the transmission is in good condition but is just old, you can consider putting in more dense transmission oil (like 10 W40).
Also, you should check the integrity of the drive/pump input shaft (21), its splints should be in great shape and its bearing shouldn’t have any play.
And you can check drive shaft bearings while at it.
Additionally, you may take a look at Tuff Torq repair tips:
Putting it all back together:
Basically a reverse process. First, install (the shafts if you have uninstalled them) the differential (19) and the gear train (22).
You can squirt some oil on the gears to prevent them from damage while there is no oil yet. Make sure that nothing is missing and everything is in the right orientation.
Make sure to tighten three 14mm bolts of the center block to 33 – 40 ft. lb. Don’t forget to install a brand new oil filter.
Use a transmission seal-maker to make a seal on the lowercase meeting suffice (don’t forget about hydrostatic and gear chamber separator wall).
Put it on the uppercase, tighten 12mm bolts by hand (put the longest two center bolts first in marked ports) and let it sit for an hour.
Then tighten your lower case bolts to 16 – 18 ft. lb. Flip the transmission (so that fill plug is facing upwards) and fill it with 2.3 liters Hy-Gard High Viscosity J20C** 10 W30 oil or any other synthetic 10 W30 transmission oil.
The oil level should be around 20~25 mm (3/4”~1”) below the lip of the (black cap) port when at room temperature, but you have to pour a little more to account for the air purging procedure.
If you have a universal socket and strong electric screwdriver, you can purge the air from the transmission by spinning the input drive/pump shaft back and forth with it for 5-10 minutes.
Put the drive pulley on the pump shaft, the washer, the fan, and the fixating c clip. Then follow the transmission uninstallation procedure backward.
Do not take the jack stands from under the tractor and don’t lower it just yet (if you haven’t purged the air with an electric screwdriver).
One less step while the tractor is still on the jack stands, purging the air (if you haven’t done it yet) from the transmission. turn the tractor on and let the transmission work in forward and reverse mode as well as in neutral by pulling the bypass valve lever at the back of your transmission into towing position.
let it run like that for about 15 minutes. Lower your tractor on the ground and enjoy.