Hydraulic shock question

Does anyone know if you can change the stiffness of a hydraulic shock by changing the weight of the oil?

 

you could if you could find a way to drain and fill it. Make sure you use a fluid that wont foam if you manage to pull this off, like motorcycle fork oil, or hydraulic fluid.

 

High performance racing shock absorbers are made to be fine tuned. Changing the viscocity of the fluid is only one of the variables. Most off the shelf stuff in an auto parts store is not in this price category. If you need stiffer to control bounce, consider a shock from a heavier vehicle, but remember the shock absorber is also designed to hold suspension within specific travel limits. Too long a front shock and the coil spring can pop out of the socket when jacked up, just a note to keep in mind.

 

To soften a shock you can drill it and add sewing machine oil. This is something most commonly done with manx buggys so thesamba should have more info on it.

 

I've heard of lever arm shocks on older British cars getting a heavier oil for stronger damping. I'd say it could work on tube shocks, but cutting into a shock that might be gas-charged would be a hazard, and sealing a regular hydraulic shock after draining and refilling would be an interesting problem.

 

Are you trying to make the shock softer or stiffer?

 

As already mentioned, shock oil is one of many variables that can change both rebound and compression rates on a shock. However, you can only change it if the shock is rebuildable, and most welded tube automotive shocks are not. You will also need a way to recharge the nitrogen (up to 400 psi) in the shock after changing the oil. Below is a picture of rebuildable Elka shocks. These are not cheap and normally racers are the only ones who spend the cash on shocks of this type.

 

used to put half mc fork oil and half stp in the lever action shocks of the AH bugeye sprite I used for auto crossing. Its all about how quickly the damping fluid can pass through the metering orifices and whether you want to control the motion equally in both directions. So you can diddle with the viscosity or you can can change the valving hole size. Or you could just buy some of those Koni, or Tokikos

 

Yes, on certain shocks. When I swapped a 289 Ford into my Austin Healey Sprite years ago I put in 90 wt gear oil to handle the extra front end weight. It helped a lot.

Don