Salisbury 4HU Diff.

[B.P.Bird]

Continuing from my note on the 'Rest and Be Thankful' report in the general forum, here is an update on my diff. failure.
   Having found the failed splines and being wary of rebuilding with old shafts of uncertain heritage, I did a bit of research: Salisbury still exist in the form of Dana Axles U.K. Ltd., but have no more of the early two part output shafts. Moreover I took a close look at the surviving shaft -
   
   
   
   
   
   As you can see the splines on the 'good' shaft are not far off being worn half way through.It follows that rebuilding with a second hand shaft on the failed side would only result in another spline failure, on the surviving shaft, in the near future.
   Salisbury replaced these early two part shafts with a single piece shaft which is a stronger design. Not sure if any Cobras used them, but certainly Jaguar went over to them. I am not sure if the later shaft has stronger splines, but if you go this route they will at least start off as zero time new items. It seems that there is a U.K. based competition transmission specialist who replicate the later single piece drive shafts, but in a stronger materiel.
   In any event, wherever the new style shafts come from, they will only fit the original Salisbury casing if it is machined to accept different bearings.
   You can see where this is going: The replacement shafts dictate some machining and there is no point in doing this and using the old bearings and seals, LSD clutches or differential gears. The crown wheel and pinion may pass crack testing, or may not. Whatever there is a sizeable bill to be paid.
   Given the years and abuse which older Cobras have endured this cost should be regarded in the context of half a century of service - leastways this makes it less painful.
   I have decided to bite the bullet and use the upgraded competition shafts, with machining and all the replacement overhaul items. I'll report again when it is all back together.

[B.P.Bird]

I am pleased to report that CSX 2033 is back in use with a rebuilt diff courtesy of Paul and Andrew of BPA Engineering http://www.bpaengineering.com/
   The painless way to swallow the bill is to divide by 50 and trust that the rebuilt unit lasts another half century, looked at this way it's just part of the annual motoring costs.
   I had always thought that the slack in 33's drive train was from the Hardy Spicer sliding splines on the drive shafts. However, now that the new output shafts and differential gears are in place, I can see that there is very little play on the original drive shafts and almost all the play was from the old worn splines on the Salisbury output shafts. If you find a lot of slack in the drive train and it is not from loose drive flanges, then do not be surprised if the diff. output shaft splines strip a short while later.
   BPA recommend using a fully synthetic gear oil in the LSD, either Castrol Syntrax 75W-140 or Mobil 75W-90. Their rebuilt diff. is commendably silent and puts up with slow speed tight manoeuvres without jerking or clunking. If you do get rough limited slip operation BPA recommend the Jaguar LSD additive - part number JLM 10814.
   Hoisting the diff back in to position was something of an Olympic weight lifting exercise and the tilting required to pass through the chassis main tubes doesn't make it any easier. Definitely better tackled as a two man job: Many thanks Graham.

[cobham cobra]