Thread: Incase of rear diff explosion. SOP?

Originally Posted by Aaron

I don't want to hijack the other thread.

What is the standard operating procedure if I got a Puma rear diff failure in the bush. How do I sort it out to get home other than a flat bed?

Pull rear drive shaft (and half shafts if needed), lock centre diff, drop front tyre pressures another 10 psi, limp home and replace winch if needed.

Edit: PS what's the 'other thread'?

axles out, flanges and rubber caps refitted to keep dirt etc out of wheel brgs. remove rear tailshaft and reattach nuts ( you will need spacers) to rear output studs to keep park brake drum on, drive home in front wheel drive with centre diff in lock.


jc

Originally Posted by n plus one

Pull rear drive shaft (and half shafts if needed), lock centre diff, drop front tyre pressures another 10 psi, limp home and replace winch if needed.

Edit: PS what's the 'other thread'?

Just the other epic thread on the puma rear diffs.

Originally Posted by justinc

axles out, flanges and rubber caps refitted to keep dirt etc out of wheel brgs. remove rear tailshaft and reattach nuts ( you will need spacers) to rear output studs to keep park brake drum on, drive home in front wheel drive with centre diff in lock.


jc

How much spacing is needed? Driving with the CDL in, should I be driving slow/slow around corners etc? or just normal?

Originally Posted by Aaron

Driving with the CDL in, should I be driving slow/slow around corners etc? or just normal?

Just normal is fine.

The centre differential allows front and rear driveshafts to rotate at different speeds. This is necessary around corners when all four wheels are being driven, because in this situation the front wheels (combined) travel a different distance to rear wheels so a mechanism (differential) is needed to allow front and rear driveshafts to rotate at different speeds. If the centre diff was locked (front and rear driveshafts rotate at the same speed), the entire driveline would keep winding up until there was enough torque to cause the wheels to spin & reset (or break something). The differentials on the front and rear axles allow the wheels on each side of an axle to travel at different rates (even more important around corners).

When the CDL is engaged, the front and rear driveshafts are "locked" and rotate at the same speed. This is necessary when you remove the rear halfshafts and/or driveshaft, as it allows drive to the front wheels. Without CDL engaged, all the power would go to the rear driveshaft flange. You don't need to worry about driveline windup because the rear wheels are disconnected from the rest of the driveline (i.e. the vehicle is effectively in 2WD mode), so only the differential on the front axle is needed / used.

Hope that makes sense.

I dont use a spacer, I just pull the UJ apart and refit the flange.

As spacers I use some M10 nuts, (Just throw a handful in the tool box, you only need 4 in an emergency like this) just slide them over the studs and refit the 3/8 " UNF original flange nuts to clamp the drum in place. (DO NOT rely on the screw holding the drum in place!!!)OR you can rob a few applicable sized nuts from less important bits of the vehicle to get you out of trouble....although I am struggling to think of any M10 nut that is NOT important on a Defender...


JC

CDL with one prop is good to go, quite possibly less wear on your transfer box than open 4wd. More torque put through one prop/diff though so no drag races. I've done the past 1500km on rear prop only, CDL. No noticable fuel economy improvements, but less vibrations.

Also no spacer needed when removing rear prop if you have an handbrake disc conversion/upgrade (x-eng). Makes dropping the rear prop real simple.

And what if only your front diff explodes?!

Apologies if you already know this, but I'm guessing since you asked the how to get home question then its likely you might be relatively inexperienced in 4WDing in general.

Put some thought into what you would actually do AT THE TIME if it does fail - particularly on a steep climb.

After the initial "WTF just happened moment" - then what??

Foot brake will still work reasonably as it acts directly on the rear wheels (as well as the fronts), but handbrake will likely be ineffective (little weight on the front wheels) even though it will be acting on front wheels through locked CDL.
If you were by yourself with no passengers you're likely screwed at that point as you can't get out to chock the vehicle unless you can somehow wedge the brake pedal.

If you start to roll backwards and apply the brakes hard you'll likely lose your steering as front wheels will lock first (again due to little weight on them).

Even if you get past all of that, and get the vehicle secured safely. There's a good chance you're not going to be able to drive it out in 2WD on the front diff only (even with reduced tyre pressures) so will need to be towed/winched out unless you are able to back down safely. I don't proclaim to be an expert at backing, but I've driven with a lot of people who have absolutely no idea how to back using their mirrors, and I've seen very near rollovers (and know of others that have actually rolled) as a result.

Stepping off my soapbox now....

Steve