JD 750C wont move.

[Vetech63]

S# 816284.
Started the machine yesterday after it had been sitting for months. I was told there was a transmission problem and after I opened the enclosure door on the left side of the cab, I can see why. The wiring has been hacked, insulation on the wiring is breaking off and rotting. Mud duabers have built several nests, one extends inside of a potentiometer housing.
I have an F691 and a F668 code on the panel and the "FNR not in neutral" light and exclamation point light are flashing (which I believe may be related).
The problem I have is NO wire schematic to trace this issue down...……..So Im here hoping one of you JD gurus possibly has something on this machine? It looks like most of the electrical parts are still available, but I would like to troubleshoot the system properly and not throw parts at this machine. Any help would be greatly appreciated!

Jeff

 

[mestizo]

Whats the SN?

 

[Vetech63]

Whats the SN?

S# 816284

 

[mestizo]

 

[mestizo]

F691

B20 Steer Sensor

Signal Wire Short to Excitation Wire

No Left Steer (1/2 mph)

See the technical manual or your authorized dealer

 

[mestizo]

F668

B11 FNR Sensor and B20 Left and Right Steer Sensor

Excitation Short to Ground

Transmission Shutdown

See the technical manual or your authorized dealer

 

[Vetech63]

Thank You Mestizo! Looks like everything I will need to trace the issue down. Im thinking the wire plugs had paper markers on them but I didn't notice if they were faded away. Im I assuming these markers are the component plug in identifiers? Im not sure where each sensor or pilot is located on the machine. Thanks again!

 

[mestizo]

Here is a component location, your machine may be a little different if it has pedal steering but the FNR and steer sensors should be in the same general area.

The wires should’ve had labels on em but a 750C is an old girl so they may have worn away. The electrical connectors should have the letter designations. You might have to break out a meter and ring out the wires from the sensor back to the X1 and X2 connectors to find your break. Good luck.

 

[Vetech63]

Your the man Mestizo. That will definitely help save time. Ill update this as I progress. Thank you again!

 

[Vetech63]

After the new owners got more info from past services on this machine, they decided that it is too old to spend any money on. If they decide to part with it, I will post it for sale.

 

[powerplusdude]

I am experiencing the same exact problem except it is not throwing any codes up. The FNR keeps flashing though. Also after 10-15 minutes of trying to get it to go in either direction, my back-up beeper finally starts working in reverse like it is supposed to. My '01 750C does not have a cab. Is the schematics and diagrams posted above the same for the non-cab model? Any more ideas on what could be causing this? I have always had the FNR flashing issue since I have had the dozer but it has not prevented the dozer from moving. Usually I can shut it down and restart it and it clears. It kinda feels like maybe the parking brake lever is hanging it up electronically somehow. Is that an option or are they not related like that?
Thanks, Mike

 

[mg2361]

Maybe the manufacturers need to start adding Bitrix to the insulation of wires like they do to antifreeze to make it bitter tasting to prevent those pesky varmints chewing the wiring.

 

[powerplusdude]

****UPDATE**** Come to find out, the problem I was having was due to the brake pedal lacking about a 1/8" being all the way up. I pushed it up with my foot and the dozer started moving. Luckily!!! I knew it had something to do with the parking brake/brake lever/brake pedal.

 

[Geno]

I don’t mean to steal our butt in on this post... But I have a 750 C with an oil leak on the rear PCP valve spool.It seems to be just an O-ring but the problem is John Deere doesn’t list the O-ring as an available part#. you have to buy the whole PCP valve. I would rather do that.. And it looks like a special type of o-ring... maybe a flat
o-ring ...Can anyone tell me what type of ring this is? Or size? And where I can find one. Thanks…Geno

 

[Geno]

Ok no problem .. I’m new here .. sorry bout that. I’ll do better next time.

 

[Randy Lee]

I have a 850c with a similar problem, flip the lever and it wont move, traced wiring to that switch and its all working, I think its something to do with the park brake valve or something but i cant find any schematics or pictures of how this all work. anyone have something on this??

 

[mg2361]

Welcome to HEF Randy!

Please start your own thread instead of piggybacking on another and post the machine's serial number.