T4 diff lock (EDL)

[Jezza]

I have a LWB 2000 model TDi T4 Syncro. I was having a looksee underneath the other day and noticed on the back of the rear diff, what seemed to be a some sort of actuator with an electrical connection. It is made up of two main housings. One is a 50-70mm round, 20mm thick section, then 80mm long x 40mm round section perpendicular to it. So it looks like a small motor with a pinion connected to a gear wheel.

My question is, is this the diff lock mechanism? I followed the wiring into the engine bay but could not find them after that under the dash. I do not have a diff lock control on my dash, but did notice a purple 2-3mm tube, possibly a vacuum line under the dash where the diff lock control normally is. I heard that the diff lock is possibly a vacuum system??

Do I have a diff lock and it is simply not connected maybe?

The vehicle is an ex. NSW Ambulance Service Patient Transport Vehicle used for rural NSW. It has had a lot of gear installed into and then removed for sale. There is evidence all throughout the vehicle with unused wires, fuse boxes and holes in the interior boby everywhere (no remaing passengers thankfully!!)

My thought is that they maybe removed heaps of wiring and forgot to connect it up.

Would love to contact anyone who knows a bit about the EDL system and ultimately get my self some more traction. I am over in Western Australia where I drive on sand majority of the time.

Thanks

[h100vw]

The EDL isn't that clever, it uses the ABS to sense wheelspin and it only operates up to maybe 10ks.

Obviously better than nothing.

The stuff on your rear diff, assuming it's the same as my Passat G60 syncro wagon, engages 4wd when you go into reverse.

Not sure how much you know about the syncro system but briefly it runs in fwd until it senses slip at the front wheels, then it diverts power to the back.

Gavin

[Jezza]

Interesting Gavin. Thanks. Why does it engage to 4wd in reverse.

Not all T4 syncros have ABS though. It was for special orders only I think. Mine does have ABS. So I wonder if the mechanism on my diff is only on ABS models then.

Also, I ocasionaly get a small cluck when I reverse and have always wondered if it has something to do with the syncro system.

[h100vw]

Interesting Gavin. Thanks. Why does it engage to 4wd in reverse.

Not all T4 syncros have ABS though. It was for special orders only I think. Mine does have ABS. So I wonder if the mechanism on my diff is only on ABS models then.

Also, I ocasionaly get a small cluck when I reverse and have always wondered if it has something to do with the syncro system.

VW must have figured that it was a useful feature. With reverse being lower than first it would be easier to pull yourself out of the crap.

Gavin

[SoVeReIgN]

EDL uses the brakes and despite having 'diff' in the name has absolutely nothing to do with the diff.

Fairly useless feature too. Just brakes one wheel so the power is transfered to the other.. rinse and repeat.

I thought it operated up to 40km/h ?

[Seano]

Jezza......the diff lock wasn't often (if at all) specified on Oz spec vehicles. However, given yours is a special order then you may be in luck. If it does have the diff lock then it was simply controlled by a dash switch....that's what my owners manual indicates anyway.

Be aware though that the rear diff with a diff lock is a special best - it is different from the stock syncro diff with a number of unique parts. It should be visibly different from a stock syncro diff......which it sounds like it is.

The vacuum line you've seen under the dash sounds like it might be the air filter indicator. It's a hard purple line that runs from the top of the air filter box and goes to a spring loaded gauge on the small flat panel at the bottom of dash centre (in front of shift).....if the filter is clogged then the vacuum created by the engine suction builds up behind the gauge, pulling a rubber diaphragm which causes the gauge to trip and show red....thus indicating it's time to change out the filter.

[Jezza]

Thanks Gents. Seano, mine as I have told you before is the ex. NSW ambo vehicle and I know that it did have some special features like the ABS, dual A/C etc. The fact that mine doesn't have the switch on the dash tells me that I may not have EDL. Would 'ze Germans' have put the diff lock mechanism in the diff in the factory but not connected it up in the cabin maybe?

Do you know if the diff lock is pneumatic or electric? Does your dble cabbie have a diff lock. I will take a phot and add it.

Also I found the purple tube. You were right, it is connected to the air filter housing. ANy idea where it should be connected under the dash, i.e. where the sensor is?

[jets]

If you have a PR no 1AD [inside your owners manual] you have EDL. I don't know if all T4s with ABS have EDL.
http://igorweb.org/equidec/Default.aspx

[Silver Caravelle]

My 2000 Caravelle front wheel drive has EDL. I think all models with ABS did

Cheers,

Scott

[Seano]

Seano, mine as I have told you before is the ex. NSW ambo vehicle and I know that it did have some special features like the ABS, dual A/C etc. The fact that mine doesn't have the switch on the dash tells me that I may not have EDL. Would 'ze Germans' have put the diff lock mechanism in the diff in the factory but not connected it up in the cabin maybe?

Do you know if the diff lock is pneumatic or electric? Does your dble cabbie have a diff lock. I will take a phot and add it.

Also I found the purple tube. You were right, it is connected to the air filter housing. ANy idea where it should be connected under the dash, i.e. where the sensor is?

Don't confuse the diff lock with the diff lock!! Syncro equipped vans in Europe had the option of a 'central' diff lock which essentially meant that the drivetrain was locked into a 50:50 power split when a dash mounted button was pressed.....normally Syncro drivetrains operate in an open fashion with the front wheel taking the dominate portion of the engine power. This is what I think you have. Mine does not have this as it would have been factory order option only (and only if you knew about it beforehand!) and I bought mine from Oz VW stock. I don't know where the diff lock mechanism might be located however as I said before, diff lock equipped syncro's have some unique parts in or about the rear diff. I'll wager that it is a electronic dash switch that activates a vacuum driven switch (exactly like the mechanism that operates to fresh air/recirculating air flap next to the fan blower) to operate the diff lock.

Here's a quick and dirty of my rear diff for comparison.

The cable coming from it is what I assume to be a temperature sensor or some such. And the shiny bits in the mounts are diff spacers to correct driveline geometry due to having a lifted suspension

EDL sounds to me like something to do with ABS equipped vans......mine does not have ABS.

The air filter display thingy should be on a small panel that sits below the centre dashboard....in your ex ambo this may have been removed....see the photo.