Thread: Life of Puma Rear Diff's

Originally Posted by Drover

Just thought I would share what I know.....hope I'm not speaking out of turn.

I have been in contact with Ashcroft's (Dave) via email.

There are currently 2 complete diff centre's here in Australia for "real world testing" both of these diff's should fitted up next week into the 2 lucky Defenders.

There are also 20 new castings being machined up now and should be ready in about a month.

Providing the testing goes well and it should, they will available shortly after.

These new diff centre's really sound like the ducks guts and will finally solve all the issues with P38 rear diff.

Hip hip to Ashcroft's for taking on this huge project.

Yep, and I've got a pretty good idea that at least one of them is being tested under a fairly heavily loaded 130 - so that should be a good shake down.

OK guys just to address the elephant in the room
I know the Puma diff has its issues but the celebration of the fitment of what is basically a Rover carrier into the back of a Defender is unusual to say the least.
The change over to the Salisbury in 1969 (ish) was for a reason and how many people trash the rear diff in their Range Rover Classic?
Run a Defender at GVM surely this will be more stressful than a classic

I respect Ashcroft's engineering prowess immensely so I presume there is something I am missing?

Ducks for cover

Originally Posted by djam1

OK guys just to address the elephant in the room
I know the Puma diff has its issues but the celebration of the fitment of what is basically a Rover carrier into the back of a Defender is unusual to say the least.
The change over to the Salisbury in 1969 (ish) was for a reason and how many people trash the rear diff in their Range Rover Classic?
Run a Defender at GVM surely this will be more stressful than a classic

I respect Ashcroft's engineering prowess immensely so I presume there is something I am missing?

Ducks for cover

The carrier is just what the crownwheel attaches to, and when using an aftermarket carrier these are significantly stronger than standard, ie something else will break. The problem with rover and p38 diffs is the meshing area between the pinion and the crownwheel is quite small and the gear teeth break. This is partly due to the spiral bevel setup with a centred pinion, and its also due to the increased flex within the p38 type diffs carrier when compared to Rover and aftermarket carriers. The new Ashcroft diff is a new hypoid design where the pinion is offset and this increases the contact area between the pinion and crownwheel, so reduces to load any any specific area of the tooth.. Ie it's stronger. The hypoid crownwheel and pinion can't be fitted to a rover diff, it's a whole new setup that ashcroft are making, except it uses a normal rover carrier in it.

Check this comparison. On the left is a Toyota 8" hypoid CW/P and on the right is a Rover 8.5" spiral bevel CW/P.

My apologies, I'm not sure how to do the picture thing with an iPad, but below is a link to the picture

http://www.slunnie.com/coppermine/di...=99&fullsize=1

Out of interest, the Salisbury is also hypoid but obviously has a larger CW/P but I'd expect with the new Ashcroft diff that you will snap both HD axles before the diff fails.

I killed my rear diff after about 80k. My fault not the cars really. It should have lasted longer but I did give it a real hard time on one hill. Blew the uni joints, buckled the center of the rear wheel and the diff got noisy.

I just found a good second hand sailsbury,had it rebuilt, fitted some maxi bits (axles and locker) and now I don't think even I could kill it. It's under the back of the puma now, silent and working well - I'm a happy camper again!!!

Originally Posted by djam1

OK guys just to address the elephant in the room
I know the Puma diff has its issues but the celebration of the fitment of what is basically a Rover carrier into the back of a Defender is unusual to say the least.
The change over to the Salisbury in 1969 (ish) was for a reason and how many people trash the rear diff in their Range Rover Classic?
Run a Defender at GVM surely this will be more stressful than a classic

I respect Ashcroft's engineering prowess immensely so I presume there is something I am missing?

Ducks for cover

Further to slunnies post.

The change over to the Salisbury way back then was for a reason, but IMHO it was and is overkill (Land Rover have never had the ability to call on a good range of parts like larger manufacturers). The only weakness with the Salisbury is the 24 spline half shafts (rover specified stub axles and shafts), but they are based on the Dana 60 and these can be had with 30, 35 & 40 spline half shafts.

When Land Rover changed over to P38 style rear axle, it was also for a reason - they reckoned it was easier (cheaper most likely) to strengthen the P38 axle housing for MOT than it was for the Salisbury housing.

The P38 is just an later upgrade of the RRC, not a commercial load carrying vehicle like a Defender 110 or 130. The design of the P38 diff is poor, the weaknesses were probably attempts to keep costs down. They could just as easily designed it better, and if the initial goal was a replacement for the Salisbury, instead of the RRC rear diff, then things would probably be different. The only improvement the P38 style diff has over the RRC is the 4 pinion diff.

Ashcroft redesigned the P38 style diff to be a lot stronger, without being overkill like Salisbury, but keeping costs practical for low volume production, and making it a relatively simple bolt in change over. Because of the extent of the initial P38 design weakness, it may not be as cheap or simple as people would like.

Over the potential life of a 110 or 130 used for what they are intended, then one Ashcroft diff will most likely see out several P38 diffs. Then the cost benefit starts to make sense.

Wonder how much the ashcroft one will cost...

theres a slight whine in james with only 7k km. more pronounced in gear/off power.

Might just do dealer replacements for the life of the warranty while i save pennies for the ashcroft one..

With the change of centres, will any modifications to the tailshaft need to be made?

Originally Posted by Gerokent

With the change of centres, will any modifications to the tailshaft need to be made?

Yep, longer dif nose = shorter tail shaft.