advice on re-machined transmission input shaft tip

[Ms6peters]

Had an NOS input shaft machined on a 55yr old military M422A1 transmission (made by _New Process_) to fit a smaller pilot bushing for an more modern engine repower swap. This transmission/transfer case assembly is somewhat similar to the M151 Mutt.

The tip section should be re-surface hardened. It will run in a bronze bushing. Any best estimates only the steel/alloy used ~1959 for common auto/truck transmissions and if the input shaft would be surface hardened or thru-hardened. Local metal heat treating outfit obviously needs info. Should I shell out for a metallurgical analysis ?

Thanks.

old draft picture prior to machining:

 

[rsanter]

Surface hardened should be fine. You don't want it too hard/brittle.

Also, did you already have it machined or you are going to have it machined?
If you have not already I would make a custom bushing instead

Bob

 

[matt_i]

I also vote for surface harden. Carburized might be your cheapest route (over nitriding).

But, I would still leave it a couple thousandths oversize(!), and have it OD ground back to size at the end of the hardening process to also clean up the surface (it will probably be slightly pitted), then polish in the direction of rotation....

 

[Ms6peters]

The shaft is already machined. The metal shop wants to know what type of steel alloy it is to harden correctly. Any ideas on alloy in 1959 - 43xx or 8xxx? My guess is the original input shaft was surface hardened vs carburized ??...not sure at all, beyond my expertise.

Was planning on induction hardening the surface of the pilot tip. The bushing will be machined to match. Good idea the re polish the tip, didn't realize the surface would pit after treatment.

 

[1wook]

I'd guess a 41 or 43 series and not an 8.

Induction hardening the shaft is probably the best route because it'd affect the rest of the shaft the least. 0.5 millimeter depth is what I'd recommend for that bearing surface.

See they can get it hard in the shoulder area where you turned it down so you don't have an untreated area where the stress riser already is. Not that it's under torque, but it maybe subjected to a bending load due to misalignment.

 

[SVE Performance]

It is running in a bronze bushing it doesn't really need to be hardened . Bill

 

[BillK]

I agree with Bill. I wouldn't worry about it. The only time the shaft is actually turning in the bushing is when you have the clutch pedal pushed in. Unless you are planning to put 100K miles on it you shouldn't have to worry about it.

 

[kerrynzl]

It is running in a bronze bushing it doesn't really need to be hardened . Bill

I agree with Bill. I wouldn't worry about it. The only time the shaft is actually turning in the bushing is when you have the clutch pedal pushed in. Unless you are planning to put 100K miles on it you shouldn't have to worry about it.

^^^ Truth Here ^^^

The pilot bushing only aligns the shaft when the clutch is pushed in.
Under power the clamping of the clutch plate [and spline] does all the work.

I've personally brazed up a worn input and re-machined it , This done 100,000kms in my ownership [and still going strong 4 years after I sold it]

 

[Ms6peters]

thanks all. This will be a ultra low mile ride. I will consider to run as is.
There should be nil, if any misalignment. The transmission bearing retainer hole in the one-off adapter place was CNC'd based on dial indicator with bellhousing bolted to the engine.