Hi
I have read your post several times and find that I do not understand the problem.
Ok there are two problems:
1: The back brakes tend to lock in the wet; this is VERY dangerous for the reasons I set out above (i.e. locked drive train -> no engine rotation -> NO power steering!
2: The front brakes overheat and fail VERY easily
It concerned me so much I rang my Isuzu dealer and spoke to the workshop manager. He said he would check their Australian defect list and ring me back.
When he got back the next day he said their were no reported failures or unexpected lockup of rear brakes in any NPS models.
Then they are fibbing! This problem HAS been reported to ISUZU not just by me but by others as well. Isuzu also had my truck tested on a brake roller (as I said above) and the only report I got back was that it was "satisfactory". My local dealer has driven my truck and has also verified that the problem exists. The problem is also well known to major truck brake outfits like Action in Brisbane. Two of the major infrastructure companies (rail and energy) in Queensland simply put concrete blocks in the backs of their trucks. At least two other motor home manufacturers are also having problems and one has commissioned a Sydney drive specialist to make a whole new front axle with disk brakes!
But what would you expect of course ISUZU will not say there is a problem and technically they are correct: the NPS passes all the current Australian ADR standard tests FOR TRUCKS! But compared to other trucks it is pretty poor: there is a reason why the other N series trucks have DISK brakes and ABS!!!!!
I have been driving mine now for 2 years with All Terrain modified wheels and have never locked a brake. But then I do not have rally experience so I may be a little more sedate.
OK perhaps you do not drive your truck with as much gusto as I do and perhaps you do not go the places we go, maybe your LSD is not as tight as mine (I know there were some issues with early LSDs being too tight etc) but that may not be the only issue. One of the remedies suggested by brake people is the "concrete block" and your truck may have this by default. My truck only weighs ~4.5 tonnes whereas I know some of Warriors approached the 5.5+ tonne mark. It depends on which options you have and which method they used for your truck. But if your truck is on the heavy side over the rear axle then you may be OK. I have only 2230kg on the rear axle (note I made a typo in a post above). It may also be that some of the bias valves are not adjusted correctly at the factory which is something we cannot test because no one appears to have the appropriate pressure measuring equipment to test the back brake bias pressure NOT EVEN ISUZU: maybe your is good and mine is marginal.
My interim fix for the problem is as follows:
1: keep front brakes clean and adjusted
2: reduce the back brake bias (->front works harder so gets hotter)
3: use high heat linings in the front (expensive @$400+ per set)
4: use exhaust brakes to supplement but ONLY in the dry
5: ALWAYS brake with clutch DISENGAGED in the wet.
6: adjust tyre pressures for optimal rear braking (initially we had too much pressure in the rear tyres)
And just in case we had any doubt we have just traversed the same back road from Grafton to Armidale mentioned above and although I can get the back to lock very easily I did not want to test this on this road but we were able get the front brakes to overheat trivially easily even in rain and hail! However this time the high heat linings recovered as soon as the drums cooled down and did not glaze and we continued without problems.
This problem is not simple as although the brakes overheated on the aforementioned road I really tested them again a few hours later on the Moonbi hills and did not overheat them. So I think the real problem lies in continual repeated high force braking building up a lot of latent heat in the drums which then take long while to cool down.
I am well on the way to a disk brake conversion and have sourced all the components required and am just waiting for prototype rotors.
