oil filling in piggyback shocks?

[v4impactor]

This is my first set of piggy back shocks, and i'll admit I am a complete idiot. What is the proper way to fill them. Should both the shock body and piggyback be completely full or do I only fill the main body and leave the piggyback empty. I've used the search feature and didnt find anything really useful

[Terranaut]

What shocks are they? I suspect not all shocks are made the same. Is the reservoir functional?

I serviced a set of piggybacks for a friend. I found the reservoir was mostly occupied by a cylinder of closed cell foam rubber, which acts like a bladder, so I filled them completely with oil. If there is no diaphram or bladder of some sort you should leave a little air space in them.

Cheers.

[dale3311]

i was told by my hobby shop not to fill the piggybacks

[WarMachine]

Correct me if I'm wrong, but I too was under the assumption that you don't fill the piggy back res. I always figured it acted as an air cushion on hard landings, allowing some initial shock absorption before your valving takes over. If I'm not off my rocker it also allows you to fill the shock body completely, thus keeping the air bubbles to a minimum when the shock cycles.

[Espeefan]

Actually, you should fill the reservoir, and there is a bit of a technique to it. If you don't fill the reservior, then you'll have all kinds of air in the shock and it will never be smooth. The problem with piggy back shocks is that they are darn near impossible to get all of the air out of them, but you can get close. Those foam cushions you see inside the reservoir also trap air. They are supposed to compensate for changes in oil volume, as the shock compresses and rebounds quickly. For crawling, piggy back shocks are not really needed. They don't do much, but they look nice.

Anyway, filling these things can be a headache. I've had the best luck by filling the shock up, as you would a normal shock, without the piggy backs screwed on yet. Start with the piston all the way down. Fill the body with oil, all the way to the top. Slowly work the piston up one time. Top off the oil, if you need too. Slowly pull the piston back down. I cannot stress how slow you must go. The idea is to get one big air bubble at a time (you will get more then one), to rise to the top and escape. If you go fast, you'll get millions of little bubbles, and you'll have to wait forever for them to escape. Top the oil off again, after the piston is down all the way. Repeat this procedure slowly, until you don't get anymore air bubbles.

Now comes the fun part. With the piston at the bottom of the body, screw on the reservoir. Flip the whole shock upside down, quickly, and fill the reservoir up at least half way. Now, slowly push the piston in (compress the shock) and let the bubbles rise out of the oil inside the reservoir. Pull the piston back down. Repeat this a couple times too, until you don't see any bubbles. Now, if you want to use the foam compensators, it's time to install them. Like I said, these things hold air, so as you drop them into the reservoir, you'll see bubbles again, and the foam will constantly try floating to the top of the reservoir, where there is no oil. Don't let them. In fact, it might be a good idea to pre-soak the foam compensators in a separate bowl of shock oil, previous to this step. This will help reduce some of the headaches. Anyway, once the foam compensators are well soaked, top off the reservoir. Add some oil to the reservoir caps. It will get messy, so be prepared. Quick as you can, take the reservoir cap, and install it. Keep the reservoir in the same position as it was when you started to bleed air out of it. Crank down the cap and catch the excess oil. When it's tight, you should be done.

Work the shock up and down some, and feel for any air trapped inside. If there is air, you'll feel a lack of resistance, through certain points of the shock stroke. Usually top or bottom. You want one smooth, fluid motion, and a constant resistance. If you notice less at the top or bottom of the shock travel, that's air. Like I said, it's impossible to get all the air out, but you can come close. If it's not bad, live with it. If the resistance drops off for a good portion of the shock's travel, you'll have to re-do the procedure. When you crack it open, you'll see just how bad it is, by looking at the bubbles, or maybe some type of foamy oil.

I don't much care for piggy back shocks, but feel free to try them.

[RobCam]

great tutorial. i had a huge headache filling a set in the past

[v4impactor]

Wow, thanks for the tutorial, I'm filling them as I read this right now, so i'll give it my best.

[WarMachine]

Indeed I stand corrected, thank you

[Everestno0b]

Hate to revive a dead thread but, here I go doing it anyway! What about remote reservoir "piggyback" shocks. I can't find anything anywhere on them except ONE and they were air shocks. Not oil. I've a set of oil and the reservoir has a metal piston, spring, and backplate for inner spring.....but the metal piston has no o rings on it. Now, the kit comes with a bunch of o rings that fit the piston but make it so tight inside the reservoir I can't see it working right....no instructions came with them either. I'm confused lol

[Phildirt]

Originally Posted by Everestno0b

Hate to revive a dead thread but, here I go doing it anyway! What about remote reservoir "piggyback" shocks. I can't find anything anywhere on them except ONE and they were air shocks. Not oil. I've a set of oil and the reservoir has a metal piston, spring, and backplate for inner spring.....but the metal piston has no o rings on it. Now, the kit comes with a bunch of o rings that fit the piston but make it so tight inside the reservoir I can't see it working right....no instructions came with them either. I'm confused lol

What would be the benefit of a true reservoir shock on a scale truck? I don’t think they need the extra fluid capacity, they don’t get hot.


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