Hints and Tips - Bent Hardened Shaft

From: Nigel Coulter
Subject: Bent shaft
Date: Fri, 26 Mar 1999

Has anyone any advice on straightening hardened shafts?

I recently had the gearbox out of my Humber 12/25 and discovered the cause of transmission vibration that has been bugging me.

The output shaft ends in a taper with two keyways positioned 90 degrees apart. The end of this taper has a 15 thou runout relative to the rest of the shaft which is straight and true. The keyways are not straight and I can only conclude the the shaft has been severely twisted. This may be the result of a back axle failure long ago which happened when the car was on duty at the previous owner's son's wedding.

Best wishes to all on the list.

Nigel Coulter
1925 Humber 12/25
(and a couple of Austin 7s)

From: Jim Runciman
To: Nigel Coulter
Subject: RE: Bent shaft
Date: Sun, 28 Mar 1999


Without seeing the precise nature of the problem its a little difficult to comment with any authority but you might consider the following. Firstly the vibration will not go away while you have runout on the output spigot so perhaps you could grind this slightly undersize to make it concentric with the rest of the shaft. If it were not practical to make a new output flange to suit the new diameter you could probably metal spray the end of the shaft and finish grind it to size.

Then there's the matter of the keyways which presumably are not parallel to the shaft axis. Could these be recut slightly oversize to suit larger keys. We routinely use this approach but on larger shafts in a roll forging operation. Good luck with the reclamation work.

Jim Runciman

To: Jim Runciman
From: Nigel Coulter
Subject: Bent shaft
Date: Thu, 01 Apr 99


Many thanks for your helpful reply. I was anxious to get the car running again and so looked for a quick fix. I have sort of followed your advice by removing some metal on the high side and then lapping on the propshaft spider with grinding paste. The keys were bent along with the slots in the taper so I have refitted these keys. The spider is a much better fit now on the taper and so these keys should suffice. Having refitted the gearbox I find that although not perfect there is a distinct improvement on before.

I shall continue to look for a replacement and have put feelers out within the Humber Register.

Regards Nigel Coulter

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