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Possible To Repair Transmission Mainshafts?

Possible To Repair Transmission Mainshafts?

Possible To Repair Transmission Mainshafts?

Is it possible to repair the splines on a mainshaft rather than replacing the mainshaft?  The state of the mainshaft is generally good, one of the output splines has a spot of corrosion which covers roughly 5% of that single spline and is about .5mm deep.  

The question arises as new mainshafts for this application are $900/ea, when they are available, and the ones that become sporadically available are poorly machined units from India with poor tolerances.  

My initial thought was to machine a shallow trough, parallel to to the orientation of the spline, to remove the corroded metal.  At this point, I would hope that typical machine shop welding techniques could be employed to fill the trough and grind it flush with the surface of the spline.  

Not going to happen that way?  Or is there a better way, or no way at all?  

The mainshaft in question fits a 1963 Austin Healey 3000 transmission.  The engine of these cars seldom produce more than 175lb/ft of torque, and even with first gear, it will never produce the kinds of torque that your typical muscle car will produce at the output shaft of the gearbox.  



RE: Possible To Repair Transmission Mainshafts?

I'd leave it alone.

You didn't want to know that...

If you grind it out and weld it then you will bend the shaft. It may be possible to straighten the shaft afterwards, but I have my doubts, when considering the tiny errors that are acceptable in a gearbox.

 A proper repair would be to turn the spline off, completely, and then loctite a sleeve over, and then grind a new spline into that. Getting the right material hardness might prove difficult, I expect the original spline was case hardened. Another option might be to make the spline up, and heat treat it, before assembling to the shaft, maybe finish grind it in situ. I'd be worried about the bending stiffness of the repaired shaft in both cases.

I must confess I don't know whether gearbox splines are machined or broached, in production.


Greg Locock

RE: Possible To Repair Transmission Mainshafts?

How many splines on the shaft? If it's only 5% of one spline out of 20 splines, i wouldn't worry about it. I'd clean it up, stone away any sharp edges that may be there, and use it.

I agree that there's no easy way to fix it.

Greg, most of the shafts i've seen appear to be hobbed/milled like a gear. I'm assuming that the internal splines are broached, as i can't think of any other way to do it.

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