33 4x4 drive train

Today I have mainly been pondering P4 drive systems.

I aim to transfer the drive train off the pink P4 onto one of my other cars. The procedure looks something like:

- Engine out and swap to P4 gearbox
- Weld viscous coupling mounts in
- Work out where the wiring goes
- Look at how much modification the boot floor needs
- Change fuel tanks
- Swap rear axles
- Sort out rear brakes (drum to disc)
- Drive shaft in and test

The difficulties lie in the following:
- Wiring needs the P4 drive ECU, extra brake switch wiring, dash warning light, P4 relay and fuse, supply to electro-magnetic clutch, seizure sensor connector. On the 16v, the relay holder looks to be in place, so I am hoping the loom is already there
- Boot floor - looking at the body panel diagrams in the workshop manual, the boot floor is quite different, and there is a strengthening beam under the rear seat. Not sure why the boot floor is so different unless it is higher to accommodate the fuel tank, so need to inspect both cars

VCU wise, the Land Rover VCU specialists may be able to recon the Alfa ones, so need to pull one off and get some details to send them.

More soon on this little project.

Just out of interest what is the drivetrain layout of the P4?

My knowledge only goes as far as thinking the 4wd was electronically controlled at the rear axle.

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Originally Posted by Steve Webb

Just out of interest what is the drivetrain layout of the P4?

My knowledge only goes as far as thinking the 4wd was electronically controlled at the rear axle.

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I could reply but wombat will do it better

Crank and gearbox are longitudinal, so a propshaft can come straight out the back of the gearbox.

However... Instead of doing this, Alfa attached the back of the output shaft to an electromagnetic coupling on the P4, and then took the propshaft off that (why they did this is described below - its quite clever really).

The propshaft then goes through a viscous coupling (VCU) - lots of plates spinning in silicon jelly, half the plates on the input side, half on the output side. When the jelly gets to a certain temperature (the range is 200 to 300 degrees depending on the jelly), it acts like a solid and locks the plates together, transmitting drive to the rear.

Rear end of the propshaft then attaches to a fairly regular live rear axle that is a straight replacement for the 2WD beam, under a modified rear floor with the fuel tank moved.

Onto the electromagnet coupling on the back of the gearbox. There is a small ECU in the boot, with a number of sensors attached to it. It has a G-Force sensor built in, and a couple of other bits and pieces. The clever bit is that under certain conditions, the ECU will decouple the rear wheel drive. This actually protects the VCU, and is somewhat of a safety feature as well. The two conditions I am aware of are under heavy braking (there is a brake light switch connection as well), and I the coupling is struggling to engage or disengage (which is done on different rotation speeds and may indicate the VCU being seized).

The system is very straight forward, and other than a transverse to longitudinal transfer box, Land Rover deployed the same on the Freelander but without the clever decoupling gadget. Land Rover VCUs fail at around the 80k mark!!

Earlier non-P4 4WD 33s had a manual engagement system, and lacked the VCU, which meant that the system could only be used for loose surfaces at lower speeds.

So there you have it, dead clever really and quite simple. I have heard people complain of electronic problems with the P4 system (warning light not going out, coming on etc, but the warning light is only triggered under certain circumstances so its likely a mechanical problem lighting it up legitimately.

Cheers for that, more complicated than I realized. I didn't know there was a VC tucked away in there, and I had assumed that the electronic clutch engaged the 4wd when it was needed, not the other way round.

I guess I didn't own/drive the P4 I had enough for anything to go wrong and need fixing.

the boot floor is different to accomodate the diff unit on the rear axle is all...

my pal is planning on putting the p4 running gear inc engine underneath the "track prepped" sud i sold him ........ we think its not that difficult, esp as he plans to go with a race style tank in boot .

i have had 2 P4 theyre bloody marvellous, i even took one to spa-italia, lots of fun,


(well til i broke it anyway, but thats another long, story)

ps mr wombat are you trying to collect all the 33s left !!! :p