Thread: Leaf spring question

I would put money on the Military IIa having the least amount of travel with its stiff springs.

Originally Posted by Ozdunc

Why do axle straps need to be used? Surely not to protect the shocks. To stop the shackle from over rotating?
Are they really needed? F40s and Fj60 don't have them for example.
If you use a more flexible leaf you could get more droop by utilising a longer shock. Although you may need to alter the top mount for the shock to allow for the longer closed length which might be a can of worms you don't want to open.

I figured they are there to protect the shocks and maybe the tail shaft from binding. Not really sure they are necessary.

I don't have any plans to modify anything, for 99.9% of the 4wding I do she is more than capabable

As far as i know they are to protect the shock absorbers. Many people have run without them without problems, but they are probably only needed in extreme conditions - heavy load, well lubricated springs, very rough conditions and shocks overheated and not damping properly so that they reach the end of their movement with the axle/chassis distance still rapidly increasing.

They fill the same role as the bump stops, but in the opposite direction. Properly installed, they should limit articulation no more than the shock absorbers themselves do.

John

From memory Rocky Mountain Parabolics recommend the check straps be set to support the axle 1/2 inch before the shocks bottom out, because they are designed, as John says, to prevent the shock itself acting as the stop and suffering damage as a result.

Some shocks may be more prone to damage than others, depending on design and quality, but it is also a matter of vehicle usage. At rock crawling speeds the shock will bottom out slowly and is unlikely to be damaged. But if the shock hits full extension and has to "catch" the entire weight of the axle, wheels, tyres, brakes etc. that are moving at high speed, then it's more likely to get damaged. Of course with rusty old leaves that are largely stuck together that may never happen, but with a newly assembled and lubricated spring pack, driven at speed down a rutted track with the vehicle being "launched" off the bumps and the rebound damping at minimum because the shock is hot, then.....

Originally Posted by Warb

From memory Rocky Mountain Parabolics recommend the check straps be set to support the axle 1/2 inch before the shocks bottom out, because they are designed, as John says, to prevent the shock itself acting as the stop and suffering damage as a result.

Some shocks may be more prone to damage than others, depending on design and quality, but it is also a matter of vehicle usage. At rock crawling speeds the shock will bottom out slowly and is unlikely to be damaged. But if the shock hits full extension and has to "catch" the entire weight of the axle, wheels, tyres, brakes etc. that are moving at high speed, then it's more likely to get damaged. Of course with rusty old leaves that are largely stuck together that may never happen, but with a newly assembled and lubricated spring pack, driven at speed down a rutted track with the vehicle being "launched" off the bumps and the rebound damping at minimum because the shock is hot, then.....

Shocks these days should be pretty good. Coil spring and notably air spring shocks all catch the axle before the springs have released all of their force in addition to the weight and inertia of the unsprung mass.

Originally Posted by Slunnie

Shocks these days should be pretty good. Coil spring and notably air spring shocks all catch the axle before the springs have released all of their force in addition to the weight and inertia of the unsprung mass.

But if the check strap is set to catch the axle only 10mm before the shock does, the question is whether 10mm of suspension travel is worth the risk (no matter how small) of a busted shock and possibly a ruined trip? For a competition vehicle that arrived on a trailer, 10mm may be important and the bust shock is part of the game, but on a week long camping trip to the middle of nowhere....

Rocky Mountain (I'm using them as an example only because they document the check strap settings etc., whilst even the Green Bible doesn't) sell and recommend a couple of brands of "quality" shocks including OME. Yet they are still insistent about the fitting of check straps. Obviously there are the normal legal requirements for them to consider, they don't want to be sued because someones shocks got smashed, but even that suggests they believe there is some kind of a risk.

It is of course personal choice, but on my LRs I don't see a penalty in fitting check straps, and I do see at least a small potential for problems if I don't. They don't cost much, they don't create any problems, so I'll fit them!

I'd very much like to see your lift test on the following...

a) a 2a 109 (to see comparison with 88")
b) 1 90 modern defender (again for comparison)
c) military 2a 88
d) military 2a 109
e) perente...


and
f) on a gunbuggy.... (it will be the same as the 88 but will mean another
photo of a gunbuggy on the forum


the diffences may be very interesting, so for the sake of science (well for my curiosity really) get out you landys , get out your forklifts, and lift, photograph and measure thanks!!

If a shock doesn't have a built in bump stop, which I imagine a 40 year old shock didn't, a check strap would be a good idea. Modern shocks usually have internal bumpstops which should negate the need for the strap, bilsteins definitely do and I'm pretty sure most foam cells do as well other wise there'd be a whole heap of defenders with check straps instead of dislocation cones.