Thread: Life of Puma Rear Diff's

Originally Posted by isuzurover

For all practical purposes, YES.

The bracing on my front diff is on top, and IMHO it is likely much stronger and lighter than MD's diff laminating. (which was mainly below the centreline of the axle).

If you started with a 130 salisbury and braced it on top (minimally), then I doubt anyone on here could bend or break it.

out of interest, what does below or above axle center line effect?

lets stick to the Sals, the fabricated Rover type housings are a different beast.

I would like to see your or John's design for a Sals. By no way is this a dig or challenge, im want to learn. Im a visual learner. I am still yet to see a top truss on a dana type housing that doesnt weigh 14 million kgs and would actually work for more than just link mounts

Originally Posted by uninformed

out of interest, what does below or above axle center line effect?

lets stick to the Sals, the fabricated Rover type housings are a different beast.

I would like to see your or John's design for a Sals. By no way is this a dig or challenge, im want to learn. Im a visual learner. I am still yet to see a top truss on a dana type housing that doesnt weigh 14 million kgs and would actually work for more than just link mounts

Rover or sals or anything else, the principle is the same. The separation between the brace and the axle centreline gives much more strength (compared to tubing internally or plating the underneath that MD used to do).

If I ever decide to brace my sals you will be the first to see pics Serg.

Originally Posted by wrinklearthur

[snip]

I can weld a bit, but I don't have the fine touch of a professional, so I would be wary of welding anything to the housing in case I caused distortion.
.

The only way you can stop distortion is to make a big jig to hold the entire housing (eg. use an RSJ), or do what Maxi Drive used to suggest and chain down the housing to a concrete floor.

I'm not fussed about the strength of my Sals for what I do, and my GVM is pretty much on or over 3000kg constantly (and the axle pads are polished from the bumps stops, front and rear)

The Telstra vehicles that were pulling axle tubes in the Territory were also cracking front diff housings, and the same drivers were cracking 79 Series 'Cruiser front diff housings and chassis's and Patrol chassis's too.

It is hard to think of any practical examples of trusses that have all members in tension - most have nearly half of the members in compression.

Tensile members don't buckle which is a great advantage allowing smaller sections.

In a truss the tension members are called ties and the compression members struts. Truss members are considered to carry pure tension or compression, unlike flexural members (non-truss) such as beams or columns that carry bending loads.

Usually a truss is designed to use the least amount of steel allowable - to reduce cost. This is done by designing so that where possible the ties carry higher loads and/or the struts are shorter.

Preventing buckling of compression elements often simply requires attention to detail E.g. the dimpling of the holes in the gusset plates used in one of the pics allows light weight construction.

In the discussion here and the example pictured the axle housing, with or without bracing, is a beam. They have tension (mostly) on one side and compression on the other, but this can reverse from normal loading if the diff sits on a rock, so the whole argument about bracing above or below so some element is in tension is not as important as getting the details right.

Grave dig -any updates to be had?

Would pegging (in combination witiny bits from Ashcrofts) be a sufficient solution for users just looking for a general increase in the robustness of the P38 (i.e. someone like me)

Originally Posted by n plus one

Grave dig -any updates to be had?

Would pegging (in combination witiny bits from Ashcrofts) be a sufficient solution for users just looking for a general increase in the robustness of the P38 (i.e. someone like me)

I think you will find that the cause of the problem is not the bits in the centre, it's merely a design fault in the P38 housing. That being the pinion shaft is too short and the bearings are too close together (this has been repeated multiple times already).

This design flaw causes the bearings to have too much stress and they flog out. Once the bearings have flogged out, this in turn then allows the pinion a little 'play' and it then flogs itself out on the ring gear. This then causes the failure of the diff. No matter what you did to the internals the problem is still the same, i.e. the bearings on the pinion are too close together.

This is why Dave has come up with a plan to build a new housing to correct the initial problem. Upgrading with HD internals at the same time is simply a smart thing to do while you are at it.

Originally Posted by n plus one

Grave dig -any updates to be had?

Would pegging (in combination witiny bits from Ashcrofts) be a sufficient solution for users just looking for a general increase in the robustness of the P38 (i.e. someone like me)

No - pegging doesn't help the pinion bearings being too close together...

while it wont help the bearings, pegging will help with pinion to ring gear deflection. The bearing spacing is not the only problem, the ring gear is thin and deflects easier than other diffs like the rover type.

I would like to know, on a well serviced diff, how many of these P38 types have "flogged out" the pinion bearings?