Magnum 7120 downshifting

[ryangpayne]

So I plowed all day with the 7120 today. Was in 9th gear all day, when I got ready to finish up the ends I went to pull it back into 8th and It didn’t click into 8th like normal. I couldn’t feel the detents until it went into 6th. This shocked me so I tried to go back up into 8th and I still couldnt feel the detents until it clicked into 9th.  After a second I clutched it and pulled it back into 8th and it was back to normal.  I ran it in 8th until I fished up and on the way out shifted into 9th and everything seemed normal. 
 

is there something I can do to fix this or could it have possibly just been a sticky shift cable or something? 
 

thanks, Ryan

[Rick G.]

It might be the accumulators for shifting the transmission might have gone bad or just need recharging. They are pressurized with nitrogen gas I believe and might just need a recharge. But what do I know. Next to nothing most of the time. Lol. 

It’s just the wee hours of the morning here. Wait a bit and as the true experts here awaken, you may see some helpful or more accurate expert comments on what to look for and do. Good luck. Hope it’s nothing too major and it will just be something as simple as those accumulators. They are located on the left side of the tractor, under that plastic cover in behind the steps. 

[Rick G.]

Zzzzzzz??? BTTT. Hey guys, any expert help for Ryan here? I’m just guessing with my non-expert comment above regarding the accumulators. Sometimes I know just enough to get in to trouble. Lol. 

[snoshoe]

Not sleeping. Just don't have the answer. Flat accumulators would cause slow or abrupt shifts not missing gears. The detents are actually little hydraulic cylinders. Not feeling them indicates a loss of hydraulic pressure. Don't remember enough about the tcv to comment further.

[756puller]

I remember a service bulletin that mentioned running for a long time in the same gear it would seem to be sticky for awhile. The remedy for it was to just shift it every once in a while. It was mentioned in the magnum transmission troubleshooting bulliten I know that for sure.

[ryangpayne]

Thank you guys very much for the replies. I do tend to run in 1 gear nearly all the time so that sure might be the problem 756puller. I do need to check the accumulator pressures as well just because it has been a couple years since they were filled.
 

I plowed another 40 acres with it today. Plowed all day in 9th again and As I was leaving went to shift into 10th and i couldn’t feel the detents in 10th so it went to 11th. After a second I pulled it back into 10th though and it worked fine. And it shifted up and down through the gears on the way home with no problems. Hopefully it is just sticky after running in 1 gear all day. Here is the old girl. Has 4300 hours, I’ve had it for about the last 1500 hours. 

[bitty]

I wouldn't rule out accumulator pressure causing weird stuff. We have had it do many things when the pressure is low

[Reichow7120]

46 minutes ago, ryangpayne said:

Thank you guys very much for the replies. I do tend to run in 1 gear nearly all the time so that sure might be the problem 756puller. I do need to check the accumulator pressures as well just because it has been a couple years since they were filled.
 

I plowed another 40 acres with it today. Plowed all day in 9th again and As I was leaving went to shift into 10th and i couldn’t feel the detents in 10th so it went to 11th. After a second I pulled it back into 10th though and it worked fine. And it shifted up and down through the gears on the way home with no problems. Hopefully it is just sticky after running in 1 gear all day. Here is the old girl. Has 4300 hours, I’ve had it for about the last 1500 hours. 

Nice 7120. What year is it? We have 2 7120s. Both 1990 models. One a FWA and another 2wd. Also recently added a 2wd 7230.

 

Funny you call yours a old girl at 4300 hrs. Both of our 20s have that beat by far. The 2wd is approaching 8000 hrs and the FWA is over 9000 hrs. Even the 30 we just bought is higher hrs than that  

[ksfarmdude]

Sounds like shift valve actuators to me

[756puller]

Where are the actuators at? It's just three spools that spin around with the shift cam. The detent spool is just a roller on a shaft with a spring.

[Maynard]

11 hours ago, 756puller said:

I remember a service bulletin that mentioned running for a long time in the same gear it would seem to be sticky for awhile. The remedy for it was to just shift it every once in a while. It was mentioned in the magnum transmission troubleshooting bulliten I know that for sure.

 

10 hours ago, ryangpayne said:

Thank you guys very much for the replies. I do tend to run in 1 gear nearly all the time so that sure might be the problem 756puller. I do need to check the accumulator pressures as well just because it has been a couple years since they were filled.
 

I plowed another 40 acres with it today. Plowed all day in 9th again and As I was leaving went to shift into 10th and i couldn’t feel the detents in 10th so it went to 11th. After a second I pulled it back into 10th though and it worked fine. And it shifted up and down through the gears on the way home with no problems. Hopefully it is just sticky after running in 1 gear all day. Here is the old girl. Has 4300 hours, I’ve had it for about the last 1500 hours. 

Here's the section from the service bulletin NTR SB 016 96 regarding delayed shifting problems.

 

[ryangpayne]

Thank you to everyone for the replies, And for that service bulletin. This tractor is a 1990 model. It’s actually nearly the newest tractor we have. We still run 86’s and 88’s for most things. 
 

I checked my accumulator psi this morning first thing. It was 82 degrees out and one had 62 psi and the other had 65 psi. So that sure could be a problem. I am going to pull them off and get them charged this week and see what kind of difference that makes. Thanks to everyone for the help. 

[lorenzo]

 I would be interested in the results.

Please let us know if thats all it was.

[Farmall Doctor]

Thanks for the bulletin print, Maynard! The "New Farmall" (Magnum) transmission and control valve is a true work of art! 

[SDman]

I guess my first thought on a tractor that vintage could be the shuttle spool in the TCV. Early tractors had missed shifts, lack of detents, etc. because the lands/grooves on the spool were too small to keep the spool stable. Could be accumulator pressure like has been mentioned, also I would be checking regulated/transmission system pressure for proper pressure spec. The TCV went through many changes in 7100 series production, what they ended up with at the last year of 7100 production is more or less what they used all the way through 8900 series production. 

[Maynard]

11 hours ago, SDman said:

I guess my first thought on a tractor that vintage could be the shuttle spool in the TCV. Early tractors had missed shifts, lack of detents, etc. because the lands/grooves on the spool were too small to keep the spool stable. Could be accumulator pressure like has been mentioned, also I would be checking regulated/transmission system pressure for proper pressure spec. The TCV went through many changes in 7100 series production, what they ended up with at the last year of 7100 production is more or less what they used all the way through 8900 series production. 

Changed a lot of those spools back in the day.

The part has now fallen in the "How  in the world do they justify that price" category and is listed as "orderable" which means none are in the depots but you can order one.

 

[ryangpayne]

Wanted to update this thread. I got the accumulators charged and have been plowing with the tractor for a couple weeks and it hasn’t acted up or had any problems yet. Hopefully that fixed it! Thanks!