Andrew Clink

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Eurovan TDI Conversion: Drivetrain

28 November 2015

2.5l 5-Cylinder AAF Removal

Anyone who's ever done a timing belt (or frankly just about any work) on a 2.5l AAF or ACU engine in a Eurovan knows it's a tight fit. There's almost no room to touch certain components, much less access them with tools. The serpentine belt tensioner is uniquly surrounded on 5 of 6 sides, tucked up between the firewall and the frame. 

This means that removal of the engine— as compared to an A3 Jetta or B4 Passat that might have provided a donor engine— is tedious. The drivetrain in the T4 hangs from two mounts, with torsional support in one of three styles provided by a transmission mount. As such it must be removed from below. 

Start by removing the entire front of the van. As the front clip is removed, the wiring harness for the headlights, turn signals, and fans will have to be separated out. For whatever reason (my assumption is sadism), Volkswagen did not see it fit to include plugs to separate wiring looms.

At this point it will likely be getting dark and the frightening reality of what you've done will begin to set in. Fear not; eventually the image of the eyesore-on-jackstands, entrails spilling out, will serve as a reminder of how far your project has come. Probably.

The rest of the removal is straightforward, if tedious. Unbolt the axles (you'll need 10mm triple-square bolts; autozone sells a reasonbly priced set), unbolt the clutch slave cylinder, disconnect the rest of the coolant hoses (the two top heater-core lines can stay), and separate the rest of the wiring.

After supporting the engine on either a trolly jack or hoist, remove the very large 21mm pin bolt from the lower transmission mount. Then begin removing the four upper 13 mm bolts. To be clear, the entire weight of the drivetrain is hanging on these mounts. Support the drivetrain before removing them. The drivetrain can then be lowered out while pulling the base forward to clear the lower transmission mount.

Fifth Gear Oiling Modification

The 02A, 02B, and 02J transmissions (and probably others) all have a design flaw by which the fifth gearset is separated from the rest of the case and can potentially be run without oil. A low oil level in the gearbox exacerbates this problem. Furthermore, the fifth gear side of the case cannot be drained through the drainplug. VW has apparently designed an oiling rail to help the gears pump oil into the fifth gear side of the case, but it doesn't solve the draining issue. 

One solution suggested on the TDIClub forums is to drill transfer oil slots in the wall separating fifth gear from the rest of the case. I had decided to proceed with this modification with one caveat. The fifth gear wall was either a design compromise or a misguided design choice; either way it acts as a baffle. With this in mind, I decided on one small hole rather than a series as discussed on TDIClub. This is done by removing the fifth gear cover plate 11mm bolts and drilling a small (10-12mm) hole between the leftmost 45° rib and the bolt for the 5th gear selector fork. Imagine my surprise when I opened the new transmission after much deliberation and found the hole already drilled. At least that means I was headed in the right direction.

 TDI Installation

The installation of the TDI is far easier than the removal of the 5-cylinder. There is a ton of space on the timing belt side that will probably be utilized by intercooler piping. Just be careful not to bind on the shift rods when pushing the transmission into place. 

If installing a newer 02B transmission, such as EWB or DUJ codes, one difference to be mindful of is the lower transmission mount. The CHP code transmission mounts with a rigid bracket bolted on to the rear of the differential. The newer 02Bs mount with a "pendulum" style bracket with bushings at both ends, part number 7D0399207B. The subframe for all but the earliest T4s accept this bracket in place of the CHP's rigid mount. At this point I believe that all North American Eurovans '93 on that came with the 2.5l gas engine will accept this mount without modifications (right side #30 in this diagram). My guess is that the earliest T4s were European-only (left side #8). I also believe that the automatic transmission pendulum mount is identical, though it has a slightly different part number 701399207B.

The installation with an engine hoist is easy enough that I'm test-fitting the engine to begin to make intercooler and exhaust pipe routing decisions. It'll have to come in and out a few times to perfect the fit, but man it feels good to have it off the engine stand.