12 replies to this topic

[Lost_In_Noise]

My 8466 currently looks like this, and the suspension is virtually non-functional. I bought it second-hand, but I've seen others mention this problem. It can either be that the springs are underdimensioned for the car, or that they have weared over time. To test this, I've decided to buy some new springs to tend to the problem.

With these springs:



The set originally contains 4 x "Technic, Shock Absorber 9.5L, Complete Assembly (Hard Spring)" (part no 2909c02), but I wanted to change it to four of these from the Unimog:

"Technic, Shock Absorber 9.5L, Complete Assembly (Extra Hard Spring)"



I've just ordered them yesterday, and will let you know as soon as they arrive with pics of the car.

Here is some pics of the model per today:

The main issue:



Normal state of display:



Front springs compressed, without any pressure applied:



Front spring position (neutral)



After a small bump:



Rear spring position:



After some pressure added, they return to this state:



The chassis is lowered approximately three studs, and doesn't come back up. I'm hoping the new springs will fix this issue.

[Rikus]

I own this model, too, bought used, but even changing the Shock absorbers with new ones (same type), the problem still persist, especially when playing with the model...
To better the recoil of the front suspension, without having to change the springs (or the whole shock absorbers), I exchanged the two 1x7 liftarms where under the engine with two 1x9 liftarms, attaching the shock absorbers at the tips.
Doing so, the suspension works much better, increasing efficiency by slightly reducing the tire excursion.
Tomorrow I'll take some pictures of it.

Edited by Rikus, 01 May 2012 - 12:11 AM.

[Lost_In_Noise]

Did you change it with unimog springs? They are stiffer according to the lego website. If it doesn't work with new springs, I'll try fitting two springs to each wheel like the 8880 has. That 20-year old car still has working springs.

[Erik Leppen]

I suspect the problem is not the springs, but the way they're mounted. I mean, 8448 has four of the smaller springs, which are much lighter, and 8448 has more parts so if you count the suspended mass only (so don't count the wheels) I think 8448 might even be heavier than 8466. Yet 8448 seems to hold up pretty well. lack of suspension stiffness is probably not the problem, so simply adding more of it won't do. Well, yes, it will do, but it doesn't suddenly make the suspension smooth.

By the way, I think the core of the problem is the design fault in the springs, namely that the connection point is not in line with the spring, but offset by a stud. This produces frictional forces. You could solve this by using the longitudinal axle hole instead of the one the set uses.

8880 simply suffers from way too much suspension stiffness by the way. 8448 did this way better.

[Lost_In_Noise]

The 8110 Unimog has also, as far as I can recall, offset front suspension. I have never had any problems with that returning to normal position even after putting a lot of weight on it.

Ricco @ Technicbricks wrote:

Quote

"We got a couple of questions on the geometry of the front suspension of the new LEGO Technic U400 Unimog. Some of you is wondering why the front suspension is offset by half a module.

There is a geometrical reason for this, the front axle is stabilized by a Panhard rod, the panhard rod is there to prevent the entire front axle from moving from side to side. The shock absorbers would simply be too flexible to support the front axle on their own.
When the suspension is fully compressed, the front axle needs to be centered right underneath the vehicle in order to prevent the wheels from hitting the chassis and wheels arches, when turning.
That means when the suspension is fully extended the panhard rod will make a “circular” moment that pushes the front axle slightly to the right of the vehicle.
In the real world, these geometries are balanced out by fine tuning the length the panhard rod.

So if your front axle is offset by half a module, you have built your new LEGO Technic U400 Unimog the right way.

Edited by Lost_In_Noise, 01 May 2012 - 02:40 PM.

[Choops]

You may want to add the lower bracing to the suspension also. It helps reduce the flex in the suspension and therefor the shocks dont need to work as hard.

Here is a link to some good photos
http://www.lxtechnic...xa.com/8466.php

Steve

[Lost_In_Noise]

I made some adjustments thanks to the comments made here. The results were much better, but hopefully I won't have to use these mods when the new springs arrive.

Rear Before compression:



Rear After compression:



Front before compression:



Front after compression:



The red beams are placeholders for L3 axles, to better indicate their position.





Side view, thin liftarms keeps the axles in place.



The rear suspension has a different setup, due to my parts availible.

Edited by Lost_In_Noise, 01 May 2012 - 09:40 PM.

[Lost_In_Noise]

Springs finally arrived. I've been setting it up tonight, and took some shots here:







Whole car without wheels:







standby front:



standby rear:











The front is actually in line with the rear after the new springs have been applied. See comparison in pre-mod shots.

Front before/after compression:





Rear before/after compression:





Up-close front:



and rear:



Everything works like expected, and I can recommend anyone who has the spring problem with the originals to try this out.

[S.I]

I'll have to try it, I noticed both my bought as used had worn out springs.
Have you noticed any issues with the tracking when the off roader is being pushed forward?

[Lost_In_Noise]

S.I, on 09 May 2012 - 07:29 PM, said:

I'll have to try it, I noticed both my bought as used had worn out springs.
Have you noticed any issues with the tracking when the off roader is being pushed forward?

None whatsoever. It works as you would expect.

[LegoJeeper]

thanks,  firmer springs are what Lego needs, to allow heavier builds or larger vehicles

[FR Rayward]

Well, I built 8466 and had the same problem. I modded my truck to fit yellow pneumatic shocks. I mounted 4
control boxes in the rear tray, and piped each shock to one. Worked awesome! Pump it up hard and you can
hardly push the truck down, or drop them right down for city driving, like a Range rover. The benefit of
this as well is having control over the four corners, so you can prop it up on a rock, and squash two, and
extend two, articulation looks great on the model.

Try it!

[TechnicFreak]

Wasn't this topic on the forum a month or two ago, same issue, with the springs?  I recall reading at as I bought a new, sealed 8466 recently.