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

 

[jakin9000]

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.

So, I had the transmission opened up, but I've since then put it back on the truck because I needed it, so I can't really use my feeler gauge on it. I couldn't find anything that specified how much end play was within spec though when I was diagnosing it. Where did you find those specs?
I will say the end play is quite minimal and possibly falls into that tolerance range.

I also suspected the 5th/reverse gear assembly for some wear or damage, but couldn't find anything. I could have overlooked something, but no missing or chipped teeth on any of the gears nor synchros. The key springs seem to be alright, although I may not know what to look for on those. The keys dont look worn either.
My only other concern was that needle bearing where the input shaft meets the main shaft, theres a small amount of slop there. Could that effect only 5th gear without effecting any of the other gears?
I was just now test driving it again with my hand on the shifter. It slides into 5th gear with no problems. It stays in for awhile sometimes. But whenever I smash the accelerator I can feel it start pushing against my hand. As soon as I let off it lets up. Something is definitely causing it to be pushed out.

 

[gw33gp]

I have been dealing with popping out of 5th gear since I had my original transmission rebuilt with 250K miles on it. I was not having any problems other than a slight whining noise in first gear when going slow with no load. I asked to have it checked out because I was going into very remote wilderness on a long trip and did not want any problems. They told me the reverse/5th gear cluster was worn. They asked if it had been popping out of 5th gear and it had not. They said it was mostly the 5th gear dog ring engagement teeth that were worn.

I told them to go ahead a replace the reverse/5th gear cluster and all the bearings and seals. They said the synchronizers were in good condition. A little less than a year later (~10K miles) it started popping out of 5th gear. They replaced the 5th gear cluster under warranty. It was good again for about another year and started popping out of 5th gear again. They were baffled as to why but decide the aftermarket parts were not as good as the OEM parts that were no longer available. They replaced the 5th gear cluster again and just charged me for the parts. It lasted about another year.

I decided to order a remanufactured transmission from Zumbrota. It also lasted less than a year. They sent me another remanufactured transmission under warranty. That one is still good and has close to 2 years on it.

I don't have a confirmed answer to your problem, but the 5th gear cluster is my guess. I am also guessing you have checked the top and bottom shifter bushings to make sure they are good.

 

[jakin9000]

I have been dealing with popping out of 5th gear since I had my original transmission rebuilt with 250K miles on it. I was not having any problems other than a slight whining noise in first gear when going slow with no load. I asked to have it checked out because I was going into very remote wilderness on a long trip and did not want any problems. They told me the reverse/5th gear cluster was worn. They asked if it had been popping out of 5th gear and it had not. They said it was mostly the 5th gear dog ring engagement teeth that were worn.

I told them to go ahead a replace the reverse/5th gear cluster and all the bearings and seals. They said the synchronizers were in good condition. A little less than a year later (~10K miles) it started popping out of 5th gear. They replaced the 5th gear cluster under warranty. It was good again for about another year and started popping out of 5th gear again. They were baffled as to why but decide the aftermarket parts were not as good as the OEM parts that were no longer available. They replaced the 5th gear cluster again and just charged me for the parts. It lasted about another year.

I decided to order a remanufactured transmission from Zumbrota. It also lasted less than a year. They sent me another remanufactured transmission under warranty. That one is still good and has close to 2 years on it.

I don't have a confirmed answer to your problem, but the 5th gear cluster is my guess. I am also guessing you have checked the top and bottom shifter bushings to make sure they are good.

Well, I'm sure that gets pretty aggravating!! It helps a bit knowing I'm not the only one having issues with it.
And yeah I replaced the shifter bushing and all to start with just to see if it was an easy fix, but it wasn't it.
I'm of a good mind just to hold it in 5th and see what happens. I did that for awhile, but it got slightly worse. Still no grinding or weird noises though.

 

[PlumCrazy]

The reverse/5th gear fork is actuated with an idler arm on an adjustable eccentric pivot. Potentially the jam nut as loosened up and let the eccentric move to a spot where 5th isn't fully engaging the detents when using the shifter. I personally have rebuilt over a dozen M5ODs ranging from 88 - 2010 and I have never had one tat the eccentric was not in the neutral (zero for/aft adjustment) positions. There is a "I" stamped on the end of the shaft to show what orientation its in from the outside. I think its vertical on all of mine IIRC....I have had issues with first gear popping out on a trans that was driven for years in desperate need of a slave cylinder and wore all the nubs off, but never 5th.