Suspension questions

[ianc]

Hi - I've built a "bad road" camper based on the Mercedes Vario 814DA (4x4). I switched to single wheel rears bu am now back to duals because it felt too tail happy. You see the camper over on: http://www.expeditionportal.com/forum/threads/78237-Pre-birth-of-a-camper-No-laughing!/page37

I've made some improvements in the handling by replacing most of the suspension rubber components and also the shocks with Koni adjustables. I still feel the camper is too quick to jump around and become unstable on moderately poor European roads. I think the next thing I want to look at are the spring rates, suspension travel and the anti sway bars.

The questions
1) What suspension travel and sag (the amount the suspension would extend if jacked up) is there on the standard and the ATW modified 4x4 Fusos?
2) That sort of anti-sway bars are typically fitted (none, light, heavy..)? Asking this because the Vario has 55mm bar in the back and about 40mm in the front.

I'm asking these questions over here because I'm hoping to be able to leverage all the experience in modifying the Mitsubishis. I cant find anyone who's made similar changes to the Vario.

Thanks

Ian

 

[gait]

Nice build.

I don't have the measurements asked for. My impression is the springs (both original and atw) are more rigid than soft. Just a guess from when I changed springs but sag is about 50-75mm. I could be wildly out.

To the best of my knowledge no anti-sway bars on my canter. The canter is bog simple, just leaf springs and axles. Steering became a tad less responsive with bigger tyres and I paid more attention to alignment (including camber kit) which discovered a bent steering connection.

Just some random thoughts after reading the build.

Silly question - have you checked rear wheel alignment? Yup, I know it can't be wrong, but .......... truck alignment guys are set up to check it.

I could also be wildly out but when designing I was concerned about the centre of gravity (front to back as well as vertical), the roll centre (more important for solid front axle than independent front suspension due to roll steer), and weight distribution (moment of inertia is proportional to square of distance from c of g). Last bit is about heavy weights at extremities add to pitch, yaw and roll. Yaw and roll effect steering.

What happens in a high side wind?

Have you tried something silly sounding like adding a big mass above or just in front of the rear axle (or wherever may be best to shift centres and distribution depending on relative front/back axle weights). Something like a full bladder from a water bed or some used air bags from container packers. On the basis that any test that shifts the problem (or not) helps the diagnosis - but may also be a red herring.

 

[alan]

Hi Ian,
Normally suspension droop or sag is 1/3 of your suspension travel, more than this may indicate your springs are to soft and need extra leafs fitted or a complete new spring pack made.

Hi - I've built a "bad road" camper based on the Mercedes Vario 814DA (4x4). I switched to single wheel rears bu am now back to duals because it felt too tail happy. You see the camper over on: http://www.expeditionportal.com/forum/threads/78237-Pre-birth-of-a-camper-No-laughing!/page37

I've made some improvements in the handling by replacing most of the suspension rubber components and also the shocks with Koni adjustables. I still feel the camper is too quick to jump around and become unstable on moderately poor European roads. I think the next thing I want to look at are the spring rates, suspension travel and the anti sway bars.

The questions
1) What suspension travel and sag (the amount the suspension would extend if jacked up) is there on the standard and the ATW modified 4x4 Fusos?
2) That sort of anti-sway bars are typically fitted (none, light, heavy..)? Asking this because the Vario has 55mm bar in the back and about 40mm in the front.

I'm asking these questions over here because I'm hoping to be able to leverage all the experience in modifying the Mitsubishis. I cant find anyone who's made similar changes to the Vario.

Thanks

Ian

 

[ianc]

Nice build.

I don't have the measurements asked for. My impression is the springs (both original and atw) are more rigid than soft. Just a guess from when I changed springs but sag is about 50-75mm. I could be wildly out.

To the best of my knowledge no anti-sway bars on my canter. The canter is bog simple, just leaf springs and axles. Steering became a tad less responsive with bigger tyres and I paid more attention to alignment (including camber kit) which discovered a bent steering connection.

Hi Julian. I've reverted to the factory fit 17.5" wheels so I probably don't need a camber kit. Which is just as well as I'm pretty sure no one makes them for the Vario

Just some random thoughts after reading the build.

Silly question - have you checked rear wheel alignment? Yup, I know it can't be wrong, but .......... truck alignment guys are set up to check it.

I had the alignment (front and rear) checked twice. Once by a company which I decided I didn't trust after they did it and then by a company that let me watch while they were doing it. It's aligned.

I could also be wildly out but when designing I was concerned about the centre of gravity (front to back as well as vertical), the roll centre (more important for solid front axle than independent front suspension due to roll steer), and weight distribution (moment of inertia is proportional to square of distance from c of g). Last bit is about heavy weights at extremities add to pitch, yaw and roll. Yaw and roll effect steering.

What happens in a high side wind?

Interestingly, despite the fact that it's high (3.5m) and is pretty slab sided, it behaves very well in high side winds. Even when its gusty.

The front axle on the Vario is also solid with two leaf parabolic springs. The available suspension compression on the front was only about 50mm before hitting the buffers (That's before I sliced the buffers in half!). That's part of the reason for asking the questions. I've looked at a number of other 814DAs and this seems to be the norm. However I think its grounding out way too early.

Have you tried something silly sounding like adding a big mass above or just in front of the rear axle (or wherever may be best to shift centres and distribution depending on relative front/back axle weights). Something like a full bladder from a water bed or some used air bags from container packers. On the basis that any test that shifts the problem (or not) helps the diagnosis - but may also be a red herring.

Not specifically, but my baffled fresh water tanks are over and just in front of the rear axle. Empty or full (500l) doesn't seem to make much of a difference.

Wheelbase is 3.7m, rear overhang is 2.1m and its 3.5m high and 2.3m wide, overall length is about 7m. Distance between the outer walls of the rear wheels is 2200mm. Box construction is fairly standard 2mm GRP, 4mm ply, 50mm dense foam and 2mm GRP.
The axle loads are 2500kg on the front (max is 2800kg) and 3300kg at the back (max is 5500kg). So loaded weight is 5800kg on a 7500kg rated chassis. There is comfortably 120mm of travel left in the rear suspension before it even begins to touch the bump stops and the stops have a lot of give in them ( I know the rear is too ridged because the bump stops have never been hit).

 

[ianc]

Hi Ian,
Normally suspension droop or sag is 1/3 of your suspension travel, more than this may indicate your springs are to soft and need extra leafs fitted or a complete new spring pack made.

Agreed - That is about the ratio I'd be thinking. I know the current figures are not good (see response above) I'm trying to understand what amount of travel would be good. I can then determine if I can address it with airbags (and removal of a leaf in the rear) or I need to get new springs fabricated.

 

[dlh62c]

The front axle on the Vario is also solid with two leaf parabolic springs.

Do you have parabolic springs fitted on the rear as well?

 

[ianc]

Three leaf Parabolic springs (tapered along their length) on the rear. One of the three (the thickest) only starts to act when the rear axle gets to about 3200kg load. I'll try to take a picture to make it clearer.

 

[gait]

another silly question .... have you tried pumping tyres up to max rated pressure to see if that changes things?

 

[ianc]

another silly question .... have you tried pumping tyres up to max rated pressure to see if that changes things?

Nope Not these tyres - I'll try that. I'm currently at 95psi and I think they go to 105 max.

I did play around with the pressures when I still had the big singles on. Originally running at about 85psi. then reduced to 65psi at Continental's recommendation. This made the ride less choppy & bouncy (Good) but a small amount more vague. On balance the lower pressure was better. However it was a different tyre set-up

 

[ianc]

I'm still keen to know what the suspension travel is on the standard and ATW vehicles - if anyone can help on this.

 

[ianc]

Three leaf Parabolic springs (tapered along their length) on the rear. One of the three (the thickest) only starts to act when the rear axle gets to about 3200kg load. I'll try to take a picture to make it clearer.

Here's the best picture I can get of the rear spring without removing the wheel (It's raining heavily today). You can see the 2 lighter leafs on top and the heavy one just engaged at the bottom of the stack


There are a couple of pics of the front

Note that the buffer beside the shock has been halved in size (I cut it). You can still see the very small travel in the buffer further down the spring

 

[gait]

its probably nothing but I'd look very closely at the discolouration to the left of the second buffer just in case there's a crack forming

 

[ianc]

The springs are very close at that point and are making contact during suspension movement and have taken the paint off.

 

[whatcharterboat]

The questions
1) What suspension travel and sag (the amount the suspension would extend if jacked up) is there on the standard and the ATW modified 4x4 Fusos?
2) That sort of anti-sway bars are typically fitted (none, light, heavy..)? Asking this because the Vario has 55mm bar in the back and about 40mm in the front.

Hi Ian,

We took these pics this afternoon.

To give you an idea of ATW parabolic suspension travel have a look at the difference at the front between the top of the tyre and the mudguard.




Rear view




The Canter would have driven off the ramps if we hadn't stopped. We put a Landcruiser on the same ramps. It has a 2" lift and 33" tyres. It got to this point and lost traction as the left rear wheel came off the ground.





No sway bars are fitted to Canters with parabolics and body roll is not too bad.....especially considering the wheel travel.

Good luck in your quest. Parabolic's are definitely a black art but results are fantastic when you get it just right.

 

[Flys Lo]

Looking at the photos of your suspension, I can't for the life of me think what the additional bump stop behind the axle is for.

I'm not familiar with these trucks, but the only usage that something like that would be for that I can think of is to engage an overload spring:
http://www.mrtruck.net/s_pic/sway.jpg
(which doesn't look to be fitted...)

It looks to be both putting stress raisers in your springs itself - note the rusted portion behind the bump stop - and will do really weird things with your axle location as your spring hits it, that could cause handling issues.
A bump stop should act thru the axle line on a leaf sprung vehicle. I'd strongly recommend removing that bump stop and hopefully you will see improvement.