6x6 Perentie performance off road?

Your calculations of 41 degrees of rotation are based on the wrong contact point. The point that the rocker beam contacts the chassis is directly above the rear shackle of the intermediate spring when the rear axle is at full droop. You can see in the picture below that the rocker only has to move 45mm for the beam to contact the chassis. In fact you can see a wear point where this happens, with a thud. I could place a square of conveyor belting there to soften the blow, but it would further reduce the limit of travel.


https://www.aulro.com/afvb/images/im...2016/04/34.jpg






The suspension initially flexes due to the rocker beam action, with the springs themselves principally flexing under load, not articulation. For the 45mm gap to the chassis to close up, the opposite end of the rocker beam needs to drop 45mm. For rule of thumb purposes, we will say the axle is located approximately halfway along the spring, so 45mm of deflection at the shackle end is about 22.5mm at the axle (if we can say there is some deflection of the spring itself, we might be generous enough to say as much as 30mm at the axle).




And here it is:
https://www.aulro.com/afvb/images/im...2016/04/35.jpg



This is the limit of articulation. You can't make it out in this picture, but the rear wheel is suspended in the air and the tyre can be turned by hand. The rear axle is doing very little to support the load, and absolutely nothing to provide traction. If the rear axle were to be engaged, the drive torque would go straight to the suspended wheel without some form of traction aid (air locker, Detroit, truetrac, etc)


https://www.aulro.com/afvb/images/im...2016/04/36.jpg


The rocker beam is hard up against the chassis and any articulation must now come from deflection of the springs. As pointed by others, the springs are designed to support a 2 tonne payload and don't deflect easily.


https://www.aulro.com/afvb/images/im...2016/04/37.jpg



The limiting cables are next to useless. Although they are now close around the axle tube, they are loose and in no way taut or restricting the travel of the axle (cable can be jiggled by hand). That is being done by the rocker beam being hard up to the chassis, and that ain't moving any further!


https://www.aulro.com/afvb/images/im...2016/04/38.jpg

If the rocker arm is touching the chassis it means the strap is installed wrong and has been installed as supplied instead of being set to length or its been stretched.

So it's supposed to have even less articulation? :o

Quote:

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Originally Posted by 303gunner

So it's supposed to have even less articulation? :o

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So, we now know that the rear suspension set up is poor at best, what are we going to do to fix it ?? :)

Both gunner and black night seem to have a lot of knowledge on the suspension. As does a lot of other people on here.


Just catching the perentie bug.

• 1990 Perentie 6x6 Air Defence GS
•2013 Range Rover Sport

Quote:

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Originally Posted by TK_Co

I got mine bogged when I was just trying to get to my mates place. It's needs lockers. I think I need to to the rear suspension travel straps off the rear axles, but I'm a bit scared as I can't really work out what the point if them is.

Do you know what the purpose of them is? I thought maybe something to do with air lifting ?


Just catching the perentie bug.

• 1990 Perentie 6x6 Air Defence GS
•2013 Range Rover Sport

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TK Having driven these a lot I can tell you they need lockers a lot less than they need the driver to understand how to drive the vehicle. Did you engage six wheel drive? If you must go and spend money on this truck, install an after-cooler. If you must have lockers I suggest you look at Ashcroft's Automatic Torque Biasing diff centres (Ashcroft Transmissions UK). We tried ARB and they were no good.

Quote:

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Originally Posted by 303gunner

Your calculations of 41 degrees of rotation are based on the wrong contact point. The point that the rocker beam contacts the chassis is directly above the rear shackle of the intermediate spring when the rear axle is at full droop. You can see in the picture below that the rocker only has to move 45mm for the beam to contact the chassis. In fact you can see a wear point where this happens, with a thud. I could place a square of conveyor belting there to soften the blow, but it would further reduce the limit of travel.


https://www.aulro.com/afvb/images/im...2016/04/34.jpg







The suspension initially flexes due to the rocker beam action, with the springs themselves principally flexing under load, not articulation. For the 45mm gap to the chassis to close up, the opposite end of the rocker beam needs to drop 45mm. For rule of thumb purposes, we will say the axle is located approximately halfway along the spring, so 45mm of deflection at the shackle end is about 22.5mm at the axle (if we can say there is some deflection of the spring itself, we might be generous enough to say as much as 30mm at the axle).




And here it is:
https://www.aulro.com/afvb/images/im...2016/04/35.jpg



This is the limit of articulation. You can't make it out in this picture, but the rear wheel is suspended in the air and the tyre can be turned by hand. The rear axle is doing very little to support the load, and absolutely nothing to provide traction. If the rear axle were to be engaged, the drive torque would go straight to the suspended wheel without some form of traction aid (air locker, Detroit, truetrac, etc)


https://www.aulro.com/afvb/images/im...2016/04/36.jpg


The rocker beam is hard up against the chassis and any articulation must now come from deflection of the springs. As pointed by others, the springs are designed to support a 2 tonne payload and don't deflect easily.


https://www.aulro.com/afvb/images/im...2016/04/37.jpg



The limiting cables are next to useless. Although they are now close around the axle tube, they are loose and in no way taut or restricting the travel of the axle (cable can be jiggled by hand). That is being done by the rocker beam being hard up to the chassis, and that ain't moving any further!


https://www.aulro.com/afvb/images/im...2016/04/38.jpg

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Team, The suspension does look tired, particularly the position of the shackle bushing washers. These look off centre. Have you had a look to see if your rear suspension bushes are warn? Also Gunner is right (must be a spanner) in that the axle restraint straps (the steel wires which are looped around the axle and fastened to the chassis) are there to limit articulation droop and protect the universal joints and dampers. As Gunner stated check these have not been stretched. Have you tried jacking the intermediate axle up to its limit while the vehicle is on a flat level surface (out of gear, front wheels chocked) with the rear axle free to hang? this may give you an unbiased view of how the suspension should be working. The read assembly is load sharing and should not allow the load beam to touch the chassis under normal circumstances. Having driven these a lot, they are awesome off road, and although a truck and not a rally car, they will go pretty much anywhere. Have driven across parts of the Hamersley Range in WA in a fully laded (5.6 tons) six wheeler with absolutely no problems what so ever.

Mine was a prototype and came with difflocks centre and rear, no check straps. I put freewheel hubs on the rear axle and if I get crossaxled only need to lock the centre diff (g,box).
Only put the FWH in, in really rough stuff.
Just in case , I have a hydraulic winch as well.:D
I wonder why they did not continue with the lockers.