I recently broke a halfshaft in my Chummy and need to get another. I have heard that there are some adjustments which need to be made with new repro ones, can anyone tell me what to look out for or would I be better trying to find an original one?
ThanksDan

Hi,
I had a conversation with Steve Hodgson who had fitted some new ones on a rear axle and they had started to show wear very quickly. He had an original and a new shaft hardness tested for comparison. I cannot remember the exact rockwell numbers but it appeared that the new shaft had not been heat treated correctly if at all. I do not know which supplier the shaft was purchased through but I believe that the issue is currently being resolved.
For now I would recommend buying an original one. Pay particular attention to the usual key way and thread but also look closely at the shaft I have seen some short half shafts which have been shortened near the centre and the marks can be clearly seen.

A couple of years ago I had an excellent halfshaft from John Barlow (usual disclaimer). The thing to watch out for is the fact that the bearing location was increased in diameter by 1/64" in around 1930 so you need to make sure you get the correct ones.
Regards
Brian

New halfshafts for your Chummy should be available in a couple of weeks (with any luck...). They are British-made out of EN36B, properly case-hardened. The short halfshafts were made with 0.875" journals until January 1931, when the diameter was increased by 1/64". 9 months later (Oct 31) the halfshafts were made longer. The new short halfshafts have 0.875" journals - replacement bushes are available if required.

Long halfshafts (with 0.890 journals) will also be available.

David

Thanks, I hadn't heard about them wearing out too quickly, the friend I spoke to said they were locking up the drive chain and needed to be machined down to work properly, maybe they had put in one of the thicker ones by mistake? I think I will look for a good secondhand one as I want to get it back on the road as soon as I can.
Dan

With regard to Austin seven Halfshafts, My opinion is that the originals were made from a high tensile material and through hardened, there is always a indentation in the shaft from the ball on the hardness tester. Ihave made a number of shafts from solid, and used 4140 high tensile ,subsequently Nitrided. Nitriding gives avery thin ,but exceedingly hard skin on the external surfaces. the bearing faces can be polished to size before nitriding. the core remains soft and there is no distortion. This gives a much better resistance to failure due to twisting, which is the major cause of cracking about the keyway . and eventual breakage. an even better substitute for 4140 is 4130 which can , should a mishap happen ,be welded. 4140 should never be welded,as it will fracture quickly due to its chemical constitution.
The problem I have with using E N 36 is that, even with careful heat treatment,distortion means that that after carburising and oil hardening,they would need straightening in a press,before they can be ground between centres. this is difficult and adds expense . this distortion does not occur with the nitriding process which is carried out at temperatures lower than the critical (600C ). if I were making axles from C/H material I would choose E N 39b ,which has a finer grain than '36 b and distorts much less. this is the preferred material for Crown wheel and pinion manufacture for this reason.I do hope this is helpful.I am a toolmaker involved with these processes on a daily basis ,and have had extensive experience with repair and remanufacture of Vintage and veteran car components-cheers Steve Hainsworth

The new halfshafts are case-hardened to a depth of c. 20 thou and have a Rockwell hardness of 60, the same as the Austin ones. Unlike the repro one tested by Steve Hodgson (which had a Rockwell hardness of 15), these will not wear out quickly.

The original Austin shafts had a hardness test at the taper end - this really should be seen as 'softness testing' - it was done to check that the hardening process hadn't spread too far. Although shafts made from EN36 will distort when heat-treated, straightening them is routine. Apparently EN39 is notorious for being even worse in this respect.

David