6x4 manual reversing transmission will not stay in gear

New member here, I have found a lot of great info on these forums and would like to thank all of the contributors. Hopefully I can also help someone in the future.

I have a "new to me" 550 backhoe with the 6x4 manual reversing transmission. Trans works well with no odd noises or anything that seems unusual except that it will pop out of gear under load. This is only the main selector and gears, the high/low selector functions fine. Some gears maybe more than others, especially the forward gears. But it is load dependent and I usually am not putting much load on the reverse gears.

The work-around for now is to either hold it in gear with hand or a bungee. Doing so I am able to work OK but obviously it would be easier to use if I could repair it to work correctly.

I found a number of posts suggesting the detent balls/springs may cause this. I replaced all of them with new parts and now have nice positive clicks when shifting in and out of each gear. However it will still pop out of gear under load.

I have changed the fluid and did not see any metal debris. Of course it could have been there and come out years ago when someone else changed fluid.

I have not found a lot of information on what to look for next. I am specifically looking for any possible next steps before completely tearing the transmission apart.

The shift forks are accessible via the top cover and they appear fine to me, not bent or loose. I can move them through the various gears with a pry bar and the motion is looks and feels OK. Could they be mis-adjusted? I have a copy of the service manual but am not finding specific info on how to adjust the forks before locking them down.

What is meant to actually hold the transmission in a selected gear? I am not familiar with tractor transmissions but am with automotive. Looking at the parts diagrams it really looks like a bunch of straight cut gears with no method of locking in gear other than the detents I have already replaced.

Are there dogs that may be worn? Are the gears very slightly beveled so that they should lock in place under load? Something else? Is there a way to check for wear without disassembly?

You move collars when selecting gears. When new they were strait with slite ramp on edges. As time has went on with lots of use the ramping has worn farther back so not staying in gear starts. Sometimes
replacing collars will be a bandaid fix. There may be looseness of shafts in trans. Bad thing is to do much of anything will require a double split.

Is it the reverser or the transmission that is popping out of gear? Our reverser go so bad we couldn't even hold it in position,
About $3 grand as I recall.

Bill

It's not a reverser, the 6x4 has 3 forward gears and 2 reverse gears plus a high and low range

Sounds like the shift collars are worn and possibly the gears
Not sure where your located but I have a 6x4 trans in my 4500 that I'll be removing in the future, I need a pto on the tractor so I'll be replacing the 6x4 with a standard 8x2
The 6x4 does have a bearing making noise so I've parked it for now but it did not sump out of any gear

I'm located about 25 miles west of Fort Knox, Ky if you are interested in the trans
email is open

Thanks guys, the collars being worn makes sense. And I have no history on the machine so may or may not have a lot of other wear in there. I will be using my work-around for a while and will plan to do the split and go through the trans at some point.

And yes, is the 6x4 manual so no reverser.

Thanks for the offer, I am not too far away in Maryville, TN. I'll send you an email to talk about it further.

On a related note, I do not see how to enter my location into my profile. I checked the FAQ but did not see it mentioned there, any tips?

For privacy reasons they no longer have that feature

I don't know if this helps or not but I bought a 4 speed in a 30+ year old 2000 that wouldn't stay in 4th....kept popping out. It was
annoying so I put my foot against the lever to hold it in 4th. I don't remember the time line, but over maybe a year, it just cured itself
and quit jumping out.

If your tractor has been sitting for a long time, or maybe had dirty/water contaminated lube, before I started tearing into things, I
would replace the fluid, maybe changing to 134 A,B Trans/hydraulic fluid if currently using gear oil and doing as I did for a time to
see if it clears up. If it doesn't you haven't lost anything but a bit of your time.

Thanks, your post made me do some more experimenting. I was having trouble with popping out of all 3 forward gears and sometimes low reverse. That was with tractor as-bought, with some milky stuff in the trans.

I changed to Traveller fluid with J20C/134D ratings and have put about 7 hours on it since. Was still using bungee out of habit. I spent a couple of hours moving some material the other day and found that most gears are holding now, with forward low still being an issue.

I'm still assuming I need to split and repair, but at least for the moment it is much more convenient than it was.

This post was edited by richards on 09/19/2021 at 08:45 am.