Experience With Preparing ISUZU NPS Camper: Suspension

IcedVolvo

Observer
The title sort of says it all but if people are interested I will start a series of threads on my experience with setting up an ISUZU NPS four-wheel-drive truck as a serious off-road camper. I'll use the same title but change the end word to address each of the general areas that we have come across.

Firstly let me say that we purchased the basic unit from All Terrain Warrior on the Sunshine Coast in Australia but I am not employed by them nor do I get any commissions or other financial gain. Unfortunately we could not afford to purchase the "bells and whistles" version of the Scout so we have had to do a lot of setting up and problem solving ourselves. Having said that I can thoroughly recommend All Terrain Warrior if you are considering one of these styles of vehicles.

By far and away the biggest problem we had to solve was the issue related to suspension. If we had the money we would certainly have engaged ATW to carry out either the coil conversion they are now doing or some sort of extended leaf set up. However doing this on the cheap has given us a real insight into how the suspension on trucks works and the problems, particularly in light trucks, of the unsprung weight of the heavy front axle versus the overall weight over the front axle.

When we first took delivery of our truck it was fitted with the standard springs and shock absorbers front and rear. The NPS is a six tonne rated truck but only weighing just over 4 tonnes as delivered. The suspension was so bad that my wife cried all the way home and both of us were shaken to pieces by the horrendous ride on the trip home. I consoled her in the knowledge that we could make the suspension a lot better. However I needed the assistance of a good friend of mine who owns a truck suspension company on the Gold Coast in order to do a lot of trial and error testing.

I will cut a long story short by telling you is simply that we have tried all the traditional fixes that one would normally try in a cab over situation. In the end we found the following things dramatically improved the ride to the point now where the truck is almost car like in suspension.

Front Suspension:

1) we modified all the hinges from the standard 19mm rubber bushes to 25mm greased pins and shackles.

2) We obtained a 1300 mm x 70 mm parabolic spring pack from another truck. Unfortunately we do not know exactly what truck these springs came from as although brand-new I found them at a wreckers; but I suspect they came from the front of a 2009 Hino 500 series.

3) We fitted a set of Boundless Rider fully in cab adjustable air shock absorbers

4) although it might not seem relevant it actually made a significant difference in the front suspension by fitting a substantial rear towbar which carries the two spare wheels. The total all up and weight of the towbar and spare wheels is ~300 kg and although I'm not sure it's exact reason I theorise that by adding a static weight to the rear of the truck acted like a counterbalanced pendulum which inhibited the front of the truck from moving up and down so readily.

5) we modified the wheels from the standard 17.5 to 19.5 inch super singles with a 265/70 tyre fitted. Although when we can actually manage to obtain a set 285/70 these will be the standard tire we fit to this vehicle (someone who shall remain nameless has purchased every tire in Australia of this size!).

6) we have had both a caster and camber kit fitted to the front and which although probably hasn't had much effect on the suspension itself it has dramatically improved the handling particularly during undulations in the middle of corners.

All up this has cost us about $3000 which although not cheap is far less expensive than the $10-$12,000 for the OEM conversion by ATW.

The next step we are going to take is to remove the third leaf from the parabolic spring pack to see if this makes the front a little bit more compliant but to be honest I think it's about as good as we are going to get it for the reasons I alluded to above; the simple fact that the unsprung weight of the front axle is a significant proportion of the total weight of the front end. As a result although will we handle compression bumps quite well drop aways or decompressions are always going to be a problem. it will be interesting to see what if any difference the fitting of a 200 kg bull bar/winch combination to the front-end does. I'll update this thread sometime later in January next year to let you know what the outcome was.

Rear Suspension:

At this stage we are only just starting down the track of getting the rear suspension correct. Because our vehicle only weighs about 4.3 tonnes we found the rear end was bouncing when we went over speed humps so we had the auxiliary spring pack removed and the main springs slightly reset so they work a little bit more. Although this has dramatically improved the rear ends ability to articulate and for comfort purposes it has also detracted a little bit from the handling of the truck as it tends to roll a little bit more in corners.

We are sort of in limbo with respect to the rear end, when we add some extra weight to the front next year we'll see what happens and if the rear suspension is reasonably satisfactory I will simply purchase another set of those stunningly good shock absorbers made by Boundless Rider and fit them into the back. Failing that I will probably go back to ATW and ask them to do that really nifty coil conversion they have been working on but I might have to take out a second mortgage on the house and sell one of the children for medical research :)

The only other thing you need to consider is the use of some sort of detachable sway bar for off roadwork (note the rear of the NPS does not have a sway bar fitted as standard). If you take the front sway bar off on the road the truck rolls around far too much especially on high speed highway conversely the sway bar is way too stiff to allow proper articulation in off road situations. I am simply going to replace the existing nuts and bolts on the bracket with a wingnut/split pin set up so that I can quickly remove the sway bar when I go into any sort of serious off-road situation.
 

IcedVolvo

Observer
Forgot to mention that I have also fitted an ISRI air seat to the drivers side and will fit another to the passengers when finances allow.

Iced
 

whatcharterboat

Supporting Sponsor, Overland Certified OC0018
Jon. Firstly, welcome to the forum. I am sure you will be a fantastic (and knowing you > impartial) benefit to these guys here and especially the Isuzu set given your previous offroad experience to date, mechanical expertise and general knowledge, "tech savvy"ness (not sure if that's a word but it fits) and given that you were one of the first in the country to secure a current model NPS for expedition style use. I'll certainly look forward to anything you post up.

BTW I hadn't posted any detailed pics on ExPo yet of the rear coil suspension you mentioned but here you go.

4100580640_3d58324ca0.jpg


Also I know everyone will be keen to see some pics of your truck but I'll just include this early one so they get an idea and maybe you could post some updated ones with the 19.5" super singles or possibly offroad action shots if you get a chance. Hope that's OK and thank you in advance..

3120217086_fea085c56e.jpg


Regards John.
 

kerry

Expedition Leader
Great information. Thanks. It would be good to see pictures. I'd especially like to see pictures of the greased pins and shackles. Where did you source them? I'd also like to see pictures of your air seats. I currently have a Stratos driver's seat but might consider an air seat for the passenger(s). Does anyone know if a double air seat or suspension seat similar to the original double passenger seat in the Fuso is available?
I find point #4 very interesting. I drove my FG across country with only the service body on it and the ride was intolerable. My wife would have been crying too. With the camper on, the difference in ride is remarkable. I had attributed this change simply to the additional weight on the truck but it you look at the pictures of my camper, the weight is quite far back on the truck. I had not considered the fact that the simple location of the weight might have substantially improved the ride in and of itself.
 

gait

Explorer
lots of useful info here. Thanks.

I'm part way through a 2004 FG (MWB) conversion and haven't tackled suspension yet. Though I've been thinking about it.

I had similar (expected) experience with driving plain cab/chassis about 800km. Even with tyre pressures way down it was bone jarring. There was an extra 100kg of steel that previous owner had added. A 10mm thick plate each side of the web the length of the chassis. Removing that seems to have allowed the chassis to flex but its still bone jarring.

I could well be wrong but to add to the simple vertical pounding from the front suspension I figured the high cab and bouncy back end / springy chassis combined with the front wheels as a pivot. The rear springs probably didn't bend at all. Back end goes up, my head pushed forward etc. Probably why I nearly broke my finger on the radio buttons (hand vibrating back/forward more than up/down).

I suspect that once there's a body added the heavy weight of spares hung off the back (levers and inertia) means the rear springs are working which reduces the chassis movement. Sprung/unsprung mass ratio is different. etc.

My plan is to keep total weight below 4.5mt (10,000lb), so far so good, but need to get there before seriously tackling tyres/suspension. I'm hoping ATW will surface with semi-elliptical.
 

KEENO

Adventurer
John...

A major WOWZER on the rear coil suspension! I don't believe I've ever seen anything similar in locating an axle laterally! Sweet!:Wow1:

KEENO
 

kerry

Expedition Leader
John...

A major WOWZER on the rear coil suspension! I don't believe I've ever seen anything similar in locating an axle laterally! Sweet!:Wow1:

KEENO

I think that system is called a Watts linkage. But it looks like it has shock absorbers on either side. I don't understand their role. Wouldn't a shock absorber defeat the purpose of a watt's linkage in keeping the axle's movement vertical?
 
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IcedVolvo

Observer
Have attached some photos showing

1: the parabolics with greased shackles
2: the rear wheel carrier
3: the ISRI seat in an NPS (which everyone said couldn't be done!)
 

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whatcharterboat

Supporting Sponsor, Overland Certified OC0018
I think that system is called a Watts linkage. But it looks like it has shock absorbers on either side. I don't understand their role. Wouldn't a shock absorber defeat the purpose of a watt's linkage in keeping the axle's movement vertical?

Not sure what you mean Kerry. The only shock absorbers are the orange ones. Not intending to Hijak here but Jon (icedvolvo) was actually the first to suggest a watts rear end in the concept phase of this but we weren't sure we could ever achieve the extreme travel with it until my boss proved it on the computer. Had some good advice from one of the other Expo members too.

Regards John.

BTW Pretty sure Jon intends to take his truck up through SE Asia in the next 18 months. Should be very interesting.
 

able

New member
Jon, First of all 'you lucky devil' that is a fantastic rig.
But just on the ride quality of a standard NPS300 it's rough alright. I have an old model 1999 and I have a service body on the back which I have now sold but have to deliver it to Narromine NSW which is about a 1200km round trip.
Should be a lot of fun coming back via the Golden Hwy as a cab chassis.
Sorry I know I was a bit off topic then, but please keep the info coming us NPS people are watching with interest. WE love what you have done so far and appreciate your information.
 

IcedVolvo

Observer
Which model ISRI seat is that? Is it on one of these two pages of ISRI seats available in the US?

http://www.suburbanseats.com/thumbnails.aspx?a=1&catid=11&page=2

Hmm wondered if someone would ask!! Nope it's a special version of the ISRI done for IVECO trucks with a low profile base and seat cushion!! You have two options: order one from IVECO (and be prepared for a coronary or stroke when you get the price!) or order a standard seat from ISRI and then order just the seat base/adjustment from IVECO as a spare part. Dave at ISRI in Brisbane knows all about if that's of any use to you.

You also have to make a special bracket and make it as low as possible. In order to get engineers approval, I made mine from 3mm HT steel and TIG welded with chrome rods. It was a pain but worth every single bit of trouble.
 

kerry

Expedition Leader
Not sure what you mean Kerry. The only shock absorbers are the orange ones. Not intending to Hijak here but Jon (icedvolvo) was actually the first to suggest a watts rear end in the concept phase of this but we weren't sure we could ever achieve the extreme travel with it until my boss proved it on the computer. Had some good advice from one of the other Expo members too.

Regards John.

I thought the pieces that connect the central pivot to the fixed mounts on the frame looked like shock absorbers of some kind (ie--larger outer component into which a smaller component slid) instead of fixed length rods. Guess I was mistaken.
 

ntsqd

Heretic Car Camper
Wow John!
The Watts system looks great! I gather that this is nearly full droop? Nice, burly looking parts there. Interesting that bell-crank hasn't rotated much yet the adjustable links are far from horizontal. I'm guessing that lateral dislocation at the travel extremes is pretty minimal.

I recently got an Object Lesson in something that I know, but had to have demonstrated to me for it to really sink in. What ever you do to one axle affects how the other axle behaves as well.
Much lighter truck, but still two live axles on leaf springs under my 1984 Toyota Xcab. I had valved the rear Bilsteins 275/78 as the supplied 255/75 valving was just a bit too light and the rear of the truck tended to buck (needing more rebound) even with the fibreglas bed-cap on it. Due to age and out right abuse I had to replace the front springs. They've been on the truck since I bought it used in 1998 and I've yet to find anyone who could positively ID them. So I bought some OME Dakars for it. They're a different spring rate which has the front valving in question and now the rear is acting up again too....

So I guess that my point is that tuning the ride quality should happen as one of the last aspects of any build. Unless you're someone like ATW and have built exactly this truck before. That the truck is going to ride poorly until then just should be accepted as a temporary thing.
 

IcedVolvo

Observer
Just a quick update on the ISUZU NPS suspension saga people.

The parabolics I put in were from a Hino 500 series but apparently are the same as the bigger F series Isuzu: a 3 leaf pack @1300x70 with a 3600kg axle rating (our NPS has ~2200 on the front axle). They are fantastic on the black stuff, the NPS handles like a sports car which is extraordinary for a high narrow 4WD truck!

Well we finally got a chance to take the NPS where we actually needed 4WD, not serious rock climbing but definitely 4WD. For those of you who know it the back road between Crescent Head and the Port Macquarie ferry (no not that one, the real back road!) and this was in pouring rain! I have to report that the parabolics did not perform as well as expected off road . They were very harsh in the ruts and would not allow articulation to the extent that they should (or we need!): we never got near the bump stops! In fact the chassis was twisting so bad that the concertina joining the cabin and the body came apart! So its back to the drawing board for us.

As a first step I have taken the third leaf out of the pack which has made the ride a lot softer but we have lost ~1" in ride height and we only have about 4" on up travel before the bump stop. When I get a chance we are going try several things:

1: cut the bump stop down even further
2: reset the remaining two parabolics to give them a little more lift
3: block up the spring pack to regain the original height.
4: pin the sway bar for easy removal so we can better articulation off road

Any way, will keep you informed as we go.
 

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