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Farm Machinery Digest: Testing your diagnostic skills - Transmission

Ray Bohacz for Progressive Forage Published on 28 September 2021

Situation No. 1

Like most farmers, you keep old equipment around since it still has some useful life left in it.

You applied this mindset last year when you bought your wife a new SUV and kept her old one with 300,000 miles on it as a “spare.” You use the old car to run to town, lend it to the hired man and as a general backup vehicle.

Well, the inevitable happened: The transmission finally went. You had it towed two towns over since you heard there was a good transmission man there. He called and said the unit would need to be rebuilt, and it would be $2,000. You spoke to your wife about it. The decision was made to fix the car since you never really put any money into it and got used to having a backup vehicle.

After getting the SUV fixed, you drive it home – and the transmission shifts fine, but the engine seems sluggish at low speed and especially away from a stop. You decide to drive it for a few days, and maybe things will break in. They do not, so you call the transmission man. He tells you if the unit shifts fine, the problem is with the engine, and he tells you to have a mechanic look it over.

This perplexes you, since the performance was fine before the transmission failed even though the SUV has 300,000 miles. When you are at the implement dealer picking up some parts, you ask around to see what they think. These are the responses you receive.

A: Farmer A says that just as the transmission went suddenly, the engine must be going. He said you were a fool for putting that much money into an old truck and got what you deserved.

B: Farmer B thinks the transmission man set the line pressure too low in the unit, which is why the engine seems sluggish.

C: Farmer C says you got conned, and the man put a junkyard transmission and engine into the truck and kept yours.

D: Farmer D tells you to ask the transmission shop if they changed the torque converter. If so, the one they installed has the incorrect stall speed.

Situation No. 2

You really do not like to haul your grain too far, but you need to make some room in your on-farm storage for the new harvest, and the price you can get for your old crop is 10 cents higher about 100 miles away. You push the pencil, and it reveals that it would be profitable to put some wheels under it.

On your third trip from the elevator back to the farm, you get detoured due to an accident that closed the two-lane. Being low on fuel, you stop at an unfamiliar small truck stop to fill the saddle tanks. They only have B-20, and you fill up and hit the road.

All is well until the next day when you are about one-quarter of the way into the second fuel tank, and the engine starts to act up. “Oh no,” you say to yourself; a tow home or road call will eat up all the extra profit you made by selling to this elevator.

The truck manages to limp home – barely. The next morning, after sleeping on it, you decide to pull the fuel filter and water separator. The fuel filter is plugged with sludge. There was an extra filter in the shop, so you change it, and the engine runs fine. You resume hauling grain but are worried about a repeat of the event. You bring it up to a couple of guys at the elevator, and this is their opinion.

A: Farmer A knows the truck stop and says that the tanks are less than 6 months old, so they must have gotten a dirty fuel load.

B: Farmer B told you that the B-20 has a cleaning effect and loosened up all the sludge in your saddle tanks and put it into the filter.

C: Farmer C just said he does not know what happened, but you should never use B-20 unless the truck maker says so.

D: Farmer D has no idea, but chimes in that is why he never hauls grain too far.


Situation No. 1: Farmer D is correct. The shop changed the torque converter. The one they installed has the incorrect stall speed for that engine, rear axle ratio and vehicle weight. In this example, the torque converter is too tight.

The stall speed identifies the engine rpm that the torque converter will internally slip to before it mechanically links and transfers the engine power to the transmission.

A converter that is too tight (not enough slip) will lug the engine, while one that is too loose (excessive slip) will respond almost like a centrifugal clutch in a UTV. The engine speed will flare up, and then the vehicle will move.

Situation No. 2: Farmer B is the most correct. I say this because any biodiesel blend has a cleansing effect and will loosen deposits in the tank and the complete fuel system. Though some of the sludge may have come from the truck stop tank, the fact that they are new would mean that the tanks did not have a high level of deposits. The grain truck is older, so it has the natural formation of sludge in the saddle tanks if the farmer used untreated fuel. That is why it took a day or so for the filter to plug. end mark

Email “The Hotrod Farmer” Ray Bohacz with your machinery-related questions. Visit his site – Farm Machinery Digest  – for technical articles and to listen to his Idle Chatter podcast, which has listeners in 67 countries. Also tune into Farm Machinery Digest Radio on Sirius/XM Channel 147.

Ray Bohacz
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