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Old 02-06-2009, 07:24 PM   #1
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Default Shock rebound

Can anyone tell me what shock rebound is?When i compress my shock
(with coil spring off) it slowly extends all the way out,is this rebound?
How do I get no rebound in my shock?
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Old 02-06-2009, 07:30 PM   #2
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to get no rebound you would be looking at a improper oil level in the shock and it will not function properly.


You should have some rebound. Depending on the shock it should be about 1/4 to 1/6th the extended length.

The reason ther is rebound is becasue there is a small pocket of air that is trapped in the end (under the bladder) to allow for the expansion of the oil level as the piston compresses.

Air being Compressable vs oil that is not will give and keep the oil from gettin gair bubbles.

If you did not install the bladder and over filled shock it would not be able to compress properly and risk blowing the cap off the end.

and too little will introduce inconsistant resistance witht he introduction of air bubbles.


I hope this was not too long
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Old 02-06-2009, 07:50 PM   #3
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Thank you jdeadman,
The shocks are on a tc5r,the set up sheet in the back of the instruction
book says no rebound for front and rear shocks.Instructions for building
the shocks tell me to extend the shaft fully before installing the bladder.
If i hold the shaft(piston)half way up the body before installing the bladder
and cap will that change the rebound?
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Old 02-06-2009, 08:22 PM   #4
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Quote:
Originally Posted by mnscott View Post
Thank you jdeadman,
The shocks are on a tc5r,the set up sheet in the back of the instruction
book says no rebound for front and rear shocks.Instructions for building
the shocks tell me to extend the shaft fully before installing the bladder.
If i hold the shaft(piston)half way up the body before installing the bladder
and cap will that change the rebound?
From what I've read, yes where you have the piston in the cylinder when you put on the bladder and cap is what sets the rebound.
I seen pictures where people use a cut piece of tubing on the shaft to make sure they get the rebound the same on all shocks.
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Old 02-06-2009, 08:56 PM   #5
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Thanks Two Tone,I will give it a try.
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Old 02-07-2009, 05:20 AM   #6
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[QUOTE=TwoTone;5398275]From what I've read, yes where you have the piston in the cylinder when you put on the bladder and cap is what sets the rebound.
I seen pictures where people use a cut piece of tubing on the shaft to make sure they get the rebound the same on all shocks.[/QUOTE


The amount of oil in the shock is what sets the rebound, too much and the shock won't bottom out and will rebound to quickly, to little and it won't rebound at all, you looking for a nice slow steady rebound. With that said, It's best to build shock per the manufacturers recommendations as there are many different types of shocks and the companies know there product best.


Fuel tubing is used as a travel limiter. It basically to shortens the shaft by not allowing full down travel which lowers the vehicle. Fuel tubing is about the worst way to do this as it's hard to get fuel tubing cut straight as it is flexible. It's almost impossible to build equal length shocks using fuel tubing as a limiter. It's better to use plastic spacers or o-rings as they are more precise.
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Old 02-07-2009, 06:34 AM   #7
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Thanks trerc,
When twotone said to use the tubing I think he meant it went on the outside
of the shock(helps hold the pistons at the same positions)and remove the
tubing when the shock finished.
I tried this and now after the shock is compressed and released it extends
out half way,if I pull it out all the way it sucks back in half way.
Is this what they call no rebound?
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Old 02-07-2009, 06:54 AM   #8
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Quote:
Originally Posted by mnscott View Post
I tried this and now after the shock is compressed and released it extends
out half way,if I pull it out all the way it sucks back in half way.
Is this what they call no rebound?
No, when the shock shaft extends half way after pushing it in all the way is 50% rebound. If the shaft gets sucked back in after you pull it out all the way, you don't have enough oil in the shock (you are basically creating a vacuum that pulls the shaft back in). I generally shoot for 25 - 50% rebound. The most important part is to make them as close to the same as you can.

Here's what works for me:
1) fill the shock body to the top with oil
2) move the shock shaft in and out (with the cap and bladder off) several times. This will cause the trapped air under the piston to be "liberated"
3) let the shocks sit for 5 minutes to allow the air bubbles to escape (with the shock shaft fully extended)
4) place the bladder and cap on
5) bleed the shock to get the desired rebound. I loosen the cap slightly, push the shock shaft in slowly (forcing some oil out), then tighten the cap. Repeat until you get the right rebound, and no shock shaft sucking back in.
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Old 02-07-2009, 06:57 AM   #9
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Here's a picture of a proper Shock rebound.

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Old 02-07-2009, 06:59 AM   #10
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Quote:
Originally Posted by mnscott View Post
Thanks trerc,
When twotone said to use the tubing I think he meant it went on the outside
of the shock(helps hold the pistons at the same positions)and remove the
tubing when the shock finished.
I tried this and now after the shock is compressed and released it extends
out half way,if I pull it out all the way it sucks back in half way.
Is this what they call no rebound?
Yes that's what I meant.

I've always filled the shock to the top.

I'm going to try and find the passage I found about shock building and post it.
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Old 02-07-2009, 07:33 AM   #11
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Quote:
Originally Posted by trerc View Post
The amount of oil in the shock is what sets the rebound, too much and the shock won't bottom out and will rebound to quickly, to little and it won't rebound at all, you looking for a nice slow steady rebound. With that said, It's best to build shock per the manufacturers recommendations as there are many different types of shocks and the companies know there product best.


Fuel tubing is used as a travel limiter. It basically to shortens the shaft by not allowing full down travel which lowers the vehicle. Fuel tubing is about the worst way to do this as it's hard to get fuel tubing cut straight as it is flexible. It's almost impossible to build equal length shocks using fuel tubing as a limiter. It's better to use plastic spacers or o-rings as they are more precise.
This is the closest definition that I've read thus far and agree with just about everything mentioned. Great post trerc.

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Old 02-07-2009, 08:22 AM   #12
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OK,now i understand.I have replaced shocks on my snowmobiles,motorcycles
and cars but never rebuilt them.I didn't think the shock should retract on its own.
I didn't know how bleed a shock.
5) bleed the shock to get the desired rebound. I loosen the cap slightly, push the shock shaft in slowly (forcing some oil out), then tighten the cap. Repeat until you get the right rebound, and no shock shaft sucking back in.
I will use the tubing for constant bleeding,the trick will be to tighten the cap
before the piston tries to change direction and draws air in.
A lot like bleeding brakes on car.
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