Forum:
Hi I'm new to this forum, I have a fourtrack with a manual 4x4 selection gearbox which is about to give up on me, I have got a seconhand box but it is the type which switches electronically, as much as I hate to replace somthing nice and simple with somthing more complicated this seems my only option other than forking out for another box. Somone told me there are more elcetroncs under the dash am I about to start a nightmere job or is it just a case of wiring up the selenoids (don't know why there are two)to new switches and connecting the vacum in somwhere. I erally don't care if the 4wd light comes on or not just as long as I can get the fromt wheels turning when I need them too.
I did notice that somone else planned to do this on the form but don't know if it worked out or not.
Any ideas? Thanks Rich
Real nasty bodge
What it comes down to is that the 2/4wd selector in the mechanical box has been replaced by a vacuum operated diaphragm. Engine vacuum is directed to the correct side of the diaphragm by a horrendously complicated system of relays and valves, dreamed up by some lunatic oriental on a paranoid depressive episode and too much saki.
The bodge is to bring both sides of the diaphragm into the passenger compartment via re-inforced plastic pipe. Also tap off engine vacuum from the back of the alternator and bring this into the passenger compartment via tube. To shift the 2/4wd mechanism, all you need to do is to swap the side of the diaphragm that you connect the engine vacuum to. The other side of the diaphragm is left open to air.
Thanks
Makes sense, elecs do look complex not such a bad bodge as long as I can find some decent way to connect the tubes and keep them out of harms way, agreed it is a system invented by a lunatic. I liked the stick and have manual free wheeling hubs so loosing the elctric is the way to go
More info
The detent on the vacuum 2/4wd selector is specified at 1/10 of the force of the manual version. The remainder if the force comes from the vacuum holding the diaphragm in position while the engine is running. This means that the vacuum should be permanently connected to whichever of 2wd or 4wd is desired.
I would suggest that a restriction is put in the pipe coming from the back of the alternator to the new kit in the passenger compartment. This means that if the connection to the gearbox comes adrift, then too much air will not enter the system and destroy the vacuum which the brake servo runs on !
Don't quote me, but I believe that vacuum applied to the side of the diaphragm facing the front of the vehicle gives 4wd. Vacuum applied to the other side gives 2wd.
This system can of course be configured to give 2wd low ratio. This shouldn't damage things, but I guess that the rear drive system isn't specified to handle the torque of low ratio without some of that torque being applied via the front wheels. We're entering the area of busted halfshafts here, as Landrover owners are too familiar with.
Vacuum
Forget the vacuum operated system, as rf man says, it is a complex system which has its own inherent problems.
Solonoids have vents to vent air to atmosphere, these often become blocked and ensure the system will not engage, if not engaged; and will not disengage if engaged, particularly if the vehicle is used off road. water ingress will cause failure of the solonoids if the vehicle is used in a lot of wet conditions, or sludgy off road conditions.
Wiring can be a problem as with most wiring systems.
Vacuum operated diagphram often corrodes and siezes, particularly with vehicles working off road on wet and sludgy conditions.
In simple terms, sell, or swap your box for a manual and remain reliable.