7400 Power Quad

[tim s]

I was wondering if any of the Deere Techs on here can give me a bit of help with a 7400 I have here, it lost all forward speeds, reverse is fine all the way through, I could hear it shift through the speeds when in forward, but no movement at all. I have the trans laying on the bench and don't see any thing wrong, can a forward reverse shift valve hang up on these?

 

[Jake Winn]

Did you check the trans pressures before you pulled it apart? If so, what did they show? Is that a mechanical reverser with the fwd-rev on the RH console? Seems like i had a 6400 that did something similar and found a blown gasket or valve issue in the shift valve body.

 

[tim s]

This one was so filthy that I couldn't do much testing,It has been used as a feed lot tractor and had a blanket of hay clippings packed and oil soaked,, and being un-familuar with this transmission system, I went ahead and rolled it apart, it worked fine in every way, loader function and all reverse gears, just nothing in forward, I could feel it shift through the speeds, but it would not move at all forward..I decided to make this my "trainer"...I had hoped that I would never need to deal with these, but here I am,,Darn it...

 

[PSU4250]

With it being a power quad, its a 4 gear range box with a 4 speed power shift in front of it with a forward and reverse clutch. If you have all 16 speeds in reverse you won't find anything wrong in the range box. Are you saying in forward you can hear it make 4 power shifts? Sounds like something is wrong with the forward enable circuit. I can't remember but I don't think there are any TCU codes in that tractor, I think it just has a BCU and HCU, nothing for the transmission.

 

[tim s]

Yes, that"s what I got,,or don"t have, It appears to be in the shift valve, I haven"t broke that apart yet, but that is next, nothing appears to be wrong in the planetary...what is the purpose of the "Air Pump",,I don"t understand that...the trans pump is worn a good bit, i have a new one coming..

 

[PSU4250]

The air pump is there to help force hydraulic fluid to rear section. When it goes bad the hydraulic oil quickly overheats, nothing to do with the shifting/operation of the transmission.

How many hours are on the clock? I've seen a few pumps worn out. Was the aluminum housing worn? Scored? Its too bad we didn't have any pressure readings before the tear down. I've done my share of hours of pressure washing just to be able to work on some pieces, mostly from dairy farms....

 

[tim s]

This one is older and rough, the aluminum housing is okay the oil pump is scored up, my thought were that if it worked okay in all the reverse gears and this all seemed to have happened all at once, that the pump was doing a fair to good job. when my gaskets and other misc. parts come in I'm going to go through the valve body to look for a fail point, clean and go back together as I go,,I'm hoping that I will not be going back in,,but Like I said this one is for learning, I have seen a lot to the operation as I go...a tuff school,,Darn it...