Hilux 4x4 Forum

My Ranger Supercab 2wd has this diff-lock, usually activated by a switch on the dash. This opens a solenoid which allows engine vacuum to a diaphragm on the diff rear cover which engages the diff-lock.

Mine started to engage itself the last couple weeks and then generally also refused to dis-engage. Usually you would switch it off and as soon as your forward speed gets to about 40kmh or so it lets go. I fiddled with the switch a couple times, had the vacuum pipe off couple times to check for unwanted vacuum etc. Never really got to the bottom of the problem as it seemed to "fix itself" after fiddling with everything for a while.

Friday it locked again, so I was determined to find the problem this weekend. Try and take a sharp turn or do a parking manouvre with this diff locked! People look at you funny too!

Long story short, I could not find any problem, the solenoid valve operated correctly, allowed vacuum to the back and blocked vacuum as it should when switched off etc. Diaphragm and return spring mechanism worked perfectly. So I was lying under the back busy blanking off the vacuum tube as a last resort fix, when my eye fell on the diff breather and I thought.....wonder if that is still OK. This is a nipple on the right hand diff pipe/tube with a long rubber hose that dissapears over the top of the fuel tank. Turns out this was blocked solid! I followed it to where it terminates just by the fuel filler cap. There it looks like someone had cut the pipe off wherever it was supposed to go and stuck a bolt in to cap it..... Dust and dirt had built up untill it eventually blocked completely.

With no-where to breath to, the diff then got pressurized at temperature and this pressure pushed against the inside of the vacuum diaphragm, thereby engaging the diff lock! No wonder I could not find anything wrong with the normal activation system. Once the diff cools (while I am fiddling to try and find the fault) the pressure drops/gets vented out and the lock releases again......