T4 diff lock (EDL)

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

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

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.

Quote:

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Originally Posted by 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.

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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

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 ?

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.

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?

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

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

Cheers,

Scott

Quote:

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Originally Posted by Jezza

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?

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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.
http://www.vwwatercooled.com.au/foru...42008001-3.jpg
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.
http://www.vwwatercooled.com.au/foru...22042008-3.jpg

Hi Seano,

Absolutely they are two different hings.

The electronic differential lock (EDL) for the non 4 wheel drives is really just an 'electronic' limited slip diff ( sort of a basic traction control) linked to the ABS and not so much a 'lock' as you indicate.

It is tied to the ABS to monitor if one front wheel is spinning faster (i.e. skidding) than the other front wheel. The ABS is applied to the faster front wheel transferring the power to other front wheel for wheel speeds over 9 to 10km/h when the ABS is activated.

Cheers,

Scott

yeah Seano, very different to mine. I have attached a photo to show you my rear diff. Taken from behind showing diff and left hand wheel. Can you see the mechanism, the small motor and the gear housing.

I am very envious that you can store your spare wheel underneath.

On the air filter indicator, the fact that my indicator is not there tells me that they may have removed the panel with the air filter indicator and the diff lock switch too maybe??

Does anyone else out there have a 2000 model ex NSW ambulance/patient transport vehicle that I could compare notes with?

Did you have to change the drive shaft in any way to lower the diff because of the slightly longer length required, like actually lengthen it or lower one of the rear drive shaft mounts. Or was there enough movement in the drive shaft to allow for the lowering of the diff.

Ok. For those that are interested, I have had a revelation. I was on the vwt4forum.co.uk forum at;

http://www.vwt4forum.co.uk/showthrea...ight=diff+lock

they had a webpage that deciphered all the codes in your drivers manual, namely;

http://igorweb.org/equidec/Default.aspx

I punched all my codes from my book into the website and came up with all the details of my vehicle. turns out that mine has the following;

1AD = Anti-lock brake system (ABS) with electronic differential lock (EDL)

Sounds good. Now all I need to know is, should it have a dash mounted operation switch or is it automatic? Hmmmmmm

If it is automatic Seano, I now know why it goes so well in the sand of WA. It is unstoppable over here.....

You obviously didn't click onto the link that I posted earlier on this thread.
Did you learn about any other options your van has from the PR nos?

No I must admit I read that message and didn't have a clue what you meant by 'PR no 1AD'!! I realise now obviosly.

Any idea if the diff lock should be automatic or should it be manually operated.

Apart from the obvious like 'steering wheel', 'four wheel drive and 'LWB', I learn't that it has an 'increased payload', 'Alternator 90A' and 'Transmission ratio, high geared'. I was hoping that I had a 110kW motor but it only turned out to be a 75kW. I am very happy with power. It has plently enough for me at 75kW. I can't quite beleive how much power it has actually, plently of overtaking power and it accelerates well when needed.

I should have explained that PR means optional equipment. I came across the term in elsawin but was able to work it out after reading the owners manual.

I don't know anything about the rear diff lock actuation, you may have to ask your dealer.

I thought my alternator pushes out 120A. Can't find my notes just at the moment.

Quote:

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Originally Posted by Jezza

yeah Seano, very different to mine. I have attached a photo to show you my rear diff. Taken from behind showing diff and left hand wheel. Can you see the mechanism, the small motor and the gear housing.

On the air filter indicator, the fact that my indicator is not there tells me that they may have removed the panel with the air filter indicator and the diff lock switch too maybe??

Did you have to change the drive shaft in any way to lower the diff because of the slightly longer length required, like actually lengthen it or lower one of the rear drive shaft mounts. Or was there enough movement in the drive shaft to allow for the lowering of the diff.

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Thanks Jezza.......yep.......you have a rear diff lock. And I am hell envious. Although since you don't know whether it is activatable or not (or even permanently on - not a good idea) then I'm not sure how great that is!! Only way to find out is to get all wheels off the ground and turn one of the rears. If the other side turns then you have a problem.....but only a minor one - mostly to do with fuel economy. CORRECTION my handbook says it shouldn't be used above 45km/h and an acoustic warning signal should sound on vehicles equipped with ABS when you do.

Diff lock switch should have been up on the dash in the switch line with aircon, rear window heater etc.CORRECTION......my vehicle hand book shows that the difflock switch (a pull knob plus an indicator) would have been on the same panel as the air filter saturation display.

Fitting the spacers required nothing else to be modified - it was to correct the drive shaft angle so the drive shaft couplings (which are flexible) don't wear out prematurely as a result of the lifted rear suspension.

Yeah, I am pretty excited about it. It wouldn't be on permanently otherwise something would have gone bang by now. It would defeat the purpose of having a lock I suppose, 'lock' meaning on and off capability. My manual says the same about the pull out lever/switch. I have followed the electrical wires but cannot find where they enter the engine bay or under dash. I have pulled the under side of the dash covers out and have found no evidence of unused wires, colour coded to the diff lock or otherwise to indicate that there is a missing switch.

The diff lock also has a vacuum line. I have followed vac line and it connects to the main vac line going to the barake booster. As I mentioned before, the fact that the air filter indicator was disconnected, I found the purple vac line under the dash too by the way, disconnected behind the heater controls, tells me that some where along the line the air filter indicator and possibly the diff lock which was removed and maybe not put back. Hmmmm.

I have a copy of elsawin now, the VW program with all the vehicle details. I haven't managed to get it going as yet. Having a few dramas with it.

Also Seano, in front of the diff on the tail shaft there is a large circualar device, 1800mm dia. approx. 250mm long which I assumme is the tail shaft vicsous coupling. I also wonder if this is lockable by the diff lock mechanism as well? From your photos on pg. 1 mine looks longer than yours. The way my diff is set up, it looks like it could be operable from the diff lock mechanism....i'll take a photo of it shortly.

Diff lock or not, I am impressed where this vehicle can take me. Maybe then the diff lock is automatic....

Jezza

The fact that the diff lock operates via a pull out switch suggests that it uses a vacuum line to the switch from the brake booster.....not electrical leads.....basically it's a tap. Exactly the same as the one in my old Range Rover - it uses manifold pressure to activate the central diff lock. So you may be looking for at least two vacuum lines.... alternatively you are looking for an electrically operated in-line tap.

That big circular device is, I assume, some sort of driveshaft balance come flywheel. If you poke your hand in behind the rubber flange you'll find a large hollow area.....probably filled with rocks and sand!! There's nothing there to lock.

Thanks Seano. There are two vac lines coming out of the diff lock mechanism. One heads straight to the engine bay, I'm happy with that, the source vacuum, the other comes from the mechanism and is then 'tee' peiced into the top of the actual diff housing then runs a bit further into the sub chassis and I can't find where it goes after that. There seems to be another vac line from else where, ABS system perhaps that is connected by a small cover into an electrical line. Vague I know but I will get under there now and have a good look and let you know.

If the diff lock is vac operated, I assume then the electrical connection is just a warning and indication light for the dash....

Quote:

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Originally Posted by Jezza

There seems to be another vac line from else where, ABS system perhaps that is connected by a small cover into an electrical line.

If the diff lock is vac operated, I assume then the electrical connection is just a warning and indication light for the dash....

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The 'other' line into the diff is probably the sensor hooked into the ECU (which mine has)

The electrical connection at the switch is almost certainly just for the dash mounted warning light but it must hook up to your ECU at some point given you have ABS and the book says that in vehicles with ABS an audible signal will sound if you go over 45km/h with the diff lock engaged.....

The missing airfilter gauge and difflock switch can be easily explained. On some vans the Ambulance upfitter added the extra radios on the lower dash, where the gauge would be. I've also seen some early vans with the switch panel there as well, iirc there were a couple of companies doing the conversions. As for the difflock, chances are it was disconnected early in the vehicles service. Ambulance drivers aren't known for being gentle on equipement, you should see the carnage they caused on the Sprinter 4wds!

Thanks for your reply. Any ides who the ambulance upfitters were. There may be a chance that the dash peices are lying oround in their warehouse. Wishful thinking I know but one must try

Jez........somewhere in a bullbar post is a link to the dudes that do/did NSW ambulances....

Cheers Seano. I'll have a looksee....