Baja shock problem

[mini ant]

Hi all

 

Need some help here. 

 

I have just got a brand new rovan baja and was told to check the shock oil before I use it. 

 

Now I have never striped a shock a part before so I watch a YouTube video and I pulled it apart. 

 

So took the shock off baja removed spring and top cap. 

 

Now oil level look low as the video said to fill it all the way up. So I did. 

 

Put top cap on went to check it worked and it sort of did but I was not able to push the shock all the way in. I would say like only half way in then stops. 

 

So I Google and more YouTube and I have tried 4 more time and still same problem. 

 

I did see one video that pulled the bottom a part instead of the top but I have not tried this yet. 

 

Please any help guides or videos would be great. 

 

I did think about pulling the bottom a part and have a look for any problems? 

 

Just want to get this done so I can run it in. 

Thanks 

[lorrylemming]

When you put the top back on you need to have the piston fully compressed that way there is enough space in the shock for the piston and shaft. Otherwise it "hydro locks". 

 

1. Fill with oil. 

2. Pump the piston slowly to get all the bubbles out. 

3. Let the shock rest for ~10 minutes with the piston at the bottom. 

4. Slowly push the piston to the top, but not past the surface of the oil, if it goes past you'll get more bubbles. 

5. With the piston still at the top, screw the cap back on. 

6. Once you've done all 4 check they feel the same. 

 

 

 

Just tried to find a tutorial that explains this and it's really difficult. No one seems to mention it, no wonder you were struggling. 

[Mack1]

It not rovan shock but a shock is a shock so it should be similar in dismantling and assembly.

 

Shock servicing

[mini ant]

Thanks will give this a try when I get a min over the weekend and will report back. 

 

Thanks 

[Steve-O2021]

Your supposed to fill from the bottom but that's a complete ball ache.

 

As said do it like lorry said or you can add bleed screws to the shock caps or buy caps with bleed screws in 🙂

[Steve-O2021]

On 01/10/2021 at 20:33, mini ant said:

Thanks will give this a try when I get a min over the weekend and will report back. 

 

Thanks 

 

You should also check and fill the diff

[mini ant]

Update tryed the way lorry said still the same it doesn't go all the way in not far of but still a bit where as the other front one (which I have not pulled apart) goes all the way in. 

 

I pull the piston right down full up to top with oil let rest, then push piston back up slowly but all what happens is all the oil just flows over the top. Is this right or is there a problem here? 

 

Just want to get the thing back together and start running in. 

 

7 hours ago, Steve-O2021 said:

 

You should also check and fill the diff

Been told to do this as well then was to change the weight of the oil as they don't know what is fitted from new. 

 

Do you know what weight for the diff I should use? 

 

Thanks 

[Steve-O2021]

44 minutes ago, mini ant said:

Update tryed the way lorry said still the same it doesn't go all the way in not far of but still a bit where as the other front one (which I have not pulled apart) goes all the way in. 

 

I pull the piston right down full up to top with oil let rest, then push piston back up slowly but all what happens is all the oil just flows over the top. Is this right or is there a problem here? 

 

Just want to get the thing back together and start running in. 

 

Been told to do this as well then was to change the weight of the oil as they don't know what is fitted from new. 

 

Do you know what weight for the diff I should use? 

 

Thanks 

 

10k from what I saw.

 

Shocks -

 

 

-Empty the shock

- set piston down at bottom / full extension

-Fill shocks

- pump up or down about an inch or 2 to release air

- push piston fully up slowly and allow excess fluid to spill out

- put cap on while piston fully up

 

Should be OK now

 

Edited October 3, 2021 by Steve-O2021

[mini ant]

Hi right had another go, got the problem one working so pulled the other front one apart did the same to that one. 

 

Now both the same feeling. 

 

I would say I not 100% happy but I think it will be fine. 

 

Going to do some running in then a recheck. 

 

Can I ask what weight oil should I use for front and back? Got no plans to go jumping with it lol. 

 

Right on to the diff now. 

Thanks again for all the help. 

 

[Steve-O2021]

Think I went 50 front and 15 rear but will depend on weight of car eg if it's all alloy parts fitted and the number of holes in the pistons etc. 

Edited October 6, 2021 by Steve-O2021

[Nitroholic]

On 03/10/2021 at 21:14, mini ant said:

I pull the piston right down full up to top with oil let rest, then push piston back up slowly but all what happens is all the oil just flows over the top. Is this right or is there a problem here

Hate to state the obvious ..... but the whole point of the 'damper' system is the restriction in flow of the oil by the holes in the piston. If your oil just flows through the holes like water, you have no damping. So when you push the piston up....the oil is pushed up and will overflow out hte top of the damper. It will try and suck the oil back down....but as the seals are not perfect...it will usually just draw in air bubbles.

 

It also makes not one bit of difference where the piston is when you screw the cap on. The only thing that matters is you don't have air bubbles trapped under the piston. Pumping the piston up and down a bit...letting it settle...then doing it again...until no bubbles come up does the trick.

 

HPI uses to supply different pistons with differing holes to vary the damping, so with that, oil weights and different springs, you can spend forever googling 'the best shock setup' getting several million differing opinions, and spend ages tinkering with your shocks to get them to behave perfectly. Only they never do. Your Baja will always handle like crap, hang the tail out, and generally be a handful. And just when you think you have it perfect, the o-rings will start weeping, and its time to start over. The 6mm shafts are better than the older 4mm...but they all rely on 2 o-rings, not a proper seal. The basic problem is the shocks on a Baja are a bad design. Too narrow for the length, and not enough oil volume...so as soon as they get warm, the damping fades. The heavier you make your buggy...the worse this will get. £100 on a set of IRC big bore shocks is the cure. Or else do what I did....stop chasing 'handling' and have fun with a car that goes sideways like a high powered shopping cart.

[Steve-O2021]

1 hour ago, Nitroholic said:

 

It also makes not one bit of difference where the piston is when you screw the cap on.

 

 

As long as he doesnt fill them right to the top with the piston down and then just screw the cap on as they would be rock solid near enough lol..

 

[Nitroholic]

You might want to think about the physics of that....

the piston moves through the oil and takes up the same volume where ever it is in the shock. There is no 'air gap' ..... or why did you fit caps with bleed screws on yours?

 

The damping is derived from teh oil passing through the holes in the shock piston. Bigger holes or thinner oil gives less damping. More restrictive pistons with smaller hoels or thicker oil gives more damping. Usually folk change oil thickness as its easier to do. Really...they should tune the piston. I had a whole range of pistons for the shocks on my old MCD. You can't hydro-lock a piston with holes in.

 

If your shocks lock up when you push them...you have used an oil far too thick for purpose. HPI spec 5W oil as standard.

[Steve-O2021]

5 hours ago, Nitroholic said:

You might want to think about the physics of that....

the piston moves through the oil and takes up the same volume where ever it is in the shock. There is no 'air gap' ..... or why did you fit caps with bleed screws on yours?

 

The damping is derived from teh oil passing through the holes in the shock piston. Bigger holes or thinner oil gives less damping. More restrictive pistons with smaller hoels or thicker oil gives more damping. Usually folk change oil thickness as its easier to do. Really...they should tune the piston. I had a whole range of pistons for the shocks on my old MCD. You can't hydro-lock a piston with holes in.

 

If your shocks lock up when you push them...you have used an oil far too thick for purpose. HPI spec 5W oil as standard.

 

 

But what about the mass of the piston that will be trying to displace the fluid? That fluid  won't have anywhere to go if the shock is filled to the top while the piston is fully out and the cap fitted

 

Traxxas guide 

 

[Nitroholic]

Of course it has somewhere to go ...... what do you think the HOLES in the piston are for? The oil goes THROUGH the holes. How do you think it moves at all? The piston moving through the oil at the top, at hte bottom, or halfway up is all the same.

 

The oil passing through the holes in the piston is how damping works?

 

"mass of the piston?' what has that got to do with it? If you are meaning the volume of the piston....then that is the same WHEREVER the piston is in the shock. Fluids don't compress ( thats how hydraulics work ).  If you put a piston in with no holes in it....it would lock up. The fluid cannot compress and cannot move past the piston. But your piston has holes in it to allow a restricted flow of oil. This allows movement...but slows it down as it can only move as fast as the oil can flow. Thats called..DAMPING.

 

The only reason anyone tells you to move hte piston to the top is to make it easier to exclude air. Air in here is bad, as it will create bubbles that effectively froth the oil up, making it easier for it to get through the piston...taking away your damping. The space the piston takes up does not matter....it takes up THE SAME SPACE wherever it is in the shock. You can even see in the traxxas pic..as the piston moves up and down in the diagrams...the oil level doesn't change.

[mini ant]

Hi

I agree with you nitroholic and this is why I was asking the all the question. 

 

That's is why I thought the holes where blocked but they was not. 

 

But I can say that if I screwed the cap on with any of the shock sticking out, then there was no why of the shock going back in all they way. 

 

The only way the shock goes all the way in is the when you push the shock all the way in then screw the cap on. 

 

Now I don't know if I have a problem with the shock or the oil is wrong (came with car no idea of weight as it does not say on it) 

 

I did read somewhere that depends on where you have shock sticking out before you screw the cap on that is the rebound setting but I don't know. 

 

Thanks 

 

 

[spents]

not trying to step on anyones toes here or anything,

but shocks should always be bled and caps fitted with the piston at top of the stroke,

as above, fill the shock, move piston up and down to remove air bubbles, then move piston fully to top of the stroke, fit cap,

thats why excess oil spills over cos the pistons rod is now taking up space inside the shock,

its not the actual piston that causes the shocks to lock up, but the shock rod when the shocks compressed,

just my ten pence worth 

Edited October 7, 2021 by spents

[Steve-O2021]

11 hours ago, Nitroholic said:

Of course it has somewhere to go ...... what do you think the HOLES in the piston are for? The oil goes THROUGH the holes. How do you think it moves at all? The piston moving through the oil at the top, at hte bottom, or halfway up is all the same.

 

The oil passing through the holes in the piston is how damping works?

 

"mass of the piston?' what has that got to do with it? If you are meaning the volume of the piston....then that is the same WHEREVER the piston is in the shock. Fluids don't compress ( thats how hydraulics work ).  If you put a piston in with no holes in it....it would lock up. The fluid cannot compress and cannot move past the piston. But your piston has holes in it to allow a restricted flow of oil. This allows movement...but slows it down as it can only move as fast as the oil can flow. Thats called..DAMPING.

 

The only reason anyone tells you to move hte piston to the top is to make it easier to exclude air. Air in here is bad, as it will create bubbles that effectively froth the oil up, making it easier for it to get through the piston...taking away your damping. The space the piston takes up does not matter....it takes up THE SAME SPACE wherever it is in the shock. You can even see in the traxxas pic..as the piston moves up and down in the diagrams...the oil level doesn't change.

 

Ok, simple test 🙂

 

Fill your bath to the brim / top  (bath is acting as the shock body, water is the shock oil)

 

Now get in the bath  (your body is acting as the rod)

 

Water will overflow to get out as your volumetric mass has technically took the space where the water was.

 

Even if your body had holes in it its still going to displace the water....

 

So where is the excess shock oil going to go when the rod enters the shock chamber? 

 

It can't overflow as it's a sealed unit so the shock will go solid or blow a oring and leak out

 

 

Edited October 7, 2021 by Steve-O2021

[Nitroholic]

congratulations....you just demonstrated Archimedes principle.

 

Wrong. Not Archimedes. He was correct.....just wrong here, as this is not what happens. Look at the diagram you put just above. You are talking about what happens when you introduce an additional volume into a system.

Because your shock piston was IN the shock when you filled it, not outside, this isn't what happens. Unless, of course, you found a way to put the shock shaft and piston in after you put the cap on. The shaft and piston assembly doesn't come out while you fill and the system is not sealed while you do it.

 

Repeat your Archimedes experiment, but fill the bath while you are in it. Your volumetric mass does not affect the system as you fill the shock up WITH THE PISTON IN THE SHOCK. You don;t remove the piston from the bore area while filling, and usually...it's not possible as the shock rod end will not allow the piston to leave the tube.

 

So, the piston volume is never displaced, as that volume never contains oil. In order to create your scenario above...you would need to remove the piston from the shock body.......fill up the shock to the brim with the oil, then.....and I will be impressed if you can do this bit....seal the system up before you put the piston in......then introduce the piston while the system remains sealed. THEN you would hydraulically lock the system, and the piston wouldn't go in.

The sealed system would not allow the oil displaced by the piston to go anywhere.

 

The flaw here is you simply can't actually do that.

 

Fill the shock body to the brim, put in the piston...and and excess overflows before you put the cap on as the piston displaces it.

 

But....if you fill up the shock with the piston IN the shock, like you are supposed to, the oil can only fill the space left. The piston is in the oil volume and you don;t get spillage. Move the piston up and down gently to make sure you get rid of air bubbles.

 

Lost count of how many shocks I have rebuilt in the last 20 years.......but I have yet to have one 'lock solid' or blow its seals out.

[Steve-O2021]

1 hour ago, Nitroholic said:

congratulations....you just demonstrated Archimedes principle.

 

Wrong. Not Archimedes. He was correct.....just wrong here, as this is not what happens. Look at the diagram you put just above. You are talking about what happens when you introduce an additional volume into a system.

Because your shock piston was IN the shock when you filled it, not outside, this isn't what happens. Unless, of course, you found a way to put the shock shaft and piston in after you put the cap on. The shaft and piston assembly doesn't come out while you fill and the system is not sealed while you do it.

 

Repeat your Archimedes experiment, but fill the bath while you are in it. Your volumetric mass does not affect the system as you fill the shock up WITH THE PISTON IN THE SHOCK. You don;t remove the piston from the bore area while filling, and usually...it's not possible as the shock rod end will not allow the piston to leave the tube.

 

So, the piston volume is never displaced, as that volume never contains oil. In order to create your scenario above...you would need to remove the piston from the shock body.......fill up the shock to the brim with the oil, then.....and I will be impressed if you can do this bit....seal the system up before you put the piston in......then introduce the piston while the system remains sealed. THEN you would hydraulically lock the system, and the piston wouldn't go in.

The sealed system would not allow the oil displaced by the piston to go anywhere.

 

The flaw here is you simply can't actually do that.

 

Fill the shock body to the brim, put in the piston...and and excess overflows before you put the cap on as the piston displaces it.

 

But....if you fill up the shock with the piston IN the shock, like you are supposed to, the oil can only fill the space left. The piston is in the oil volume and you don;t get spillage. Move the piston up and down gently to make sure you get rid of air bubbles.

 

Lost count of how many shocks I have rebuilt in the last 20 years.......but I have yet to have one 'lock solid' or blow its seals out.

 

 

It's OK you have made a mistake and miss read my post and got confused, people make mistakes 🙂

 

You said the piston can be positioned anywhere when it is capped

 

I Said as long as he didn't just fill the shock with the piston fully down and cap it.

 

Then you said to start thinking about the physics which I did 😉

 

A shock that is fully extended and then filled to the top  and then capped while the piston is still fully extended  won't compress as it is too full as the piston rod will be trying to fit in as well (the piston rod will need space unless you have some magical shocks that don't use a traditional piston rod assembly) 🙂

 

 

 

 

Edited October 7, 2021 by Steve-O2021

[Nitroholic]

Funny how my shocks just seem to work....... but hey. You do you. Must be magic