A cautionary tale - Terrafirma Dampers

[Ed Poore]

2 hours ago, Snagger said:

A triangle is only rigid if the sides can’t change length; dampers are made to do just that.

I've been wondering about this.

Irrespective of everything else you can't escape the fact that adding extra dampers will add some resistance to axle movement, otherwise what's the point of the dampers. What I haven't figured out is whether there's any difference between a single forwards, dual forwards or triangular configurations.

[mmgemini]

3 hours ago, Ed Poore said:

I've been wondering about this.

Irrespective of everything else you can't escape the fact that adding extra dampers will add some resistance to axle movement, otherwise what's the point of the dampers. What I haven't figured out is whether there's any difference between a single forwards, dual forwards or triangular configurations.

The triangular would make it solid

[Daan]

I'd say the forwards/backwards configuration is done to reduce axle roll up when cycling up and down, and therefore reduces wear on the bushes. I can't think of any other reason why you would do it otherwise. It obviously didn't matter much in the end so was changed to both shocks going forward.

[Bowie69]

2 hours ago, mmgemini said:

The triangular would make it solid

Sorry, but it just wouldn't.

Imagine a rubber band around two nails, put your finger in the rubber band and pull down, the elastic band stretches (like a damper would) on either side as the 'axle' (your finger) moves.

If I remember right, the early RRC arrangement was to curb axle tramp.

 

 

[Snagger]

20 hours ago, Ed Poore said:

I've been wondering about this.

Irrespective of everything else you can't escape the fact that adding extra dampers will add some resistance to axle movement, otherwise what's the point of the dampers. What I haven't figured out is whether there's any difference between a single forwards, dual forwards or triangular configurations.

LR had the one fore, one aft configuration to try to reduce axle wrap/tramp, as I understand it.  I’m surprised there was much of a problem, given the nature of the trailing arms and A-frame, but I have read that many times, and they must have had a good reason.  As long as the bushes have enough flex, I can’t see why having a triangular configuration would be worse than parallel twin dampers, but I can see how it may be better.  What would give potential oddities is the asymmetrical original RR and 110 configuration with single dampers fore on one side and aft on the other; I’d expect that to put skewing forces on the axle whenever the springs compress or unload.

 

But for most people, twin dampers are too much, giving an unduly harsh ride.  It’s like all the other HD mods - most are knowingly mis-sold.

 

[Snagger]

20 hours ago, landroversforever said:

How would it cause any bump steer?! The geometry of the suspension doesnt change

Flex and wear in the bushes, mainly.  On spring compression, the leading damper will push its side of the axle aft, while the other side’s trailing damper will push that end of the axle forward, giving some rear steer effect.  It shouldn’t be much with firm bushes, but worn or soft bushes may have an effect.  Just how LR had a reason for initially using this asymmetric arrangement, they must have had a reason for abandoning it.  That the change happened several years down the line suggests it was the result of something that showed up as the cars aged, which makes me suspect aging bushes and handling.

[mmgemini]

15 hours ago, Bowie69 said:

Sorry, but it just wouldn't.

Imagine a rubber band around two nails, put your finger in the rubber band and pull down, the elastic band stretches (like a damper would) on either side as the 'axle' (your finger) moves.

If I remember right, the early RRC arrangement was to curb axle tramp.

 

 

Then the axle would turn on its axis as th shocks moved ut not up and down

 

[Bowie69]

Why would it rotate?

[mmgemini]

1 minute ago, Bowie69 said:

Why would it rotate?

Because only one damper would be ably to move upards

 

[Bowie69]

Why only one? They can both telescope?

[mmgemini]

3 minutes ago, Bowie69 said:

Why only one? They can both telescope?

I suggest you mke a model of what we are discussing. In the siuation neither can move more than a couple of mm upards onle in a rotational direction

[sean f]

To envision what is happening with a triangular shock arrangement take and elastic band and stretch it between two finger and your thumb on one hand, the two fingers are the chassis mounts so keep them the same distance apart and move your thumb up and down. The elastic in the sections going round your thumb will change length just as shock absorbers do, they will also change angle at the top and bottom (chassis and axle) on a vehicle this will be taken up by the shock bushes.

Hope that makes sense, I have always found it easier to envision things or explain them with an actual example.

[Bowie69]

Like this.... Reprising my example from above?

[mmgemini]

8 minutes ago, sean f said:

To envision what is happening with a triangular shock arrangement take and elastic band and stretch it between two finger and your thumb on one hand, the two fingers are the chassis mounts so keep them the same distance apart and move your thumb up and down. The elastic in the sections going round your thumb will change length just as shock absorbers do, they will also change angle at the top and bottom (chassis and axle) on a vehicle this will be taken up by the shock bushes.

Hope that makes sense, I have always found it easier to envision things or explain them with an actual example.

The trouble with an elastick band it is flexable. The shockers are not. I do have the brackets for the axle and the crowfoot mounts for the chssis. Who want's to try them

 

Edited August 25, 2020 by mmgemini

[Bowie69]

As you can see in the video, the elastic band does not need to bend, only extend.

[Chicken Drumstick]

On 8/23/2020 at 8:05 PM, Maverik said:

This has been brought up before regarding terrafirma shocks.

I ran a set of big bores for 8 years with no problems.

A friend runs these on his 90. Has been to Morocco heavily laden with a roof tent setup. Done a lot of laning and the like. No probs so far. Think they have been on there 4-5 years.

[Nonimouse]

The few twin shock conversions I've not managed to clients out of, I've always made up a parallel mount for on the outer radius of the axle. I've always used one 'harder' shock and one 'softer' shock. Pointless though. Much better to just get one decent shock with either a big bore or a reservoir

[landroversforever]

16 minutes ago, mmgemini said:

The trouble with an elastick band it is flexable. The shockers are not. I do have the brackets for the axle and the crowfoot mounts for the chssis. Who want's to try them

 

The rear shock just moves like the front one. Extends or compresses and like a single shock setup, the bushes take up the misalignment.

[Snagger]

With the rear axle moving in an arc around the front ends of the trailing arms, the movement of leading vs trailing dampers will differ slightly, but not a great deal.  Both positions will have enough flex even with stiff bushes to allow the axle to move (stiff bushes would just put more strain on the damper fixings and potentially break them like the vehicle in the original post).  Certainly, trailing, leading or any combination of both is not going to cause any binding as all dampers can vary in length independently for any form of axle movement, symmetrical or not.  For those who think having leading and trailing dampers will cause binding, have a look at the suspension on tanks and many train carriages.  If that doesn’t convince you, have a look at the triangulated oleos on flight simulators and see just how much freedom of movement they have.

[Naks]

First time going off-road with plenty of cross-axles/articulation. Friend of mine in a D1 comes on the radio and says he's dislocated a spring and needs a hi-lift jack, so we drop one for him and keep going.

A few minutes later I start hearing a knocking sound, and the two vehicles closest to me stop to ask me if I've broken something. We drive back to the rest camp, and whadayaknoe. This is a 6-month old damper, fitted at the beginning of Nov 2020:

 

So the friend in the D1 who needed the hi-lift? Yeah, same TF shock, broken in exactly the same place, also on the left rear wheel. He also fitted these around the same time, also bought from the same distributor.

ditching these TF p.o.s and just ordered a full set of Bilstein B6s. 

 

[SteveG]

Or go for the pin pin OME shocks and Gwynn Lewis mounts that offer more rotational movement of the shock instead of the eye mount.

[Nonimouse]

Or go for Raw 4x4 shocks, Fulcrum 4x4 shocks, Monroe Adventure... etc etc

[Bowie69]

Pin-Pin really helps with stopping this sort of thing happening when you have big flexiness.

[Naks]

My friend with the same failure just messaged me now, and thinks he's found a solution:

"The chromede rod diameter is 16mm , but the thread diameter holding the rod in the top mounting is 12mm. There is a sharp change from the rod diam to the thread, and this transition is the point of failure because of the combined bending and tensile load when the axle is hanging off the shockabsorber.

I am going to rethread the rod to 16mm. The load bearing area goes from 12 squared (144 mm2) to 16sq (256 mm2) .....almost 2 x."

Edited May 12, 2021 by Naks

[FridgeFreezer]

Why thread it - just weld the b*****d on.