M5r1 slipping out of 5th gear

[jakin9000]

So, everything runs really smoothly on this transmission. No grinding or noises while driving, and it all shifts excellent. Its just that 5th gear started randomly slipping out from time to time while under load for an extended period of time. And than it got worse and worse.
So I pulled the thing and opened it all up and everything appears to be in really nice condition. (When I bought the truck about two years ago they had replaced the transmission and it had a few thousand miles on it.) All the gears and synchros seem to be in perfect condition and from what I could tell everything is doing fine. Shifter forks looks good. All the shifter rails snap into gear with a good firm hold.
The only thing I found that I wasn't sure about is the countershaft had just a little play in and out. And also the main shaft had a little wobble where the input shaft meets it at the front. That bearing could move just a bit, but it didn't seem terrible.
Does anyone have any ideas on what might be the issue here.
Thanks

 

[franklin2]

If one of the shafts has excessive end play, that can knock it out of gear. The end play is critical on a modern transmission with the helical gears. They put a thrust load on the shaft. When you are on and off the throttle, the shaft can shift forward and backward knocking it out of gear.

 

[jakin9000]

If one of the shafts has excessive end play, that can knock it out of gear. The end play is critical on a modern transmission with the helical gears. They put a thrust load on the shaft. When you are on and off the throttle, the shaft can shift forward and backward knocking it out of gear.

I did wonder about that. What would be needed to fix that? Does it need shimmed?

 

[Shran]

Yes both the input and countershaft have shims under the front cover. I guess I would see how much endplay you have before tearing into that. Do you have a dial indicator you can use to measure that on the countershaft? If I'm reading the book correctly, "0.15 to 0.25mm (0.006-0.010 inch)" is the allowable end play tolerance.

I guess I would be more inclined to look at something in the 5th/reverse gear cluster as a cause more so than the countershaft though. Perhaps worn springs or keys on the synchronizer... worn bearing somewhere in there, worn teeth on 5th gear itself, etc. I have seen a few of these with really worn 5th/rev shift forks so that was my first thought. Generally popping out of gear is caused by shafts having slop somewhere as franklin said or something in the shift process not fully engaging the gear.

 

[85_Ranger4x4]

You may find these helpful:

Manual Transmission Troubleshooting - The Ranger Station

Here is a quick guide to help you with your Ford Ranger Manual Transmission Troubleshooting for a slipping noisy transmission

www.therangerstation.com

https://www.therangerstation.com/tech_library/pdf_documents/ford_m5od_manual_transmission_shop_manual.pdf

More reading here:

Transmission, Transfer Case & Driveshaft - The Ranger Station

Ford Ranger & Bronco II transmission, transfer case, and driveshaft guides. Manuals, troubleshooting, rebuilds, and swap tips for 1983–2011.

www.therangerstation.com