When we started this I thought the suspension was going to be the major problem but I was wrong! It has turned out the the brakes are becoming the real killer of this project!
To be blunt the standard brakes on the NPS are crap! (I do not know but the Fuso's could be even worse or better but perhaps WhatCharterBoat might like to comment here!).
The problem was detected as soon as we drove the truck and can be summed up in a two sentences:
1: the front brakes are NO WHERE NEAR strong enough and overheat way too easily
2: the rear brakes are WAY TOO strong and lock up way too easily
Now at first you may think this is not a serious problem but it is when you consider the following:
1: the rear brakes lock suddenly and unexpectedly; especially on wet roads
2: this truck has a VERY tight LSD fitted to the rear so when one wheel locks up so does the other
3: now you have the drive train locked up and if you have the clutch engaged, which is usual, you now have no engine and no power steering
4: all while sliding sideways in a truck on a wet road!
As well as ISUZU we have also had two very large truck brake specialists look at the problem (one in Sydney and one is Brisbane). They have both seen this problem in other lightly loaded NPS' (ours has 2400kg and 2500kg on the front and rear axles resp) and the only solution they have found is to put “lumps of concrete” in the rear of the trucks.
On our journey we have found a list of issues we have addressed:
1: The NPS does not have auto adjusting front brakes so they require constant adjustment to maximise pedal travel. I adjust mine every 2-3000km!!
2: The load bias valve in the rear required reseating and readjustment on a specialist brake roller (not just the arm but the whole valve body!).
3: The standard front brake linings not heat resistant enough, after several overheating episodes we have replaced with “tougher” linings. Note that the replacements are the same "hardness" as original linings but more heat resistant).
4: The front brakes need to be de-dusted routinely or else efficiency drops off and overheating increases as dust accumulates. No problem you say ...... but there's a catch: to remove the drums on this beast requires removing ALL the bearings, you cannot simply pull the drums off and blow the dust out! It takes about an hour at least and you should replace the seals when you do this.
HOWEVER ALTHOUGH IMPLEMENTING THE ABOVE HAS IMPROVED THE PROBLEM; NONE OF THESE MEASURES HAVE FIXED THE PROBLEM: THE BRAKES ARE STILL CRAP AND IN MY OPINION DOWNRIGHT DANGEROUS IN THE WET!!!!
The real problem is that lockup occurs very suddenly in both wheels and with no apparent reason: there is no apparent change in road surface, brake pressure or other outside influence that we can discern. You will be in a completely controlled braking and “BANG” suddenly both rear wheels will lock up and freeze the drive train. Because of this I now brake with the clutch in which places more demand on the brakes (no engine braking.......) and of course we end up getting the front brakes hot.
The problem is so bad that even as an ex rally driver I am actually scared to drive the truck in the wet and any extended downhill section in the wet can be truly terrifying. In a recent trip coming down from Armidale to Grafton the rear locked up unexpectedly and we almost went off the edge of the road over a cliff, despite literally “tip toeing” at the time.
There is one thing to left to try, both brake experts suspect that the rear axle could be moving around causing the rod that acts on the brake bias valve (more load => more brake force) to “jerk” on and off causing sudden pressure changes in the regulating valve pressure. Us altering the suspension to give more travel and softer spring rates could have made the problem even worse but as noted the problem does exist in "stock" trucks as well. So the last thing left to try is to disconnect the load sensing rod from the axle and use a simple pre-set manual adjustment (these trucks have a constant load so we don't need it to be variable anyway). this may help with the the problem.
I have investigated the problem extensively (as have some very smart brake experts) and there appears to be no real solution. Personally I would do ANY/ALL of the following regardless of cost, if they could be done:
1: retro fit an ABS system (stop back brakes locking). I have considered using an old 3 channel system from a Commodore.
2: fit a centre differential instead of the standard 4WD transfer case so we are in constant 4WD. This will spread the braking load to both front and rear axles.
3: fit disk brakes to the front. I could replace the standard front diff with a Dana front diff. This would allow much more braking force on the front wheels.
4: replace the LSD with a manual diff lock so both wheels do not lock at the same time and at least keep the engine (and power steering!!!!) going.
But after literally hundreds of phone calls I have not been able to find anyone in Australia who can do any of these modifications!!!
In retrospect if I had known this issue existed I would probably not have gone ahead with this chassis! That may seem a pretty harsh thing to say but this problem in combination with the suspension issues and a whole lot of body related issues (e.g. wading depth, fuel tanks etc) really has spoiled some significant part of the pleasure of the motorhome.
Ironically the problem goes away in off road 4WD because the braking effort is spread across both axles through the transfer box so perhaps the moral of the story is: STAY OFF ROAD AND IN 4WD!!
So in summary my advice to anyone considering this sort of project where you will spend a lot of time on the blacktop would be to bite the bullet and spend the extra $40k on a purpose built 4WD truck chassis like a MAN or Mercedes. I know the $120k+ might seem a lot but in the end it is worth it! Although they are bigger trucks (8-10 tonnes as opposed to the 6 tonne NPS) they come with full time 4WD, centre, front and rear diff locks, ABS, brilliant fully in cab adjustable suspension, 12 speed auto gearboxes, 22.5 wheels super singles, auto fill tyres, blah blah blah and so many extras that it makes every cent worthwhile.
I am sure WhatCharterBoat will have something to add to this :-) What say you WCB????