Half shafts.

N

Nigel Johnson

New Member
I'm not sure if this is the correct section. This evening the British Gas man came round to read the meters and noticed the P6's in my garden. A very interesting conversation ensued. He was apprenticed to Lockwood and Greenwood the local Rover agent in Audenshaw during the early 1970's. A point he made was that the P6B in particular broke half shafts for fun. I had never heard before that was a problem. Any thoughts on the matter? Regards, Nigel.
 
As far as I'm aware it's not the drive shafts as such,but the output shafts in the diff, but it requires pretty severe provocation (tuned engines, wheel spinning etc), and is certainly not a common occurance.
 
Hello Nigel,

I did some reading not too long ago on universal joint specifications and the loads that they can withstand in normal use. So in that context, if the half shafts are of the same standard as the universal joints, and given their size I would certainly think so, then well in excess of 400 horsepower they could easily withstand.

As Richard pointed out, it is the differential drive shafts which are the weak link in the chain, but only if treated in a manner which they were not designed for as Richard said.

Ron.
 
The little output flanges on the diff can twist and shear. I've seen it happen twice, once on a friend's V8 and once on my own car a few years ago. I drove the car home without trouble, next morning I started her up, put her in Reverse and... nothing! Just a rumbling noise from under the back end. I hadn't really been abusing it but it did have about 180,000 miles on it.
Funnily enough, the exact same thing happened to my '87 Mazda Luce. However that was most definitely from abuse! I was heading through a roundabout in second, slightly sideways with both wheels spinning when the inside wheel clipped the kerb. :oops: (I was younger then :D )
 
Our studies showed it was mainly on the V8 Auto output shafts, where people dropped it into 'D' on full choke every day until one day, clunk/bang! broken shaft :roll: The torque has to go somewhere :)
 
So as long as there are no sudden shocks everything should be alright! The guy also said Landrovers broke halfshafts to. I remember my neighbour saying he fitted a Jaguar back axle to his 110 Regards, Nigel.
 
I found most broke on wet days after dry spell, pulling out of a side turning, the inside wheel spins, and when it grips again, the shaft snaps, and after tune-ups, particularly after replacing the throttle bush taking all the play out of the linkage, people boot the throttle the same amount as they did when it was out of tune, and there was a couple of inches of free play on the pedal, and all the instant exta grunt snaps the shaft. The pinion shaft was supposed to have a built in weak link, but I only ever had a couple of those break.
 
Hi, I used to break them on a regular basis in the early days ( 5 times on the first 3 cars )
all V8 auto's. So much so I used to carry a couple of spares with me all the time. I use to
think it was because the shaft was so short, not enough length to absorb the torque and
the splines were square cut. but I now realise it was probably my driving style if you can
call it that. Changing direction without stopping and wearing divers boots.
 
The UJ's and driveshafts are the means by which all the cornering forces get back to the diff and hence into the body. So it's no surprise that they are bomb proof as far as power transmission goes. But the diff input shaft - sometimes (incorrectly) called a quill shaft - and the output stub shafts are not made of the same stern stuff. Both are known to fail in torsion during racing use. The input shaft is reasonably easy to make out of decent material, and if you ask Alan Ramsbottom at Classeparts he can supply. However the size of the flange on the output stub shaft means a very large blank and lots and lots of machining if making from a solid blank, or a very difficult welding operation in a critical area if making in two parts. So far this has put off Alan from producing any tough ones. This can't go on for much longer as he and I have most of the remaining new output shafts in captivity between us.

I agree with both Harvey and Grim on failure mode. I think you're both right! ie shock load on engaging drive at too high a revs on an auto and the shock load as the wheel stops spinning after a "light up".

The diff internals are also bomb proof, so just those two components to upgrade. However, as others have discovered recently, the rear diff bracket is less than ideally robust also. Even supposing it is in one piece and correctly bolted up to the diff, it flexes quite badly under cornering loads. Alan adds a second skin to the back of it to generate a box section. Fine as far as it goes, but difficult to achieve without distortion. And you still have the problem of a lack of triangulation in the panhard rod that braces the diff against the body, so twist remains possible.

Alan's final trick is to have his own LSD components made up to go inside the existing casing. But with so many areas to address to achieve a robust LSD for a tuned car, it's no surprise that Simon Owen went on to use a Jag diff.

Chris
 
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