C.V.A. Shock Absorbers

C.V.A. stands for ‘Constant Volume Adjustable’. These shocks combine the action of the oil in the piston chamber and the spring.

When the shock absorber is compressed due to a bump or jump acting on the suspension (picture left),the mechanical action of the piston compresses oil, which is forced to pass through holes in the yellow piston from the upper to the lower chamber. Oil is an incompressible liquid and this forced passage in a limited space (the holes, which are usually two) transforms the kinetic energy of movement into thermal energy: heating oil. The same situation occurs when the shock absorber extends pushed by the spring to return to its rest position (image right), the mechanical action of the piston compresses oil which is forced to pass through the holes from the lower to the upper chamber. This forced passage in a limited space transforms the kinetic energy of the movement into thermal energy by heating oil.
Transforming kinetic energy into thermal energy allows the oil to dampen the suspension action:
– in rebound due to a bump, a jump, uneven ground, etc.
– in extension due to the spring
Physically dissipating energy prevents annoying suspension rebound. To adjust the action of these shock absorbers you can
– change the oil inside using oils of different viscosities and/or
– change the ‘hardness’ of the springs by inserting spacers or changing the springs themselvesthe mechanical action of the piston compresses oil, which is forced to pass through holes in the yellow piston from the upper to the lower chamber.

These are the steps for the correct construction of the C.V.A. shock absorber, if carried out incorrectly they can impair correct functioning:

1- On the metal piston rod (highlighted in blue) install the two C-rings (highlighted in red) and the plastic piston head, which has two holes (highlighted in orange). The holes are used to pass oil from the upper chamber to the lower chamber when the shock is compressed and vice versa. As the number of holes in the disc increases, the oil action decreases and the shock absorber becomes soft. The viscosity of the oil determines its action on the movement of the piston in the chamber. This system gives the name C.V.A. to these shock absorbers.
2- Screw cap Y2 (highlighted in orange) onto the cylindrical body of the shock absorber (highlighted in green). Insert the piston just assembled together with the X1 spacers (highlighted in red) and the Orings (highlighted in blue) into the cap of the shock absorber’s cylindrical body (highlighted in orange), following the order shown in the figure.
3- The most complex operation to perform is to fill the shock absorber chamber with oil (highlighted in purple), if you leave air bubbles (highlighted in white) inside the chamber the hydraulic reaction due to the oil will not be predictable and constant. Air is compressible and therefore changes the reaction of the fluid formed by a mixture of air and oil, which is incompressible. Two technical precautions must be taken to avoid having air bubbles. First of all, abound with oil and do not follow the instructions completely; avoid cleaning the shock absorber with a cloth (highlighted in blue) before applying the cap (highlighted in red) and screwing cap Y2 onto the shock absorber body. The second suggestion is to fill the shock absorber with oil, leaving the piston at a height of 1/3…1/4 of the cylinder to prevent an air pocket from stopping at the bottom. If this method is applied, make sure that the lower chamber does not contain bubbles: fill the cylinder halfway with oil, wait until the bubbles all come to the surface, facilitate the passage of the bubbles from the lower to the upper chamber by tilting the cylinder slightly. The two techniques can be combined.

4- insert the spring and screw in the lower eyelet. Springs can be of various types depending on the model on which the shock absorber is installed.
5- select and install C-shaped plastic insert, which has the task of stiffening the spring. The higher the insert, the stiffer the spring becomes

The shock absorbers of the C.V.A. family are divided by the length of the shock absorber itself:

– Super Mini’ with a maximum length of 55 mm; available in black plastic; in the black version code number 50519,
– Mini’ with a maximum length of 63 mm; available in blue, black, grey, white and yellow plastic, in the yellow version code number 50322;
– Short’ with a maximum length of 82 mm – 77 mm; available in red, black, grey, white and yellow plastic, in the yellow version code number 50305;
– Long’ with a maximum length of 103 mm; available in yellow plastic, in the yellow version code number 50304

Within the same family it is possible to change the length of the shock absorber by changing the shock axis (highlighted in blue) and springs; here are some tables showing how the shock absorbers can be adapted to various lengths.

The first model to install these shock absorbers was The FOX released for sale in 1985, soon after this shock absorber was released with different chassis and models. List relating the various C.V.A. shock absorbers to the models:

– The Fox model 58051: single front shock absorber in the yellow Short version with piston for length 82 mm; double rear shock absorber in the yellow Short version with piston for length 77 mm
– Super Shot model 58054: double front shock absorber in Short version yellow with piston for length 82 mm; double rear shock absorber in Long version yellow
– The Boomerang model 58055: single front shock absorber in Short yellow version with piston for length 82 mm; double rear shock absorber in Long yellow version
– Falcon model 58056: double front shock absorber in the yellow Short version with piston for length 82 mm; double rear shock absorber in the yellow Long version
– The Big Wing model 58057: double front shock absorber in Short version yellow with piston for length 82 mm; double rear shock absorber in Long version yellow
– Ford F150 Range BlackFoot model 58058: double front shock absorber in the Black Short version with piston for 77 mm length; double rear shock absorber in the Black Short version with piston for 77 mm length
– Monster Beetle model 58060: double front shock absorber  in the yellow Short version with piston for 77 mm length; double rear shock absorber in the yellow Short version with piston for 77 mm length
– Striker model 58061: double front shock absorber in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for 77 mm length
– Hot Shot II model 58062: single front shock absorber in the red Short version with piston for length 82 mm; double rear shock absorber in the red Short version with piston for length 82 mm
– Lunch Box model 58063: double front shock absorber in the yellow Short version with piston for length 77 mm; double rear shock absorber in the yellow Short version with piston for length 77 mm
– Clod Buster model 58065: quadruple front shock absorber in the red Long version; quadruple rear shock absorber in the red Long version
– Super Sabre model 58066: single front shock absorber in the red Short version with piston for 82 mm length; double rear shock absorber in the red Short version with piston for 82 mm length
– Thunder Shot model 58067: single front shock absorber in the yellow Short version with piston for length 82 mm; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Lotus Honda T99 model 58068: single rear shock absorber in the yellow Mini version
– Willimas FW14-B Honda model 58069: single rear shock absorber in Mini yellow version
– Midnight Pumpkin model 58070: double front shock absorber in Short yellow version with 77 mm piston length; double rear shock absorber in Short yellow version with 77 mm piston length
– Sonic model 58071: double front shock absorber  in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for 77 mm length
– Thunder Dragon model 58073: single front shock absorber in the yellow Short version with piston for length 82 mm; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Grasshopper II model 58074: double front shock absorber  in the yellow Mini version; double rear shock absorber n the yellow Short version with piston for length 82 mm,
– Terra Scorcher model 58075: double front shock absorber in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Vanquish model 58076: double front shock absorber in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for 82 mm length,
– Mud Blaster model 58077: double front shock absorber in the yellow Short version with piston for length 82 mm; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Fire Dragon model 58078: double front shock absorberin the yellow Mini version; double rear shock absorberin the yellow Short version with piston for length 82 mm,
– Astute model 58080: double front shock absorber in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Nissan King Cab model 58081: double front shock absorber in the yellow Long version; double rear shock absorber in the yellow Long version
– Mad Cap model 58082: double front shock absorber in the yellow Mini version; double rear shock absorber in the yellow Short version with piston for length 82 mm
– Saint Dragon model 58083: double front shock absorber  in the yellow Mini version; double rearshock absorber in the yellow Short version with piston for 82 mm length,
– Ferrari F189 Last Version model 58084: single rear shock absorber in the yellow Mini version
– Avante 2021 model 58085: double front shock absorber in black Mini version; double rear shock absorber in black Short version with 82 mm piston length,
– Toyota Hi-lux Monster Racer model 58086: double front shock absorber in the yellow Long version; double rear shock absorber in the yellow Long version
-Manta Ray model 58087: double front shock absorber in the Short yellow version with piston for length 82 mm; double rear shock absorber in the Short yellow version with piston for length 82 mm
– Merceds Benz C11 model 58088: single rear shock absorber in Mini yellow version
– BullHead model 58089: quadruple front shock absorber in Long red version; quadruple rear shock absorber in Long red version
– Tyrrell 019 Ford model 58090: single rear shock absorber in the yellow Mini version
– Nissan 300ZX IMSA GTO model 58091: single rear shock absorber on yellow Mini version
– Jaguar XJR Daytona winner model 58092: single rear shock absorber in yellow Mini version
– Bear Hawk model 58093: double front shock absorber in Short red version with 82 mm piston length; double rear shock absorber in Long red version
– Honda NSX model 58094: single rear shock absorber in Mini yellow version
– Lotus 102B Jubb model 58095: single rear shock absorber in the yellow Mini version
– Celica GT-Four model 58096: double front shock absorber in the blue Mini version; double rear shock absorber in the blue Mini version
– Super Astute model 58097: double front shock absorber in the black Mini version; double rear shock absorber in the black Short version with 82 mm piston length
– Ferrari F40 model 58098: single rear shock absorber in the yellow Mini version
– Skyline GT-R model 58099: double front shock absorber in the blue Mini version; double rear shock absorber in the blue Mini version
– Top Force model 58100: double front shock absorber in the black Short version with 77 mm piston length; double rear shock absorber in the black Short version with 82 mm piston length
– Bush Devil model 58101: double front shock absorber in Short red version with piston for length 82 mm; double rear shock absorber in Short red version with piston for length 82 mm
– Mazda 787B model 58102: single rear shock absorber in Mini yellow version
– Jordan 191 model 58103: single shock absorber at the rear in the yellow Mini version
– Mc Laren MP4/6 model 58104: single rear shock absorber in the blue Mini version
– Williams FW14 model 58105: single rear shock absorber in the blue Mini version
– Mercedes 190E AMG model 58108: double front shock absorber in the blue Mini version; double rear shock absorber in the blue Mini version
– Nissan R91CP model 58109: single rear shock absorber in the yellow Mini version

The basic concept of the oil chamber with perforated plunger and counter spring has remained unchanged over time, the C.V.A. family is still used today (2024) in Tamiya production and has evolved by changing the shape of the spacer to stiffen the springs and the cylindrical body. Hi-Cap shock absorbers are the evolution of C.V.A. shock absorbers with an aluminium cylinder.

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