Fifth gear nut - Which version is best?

[dieselburner]

See thread titled "Replacing input shaft" to see how I got here...



I took the new split nut back off of the fifth gear. I had to cut it off with a grinder. I managed to do it without messing up the threads on the shaft. I called up Standard Transmission and they are sending out another split nut. I now have this question to anyone who has done the fifth gear nut fix successfully. Would you use the new split nut that they are sending out or just put the original one back on? It turns out that the original one that I had on there was an upgrade from the earlier nuts and it was staked into a groove that was ground into the shaft. The nut is in really good shape except it has some dings on the edges where I beat it off with a chisel. I plan to stake whichever nut that I use. What would you do?

 

[C Schomer]

There's no 'nut only' fix that's reliable once you've had the problem because the gear wears into the shaft and no nut made will hold the sloppy gear on. I sucked it up and did the ST shaft and gear fix right off the bat. Thoroughly cleaned the splines and threads, drenched inside and outer surfaces with red Loctite and torqued to 400. If that doesn't do it... I'll cry!! Craig

 

[LWilliams]

Get the modified mainshaft, gear, nut and everything you need from Standard Transmission. Just replacing the nut won't hold it for good. Fix it right while you are in there by replacing the mainshaft. Then you won't worry when and if it will fail again.

 

[dieselburner]

C Schomer and LWilliams,



Do you remember which nut came with the kit? Was it the split nut or the solid nut that is beveled on the nose?

Steve

 

[LWilliams]

Honestly, I don't remember. If I picked one it would be a guess. But the nut is not the remedy to the problem. The way the stock shaft is splined under the 5th gear is the cause of the nut coming loose. Other posts state that various things have been tried, including tack welding, to keep the nut from coming loose. When my 5th gear went out and I took the mainshaft out, it looked perfectly fine and so did the gear but seeing the minimal amount of splined area on the shaft that the gear rides on shows how the gear is constantly being flexed on the shaft. Compare the two mainshafts and you will see a big difference.

 

[MikeBeggy]

I just received my upgrade kit from ST and it has the split nut with a modified washer that goes between the nut and gear. BTW, I was wondering from those of you who have replaced their mainshaft if there are any really special tools needed to complete this job? I have a good selection of pullers, bearing removal jaws and a shop press. The shop manual refers to a lot of specially designed tools for this job. Any experience would be appreciated. Thanx...

 

[LWilliams]

The guy that replaced my mainshaft didn't use any really special tools other than a small curved pick to get some of the lock rings out. There is a small pin in there (about the size of a pencil point) that will fall out and be lost if you are not looking for it. There is also one gear, and I don't remember which one, that he had to use a press to get off of the old shaft. Other than that it's just a matter of taking stuff off the old shaft and putting it on the new. Good luck.

 

[TxPope]

It's more than the nut!

The standard transmission fully splined shaft is the way to go IMHO. The full splines, split keeper washer, spring washer and the split nut all work together to make this the most reliable fix I have seen. After pulling transmission, it only took a couple of hours to install and I needed no special tools other than making a wrench to fit the nut. If you do not want to make a wrench it is available off of the tool trucks for around 40 bucks. They might have to order it though. Oh yeah, it helps if you have a really big torque wrench!! Be sure and watch for the little pin on the lower shaft that was mentioned earlier, it is important!

 

[C Schomer]

My kit had the split nut. My nephew owed me, he did most of the shaft change after I got the box out. You need a pin punch for the 5th shift fork, big snap ring pliers(it's easier), splitter/puller is nice for the 4th gear hub and a press would be nice. Have shim stock around to set the endplay. The biggest thing is knowledge of the syncro parts - that's why I got help. The new gear is a medium press fit, which means it's pretty tight! Make sure you're prepared before putting all the loctite on! If I did it again, I'd set the endplay(. 002-. 006"), pull the input shaft back out and put the box in a press with blocks up to the front end of the mainshaft to press the new gear on. Then put the input back in. Otherwise you are beating against the thrust needles if you use the hammer method. Craig

 

[TxPope]

I agree with you

I agree with Craig, that big snap ring can be a challenge! Funny how much difference there is in the ST mainshaft. My fifth gear slipped right on by hand!

 

[C Schomer]

TxPope, that's interesting! Makes me wonder about their QC. Scott had a pipe that was suitable for a driver and we WALED on it with a sledge. I'm glad it was tight but I was worried about damaging the thrust needles so I pulled it back out and checked them. I'm still not sorry I did, even tho they were fine. The end of my 2wd shaft is tapped for 1/2" fine thread. I've wondered if 1/2" allthread and nut would have been able to pull the gear on - I would try it, if there's a next time but I have doubt as tight as it was. Craig

 

[danandamy]

All I can say after reading this and some of the other threads is, at least in my automatic, all my nuts stay right where they belong!!



DTTdan

"Keeping my nuts where they belong!"