Hello.1980 4-speed tranny.I messed up the threads on the mainshaft under the clutch hub nut. Looking to get a die to clean them up. I'm guessing 3/4 inch, 18 threads per inch, left-hand thread. But, I don't really know how to tell for certain. Can anyone help me get the info for ordering the Right one?
Thanks,
Pat

 

I dont know the size but you can measure it.
Measure the OD of the thread with a dial caliper or mic.Then measure the thread pitch with a pitch gage.
Or get yourself a set of jewelers files.You need to use one that is angled enough to to file the sides of the threads.
Or just replace.

 

I've done that. I got confused reading an old machinists book which described "pitch" as the number of threads in the length of the circumfrence, i.e. wrap a paper around the bolt, mark it, then count the threads in that distance...
theOD of the threadsmic'd out, if I remember, at 0.72 or 0.73 inches diameter. pitch gage reads 18.
I'd file it, but it was a twelve point socket that some bonehead jammed on it, so there are a number of places. It's not bad enought to replace, though.the tranny is good.
Thanks. let me know if something(s) I said here don't seem reasonable, and I'll get the die.

 

.720/.730" dia sounds small.The size should be .7486/.7399". for a 3/4-18UNS externalthread according to the Machinist's handbook.
To double check,you can measure the ID of the nut.The minor dia. of the nut(ID) should be .690/.703".
You could also verify by checking the nut with a 3/4-18 bolt before you buy a die.
The pitch is the number of threads in 1 inch,has nothing to do with circumfrence.
I would try to file the thread to see if it is soft.If the shaft has been hardened then the die may not cut it.

 

I'll recheck the size after I get home/back--I think you have it right. I'd check with a regular bolt except for the left-hand thread.
Pat

 

Go to a hardware store or an auto parts store and ask for a thread restoration file. It has a square shape and a different thread pitch per side. Be sure the file you buy has a thread pitch that matches the pitch you want to restore. Stroke the damaged threads as you go around the shaft untill the threads clean up enough to install the nut.

 

Ah, a thread restoration file. Never heard of the animal, but I like it. Thanks.

 

View the tool here:

http://buy1.snapon.com/catalog/item....mp;dir=catalog