IH 3400a Hydro Payloader

I have a 1973 IH 3400a with a backhoe installed and it will not move now.

Everything was going good while I used the loader on a small job in front of the house. Then I noticed that foward was getting weak while using the loader.

Next thing you know I lost the foward pedal then reverse started to get weak. Then reverse came back strong and foward was still gone. Now foward and reverse are totally gone. There is no noise when I step on the pedal. When I lift the rear The tires spin when I apply the pedals in the proper direction.

The backhoe and the loader function perfectly... well perfectly for a 40 year old hoe.

Any Idea where to start? I have changed 1 hydro filter. I have added 5 gals of the correct hydro oil. It is now a little over full. I have a leak on one of the boom rams but everything else does not leak.

I am an auto mechanic and have all manuals on the beast, there is little on the symptoms of the hydro transmission. I do have the hydro trans service manual. Any idea where to start???? Help Please!!

Jim

I am not familiar with that model and really never worked on the foot operated hydrostatic drive machines. However, if it does have a dump valve pedal etc for starting like the 656 with pedal hydros, that is the first thing I would suspect. If you unhook the return line from dump valve no oil should come out of valve, (ALSO VALVE HAS TO SEAT COMPLETELY WITH NO INTERFERENCE FROM DIRT OR STRIKING PLATFORM ETC). If that is ok, I would remove both lines that go to the reverse alternating check valve block and plug the fittings to eleminate any outside problems from internal problems. I'm not even sure your tractor has these valves so good luck.

I have all the valves you are talking about. Thanks for the reply. I will check into it and see.

thanks
jim

I don"t know a lot about these things, but I"ll try to help...

Hydros are a blessing when they work and a curse when they don"t, but as long as nothing bad happened (ran it with no oil) the problem is likely minor. Hydros tend to fail slowly, not all of a sudden. As the previous fellow indicated, the dump valve pedal (what you might call the clutch pedal--if your tractor has a pedal there) is a good place to begin. If it is stuck open, the wheels may spin (I"ve never tried it with them in the air), but they won"t pull if they"re on the ground.

If the dump valve checks out okay and the problem persists, a variety of problems may exist inside the hydro itself. All of these might be minor once they"re on the bench in front of you, but you have to rip the machine apart to get to them. By this I mean that if a bit of dirt, rust, corrosion, or slug of sludge/moisture got stuck in the right place, it could disable the machine without causing much harm. The problem is finding out where to dig before you rip into it.

The key with hydros is prevention. Keep the oil clean and filters changed regularly. Change the oil regularly as well. If you"ve not done this recently (in the last two or three years or in the last thousand hours of run time, drain the oil and replace it with new. Change the filters too. Run any part of the hydraulic system that does work before draining the oil as the oil should be hot when you drain it. As it drains, hot oil will carry out more dirt, contamination and moisture than cold.

If new oil and filters do not bring your machine back to life, or if all these have already been changed recently, you"ll need to get serious about learning how this thing works because unless they have experience with hydros, most mechanics won"t have a clue.

I&T sells a nice shop manual for the overhaul of Farmall tractors equipped with hydros. I don"t know how much help they are with diagnosis, but for twenty bucks, you can probably begin there and see if it is of any help. IH used to sell a hydro manual which was filled with fold-out illustrations of the inwards of hydros--I have one for mine--but I don"t know if anyone can get you a reprint of these. Besides--the schematics are in multiple colours, and I find that even the black and white reprints are not of the best quality.

The upshot is this: Though the hydro is a mysterious thing buried deep inside your tractor, there are test ports, pipes, and fittings which come to the outside world. These provide ways to measure pressures and flows inside. Acquire the proper tools and knowledge, and narrow down where the problem is before you tear it apart. It may be as simple as opening some access panel and replacing an o-ring, or removing a bit of grime that"s making some valve stick.

Best of luck.

Found the problem. There are 2 hydro controll lines going into the top of the transmission. They go to the dump valve and a valve on the HI LO range shifter. One of the orings on the foward line was blown and leaking pressure into the transmission. Replace the 39 cent ring and I have full foward and reverse.

thanks guys for your help.
Jim