Wednesday, 20 June 2012

More prop shaft woes

Removed the remains of the prop shaft today and had a good look at them. Clearly the weld between the front CV-joint and flange failed completely. And on closer inspection it became clear that a fair part of the crack (almost half of it) is older than the other half ...


Another interesting bit is that there are clear markings on the inside of the broken off part, where the centre of the CV joint made contact ...


I can only explain this as the prop shaft being too long, resulting in the centre shaft of the front CV joint touching the front flange. Which reminds me of an “incident” that happened while restoring ‘t Kreng in the mid 90’s. As I didn’t (and still don’t) rate the CV jointed prop shafts very high I decided to have one made locally with standard UJ’s, using the original one as template. When I fitted this prop shaft it turned out to be too long, with no movement left on the sliding splines. Didn’t think much of it then because they didn’t charge me for shortening the prop shaft ...  


But with the original old shaft removed from the DHC I compared it with two spares I have lying around. They are both from late Solihull built FHC’s. The one in the middle is the same as the one that failed (PKC1979) and the one on top is the prop shaft that was fitted to ‘t Kreng when I bought her in the early 90’s (could be part number PKC1420, but not sure). I fitted the last one for obvious reasons


When fitted the sliding splines are well over an inch extended from the shaft, so enough travel left. But this brings me to the reason why I think the original shaft failed.

When I bought the DHC it was sitting at the original ride height at the rear for a TR7, so with a little more room for the prop shaft the move. But I lowered it a little and after that I mostly used her for long holiday trips, so fully loaded. And I think the stresses that were put on the prop shaft as a result, killed it in the end. And this might also be the reason why the gear changes were sometimes rather awkward. With the prop shaft pushing onto the gear box’s main shaft, this might lock up a few bits inside the ’box. Test drive scheduled for tomorrow afternoon or Friday to see if my assumption is correct ...

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