# IH 3400a Hydro doesnt move



## jimjc038 (Aug 26, 2010)

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


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## Hoodoo Valley (Nov 14, 2006)

Welcome to the forum. Unsure about it, but It sure sounds as though the linkage has gone out of adjustment for the pedals or something is wearing out to the point of almost breaking.


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## BrianRideout (Mar 31, 2011)

Look at linkages, Do you know if the foot and inch valve is worn allowing oil to go to sump. The backhoe should be running off a separate circuit then the hydrostat. Does it have a separate filter for hydrostat to rear end? Check servo pressures and look at contol valve for debris in the valve.


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## wjjones (May 28, 2010)

Is there anyway to purge the hydro?? You may also want to be sure the vent is not restricted. Welcome to the Forum!..


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## cyrush (Apr 20, 2010)

I Presume the manual you have is ISS=1546 ???

Asuming it is. some checks, Turn to page 4, top photo shows fwd & rev test ports You need a 10,000psi gauge and class1 steel pipe work. What pressures does system register Operating pressure should be 6,500 psi. If it wont drive install a 1,000 psi gauge to get an accurate reading of lower pressure, be careful it is easy to burst a1.000 psi gauge in a6,000psi system !!!!

Secondly get 2 x 7/16 JIC caps, and undo pipework on opposite side of valve to test ports, put caps directly on adaptors on valve block *DANGER!!!!!!! FOR THIS TEST MAKE SURE THERE IS RUN OUT FOR DIGGER AS YOU WILL HAVE NO SAFETY CUT OUT *

if tractor drives, measure pressure in each port, slowly apply brakes to see what max pressure you get , do this slowly and do not exceed 6,600 psi.

Let us know what you find (Drop me aPM to tell me you have results, because i dont always look @ this section of forum) Post results on forum, not in PM.±±±


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