proper shock rebound

[JoeF]

Just bought my first after market shocks for my stampede. Put the oil in and pressed the piston and it rebounded back almost all the way out. Then checked the stock shocks I removed from the car and there is no rebound at all. I emptied and refilled the stock shocks for later use. But when i depressed the stock piston there is no rebound. I chatted with Traxxas support and they said that was okay. The stock shocks do not rebound according to the Traxxas spec. Both sets of shocks were loaded with 30 wgt. oil. The youtube sessions I watched show the shocks rebounding. I am confused, should they rebound out or not. Any feedback? Thanks.

 

[WickedFog]

Just bought my first after market shocks for my stampede. Put the oil in and pressed the piston and it rebounded back almost all the way out. Then checked the stock shocks I removed from the car and there is no rebound at all. I emptied and refilled the stock shocks for later use. But when i depressed the stock piston there is no rebound. I chatted with Traxxas support and they said that was okay. The stock shocks do not rebound according to the Traxxas spec. Both sets of shocks were loaded with 30 wgt. oil. The youtube sessions I watched show the shocks rebounding. I am confused, should they rebound out or not. Any feedback? Thanks.

Rebound is caused by pressure built up behind the shock piston. It is likely your stock shocks are not as well sealed as the aftermarket ones. This lack of sealing allows the pressure to bleed off, suck air in when the shock is deployed, and bleed back off on compression. The holes in the shock piston will also account for some rebound if they are small enough.

 

[Greywolf74]

Did you bleed the air out of the shocks before putting the bladder in them?

 

[JoeF]

Yes I did bleed all the air out. The after market shocks behave just like a car shock. The stock shocks just sit there. Traxxas told me the rebound comes from the springs ????. If that is the case, why do they need the shocks. Thanks for all our feedback.

 

[Greywolf74]

Yes I did bleed all the air out. The after market shocks behave just like a car shock. The stock shocks just sit there. Traxxas told me the rebound comes from the springs ????. If that is the case, why do they need the shocks. Thanks for all our feedback.

The springs are supposed to be to push the shafts out to their intended length. The shock oil inside controls how fast the shaft can be compressed. Got a pic of the stock shock piston and the after market shock piston?

 

[WickedFog]

Without oil in the shock, the springs would cause the car to bounce up and down. The oil shock dampens that.

In automotive shocks, compression and rebound is controlled by valves in the shock pistons. The compression and rebound can be different in a shock by way of one way valves. The compression ports will typically be smaller than the rebound ports to soften bumps, but allow the shock to quickly rebound into dips because the oil can flow faster on the rebound stroke.

Drag shocks are setup this way but are more drastic. Rebound basically has very little resistance, while compression is very firm. This allows the car to lift on launch, the front wheels quickly extend to the pavement, and compression is there to keep the front end up, so it keeps the weight on the rear of the car.

In the RC world, there isn't any control over that, as we just have holes through the pistons that allow the same flow each way.

I think the term "rebound" has been associated with the shocks (without springs) rebounding on there own due to internal pressure. It's technically not what the term rebound means. Maybe I am reading comments wrong here and there, but that is what it seems people are referring to sometimes.

So yes, the springs are there to cause your shocks to rebound, and keep the car lifted off the ground.

 

[tntpoof]

stock shock as said by traxxas already dont rebound unless compressed .its a little deeper than just the spring shock piston holes count shock oil weight along with spring

 

[Dan B.]

Yes, Traxxas shocks do rebound if properly set up. How much they should rebound is a hotly debated conversation. I never set mine to rebound more than around 1/3 stroke.
That said, the reason Traxxas shocks may not rebound is the notoriously bad plastic caps or diaphragm not seated properly.
The youtube vids you watched were correct. They should rebound.

 

[JoeF]

Thank you. You helped clarify what my thinking was. I will play with my stock shocks some more. If I need to get new caps I might as well replace the whole shock with the aftermarket units that are all aluminum.

 

[Dan B.]

Yes I did bleed all the air out. The after market shocks behave just like a car shock. The stock shocks just sit there. Traxxas told me the rebound comes from the springs ????. If that is the case, why do they need the shocks. Thanks for all our feedback.

Traxxas technical support is the worst in the industry. I think the custodian must answer the calls. Just for grins and giggles, call and ask them about their spring rates some time. Last time I did they said “stock spring rate is black.” I’m like, yeah, I see the black stripe, but what’s the rate? “It’s black!” I asked about the pink ones, are they a higher or lower rate? He said “pink are the optional springs.” It was a total “who’s on first” routine that went on for quite some time and yielded absolutely zero useful information. If you called Losi, Associated, Tekno, etc. and asked the same question you’d be directed to an actual professional that would tell you not only the spring rates, but how to set them up with specific fluid weights, what damping discs to use, the effects of smooth tracks, fast tracks, jump heights, temperature, etc. The Traxxas forum isn’t very helpful as others either. You can’t even find setup sheets that aren’t years old. In all fairness though, Traxxas is geared toward noobs and bashers, and they offer a pretty good product for them, IMO. They seldom ever get around a track faster than a Losi 22 or an Associated 10 series, but they’re not nearly as fragile either. I still very much enjoy bashing my Traxxas 1/10 SCT’s.
Enjoy playing with your setup, make one change at a time, and keep track of it all by printing some blank setup sheets and using them.

 

[VSK$78]

Just bought my first after market shocks for my stampede. Put the oil in and pressed the piston and it rebounded back almost all the way out. Then checked the stock shocks I removed from the car and there is no rebound at all. I emptied and refilled the stock shocks for later use. But when i depressed the stock piston there is no rebound. I chatted with Traxxas support and they said that was okay. The stock shocks do not rebound according to the Traxxas spec. Both sets of shocks were loaded with 30 wgt. oil. The youtube sessions I watched show the shocks rebounding. I am confused, should they rebound out or not. Any feedback? Thanks.

Depends on what kinda rebound u want

 

[RustyUs]

What VSK$78 said. No wrong answer on proper shock rebound. How much shock rebound you want, and if you use bladders, or no bladders... it's all a personal preference on how you put your shock package together.

1/10 scale, or 1/8 scale RC shocks... I prefer emulsion/bleeder caps, and skip the bladders all together.

Without oil in the shock, the springs would cause the car to bounce up and down. The oil shock dampens that.

In automotive shocks, compression and rebound is controlled by valves in the shock pistons. The compression and rebound can be different in a shock by way of one way valves. The compression ports will typically be smaller than the rebound ports to soften bumps, but allow the shock to quickly rebound into dips because the oil can flow faster on the rebound stroke.

Drag shocks are setup this way but are more drastic. Rebound basically has very little resistance, while compression is very firm. This allows the car to lift on launch, the front wheels quickly extend to the pavement, and compression is there to keep the front end up, so it keeps the weight on the rear of the car.

In the RC world, there isn't any control over that, as we just have holes through the pistons that allow the same flow each way....

There are pistons available out there that will affect damping/rebound differently depending on direction of pistons, thickness of valves, or two stage piston direction. Pictured below is VRP's GameChanger pistons and are the latest design that I know of.