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Question For Dave Ashcroft


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Hi Dave could you take a close look at these two pictures then give me a ring (i'll pm you my mob no.)

pic no.1

output shaft of a hp22 auto box.


Pic no.2

Main shaft of a lt77 200tdi(short bellhoiusing) manual box


Can I mashine the shaft in pic 1 to the profile of the shaft in pic 2.

When I get to talk to you I shall explain why.

Cheers Rob.

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It is difficult to say how much weaker the modified spud shaft is.

The weakest part of the original shaft was where the splines "ran out".

If the shaft was necked down to the root dia of the splines with nice large radii, before heat treatment, it would not affect the fatigue strength. In fact the resilience of the shaft would be improved, making it better for resisting shock loads.

When the shaft was originally heat treated, the hardness would be greatest at the surface and will reduce toward the centre. Now strength is related to hardness and the shear stress due to the torsional loading is also greatest at the surface and is zero at the centre (of a solid circular shaft).

The disadvantage with necking the shaft after heat treatment is that the strongest material is removed from the part of the shaft that carries most of the tosional load. This is my main concern.

The weak point is still at the end of the splines, and I am in no position to evaluate the hardness or how the hardness varies through the section.

The other comment I have regarding strength is that I would like much larger fillet radii at the end of the splines and at the new shoulder at the gearbox end of the necked down section.

You will be better off with the proper spud shaft, because the splined length in the cross drilled input gears was increased as part of the solution to overcome the spline wear problem that plagues the earlier gears.

If you only want to use this temporary, then you will probably be OK.

BTW, the spud shaft can usually be replaced through the PTO cover. No need to remove the transfer case. However I am not sure if this is possible with all transfer ratios - the larger dia input gears can be a bit tricky to remove (have to get the intermediate gear lined up properly so the teeth clear).

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I intend on using this spud shaft into use as a temporary (fix) but I can see that I should get the replacement shaft with longer splines.

I have not had reason to remove the end cover from my transfer box, I presume that I can remove the transfer input gear on my crawler box in the same way as I could with a conventional box, A question for dave me thinks.

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IIRC when I was doing my gearbox swap I was told that with the 1.22 ratio transfer box the gear will not come out of (or in my case go back in) the PTO hole due to the way the gears mesh. I understand the 1.4 1.6 boxes are ok. I'm sure Dave can confirm, especially as the crawler box may well be different to a normal 1.22 ratio box.

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