Thread: My county is better than your puma

Originally Posted by isuzurover

On this note John - When I install my new (locked disc brake) sals into the 110, I was considering welding some sort of brace/strengthening bar between the axle tubes. However I am unsure how well that would work ( and if it would just concentrate stresses where the brace is attached instead of where the tubes are pressed into the centre casing). Any thoughts? Or tips on brace design?

EDIT:
Truss designs like this seem common, however they would interfere with the A-Frame ball joint mount.


However all these trusses only spread the load out a couple of inches further than the casing. Surely it would be best for the truss to spread the load out as far as possible???

When I have seen that kind of bridge on Dana axle assemblies, I assumed the main reason was to provide something to support upper link mounts - not wanting to weld the mounts to the cast housing.

As long as the diff housing is stronger than the tubes and the tubes are fitted properly, you are better (IMHO) to use heavier wall tube.

If the material strength of housing and tube were the same, then compare section properties, in particular the section modulii ('Z'), at the bosses where the tubes fit and the tube.

These are both hollow circular sections so, where 'D' is OD and 'd' is ID:
Z = 3.1416(D^4 - d^4) / (32 x D)

Housing is ok if Z for housing bosses > Z for axle tubes. Then wall thickness of axle tubes can be increased until both Z's are similar.

If allowable material strengths are different, then multiply each Z by the associated allowable material strength and compare those values.

i.e. allowable strength = tensile strength / SF

Generally I would use a larger safety factor for the cast housing material to determine allowable material strength. The larger factor is to account for such things as casting variations/flaws and lower ductility.

The diff housing and axle tubes are subjected to combined torsion (reaction from link forces) and bending (reaction from wheel and spring forces).

If the section modulus of the housing bosses is > = to the axle tubes, then the housing will withstand the torsional loading better - simply because the od of the bosses is larger than od of tubes.

There are many possible bending cases or combinations to consider.

Vertical loads from the vehicle weight when supported by the wheels, or when supported by the diff housing (on a rock for example). Which induce bending in the vertical plane.

Horizontal loads from tyre traction, link forces, steps/ledges at tyres and or diff.

Bending is proportional to the algebraic sum of the different forces and reactions to one side of the section under consideration x distance from the section to the force - force x distance is called the moment of the force and will be assigned either clockwise (+ve) or counter clockwise (-ve).

Without getting into a discussion of why, the worse case bending loads and critical section locations are:

For low impact loading (not landing from a jump) and vehicle supported on one wheel (other wheel in air) the critical section is at the location of the spring, the forces to one side of this section are wheel loads (vertical and horizontal) and link load. This case is worse than when both wheels are sharing the vehicle weight - the vertical wheel load will be approx double that when both equally share the weight equally. If up against a ledge, the horizontal load may be significant.

For landing from a jump, the dynamic vertical load can be much higher and it is important to reduce it by transform the kinetic energy into strain energy in the springs at as low a spring force as possible (i.e. large bump travel). The critical section is at the location of the springs. This is assuming the landing impacts on the tyres and not the diff housing.

In both of the above cases, if the distance from the wheel to spring is increased, the bending will also be increased proportionally.

If the weight is supported by the diff sitting on the ground, the reaction from the ground will be pushing up and the spring forces and wheel weight will be down.

The critical section will be either where the bosses protrude from the diff housing or where the axle tubes protrude from the bosses (depending on comparative section modulii). Without a more thorough check, it is probably fair to say, if the distance from the critical section to the springs is more than double the distance from the spring to the wheel, this case is likely to be worse than the 1st case above (weight on one wheel).

In this last case a truss will help by moving the critical section out to where the truss connects to the axle tube. It does this by reducing the distance form the critical section to the loads (and hence reducing the moment).

Thanks John.

FYI, I recall the tubes are 80 mm OD and 5.6 mm wall (however they may be machined down slightly where pressed into the housing. I will measure the housing up tonight.

I notice theres a few threads asking about high KM pumas, TD5's, TD6's, etc

Can I ass assume people will start asking high km Isuzu's in around 15 years time, with people questioning:

"My Isuzu has clocked up 1.8 million k's should I think about replacing the welch plugs anytime soon?"

"GRRRR torque impulse just destroyed the LAST LT95 in the state, anyone know of a truck box that will fit with minimal mods?"

when that happens there will be some smart ass saying something like.

"no, you dont have to worry about the welch plugs during the run in period"

or "Hi Guys, just bought my first Isuzu, got a tonne of K's on it and just about deafens me at 100km/h..... is something about to break?"

or....

Hi guys, I just bought an isuzu powered landy and Im a little confused when I put it in 1/low the engine revs dont increase. I think theres something wrong with the anti stall but it still makes it up hills ok

or

Help, Im stuck up at the top of mount somewhereorother, using my Iphone. I've left the wine cooler on for too long or used the aperitif warmer too much and the batteries flat. Is there anyway I can start this thing without getting someone up here to jump start me?

or

Help, I think I'm getting scammed, I had a problem with my isuzu powered rover being low on power and revs so I took it to a dealer. Instead of multiple visits It took them 20 minutes to fix, they only charged me $70 including labour to replace the lift pump strainer and didnt mention anything about having to bring it back later for a software update.

When you get back to it in the car park and some poor lady is waiting in a beat up people mover because she just backed into the wing you can just panel beat it out on the spot with a tyre mallet, not worry about the paint work then send her on her way with a "no harm done"

yesterdays experience

Picked up a cheery picker from access and headed out to Mt barker. how usually doing 80 klm in 3rd up the hill, empty or laden as I was yesterday.

I over took a puma with a camper trailer, he didn’t smile or wave