Building Shocks

[Martin S]

Something I seem to hate is building shocks and I'm never sure if I am doing it correctly. Would some of the pros in the club offer some advise on the best way to fill, bleed, how much rebound etc.
I am sure many of us would find it useful.

[Mark Townsend]

Firstly put some oil or "Green Slime" on your O rings. Assemble the shock and fill with oil. Pump the piston a few times gently to release the trapped air bubbles. Careful you don't pull too hard or you'll get an eyeful of 30wt oil!

Then either leave to settle for half an hour while you have a cuppa or stick them in a vaccuum pump (Tamiya and Ride make them) that removes all the bubbles nicely.

Another few pumps of the piston to double check air bubbles.

Then I fill 2 shocks to the same level by eye. Usually so the miniscus is 1-2mm below the top of the shock body, slide on the bladder and add any rebound foam/ o rings you want to use. I use either nothing or a little foam spacer Tamiya supply. Gently screw on the cap with the shaft fully extended. Repeat for shock 2.

Push in the shaft and compare by eye the rebound or use a Losi shock matcher. I've never used one so I can't comment but they look fairly accurate but complicated. If one is not rebounding quick enough or far enough addd a drop more oil or loosen the cap push the shaft in a little and retighten. Reverse applies if the rebound is too aggressive.

Personally I have about 50% rebound on all four shocks i.e the shaft returns to half distance. The top boys will tell you they can feel the difference between rebounds but I can't.

I reckon a little rebound helps at Bashley to return the shock to it's normal state faster than no rebound at all, but realistically you'd probably go up a spring rate if the handling was off.

Weight wise I go for 40 front 30 rear. If you need faster reacting steering go for 30 up front as well.

Hope the pros don't mind me posting my method

[Simon Crabb]

Interesting! That's not the way I've been shown how to set rebound!

The way I've been shown is to put an o ring on the shaft on the outside, then hold it right in against said o ring when you put the bladder (+sponge bob) on and tighten the cap. Test the rebound by releasing the shaft.

Usually results in same rebound all round. And about 50% ish.

(Got that off Ed's site, I think, so I'm sure he'll pitch in... don't know when he heads off tho.)

I've got one of those Losi measuring things, anyone want to try it, I can't work it out!

[Robin Howett]

For the building of shocks and every thing else have a quick look at Hara's build tips here

Its on ed's site here

www.thard.co.uk/viewtopic.php?f=24&t=29&st=0&sk=t&sd=a&start=10

[TryHard]

sounds about right Si.... www.thard.co.uk/viewtopic.php?f=24&t=61
The o-ring simply acts as a spacer to make sure you get nice consistent rebound all round You just need to make sure the ball joint is wound on the same for each shaft.

More often than not (and you all know how often I do my shocks), using that method, I'll get all 4 the same first time.

Happy to run through it with you on the weekend Martin, no doubt my shocks will want a rebuild at some point

HiH
Ed

[Martin S]

Sept 23, 2008 10:14:09 GMT Robin Howett said:

For the building of shocks and every thing else have a quick look at Hara's build tips here
www.google.com/translate?u=http% ... en&ie=UTF8

Rob , can you repeat or tinyURL.com that address as part of it is missing, or PM

[lesbaldry]

Draw the piston down while filling slowly with oil "hard to do with one hand but can be done" leave piston at the bottom and rest shocks upright on somthing suitable and stable,heat gently with hair dryer or heat gun to thin the oil and this will bring the air to the top very quickly(expands any air left in shock) opperate piston a few times and check visually for air,should be gin clear or slightly milky if air is in the oil!! push piston back to your rebound position,normaly 50% stroke lenght should give 50% rebound? slide diaphram gently across and into shock body "this should displace a small amount of oil if filled correctly" screw on top and hopefully job done?

[keitheroonie]

thanks for the advice everyone, just what i needed as tonights job is building shocks and fitting electrics.

[lesbaldry]

Keith dont worry about rebound it will confuse the hell out of you trying to get it equal...just run them nutural

[Robin Howett]

Whats nutural les? i'v not seen that on any setup sheets

[Mark Townsend]

You've got to make the rebound at least equal left to right. Or your handling will be all over the place jus like the chassis being tweaked.

[lesbaldry]

Sept 23, 2008 14:45:37 GMT Robin Howett said:

Whats nutural les? i'v not seen that on any setup sheets

would'nt know,I've never found the need to read set up sheets. ..I think it must be latin for no rebound BOB

[Martin S]

Sept 23, 2008 15:06:54 GMT Mark Townsend said:

You've got to make the rebound at least equal left to right. Or your handling will be all over the place jus like the chassis being tweaked.

Thanks for all the input guys. At West London the car was a pig but I think it was my fault. It was just like tweek, the car just wouldn't point in the right direction. One shock was losing oil, one of the E-clips had come adrift so the piston was loose. A quick fix at in the pits and a bad case of bleeding meant that the car still wasn't right so we pulled out before the last final so as not to be in the way.

Anyway with all your help I have stripped and rebuilt the Cyclone paying particular attention to the shocks to get then all the same. Just back from a quick test run at Bashley to scrub up some new 32's and it was alot better so hopefully we'll do a bit better at Cotswolds.

Martin
ps. Keith: Adam is looking forward to the Cyclone v Cyclone on 5th
pps. You've gotta see Haras tips on Cyclone building translated from Japanese by Google its on tinyurl.com/3mg9da especially 5. SHOKKUASSENBURI - thats Shock building!

[Simon Crabb]

Sept 23, 2008 17:08:26 GMT Martin S said:

pps. You've gotta see Haras tips on Cyclone building translated from Japanese by Google its on tinyurl.com/3mg9da especially 5. SHOKKUASSENBURI - thats Shock building!

"To recover the concentration will enter into meditation."

[yellowshark]

I assume you have done the physical build.
You are best served by having a shock stand that will hold the shocks vertically. Some of the car stands have these; I bought a plastic shock stand for about £4

1. Check that the two rear shocks are the same length. You need a digital vernier.
Push the piston fully in and place the calliper over the top and bottom ball joints to measure the length. If unequal you need to screw in or out one of the bottom ball joints. If you have built as per the instructions any difference in length should be very marginal. Ditto for the front 2 shocks.

2. Fully extend the piston and fill the shock body with oil. Do not squirt it in, this will trap air. Drop the oil in; by this I mean press the oil container softly so a drop comes out, no need to wait after each drop, just keep on dropping in a continuous stream of drops.
Fill the shock body right to the top; indeed slightly overfill. Set aside for a few minutes to allow the oil to settle and allow any air bubbles to rise and escape. May as well start on your next shock while you are waiting.

3. Hold the shock in one hand and move the piston up and down. Try rotating the piston too whilst moving it vertically. Personally I do not push the piston all the way up. I probably take it about 50% up, no more than 75% up. I can’t justify that statement, that is just how I do it. On the down stroke I make sure the connects with the bottom of the shock body.

4. If you have adjustable pistons then after a few push and pulls click them onto the next adjustment and carry on, then click onto the next adjustment etc, then repeat clicking down the adjustment range. This will release any air trapped in the adjustment holes

5. If you have air bubbles, set the shock down again and wait for the bubbles to expel. Then repeat 3 and 4 again until no air is present. There is a vacuum pump thingy that is meant to speed up air removal but I have only used it once and can’t say it really improved my technique/speed but to be fair I ought to persevere.

5.5 Insert the diaphragm into the cap so it is fully inserted alround with the top flat part of the diaphragm sitting level. Now Xray on different models have instructed two methods for presenting the cap to the shock body. One is presenting the cap "laid back" at an angle of around 45 degrees, the other is to present the the cap in the vertical position. These days I use the latter. I did use the former. Does it make it any difference, can't say it does. At the end of the day the whole point is to prevent air getting in.


6. Now for re-bound. The exact process will depend on your shock design. Pull out the piston fully and measure the exposed piston shaft; this is 100%. Key is getting the rear the left and right the same and similarly on the front. Personally I aim to get all 4 the same. By the same I accept a margin. So if my exposed piston length is 10mm I would aim for 7.5mm to give me 75% (I go for this as this is the recommended % by Xray). I would be happy to get 7.3 to 7.7 with a 0.2 difference between left and right. I am not saying a greater variation is bad its just that I can regularly get within that variation on first try and the car handles fine.

I assume (because you do not have an Xray) that you will either loosen the top cap or the bottom cap a couple of turns to allow oil to expel. Push the piston in fully slowly then pull it out fully slowly. Close the cap. The key on this is to use the same speed on all 4 shocks. Slow means slow and reduces the chances of air getting in. How many times you will have to do this on your shocks to get to your target I do not know. For me it is one full depression and about one half depression,. The Xray manual says 10 depressions to get to 75%!!

Final step is to check the balance between the 2 shocks. Losi have a great tool for this, its called something like a shock balancer. You screw the 2 shocks onto the balancer and it will show you if you have the same level of resistance on both shocks and also it is great for ensuring the shocks are the same length; so you can miss step 1 above.

[lesbaldry]

Blimey Pete did you eat a bowl of spaghetti letters yesterday with a small encyclopedia as desert ;D

[yellowshark]

It was probably the figs Les ;D

[oldtimeracer]

How soon before electronic computer controlled shocks are available. I see that one guy in the states has experimented with this system on his monster truck. There are no springs and no oil. The movement is controlled by small servos and damping, length of movement and "spring" rate can be programmed into a little chip using a lap top. I think they used something similar in F1 a few years ago. Sounds like a good idea to me.