How do they do it?

Any­one who has spent time out in the bush knows that the re­li­a­bil­ity of the gear you choose is para­mount to both safety, and hav­ing a good time. The sus­pen­sion in your ve­hi­cle is no ex­cep­tion. This month we find out how Tough Dog foam cell shocks – which

Leisure Wheels (South Africa) - - CONTENTS - Text: David Cook Pho­to­graphs: Tough Dog 4WD Sus­pen­sion

Op­po­site Lock shows us how

Let’s face it, ev­ery­body wants to ar­rive at their des­ti­na­tion in one piece but no­body wants to ar­rive with a fused spinal cord from a rough ride.

We know that sus­pen­sion plays an im­por­tant part in com­fort, ca­pa­bil­ity and safely keep­ing your wheels on the road.

Foam cell shock ab­sorbers help to re­duce shock fade by keep­ing ni­tro­gen gas and oil found in­side the shock, sep­a­rated. So what is a foam cell shock, and why is it so re­silient?

All shock ab­sorbers con­tain oil, with some choos­ing to insert ni­tro­gen gas, too. When the shock works hard, the oil heats up and ex­pands, and the gas con­tracts to al­low this to hap­pen. In tra­di­tional ni­tro gas shocks, the gas is placed in the shock on top of the oil, with no sep­a­ra­tion. This is called an emulsion shock.

While the shock is work­ing, the oil and gas can be mixed to­gether by the ac­tion of the pis­ton. When the gas bub­bles pass through the valve as­sem­blies in the shock ab­sorber, the lesser vis­cos­ity causes the shock to fade, and fail to per­form.

The foam cell con­tains the ni­tro­gen gas in bub­bles within the foam, so it con­tin­ues to per­form its task in reg­u­lat­ing the pres­sure of the oil, but be­cause it is trapped within the foam, it can­not mix with the oil. It is in this way that the foam cell shock guards against aer­a­tion, and has su­pe­rior re­sis­tance to fade.

Here’s how Tough Dog’s award-win­ning 41mm foam cell shock ab­sorbers are made.


The outer body is made from sheet steel, is rolled, then seam welded to size. Rolling the tube and seam welding is a tra­di­tional, cost-ef­fec­tive way of mak­ing the tube. Tough Dog shocks are a twin-tube de­sign, mean­ing that the outer body tube con­tains oil, but is not part of the pis­ton’s work­ing sur­face. If the ap­pli­ca­tion de­mands it, the ends of the newly formed tube are swaged to size.


While the shock body is be­ing formed, the shock ab­sorber rod is formed from mild steel. The rod be­gins life on a cot­ton reel and is drawn out, stretched and cut into one-me­tre lengths. The stretch­ing process helps to straighten the rod, and is in­te­gral to giv­ing the steel its core strength.


The drawn and straight­ened rod is then parted on a lathe to pre­de­ter­mined lengths. Thread is then cut into the end of the rod in prepa­ra­tion for the pis­ton to be fit­ted fur­ther down the line.


The parted rods are cleaned thor­oughly and put through heat treat­ment in prepa­ra­tion for chrome plat­ing. The heat treat­ment is also the last stage of the strength­en­ing process for the rod. The 41mm foam cell shock uses an 18mm di­am­e­ter rod for max­i­mum strength to guard against be­ing bent by the forces of of­froad use.


At this stage, the rod is han­dled in a man­ner akin to the royal jew­els. Each rod is placed be­tween lay­ers of protective ma­te­rial. Any im­pact,

chip­ping or other mark on the chrome rod plat­ing can ruin the rod and ren­der it use­less. From this point on, the shock is as­sem­bled in a clean room en­vi­ron­ment with the high­est care.


The rod is held with Te­flon (which doesn’t mark the sur­face) and the pis­ton head and valve ar­range­ment is threaded onto the end of the rod, and staked in place. The stak­ing process stops the pis­ton from un­wind­ing from the rod end, which would lead to knock­ing and per­for­mance is­sues from the fin­ished prod­uct. Travel-lim­it­ing de­vices are in­stalled to the rod also to en­sure that the pis­ton assem­bly does not come into con­tact with the top body seals in the shock dur­ing use. Tough Dog 41mm foam cell shocks are fit­ted with Te­flon stop rings.


While all this has been hap­pen­ing to the heart and soul of the shock ab­sorber, the outer shell has not been sit­ting idle. The base cup piece is welded by ro­bot to the bot­tom of the outer tube. The newly united assem­bly is flipped up­side down and placed in water. Pres­sure is then in­tro­duced to the cylin­der to test the weld to en­sure it is com­pletely wa­ter­tight.


The in­ner tube, the work­ing cylin­der, is parted to length from seam­less tube. Seam­less tube is used for the in­ner work­ing tube for its ac­cu­racy in man­u­fac­ture. The foot valve assem­bly is pressed into place in the base of the in­ner tube. The in­ner tube and foot valve are placed into the outer tube.


One of the most im­por­tant pieces, the foam cell, is made by pres­sure in­ject­ing ni­tro­gen gas into the foam in large sheets. A pre-cut piece is in­serted be­tween the in­ner and outer tubes. The shock is then filled with oil.


The mar­riage of the pis­ton and rod assem­bly to the tubes is the link in the chain. The top body assem­bly is put in place to hold ev­ery­thing to­gether. Tough Dog shocks re­ceive a DU bear­ing, to en­sure the shock rod runs straight up and down, and to guard against side load dam­ages. This is fol­lowed by multi-lip oil seal and the dust scraper seal.


With the top cap in place, the shock goes through a qual­ity as­sur­ance check. Be­fore it is welded or folded closed, the shock is dyno graphed to en­sure it per­forms to the spec­i­fi­ca­tion. Any mishaps in the pis­ton head valv­ing, or from the foot valve will show up as be­ing dif­fer­ent in pres­sure re­sponse to the spec­i­fied tol­er­ances.


Shocks that pass the test get the green light to move on to fi­nal welding of the top cap, which is per­formed again by ro­bot. Once welded shut, the shock is on the home straight. Af­ter thor­ough clean­ing and heat treat­ment to com­pletely dry the sur­face, the shock goes through a multi-layer paint process, fol­low­ing by a heat treat­ment to dry and set the paint layer.

Main, left: A Tough Dog Nis­san Navara ex­plor­ing the in­land tracks of Fraser Is­land in Queens­land, Australia. Above: The in­ner work­ings. A cross sec­tion of a Tough Dog Foam Cell. Note the foam insert be­tween the in­ner and outer tubes. Be­low, clock­wise...

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