Murray Riding Mower - Runs great but loses speed

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Sep 17, 2024
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I have a 42" Murray Riding Mower (Model 42598x92A) that runs great. I'm not super mechanically inclined but I'm handy enough. I feel confident enough until I get into the engine/transmission issues.
The engine doesn't bog down or stop ever but I sometimes lose speed and sometimes the mower refuses to move at all. The engine runs totally fine and the blades will rotate and blow grass just fine. It is worse going uphill.
My assumption was it was the motion drive belt. I was given this mower by a family friend that upgraded to a zero turn. He's a mechanical engineer, maintains his equipment well, changed the drive belt before gifting it to me, and sent the original manual and spare parts he had for it. I talked with him and he was convinced it wasn't the drive belt because he just replaced it but after countless tinkering I went ahead and replaced it anyway. No improvement so far. I'm thinking it may be the tensioner pulley but I really don't know how to check for that. When I engage the brake, the pulley does move.
When it stops moving, I can hold the brake, engage the gas pedal, and when I release the brake it'll lurch forward. It often continues forward if I'm on flat land or downhill, but it usually is at a snail's pace. If I let it sit for a while (usually a couple hours), It'll work fine for a while and then go back to this problem. I've been mowing my yard in multiple shifts this summer because I can't figure this problem out. I would love some help. I may need you to explain it to me like I'm a 5 year old depending on the solution.
 
Couple of questions for you. Any idea of hours on the machine? Or how old it is, if we need to guess at the hours? Secondly, what type of transmission does it have?
 
Whoah, I love the help. I did not expect this many responses.
1) The mower is fairly old. Google says the model is from 1999. Automatic Transmission. The forward/reverse is on one pedal.
2) I haven't changed the transmission fluid. I thought about that, but I couldn't find where to add to it. This is maybe where you have to treat me like a year old. There's a drive brake attached to the gearbox if that helps you, idk. There is gunk that I tried to blow off with an air compressor but I don't know what else to clean it with.
3) I'm not sure how to check the drive belt pulleys. They all spin freely and the tension pulley moves when I engage the brake.
4) I have no idea how to check belt tension. I have a new belt though. The e-brake is releasing completely as far as I'm aware.
 
The bad news is that on most riders, you have to drop the rear axle/transmission to access the oil fill plug. If the transmission greasy and covered with crud, there's a chance that it's been leaking and doesn't have enough oil in it to function properly. Sometimes the plastic plug (which just pops in and out of it's hole) is loose or damaged and lets oil escape. It can also be seeping out at an axle seal near a wheel or also the top where the pulley shaft comes out the top.
 
Yep, my thought is low fluid in the transmission or worn transmission. Finding the make and model number on the transmission would be a good start.
 
1999 with the original transmission fluid.
Now all you have to do is figure out how to change it and what fluid to use.
Find a YT video on the tractor and go from there.
 
I've discovered its a Peerless 205-024c Tecumseh Transmission. I have to use a grease gun on it and it used Bentonite grease. Way out of my wheelhouse of knowledge but the owner's manual has spots where I'm supposed to grease it.
Does that change your thoughts on what it may be?
 
If the belt isn't slipping(would smoke and stink of rubber) its a well worn hydrostatic transmission. Since it works until the fluid heats up, you might have a chance it working ok with new fluid. On my 25+ year old disposable HST mower I could take out the battery and tray under the seat and unscrew the vent tube, and suck out the old fluid(looked almost like mercury!) and I pumped in some 15W40 and got a bit better performance. Next time I'll go for 20W50 or better. Maybe 75W140 gear oil? That would be 20W70-80
Mine will slip about 30% going that much slower up a 20% grade or 30% faster going down that grade! But has done so for years now. At least its easy to modulate speed with the HST.
 
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