Shock absorber config - what's best?

[Gareth Dickens]

I've fit Hilux leafs to the front of my 109 s3 with the std rears at the back and now want to look at how to fit my dampers. ( Since I can fit them any way I like now.) I've been paying attention to other vehicle manufacturers and have seen a few different setups. I'm looking at the rear axle mostly as no modern vehicle manufacturers have SFA vehicles with leafs. I have a set of Armstrong shocks Which are 480mm compressed and 760mm extended with round (eyebolt) mounts top and bottom.

1) Isuzu use both dampers behind the axle going aft at a longitudinal angle.

2) Toyota, Mazda, Ford have one damper in front and one aft of the axle both fitat a longitudinal angle

3) Land Cruiser have the dampers going inboard outboard at an angle (Viewed from behind it forms a V)

I noted all are fit to inside of the longitudinal chassis beams which is difficult to do on a landy.

Which is best and for what conditions?

[ToyRoverlander]

Simple.... straight up! That way they perform the best. The greater of an angle they're installed in, the less effective they become. A shock that is on, say a 45 degree angle, has to be much stiffer than a shock that is vertical to give the same results.

One advantage from installing on an angle is that you can get away with a shorter shock that doesn't restrict articulation. A vertical shock would need to be longer. But the one installed on an angle needs to be stiffer to compensate.

I've got Bilsteins 5125Series with 14" travel. They're 89cm or so extended and 54cm collapsed. And I've mounted mine vertical, front and back. As mine is lifted a fair bit I can get away with them mounted vertical.

Those shocks will let the front end flex nicely! Post some pics

[secondjeremy]

I think there's some black magic amongst chassis engineers about shock absorber positioning. I think the early Range Rover had one mounted ahead of the axle and one behind - which I think was considered a trick to reduce axle tramp. Other similar Rover vehicles don't have this feature - so it must have been considered a success!

I'd have thought diagonal mounting reduced the rate but may have advantages in allowing greater suspension travel.

[Gareth Dickens]

It's said that having both shocks behind the axle is good for tar and gravel road travel but transfers a lot of shock when going over a speedbump. (both shocks loaded simultainiously) I can feel this in my Isuzu, cause speedbumps are bone jarring. I thought of having the shocks at a slight angle behind the front and rear axle as the leafs get a little longer and rotate about the front spring hangers.

The shocks I've got are fairly stiff and require a fair amount of effort to extend and compress. I'll have to fit the front and rears outside the chassis rails. I'm a bit concerned with how responsive the suspension will be. Once these shocks are knackered I'll get some nice gas shocks.

What about the height at which to attach the shock upper end? Am I correct in saying that my bumpstops should contact about a inch before my shocks bottom out? That should give me maximum down travel with a small safety margin for up travel so the shocks don't bottom out.

Thanks

Gareth

[Gareth Dickens]

More Questions!!!

Is the resistance of a shock the same for compression and extension ?

This would (in my mind) be a great contributing factor in deciding where to mount the shocks?

I've also heard that having one shock in front and one behind is supposed to reduce tramp..... will this work up front?

This should only be done with shocks that have the same compress/extend resistance or the vehicle will behave differently when loading the left and right wheel - or am I smoking my socks?.......... or do they work as a pair where they give a resistance as the sum of both?

Thanks

Gareth

[secondjeremy]

Some shock absorbers work in one direction only - I think Rover P6 were only supposed to work on rebound. I'm not convinced that ordinary Land Rover ones aren't stiffer in one direction but haven't carried out a definitive test - I'm normally just happy to get the things fitted!

Interestingly Land Rover slant the back ones but the front ones are straight. I'd have thought that with a leaf spring a slanting action would deflect the spring a bit which could interfere with the steering - and with a link system it would move the axle due to compliance in the bushes.

[Snagger]

Early RRCs had one damper ahead of the rear axle and one behind for the axle tramp reason mentioned before, but it didn't really work and reduced the effectiveness the dampers in their normal mode. It also creates a torsional force on the axle, trying to skew it in relation to the chassis, which is why it was dropped before the Defender and Discovery came along - my RRC has symmetrically set dampers that slope aft towards the rear axle, just like on a 109. As also previously commented, that trailing slant allows the suspension to travel further for a smaller damper movement and thus prevents over-damping of the rear suspension. All LR models have vertical front dampers as this is the most effective orientation and helps the suspension deal with the weight of the engine.

The rear dampers on coil sprung models also slope outeard towards the hubs. This resores a little of the lost motion caused by having them trailing, as the hubs will move up and inwards on cornering or uneven ground, so the dampers will have a small beneficial effect on the rate of body roll when cornering. It also means that the movement of the dampers is amplified when cornering, though not when both springs are compressed, because the lower end of the damper is mounted where the axle moves more with assymetric suspension loads, further increasing their resistance to body roll. It's also likely that this outward set helps with reducing rear and perishing of the rubber bushes at each end.

I suspect the front dampers are only mounted vertically on all models to keep them out of the way of the steering system and out of the path of the wheels and tyres on all steering and axle articulation positions, otherwise they'd probably be set the same as the rear dampers on that model.

[Gareth Dickens]

Some very good points made.

So, for me it's settled as far as the fronts go: VERTICAL

So what do you think about me fitting the rear shocks to the u-bolt plates with the shock trailing the axle and going up vertically?(like the fronts)

WHat about the bolt direction through the shock eyes (fwd/aft or left/right). If my logic is correct for every inch of suspension travel up/down there is a greater change in angle down the length of the leaf (from the fwd spring hanger to the shock mount point) than twist of the axle. Am I correct in assuming this? So should my rear shocks be fit the same way as std fronts with higher upper mounts?

Thanks

Gareth

[ToyRoverlander]

That will work very nicely!

Fit the bolts in-line with the vehicle, front to back. The leafspring doesn't get very much longer/shorter on compression/rebound during normal driving or even when it's articulating. The length difference there is will be easily absorbed by the bushes.

At least the shocks can rotate around the bolts when the axle articulates...

[Steve Hiatt]

Sometimes the shocks are mounted at an angle to give a non linear shock rate, your damping proportionately increases with compression even though you have a linear rate shock absorber. That's fine if you're building a race truck or 100,000 units but in your case your plan seems fine.

[ToyRoverlander]

Correction.... it DEcreases... as the axles moves up, the angle the shocks are in becomes greater and thus the shock becomes less effective.

[Gareth Dickens]

Toy -are you sure about the bolts for the shockmounts going longitudinally (lengthwise fwd/aft)? Standard they're transversely fixed (left/right) in the front and that seems to make sense to lessen the load on the shock mount bushings.

[ToyRoverlander]

Yes. Because a stock front end doesn't flex much at all. With so little flex the bushes can take it easily. When you're allowing it to flex way more dus to longer springs and shocks than it makes sense to put them lengthwise so the shock can rotate around the bolt on articulation. The little fore/aft movement it sees due to the spring getting longer and shorter will be way less movement and can easily be absorbed by the shock bushes.

That's how I have it front and back for a few years now, and the shock bushes are still fine.

[Snagger]

I have just taken the old back springs off our Lightweight as one of them has lost 2" of its camber, though it still retains most of its positive camber. the spring has ecome about 2.5" longer than the other, and if the spring had flattened, this would be 3.5-4". At the mid point, this translates to a 2" move aft as the spring flattens under load. That's a lot for the bushes to take, and is probably why LR fitted the bolts transverseley, rather than longitudinally. I can see Toy's point, too. In an idea world, rose joints would be best...

[Gareth Dickens]

I don't think it's purely for the lengthening of the springs that the bolts are transversely fit......eg. If my right leaf moves 1 inch up and the left remains stationary, the distance from the front spring hanger to the mid point of the axle is about 17 3/4".... the distance between the spring centre bolt from left to right is about 27 3/4". So you end up getting a larger change in angle for every inch of travel in the fwd/aft direction than left/right. You would get more rotation about the lateral axis than the longitudenal axis.When you add the spring lengthening to the greater angle change you end up with a much more rotation about the lateral axis. This is based on standard springs. With my longer springs it's 21 3/4" vs. 27 3/4".