rear shock/suspension down-travel

[simonr23]

my d2 has a 2" lift, via aftermarket springs and shocks. i think that the rear shocks are either a bit buggered or they just dont have enough downtravel. driving on some very tame sandy tracks, that have medium whooped sections, the back end bangs on rebound as, what i imagine are the shocks finding their end limits. its real annoying, as it happens any time that my speed is enough to make the suspension work AT ALL. doesnt do it on speed bumps, just this rolling terrain.

it feels as though the car compresses at the rear and then rebounds more than it needs to. when doing the backyard 'jump about on the towbar' test, there is no excess movement. its compression and then stop where it's meant to on the rebound.

any tips. i'm thinking perhaps the shocks are too light for the springs. so i guess what are decent shocks to replace with, that are still cheapish.

since there are no markings on the springs or shocks, i dont know how i can go about getting some matched shocks. the current setup is a pale yellow, ever so slight mustardy colour springs(king perhaps?) and plain white shocks. the bushes are also white.

[Blknight.aus]

jack up the back end of the vehicle.
by the chassis so the rear axle is at maximum droop

measure the clearance to the bump stops.
measure the total length of the shock (that gives you your current max lenght

put it back on the ground
measure the same 2 items

now work out how much more shock lenght will dissapear if the bump stop clearance goes to 0

take an extra inch out of that calculated minimum length and thats about what you need for your shock under max compression.

thats only a field method...

[simonr23]

when u mention bump stop, are u referring to an internal stopper in the shock, or the bump stop that limits the axle? my problem isnt with compression(axle bump stop) but rebound(articualtion away from wheel arch)

that might have been your point all along, but i read it as compression reading/adjustment. it feels like that the car is raised to almost the limit of the shocks travel. just from my offraod travels, i know that i dont have much droop. and this is what i wanna get back into the car.

[Slunnie]

Some shocks are better than others at dealing with the clunk when they reach full extension. The factory ones that came out of your D2 are about as bad as they come in this regard. Interestingly enough, I've seen 2" lifts where there is almost no drop travel at all, and I'm not convinced either that this is an appropriate way to setup the suspension.

In a nutshell, and without getting into surgery with your car, the best bet is to replace the rear shocks with some good long travel rear shocks that are designed for the D2. Shocks like the OME and Toughdogs are spec'd up so that they get the most travel out of the suspension without having to deal with extended brake/ABS lines etc, and they seem to have done it with enough internal efficiency in the D2 to not require extended bumpstops. These will return as much drop travel as what you're going to get without getting expensive or fiddly.

[simonr23]

cheers slunnie. i'll go and have a look at both those brands. will i be fine keeping my current front setup(which is same as rear) as this performs and feels very good on road and off.

ps- ome= old man emu?

[simonr23]

theres a uk ebay ad for 4x monroe shocks for d2's. would these be any good? about 230 shipped.

[Slunnie]

Yep, if the fronts are working well, then hang onto them. If they're a softer type of shock then you may find a tendancy for some increased understeer if stiffer rear shocks go in, as the stiff shocks produce more control over rougher terrain than a soft shock. I'm not sure what other shocks use the full available travel besides these 2 brands.

If you play in the bush or use it as a town car, then it wont matter which shock you use, but if you tour in it then I would be inclined to stay away from any foam cell shock (ie, I would look at the OME first)

OME = Old Man Emu.

[Slunnie]

theres a uk ebay ad for 4x monroe shocks for d2's. would these be any good? about 230 shipped.
Monroe's are fine. I'm not sure what their lengths are though.

[simonr23]

cheers again. i'll see what sort of $$ the ome's are first then. then i'll look at toughdogs. i'll leave monroes until i can get some more info.

do u know the rough price for the 2 you recommended.

[Slunnie]

Not sure re the TD's but the OME I think are about $125ea.

[broonski]

Yep, if the fronts are working well, then hang onto them. If they're a softer type of shock then you may find a tendancy for some increased understeer if stiffer rear shocks go in, as the stiff shocks produce more control over rougher terrain than a soft shock. I'm not sure what other shocks use the full available travel besides these 2 brands.

If you play in the bush or use it as a town car, then it wont matter which shock you use, but if you tour in it then I would be inclined to stay away from any foam cell shock (ie, I would look at the OME first)

OME = Old Man Emu.

any particular reason you would stay away from the foam cells for touring, Slunnie?

[Slunnie]

any particular reason you would stay away from the foam cells for touring, Slunnie?
G'day Broonski,

If the foam cell shocks become overheated which a loaded 4by on fast dirt can/will do, the foam cells break down and they never properly recover back to full operation. The damage is cumulative. In a normal shock, when the shock cools and the oil deairates, then you're back to normal again.

[Trevhoare]

From the original description it sounds as if the suspension has been raised without fitting longer shocks..... so after only a few cm of further extension they are at their limit...

With the design of the rear suspension the shocks provide the limit to travel for the rear suspension extension.. so I would be checking the shock length especially at full extension..

Also the stiffness of the springs can have an effect. if the taller springs are stiffer as well as longer they will be over powering the extension resistance of the shocks on the extension stroke and getting it to the limit more easily.. Shocks and springs must be carefully matched so that the damper rates and length allow the springs to use their full travel without over extending or reaching the bump stops.

Cheers

Trevor

[simonr23]

my thoughts are along those lines too. the thing is though, under normal driving the setup is great, same for severe chassi twister type tracks. its only on medium frequency and amplitude bumps that it gets all sucky. a bit of an after bounce over speed humps too. the front end is perfect, with the same suspension components.

[broonski]

G'day Broonski,

If the foam cell shocks become overheated which a loaded 4by on fast dirt can/will do, the foam cells break down and they never properly recover back to full operation. The damage is cumulative. In a normal shock, when the shock cools and the oil deairates, then you're back to normal again.

G'day Slunnie,

thats someuseful info! thank you! as i'm deciding what kind of suspension setup i want in my defender (mainly used for touring) how would you rate tough dog compared to ome (i understand that different vehicles ride and handle differently with different brands and different setups all according to the drivers preferance, but i'm just after a ganeral comparison)

also, i was under the impression (from reasearch of my own and working, to a limited extent, with tough dog foam cell shocks) that the foam cells were designed to eliminate airation?

cheers,
bryce

[Slunnie]

G'day Slunnie,

thats someuseful info! thank you! as i'm deciding what kind of suspension setup i want in my defender (mainly used for touring) how would you rate tough dog compared to ome (i understand that different vehicles ride and handle differently with different brands and different setups all according to the drivers preferance, but i'm just after a ganeral comparison)

also, i was under the impression (from reasearch of my own and working, to a limited extent, with tough dog foam cell shocks) that the foam cells were designed to eliminate airation?

cheers,
bryce
I can't give a definative answer, and the two companies will valve their shocks differently. In that respect it's probably better to get an opinion on users with that vehicle with that shock and in that setting. This said, OME should supply in comfort and performance spec valving and the Tough Dogs, depending on which ones you look at may come with adjustable valving. The adjustable valving is good to learn shock setup and for the times when running laden or unladen, but the foam cell is the let down.

At the end of the day though, the best answer that I can give is based on what I'd put my money on... well, I've tried twin shells, I've tried foam cells and I've tried mono-tubes... Foam cell I can kill on demand, twin shells were fine, and I found mono-tubes to be outstanding. I run Bilstein (monotube). After Bilstein I would probably then move to OME (twinshell). Koni (twinshell) are supposed to be a very good quality twin shell shock, though at the end of the day it is still a twin shell shock design like the OME and I cant justify the cost of them for the performance although in the long term there may a durability gain, and so would use OME which I think most are happy with and fit the vehicles very well in terms of length and valving.

Re the foam cell design, that is correct. They are designed to eliminate fade by maintaining the gas in the foam cell, and this is what gets compressed when the piston shaft is compressed into the shock body. It's quite a good design in theory, but the problem is when they run hot the foam cell breaks down and the gas is released from the foam cell, the oil quickly airates which means that the shock fades. Air/oil mix passes through the shock valving with a lot more ease than just oil.

[broonski]

thanks for all your info Slunnie! i'm now well on my way to making an informed decision! :D

cheers,
bryce

[rick130]

a slight correction on the foam cells used in some shocks.
My understanding is it's more a marketing concept than any sound engineering principle.
The 'foam cell' is just some closed cell foam, there is no 'gas' involved, that takes up the space in the outer tube reservoir normally occupied with air ( or nitrogen in the case of some like OME and Koni low pressure gas)
It should slightly reduce aeration, but I feel it reduces heat transfer, and in designs like Rancho, there is actually another tube which further reduces heat transfer.
The low pressure twin tube design, as used by OME on their Nitro Charger and Koni on some of their later model twin tube dampers is a superior design.

There is no doubt that mono tube dampers transfer heat better than any other design, but twin tube shocks have certain design characteristics that can make them a better design for some applications, (better bump valving for one) and if they are made big enough, with a large enough reservoir, (Koni Raid, Tough Dog Ralph, Powerdown/Raw 4x4 big bore whatever it's called, etc) they can cope with the extra heat generated from rough roads/heavy loads/high speeds, although if you are off road racing, a mono tube with a remote reservoir is the hot ticket, all things being equal.
Interestingly, the best circuit racing dampers (Ohlins TT44, Sachs), have gone back to a twin tube design, but I won't confuse you as to why. ;)

There's a fair bit of info on shock design and characteristics on the forum, might be worth doing a bit of a search.