Over time dirt and crud can collect on your shocks and affect their response leaving your truck with inconsistent performance. Regular shock maintenance will give you more consistently responsive shocks and therefore truck!
Today I will go over a general guide on how to rebuild your oil filled shocks. For this demonstration I will be rebuilding one of the HPI Blitz ESE’s stock shocks, however, most shocks are constructed in the same manner. If you are building the shocks for the first time you can skip the disassembly portion
Reasons for rebuild:
- Changing oil weight
- Performing shock maintenance
- Building new shocks (okay you aren’t ‘rebuilding’ here!)
Remove the shocks from your truck. I would recommend rebuilding all the shocks at the same time. Generally the shocks are mounted on your truck at two places – the a-arm and shock tower. Remove the bolts at these two locations.
- Clean the shocks if they are dirty – a used toothbrush is great for this task
- Inspect the shocks while compressing them a few times to see if they may be leaking oil. If you notice anything more than a trace of oil you may have some worn out parts that need replacing.
- Remove the spring cap – compressing the shock while applying pressure on the shock cap and spring cap will pop it off
- Remove the spring
- Remove the shock cap and empty out the spent oil
- Remove the shock mount at the end of the shaft – pliers on the shaft and unscrewing with an Allen wrench through the mounting hole does the trick
- Slide the shock piston through the shock body and remove
- If your shock has it, remove the lower part of the shock body to gain access to the o-rings
With the shock fully disassembled, clean and inspect each of the components for wear and tear or other signs of damage – cracks, bents, etc…. If the shaft is slightly bent you may be able to bend it straight, otherwise replace bent shafts. Bent shafts will not allow the shocks to perform correctly and will contribute to leaks. O-rings are another component that can contribute to leaks if they are worn.
Now is the time to change the shock springs/piston/oil weight if you plan to….these components are part of a system – the shocks – so to see the effect of changing a component, keep the other components the consistent. Experiment with each of the three parameters to find what works best for your truck for the track you are running on. (overly simplified! )
Springs affect how your truck reacts to terrain conditions. Stiffer springs will give you less traction/less chassis role and are often better for smoother terrain. Softer springs give you more traction/more chassis roll and are better on bumpier terrain. Spring preload affects the truck’s ride height.
The holes in the pistons control how much oil can move through them affecting the dampening ability of the shocks. If you want a stiffer reaction, change to a piston with fewer or smaller holes. Stiffer dampening means your shocks will react slower to changing terrain – i.e. good for landing jumps. If you want a softer reaction, change to a piston with larger or more holes. Softer dampening means your shocks will react quicker to changing terrain – i.e. giving you more traction.
Shock oil weight has a similar effect as the piston hole sizes. A thicker weight is like having a piston with smaller holes. And a lighter weight is like having pistons with larger holes.
Reassemble the shocks working in reverse order of the disassembly steps above. Lubricate any o-rings with some of the oil you will be using.
Before putting the spring and spring cap back on fill the shock with the new oil and cap it off.
- Start with the piston at the bottom of the shock body
- Fill the shock about 3/4 of the way with oil
- Slowly move piston up and down while keeping it submerged in oil. This will release any air bubbles in the shock
- Set the shock aside for a few minutes to let any remaining air bubbles come out and repeat moving the piston up and down slowly
- Add more oil to fill the shock almost to rim with oil – about 1/8 inch from that rim is good
- Ensure the diaphragm/o-ring in the shock cap is seated correctly is there is one
- Push the piston about 3/4 way into the shock body, raising the oil level. This will allow the cap to be put on with minimal air in the oil
- Tilt the shock slightly to one side and screw on the shock cap. Your shocks may have a bleeder hole to allow excess air/oil to escape as you tighten the shock cap (more below)
- wipe off any excess oil
- Continue installing the spring and spring cap!
Shocks can have different methods for bleeding air/excess oil but not all shocks have this feature. Some have a bleeder hole that works when the cap is close to being tightened and others have a bleeder hole that accepts a set screw after you have let out the excess air/oil. Refer to the specific manufacture instructions on this aspect.
With the shock fully assembled compress the shock a few times making note of the sound produced as you compress it. You should hear a fluid sound of the oil moving through the piston. If you hear any ‘sloshing’ or ‘bubbling’ sounds then you likely have air bubbles in the shocks. Remove the cap, add more oil and try again.
Install the shock back onto your truck like how it was removed.
That’s all there is to rebuilding oil filled shocks!! Take your truck for a spin and see if you notice a difference in its performance. Check out our video on changing shock oil.