Sunday, Mar 11, 2012 at 13:41
Hi all,
firstly many thanks to all who contributed with suggestions. I have made some progress and although I have not finally solved the problem,I am fairly sure it is electrical...specifically earthing issues.
Progress so far:
-I have disassembled the hub of the worst wheel that gave me the blisters on the hand from being so hot.
- bearing grease was
well burnt BUT,bearings and stub axle were fine(thankfully),seal not so good as you might imagine(I will replace the bearings).
- drums have some uneveness but look to have been machined not too long ago and in my view they are very serviceable.
- magnet looks fairly evenly worn and has plenty life left with all wear holes visible and 2-3mm left all round.
- return springs seem fine as is the brake assembly which is free moving.
- handbrake actuator also OK.
- shoes look evenly worn and apart from the bottom of one shoe which has 3.5mm -4mm,they have 4-5mm left all round.
From the above I am assuming it is NOT a mechanical issue.
So as per a suggestion in this thread,AND on advice of a local ALKO agent I found,I began a full trace of the electrics. I cannot get inside the subframe where most wiring is but I have fairly confidently deduced:
- the wiring loom from the trailer plug enters the subframe and re-appears at the rear interior of the caravan and is terminated at a fuse panel with the exception of the EARTH wire. The blue service brake wire is fused with 15A.
(all OK so far).
- the blue serv brake wire then re-enters the subframe and supplies all 4 brake magnets (in parallel) - this is OK as it is a dedicated wire to the brakes.
- the earth wire from the car loom exits the subframe under the caravan and is terminated on the external rear chassis rail.
- I can find no other earthing arrangement for the wiring loom OR the brakes. The return (earth)wires from the brakes enter the subframe at the drivers side rear caravan wheel and go REARWARD,therefore i can only assume that in the subframe or behind some cupboard wall,the brake earth joins with the lighting earth(see above) and shares the same earth termination on the rear ext chassis!!!
- now as my van batteries,ext park,brake,clearance lamps,etc are all sharing a common earth which is either the subframe or the side alum cladding,I see significant potential for reverse current paths through the magnets (shortest path and all that).
- as mentioned previously,I have earth troubles sometimes with my clearance lights so there is a clear case here for a separate earth run from the brakes direct to the trailer plug.
-I also believe I had my clearance lamps on, on the day of the troubles due to significant rain
As mentioned,I found a local ALKO agent with many years experience. When he heard my problem,he asked - do you have an off road(poly block) coupling.When I replied in the affirmative,he said it was "electrical" and he was prepared to bet one part of his anatomy on it!!! (I asked if he had one to spare?). He indicated DEDICATED brake wiring to the tow vehicle plug has fixed these problems in EVERY instance he has seen over many years -and there have been many.
So next step is to just confirm today's analysis by taking my brake parts to the ALKO guy for inspection and confirmation that the mechanical side is OK.
If that goes as expected,I'll re-wire the brake earthing circuit direct to the plug.
Also inspect every hub,bearing and brake assembly to ensure all is OK.
If anyone has any ohter thoughts,please advise - all
feedback most welcome.
Rgds
Ron
AnswerID:
480081