Originally Posted by
PAT303
... I do all my taking from out in the bush,not behind a keyboard ...
Pat
Pat wants us to believe this makes his take on the subject more credible. IMO he is naive, it does no such thing.
If we examine the failure evidence and compare Salisbury, "P38" style diffs and for good measure "Rover" diffs it becomes clear that these three fail in different ways and circumstances.
Salisbury is an adaptation of the Dana 60 axle. Dana is part of the Hardy Spicer group, producing a large range of axles for many types of vehicles from cars, through to trucks and large earth moving vehicles. Although they don't have Pat's expertise, or do their taking out in the bush, it is fair to assume that they know what they are doing when it comes to drive axles.
Refer to the following pic (copy and paste of a small part from their "Condensed Specifications Axles, Transaxles, Driveshafts, Transmissions,
Torque Converters, and Electronic Controls" catalogue) for the particular range that includes the Dana 60.
Note in this catalogue, the Dana 60 has a 1500 kg load rating in both the semi-float rear and front axle versions, or 2700 kg load rating in the full-float rear axle version. We should not conclude that all Dana 60's have these ratings, as Dana may have made changes to suit the customer's specific requirements - for example diameter of half shafts does differ.
The Salisbury version produced for 110 and 130 Defenders (full-float axle BTW) came in two versions to which The following pic (copy and paste from a Land Rover manual for the range of TD5 Defender Cab chassis vehicles) shows a rear axle load rating of 1850 kg (110 Standard), or 2200 kg (110 Heavy Duty and 130).
The following 2 pics (cut and paste from LR manual list the Salisbury versions, first pic for drum brake versions and second for disc brake versions.
Note: the Salisbury axle may have been changed again for Defenders after the printing of the particular parts manual that I copied those pics from, but anyone looking at the serial number stamped on the axle tube of a Salisbury can conclude the following:21S - was a standard 110 Salisbury with drums (FTC2352)
24S - was a HD 110, or 130, Salisbury with drums (FTC2353)
39S - was a standard 110 Salisbury with discs (FTC3304)
38S - was a HD 110, or 130, Salisbury with discs (FTC3232)
Now one thing that has been confirmed by others (I don't know if they went out into the bush to take this) the Salisbury used in 130's has thicker axle tubes, so it is fair to assume it was to achieve the higher load rating.
What hasn't been confirmed is whether any of these thicker axle tubes have failed. We have seen pics of failed axle tubes in 110's that were obviously heavily loaded. We can't tell if any were the HD version or whether their axle load exceeded that stipulated by Land Rover.
Apart from those small numbers of axle tube failures, the only Salisbury failures I'm aware of are half shafts; breakage or spline wear. It should be noted that the same diameter half shaft is used with the P38 and Rover style axle assemblies so no advantage to any one of those as they all suffer the same, i.e. dead heat as far as half shafts go.
As far as breakage goes the stock 24 spline shafts are on the small size, but adequate for most users and stockish diameter tyres.
For those who want to drive harder and/or use larger tyres, there are aftermarket replacements that are stronger (same diameter, but stronger material). For even stronger half shafts it is reasonably easy (just $$$$) to upgrade to 35 spline, an option not easy or practical with P38 or Rover diffs.
The diff in a Salisbury, with 248mm (9.75") ring gear/crown wheel, is overkill for almost all Land Rovers, and should not fail if maintained.
I'm not aware of how the Salisbury has performed in the "Perentie" used by the Australian Army. And it is worth noting that for a heavy duty front axle they changed the Rover housing to a construction similar to the Salisbury.
However it should be pointed out that the "Wolf" used by the British changed to the P38 style rear axle. IIRC Dave Ashcroft has said something to the effect that this change was made because it was easier to strengthen the all steel P38 housing than the steel plus cast iron Salisbury housing.
This implies, for their required duty, a strength issue with Salisbury housing, but also stock P38 housings require strengthening. So perhaps changing the Salisbury from a 130, to a P38 from a "Puma" will not immediately gain a stronger housing. However the "Puma" axle housing can be strengthened and made stronger than the Salisbury - the same comment should apply to the "Rover" axle housing. So not benefit to "P38" over "Rover" in the housing issue.
If I had a 130 with Salisbury, would I change it to a P38 from a TD5 or "Puma" Defender to gain a stronger axle housing? Nope, and BTW I have a 120 that came with the weaker 21S housing, and neither will it get changed to a "problematic", "P38 style" - I need rear diff problems like I need a hole in the head.
The following pic is a copy and paste from a MY12 workshop manual and shows the axle load ratings for 110 and 130 Defenders. It begs the question, if a rear axle from a 110 "Puma" was used to replace the Salisbury in a 130, would the GVM and allowable rear axle load be reduced to that of the 110 that the axle came from? Going from the information in that pic the answer would be yes. However if you could show that the 110 axle assembly was the same part as the 130 axle assembly then that should not be an issue - I don't have a parts book for the "Puma" to check if that is the case, but I wouldn't be surprised if the only change for a higher axle load in the 130 was the suspension springs.
Land Rover used the "Rover" diff from the beginning of the RRC, the Disco 1 and D90. They had good reason (the weak 2 pinion diff centre) not to use it for the rear of 110's and 130's. I'm sure they anticipated/expected the 4 pinion centre that they used in the "P38" diff would make it strong enough for use in the rear of a 110 or 130. However they were too optimistic, the 4 pinion diff centre was OK. but the crown wheel flexes too much and so does the pinion because its bearings are not far enough apart.
Regarding the following quote from newhue:
From my reading the P38's issue is pinion length, and it's relation to movement on it;s short bearing mounts, in relation to heavy loads or towing. The movement flogs the gears and bearing out and it all fails. Perhaps pre Tdci have better build quality, but if you are going remote, with family, or work, than the piece of mind knowing a late build P38 is no longer under the truck is worth the conversion ...
And this from n plus one:
... it appears that any issues around poor P38 build quality (from LR) can be addressed by improving the build quality at relatively low cost i.e. a rebuild by an experienced diff specialist.
Issues relating to the design (to the extent they are a material consideration) can be addressed via the Ashcroft long-pinion conversion.
I get the impression that it is slowly becoming quicker/easier/cheaper to strengthen a P38 than swap in a Sal. ...
Basically I agree with those points, but want to add the following:
As far as I can tell, most of the replacements under warrantee were for noise issues, and some ran in that condition for a reasonable length of time before the diff could be replaced. They hadn't failed catastrophically. It certainly looks like most of those were a result of poor assembly, or some issue with the quality of the gear cutting.
The problem that arises from the short pinion, or more to the point, the small separation between the pinion bearings, is that if the bearing pre-load is too loose, either initial set-up, bearing wear, or both, results in greater misalignment of the mating gear teeth. The strength of gear teeth is greatly reduced by misalignment and tooth breakage will occur under a lower load/torque and wear is also more rapid. The misalignment and increased backlash also result in higher dynamic tooth loads.
Noise is a result of loss of conjugate action and the dynamic tooth loads. It is a warning that should be headed for what tells you about you diff, not something that you should ignore.
IIRC, leaking pinion seals are another common problem with the P38 diff. This can be caused by the same bearing and pinion alignment issues. These seals are designed to keep oil in and contaminants (dust, water, etc) out. If the seal leaks oil, then they might be letting contaminants in - the biggest causes of bearing wear are poor lubrication (e.g. from loss of oil), and contamination (e.g. dust).
Now if the P38 diff is known to be good, i.e. doesn't leak oil, no play in the pinion shaft, runs quiet, doesn't get abnormally hot, etc., and you will not be abusing it, then there is no reason why you should not take off into a remote area for a few weeks, with reasonable confidence. There should be warning signs in time to change your plans and avoid disaster. If for example if you get to Mount Dare, and the noise is getting worse, or the pinion seal has started leaking, then you should be checking your oil levels and for play in pinion, etc. If these are not right I would be thinking twice about heading off on the Madigan line, or even one of the shorter, popular Simpson crossings.
It is a different situation if you want to tackle hard tracks, then the strength of the P38 diff is found wanting. This is as much an issue with the TD5's as the Puma's. IIRC Max broke 2 diffs in Tusker before he bit the bullet and replaced the axle assembly with a Salisbury.
The Ashcroft replacement, long pinion, diff looks like it will be a reasonable (though $$$$) solution, and aftermarket 24 spline half shafts will set the load limit which they can handle (same boat as Salisbury).
The failure mode of the "Rover" diff is usually begins with wear of the bores supporting the shaft for the two pinions in the diff centre. This leads to a broken shaft and/or gears.
The fix is easy. Fit a locker, or ATB centre. Then the stock 24 spline half shafts will be the weak link. Fit stronger aftermarket half shafts and the crown wheel and pinion becomes the weal link. Fit stronger Ashcroft CW&P and you are level pegging with the Salisbury or Ashcroft Special P38 with aftermarket half shafts. However one advantage over the Ashcroft Special P38, is that if you do experience a diff failure, a readily available, second hand diff centre will soon get you back on the road.
To my way of thinking, if you are only going to run 24 spline half shafts (stock or aftermarket), and maximum 33" tyres, a level which will apply to most on here, then it is a line ball upgrade between fitting a Salisbury, replacing the P38 diff with the Ashcroft long pinion diff, or fitting a rear axle from a Disco 1 or RRC that has been upgraded.
The other alternative is to maintain the P38 diff, which will required the diff to be out more frequently than the previous 3 options. It will never be as robust, will suit many, but not all.
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) - but my P38 is holding up, so that's something I guess!
Re Salisburys, I love them... The 101 has two of them, with oversized axle shafts to suit. I have no idea how thick the axle casing is, but I know that if I ever break one....there won't be much of the 101 left! I'm hoping that the Salisburys will have a better chance of handling the 200+ hp and 500+nm of torque that the new engine will turn out... I know a Rover Diff wouldn't be to happy with that. Interesting to here the opinions so far tho! 
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