Farmall M 4-5th gear shifter fork---are most of them bent?

Having a constant problem with my Farmall M not staying in 5th gear.

About 5 years ago, the 4-5 shifter fork on my M broke. So I go to the nearest salvage yard, pick one up, and install it.

I noticed after the install, it didn't quite move the 4-5 gear fully forward, when placed in 5th gear. So it kept popping out.

I go and get another used shifter fork. This one moved the gear somewhat closer to the transmission drive shaft, but still not as far ahead as it should, and still getting slipping out problems.

I have re-welded the end of the gear shift to specs. Replaced the detent balls and springs.

The internal teeth on the 4-5 sliding gear are in great shape. The teeth on the transmission drive shaft are ok. Bearings are tight, etc.

I am beginning to think that the vast majority of used M 4-5 shifter forks out there are bent. The reason I think so---is because probably 95% of these tractors have had the transmission shaft front pilot bearing go out at one time or another. And when this happens, the front of the transmission shaft wobbles and bends the shifter fork.

There isn't a lot of engagement distance on the teeth of this 5th gear. So if it isn't moved fully forward and held there properly, it will slip out of gear.

I really need to have a reliable fifth gear on my M, since I use it for farming. Any advice on what I should do would be appreciated. Thanks!

Yeah the pilot brg [or brass bushing]is pretty important, but i got 4 m's and a 450 they all stay in 5th

Something is wrong that you are not addressing/fixing.I've farmed with M/SM for 40+ years. Never had one pop out of gear. Have never heard of bending shifting fork,either.Dig deeper and find the root of the problem. May require a 'split'

That input shaft pilot needle bearing could be bad along with gear or two.

I will check again. Going to take the belt pulley cover plate off tonight and look at the gears.

Thing is, I've looked and looked and just can't seem to find why this is happening.

I will try and post some pics after I take the cover off tonight.

You may have to split it to find the problem. As was said ,it could be the pilot bearing or something not visible from the top.How long have you owned the tractor? do you know it's history? did someone do something to it in the past. A lot can happen in 60+ years......

Two items: one is that the 4th 5th slider can walk off of the input shaft if there is any play in the center pilot bearing (where the gear slides) this, and any play in the front main input shaft bearing/carrier, let them walk apart. The second is the fact that the tips of the slider splines and splines on the input shaft get worn shorter from thousands of grinding shifts into High from Fourth. A minor contributor can be a bad spring in the detent ball/spring that positions the shift rail in gear. A test: With the engine stopped, and a friend pushing on the top of the rear wheel with the shifter in 5th gear, move the shifter toward neutral. If the distance it moves is less than 1/4 inch, it is usually gear and input shaft time. New that move is around 5/8" Jim

If they are to be changed, I think that they can be changed without a split. Top cover removal, and belly pump removal are necessary. Jim

When you determine all parts , bearings shafts etc are in good condition, no excess movement back and forth or up and down then you can do one of two things. Move the input shaft back a little with a washer in the correct position to further engage the direct drive. Doing this will change the gear contact with counter shaft though and may create a little gear noise. Other option is to fill the notch in shifting fork with weld and relocate notch the amount you have determined the gear needs to be moved farther engaged.

Removing cover to replace forks is just as much work as doing the relocation of the notch for the detent ball. Of course, it is pretty easy to determine if forks are actually bent or not but I doubt it would ever be bent enough to create your problem or it would be very obvious to naked eye.