c120 automatic--transmission engages...sometimes

[crm227 0]

Folks--

Need a little help here. Have a '76 c120 automatic. Starts right up and engine runs great. Moved fine in fwd and reverse at the beginning of the snow season, but past two times I've plowed with it the transmission (or something) has quit on me in the middle of a plow. Usually first happens when I'm stopping to put it into reverse. Might catch a little, but then stops. No noises, nothing else noticeable. If I had to find something to comment on, it would be that the lever to engage the transmission feels like it has less resistance than normal. In the past, I've let it sit for a little and then it's worked. Other times it will start working, then I'll shut it off a minute later and when I restart--nothing. Last night I went to turn it around in the garage and got halfway through a 3 point turn before she just stopped moving. Again--no noise and no engine problems.

 

One other point--when this happens the tractor can be pushed without having to unlock the push valve. But I've never tried pushing it that way--just noticed that I could. Valve opens and closes fine, but at this point there isnt any noticeable difference when it's open versus when it's close. It's that last point that worries me.

 

Whaddya think? 

 

Chris

[rmaynard 17,221]

Have you checked the transmission oil level?

[crm227 0]

yes--checked it last night and it was within a normal range.

[squonk 46,857]

I'm thinkin you have a worn out trans. I had almost the same problem a few years ago and had to replace the hydro motor. I have a spare transmission that I would offer you for little money but you're kind of far away.

[daveoman1966 3,883]

You MAY have broken the tab that locks the shaft of the motion control lever aparatus. 

 

Look at this pic of my C-160 (same hydro unit) and locate this on your C-120.  This shaft has a tab on the end of it that is bolted to the hoodstand to keep the shaft from turning with the motion control parts.  Very often this gets cracked, then breaks, allowing the shaft to move freely when it should not.

 

In the schematic, I am referring to item # 6-40.  Look at the little flat tab on the LEFT end of that shaft. 

Edited February 4, 2014 by daveoman1966

[daveoman1966 3,883]

As a 2nd possibility, there MAY be an issue with the FWD / REV valves in the MOTOR section of the hydro unit.  Either could be stuck or the spring between the two valves MAY be broken. 

 

These are located toward the bottom of the Hyd MOTOR on LT side of tractor.  Here are a couple pics...hope they help.  PS...take CARE to keep these CLEAN and be ABSOLUTELY CERTAIN to replace them EXACTLY as they came out.  Don't use a steel object to push the valve and springs out of the cavity.  I use the rubber tip of a pencil and a Magnetic pick-up tool. 

 

NOTE.... These valves have a FLAT surface on them, one FLAT being a bit wider than the other valve.  Be sure you get it right! ! !.   

[TT-(Moderator) 1,170]

Just because it's easy........

Check the rear wheel hub(s) & axle key(s).

[crm227 0]

thanks, all. I quickly glanced at the tab Dave pointed out and it looked fine. Will move on to look at the others next (starting with the hubs and keys). Will let you know what I find.

[crm227 0]

Folks-

What exactly am I looking for when I check out the hubs and keys? Any step by step instructions or tips? This is new territory for me.

 

Thanks

Chris

[can whlvr 994]

when the tractor wont move,get someone to look at the axle in the middle of the hubs,see if they are turning inside the hub,which they shouldn't,the axle and hub should move as one,its the key inside the hub that splines them together,if its sheared the axle can spin inside the hub

[crm227 0]

OK--a quick update.More snow this week. Crossed my fingers and started her up. And she moved. Didnt give me any trouble. So now I'm thinking that perhaps it has to do with either really cold temps. Does that sound possible? What could be affected by cold like that? 

[876wheelhorse 46]

my c141 did this. sometimes go sometimes no go. i recall i was moving one day hit a big dirt clod it quit moving. there it sat. my frame was busted got it welded back up and i had a bad hub. both of these are fixed now and this year it hasnt let me down now that i said something its going to be the biggest pile ever...