Allroad BHW/02X TDI Conversion

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Figured it's finally time to write up my swap. I have been toying with the idea for a couple years, and pulled a BHW from the local pick'n'pull in 2021. In 2022 I found a '03 in reasonable condition, running and driving, with a decent amount of options. The original drivetrain was the 2.7T with auto transmission. The goal with this car is, as I'm getting less interested in power and more interested in practicality, to build something nice to drive, with room and capability, but also lots of features (I love electronic gadgets).

This is the car the day after I bought it. I drove it home 6 hours and it didn't give me any trouble; there were some warning lights, some bulbs out, and there was no heat coming out of the vents (in February). Heated seat kept me plenty warm for the drive home.

I addressed a few things shortly after buying it. The sunroof wouldn't close, and there was a self-serve wrecker on the way home with a couple A6s, so I grabbed a whole sunroof assembly, and when I got home, lowered the headliner enough to replace the whole thing. Other than that, it needed a hatch latch, had some burnt out bulbs, and a suspension height sensor needed the connector cleaned and plugged back in. Air suspension was still on Audi branded parts at almost 300,000kms which was nice to see, and the rears didn't start leaking until the next winter (sitting in the parking lot of our building). Body has a few small scratches and dings, but this is a car I want to drive, not a show car, so it doesn't bother me much.

Next was the research stage and parts gathering stage. To help minimize downtime, I planned as much as I could in advance and ordered loads of parts. I was planning to delete the balance shaft module, but when I took off the oil pan, I found...

... a geared balance shaft module. Checked for play in the hex drive and there was none, so I opted to keep it. Since I want a nice smooth car, this engine turned out to be the perfect find, and this is probably a good sign that it was cared for at some point in its life. The car I pulled it from had 360k kms on the odometer and had obvious side body damage. This engine also had an oil pan with an oil level sensor, even though there was no sensor plug on the harness, which is a bit of a mystery. I don't think these engines were ever offered with an oil level sensor in North America, were they? It's not a 1.8T pan, definitely a BHW or BGW part.

I prepped the engine with a new 'stage 2' Colt cam (original was worn), INA lifters, injectors rebuilt with new nozzles, new tandem pump, timing belt, water pump, and got almost all new hoses/plastic coolant fittings. The engine was pretty clean inside. The oil galley plugs on the ends of the rocker shafts were still in place but a little loose, so i just drove them all back in and staked them a bit. Also picked up a brand new stock-replacement Mahle brand turbo for a steal (had some cosmetic damage), a friend sold me a stock catalytic converter from a parts car, and the parts for coolant glow plugs. To add coolant glow plugs I needed 038121133A (found in NA on ALH/BEW manual trans engines), 038121145 (Euro-only coolant glow plug flange), coolant glow plugs for a BEW/ALH engine, and one of the EGR cooler hoses was replaced with 8D0819337 (it uses a quick connect fitting instead of a clamp, and a different exit angle). Pulled another engine harness later on since the original was hacked up quite a bit (I guess it was too much in the way when the people who work at the yard pulled the catalytic converter; the also cut the compressor housing off the original turbo )

During the research phase I theorized that I could keep most or all of the 2.7 A/C system including compressor if I switched to a BPW accessory bracket instead of the BHW one. As a bonus, that accessory bracket also moves all of the accessories to one side of the engine and deletes the clutch fan. I ended up ordering one off ebay for around 75 CAD shipped (03G903139D). The belt tensioner interchanges with the FWD CR TDI engines sold in North America, and the idler pulley (03G145276) is the only other Euro-only item in the setup besides the bracket itself. To complete the setup, I ended up getting some more stuff from the local pick'n'pull; B7 A4 2.0T power steering pump and line, BRM 6-rib harmonic damper, and a Mk6 Jetta 2.0L alternator (140A and direct fit). The lower bracket bolts are different from the BHW bracket and a Euro-only part (very long), so for those I ended up pulling some head bolts out of a Ford V6 in the yard that were a perfect fit in terms of length and threads. I'm sure they're TTY, but they have a much easier task in this application... More on the A/C compressor later.

 

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I hummed and hawed for a long time about what to use for a clutch. The 02X transmission can use all the same clutch setups as the 01E and 01A/012. It seems like the 1.8T 228mm Luk DMF/clutch is probably the best option for those staying close to stock power levels and/or on a FWD chassis. However I felt like for longevity and reliability, with the added weight/stress of the Allroad chassis and AWD, it would be best to go with a 240mm TDI DMF/clutch. Here's the parts list I settled on:

DMF - Luk 415 0244 10
Clutch - Luk 624 3342 00
Pilot Bearing - 06B 105 313 D (more on this later)
TOB - Included in clutch set
Starter - 03G 911 023 (needed for the flywheel)
Turbo Brace - 038 145 535M (needed to clear the starter)
Bellhousing Spacer - 01X 103 551
Bellhousing Dowel Pins - 01E 301 153G (needed because of the spacer)
Bellhousing/Starter Bolts from a B7 2.0T car
Typical TDI DMF bolts
Typical Audi clutch pressure plate bolts - N 903 086 07

Optional - Right Side Engine Mount Bracket - 8E0 199 308AR, more on this later

Everything except the DMF/clutch, starter, and turbo brace interchange with B7 2.0T parts. I do plan on eventually keeping a spare starter in case I ever need one in a pinch. I was lucky to get all of the hardware and the spacer from the same car I pulled a 02X from in the junkyard. Clutch and flywheel were about 600 CAD shipped from ebay in Europe.

The bellhousing dowel pins twisted out quite easily with a pair of pliers, and the new ones went in with minimal effort:

For the pilot bearing, I've seen a lot of creative ways to go about managing the short crank snout of the BHW. But why not one more. I found that the B7 2.0T pilot bearing uses the same internal and external dimensions, but has a cup on the end not present on 1.8T bearings, making it a bit longer. To give this the best chance of working, I started by placing a washer slightly smaller than the opening of the crank flat at the bottom of the hole. This was a bit tricky, but it helped to tilt the front of the engine down quite a bit:

Next, I drove the pilot bearing in all the way until it was pressed against the washer. I believe this will help support the bearing as it is protruding from the crank quite a bit. The pilot engagement is perfect with this setup, and as of this writing I have over 6000 kms on it:

The pressure plate as it arrived did not appear to have the self-adjusting mechanism fully reset, so I put it in the press, supported by the bolt locations, and used an old TOB/pulley arrangement to fully reset it:

After clutch install, the transmission was bolted on and the drivetrain prep was mostly complete:

 

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I started removing the old 2.7/auto in February. Removal went fairly smoothly, with not many hiccups. One of the infamous pinch bolts came out easily, the other one broke, but I was able to use the nut to just pull the rest of the bolt through; not too bad overall.

I was able to sell the old drivetrain and cats which was nice. Made a bit over 1000 CAD back from the initial purchase.

Was really nice to see that the car really is as rust free as I was hoping for. The worst is some surface rust on the rear suspension parts, but I will eventually refurbish all that and install an aluminum subframe back there anyway. I left all the A/C stuff on the car since I was hoping they would be a direct fit for the BPW accessory bracket I'm using.

With the drivetrain out I could clean up and re-bush the front subframe. The Allroad subframe bushings are NLA, but A6 bushings are a direct replacement after drilling holes for the dowel pins that align the subframe spacers. The old Allroad rear bushings had plastic inserts in them that the A6 replacements did not, but I was able to just transfer them over. I opted for Lemforder brand replacement bushings as they are an OEM brand and they were very reasonably priced. The subframe cleaned up really nice and has almost no surface rust:

And I used some 1/2" extensions wrapped in electrical tape at strategic points to align the subframe. I had it aligned at an Audi dealership later on and they said they didn't need to adjust it.

 

[JordanTr]

This is a fantastically done write up, and perfect timing to boot. Thanks!

 

[Petra's cousin]

Following with great interest - I owned a 2004 manual Allroad which I turned in for a cheque when insurance wrote it off. My 1 1/2 years of ownership was very expensive for a number of reasons (and it was low mileage to boot). I used that insurance cheque to buy our 2011 TDI sportwagen and would love to own a diesel version of my Allroad instead.

P.S. pinch bolts never caused me any grief but I did fight the lower front ball joint on our B5 Passat wagon and was ready to break out the torch to remove an assembly retainer on our Allroad when replacing one of the front airbags.

 

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Next task was adapting the B6/7 transmission crossmember to the Allroad. For the main rear subframe bolts, since the subframe adds thickness to the stack, I opted for B8 rear subframe bolts (N91227901), about 15mm longer than the original Allroad bolts. Maybe not totally necessary, but can't hurt to have the extra length.

Normally, this crossmember doesn't fit B5/C5s because it requires substantial cutting to clear the body. However, with the 25mm subframe spacers used on the Allroad, the crossmember clears the body with only relatively minor grinding, and some trimming of the trans tunnel heat shielding. There is an alternate crossmember used on Euro CR TDI B7s with only one hump on the right side. That Euro crossmember (8E0399263BE) may fit without any grinding and may even fit B5s, but they're far less available.

So after test fitting the crossmember with the two rearward subframe bolts, I started out with some 3/4" flat bar.

The brackets are close to mirror images of each other. One bolt on each side needs to use a countersink bolt because the crossmember covers it when in place. I went with stainless steel countersink bolts to avoid future corrosion to the brackets. Since the crossmember mounting bolts use two different planes, there also needs to be a spacer between the crossmember and the brackets for one bolt on each side. For the bolts, I took some junkyard engine bracket bolts and cut them down as necessary. This also gives all 6 crossmember bolts 18mm heads which is nice. Also, since the undercoating prevents the brackets from laying flat, I scraped off enough undercoating to allow them to lay flat on the body when installed. Some extra holes were also drilled in the top side of the brackets to clear spot welds on the body.

I'm currently designing some CAD files to re-create these with an improved design (no need to scrape off undercoating, no additional spacers needed), and it seems that 3/4", while close, is slightly on the thick side of what is needed. I believe the ideal thickness is 18mm with an additional 9mm step. These original brackets were made with only an angle grinder and a drill press.

This crossmember is also used on 01Es, 01As, 0A3s, and CVTs in the B6/7 chassis, so these brackets are also potentially useful for adapting other transmissions into an Allroad.

 

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Last thing I did before installing the drivetrain was to fabricate an exhaust hanger for the rear end of the catalytic converter. Very likely the B7 BPW hanger 8E0253047D would be a direct fit, but it wasn't too bad to make my own out of some stainless steel sheet metal. I reused one of the rubber exhaust hanger mounts that was attached to the Allroad auto transmission.

 

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With the crossmember adapted, the drivetrain was ready to install. Before putting it in I did some repairs to the wiring harness (was cut in a few places when I pulled it) and installed it on the engine, since some of the securing brackets are far less accessible with the drivetrain in place.

Everything slipped in fairly easily. The 4 cylinder engine mounts fit into a different hole on the left side than the original V6, but they slipped right in with no modification. Both engine mounts were replaced with brand new OEM mounts, as one of the junkyard ones showed signs of the hydraulic fluid leaking out.

As predicted, the original 2.7 A/C compressor bolted right up to the BPW accessory bracket, however, the pulley spacing was considerably off, so that's something that needed to be dealt with. The A/C lines also hung down lower than on the V6 and would need some bending to tuck nicely under the oil pan.

The stock auto driveshaft bolted right up with zero issues. I also used the 02X CV joint cover, though I'm pretty sure the auto trans one or 01E cover would also fit no problem. The 02X trans mount lined up perfectly; also replaced with a new one, these are just rubber mounts, not hydraulic, even in the B7 TDI cars.

Also grabbed the firewall insulation from a B5.5 TDI car in the yard. Just needed some minor trimming in a few places to fit onto the C5 firewall. C5-specific insulation exists, but was only used on 4.2 V8 and TDI cars. The B5.5 TDI cars also have some insulation around the steering rack and shock towers. The steering rack insulation should also be a direct fit.

The bracket that holds the glow plug module in the B5.5 is spot welded on, so I relocated it a bit and made a small bracket to attach it to the ABS pump bracket.

Also picked up this BPW engine cover from Europe and modified it to pop on and off. It's very similar to modifying an ALH cover, but two of the grommets have to be trimmed to clear the round covers, and the stud on the intercooler pipe needs to be pressed out and replaced with a ball stud and nut.

 

[caffeine]

So dealing with the A/C, I had a couple options to deal with the pulley spacing. Either find another pulley to fit the 2.7 compressor with correct spacing, or convert to a B6/7 direct-drive compressor. The C5 climate control unit can be coded for a direct drive compressor, as direct-drive compressors were used on the 3.0L A6s and 4.2 Allroads. To convert to direct drive also requires adding an evaporator outlet temp sensor inside the car, but that is relatively simple, as it's just two wires to the climate control unit, and the hole for the temp sensor is already present with a rubber plug in it. It's accessible with the glove box removed. However, by keeping the 2.7 compressor, there's no need to evacuate the refrigerant or recharge it (if it was working well prior to the conversion).

I ended up searching through the rockauto catalog looking at photos of other cars that use the same type of compressor, and found that the 99-03 Saab 9-5 uses the same type of compressor with exactly the pulley spacing I needed. So I ordered a replacement clutch/pulley set for that car and installed it on the 2.7 compressor. Result was a perfect fit, and the ideal belt for this setup turned out to interchange with an ALH Mk4. The Saab clutch uses a different plug, so I cut it off and spliced on the plug from the original 2.7 clutch.

I then bent the A/C lines from the compressor to fit nicely behind the oil pan sump, and made brackets on each side to hold them steady in that position.

 

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One issue with the right side engine mount bracket is that with the Euro 240mm starter, and the alternator and starter cables attached to the starter post, there is almost zero clearance between the positive wiring and the engine mount bracket. I originally did some grinding to the Passat bracket, but ultimately decided to order a BPW bracket as it was fairly inexpensive and I knew it would be a direct fit. I transferred over the 1.8T heat shield to it, and bent the ground strap lug to fit the BPW bracket as the location is different.

 

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Most or all people who have done this swap, seem to trim the rad support and modify the Passat intercooler crossover tube to fit the Allroad. Inspired by the fact the 2.5 TDI A6/Allroad use a front mount intercooler, I decided to keep the rad support original on my car and go with a FMIC rather than using the Passat SMIC. Since the Passat crossover tube also places the snub mount, I needed to come up with a custom solution for the snub mount instead.

I hypothesized that a B7 snub mount bracket might work with some minor modification, since the BHW oil pan already has the bolt bosses for it, but the V6 snub mount location is too far to the right side for that to work. I then cut the end off the B7 snub mount bracket to make something custom with. It might be possible to place the snub mount directly on the lower rad support brace, but with the BPW accessory bracket and the clutch-driven compressor, there's almost no belt clearance, which leaves no room for adjustability as the mounts wear. With a direct-drive compressor, there would be a bit more room for adjustability, as the direct-drive compressors have a smaller pulley.

What I ended up doing was making a custom snub mount bracket to utilize the original location on the V6 rad support. I used the cut-off end from the B7 bracket to support the actual mount, and drilled out the middle to use an M14 bolt/nut to attach it to the rest of the bracket. I added a tapered washer from a BMW wheel bolt. The main bracket was made from 3/8" aluminum flat bar, and the nub was spaced out with some leftover aluminum from making the trans crossmember adapter brackets.

Because the V6 mount cup was a bit taller than the BHW one, I also riveted a piece of aluminum to the top of the cup so that the mount would be just as snug as the factory BHW setup.

This setup moves the adjustability to the rad support side, just like the V6, but I slotted a couple of the holes on the main bracket for some extra adjustability. I'll probably replicate this design in CAD eventually, at least make it more professional looking.

 

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Axles/VSS. I played around with a few different types of axles before settling on my solution. Previously I had seen that the recommended axles to use for this conversion in an Allroad is an Allroad 01E right axle on the right side, and a right side B6/7 manual axle on the left. Aftermarket axles are known to be inferior to OEM ones, and OEM Allroad manual axles are quite difficult to find, so I needed a different solution for the right side. In addition, I needed a solution for the lack of VSS. Cars with ABS 5.7 can have a wire added to the ABS module plug that provides an appropriate VSS signal, but mine has ABS 5.3 which lacks this output signal.

The right side B6/7 axle is only about 6mm shorter than a right side Allroad axle (compressed length), and I stumbled upon this axle spacer/VSS ring (https://www.ultraperformance.co.uk/0a3-gearbox-vss-trigger-wheel). While this is intended to be used on a B3/B4 Audi on the left side, it both solves my axle problem and adds a reluctor for a VSS on the right. It spaces the axle out about 16mm which is even more ideal than an Allroad 01E axle, as the inner joint will be closer to the middle of its range instead of nearly fully extended at higher suspension levels. So for axles I ended up using 2x B6/7 right side manual axles. They can be sourced from both 01A/012 and 01X/02X cars, maybe also 0A3 S4s. There may be some minor variations between them, but the important dimensions are all virtually the same.

The same website also offers a VSS bracket w/sensor, but that bracket cannot be used with my setup because I'm using the spacer/reluctor on the opposite side of the transmission. So next step was to source an appropriate sensor and make a custom mount for it. I found that an intake cam sensor used on various BMW I6s in the 00s not only uses the same plug as the original Audi VSS, but has a long enough cable on it to reach the original plug location on the other side of the transmission. There is one wiring modification needed though; the Audi VSS only uses two wires, signal and ground, while the BMW sensor needs a 12V+ reference wire, so a pin needs to be added to the VSS plug on the harness that provides IGN+ to the sensor.

This is the bracket that I came up with. The mounting bolt holes are a bit larger than necessary to be able to get the sensor at the perfect distance from the reluctor.

Longer axle bolts are required on that side to pass through the axle spacer, so to keep continuity with the other side, I cut down some rear B7 axle bolts (same as used on the rear of the Allroad as well) so they have 10mm triple square heads just like the other side.

On a side note, I also played around with C6 manual axles (from Europe). The C6 axles' outer joint cannot be used because it lacks a VSS ring, but the B6/7 S4 outer joint is a direct replacement for it. The left side C6 axle is actually almost the same length as the right B6/7 axle, maybe a few mm longer, but since the S4 outer joints are larger in diameter, I found that the boot would be rubbing the shock at full steering lock. I ended up just keeping the one as a spare, since it will still physically fit. The right side C6 axle is too long to the point that at normal ride height, it will shift the transmission to the left.

 

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Fuel system. It seems that most people who swap these add a tee between the feed and return lines, coupled with the original high pressure pump, which reduces the pressure down to a workable amount. I didn't particularly like this setup, since a) it can potentially make it more difficult to purge the air out of the system, and b) you really have no control over the fuel pressure, and it is almost certain to vary with voltage and as the pump ages and wears out.

First thing I did was pump out as much gasoline as possible with the original pump by jumping the fuel pump relay. Next was to remove all the Allroad fuel lines up to the rear end, delete the original fuel filter, and remove all the evaporative emissions equipment, since it is no longer needed. The Passat TDI fuel lines are a near-direct swap into the Allroad. Note that the attachment nuts need to be used from the Passat, since the Allroad ones don't fit properly.

The Passat fuel lines also have a built-in fuel cooler which is lacking on the original Allroad lines. The 2.5 Allroad TDI uses a much more complicated fuel-coolant cooler in the engine bay. The main modification needed to the Passat lines is to cut one of the rear lines down, since it is far too long. After cutting the line, I slightly flared it out with a screwdriver (just as a safety measure to keep the clamp from slipping off), and bridged the original Allroad hard lines at the rear with short sections of rubber fuel injection hose. The other line needed to be extended a bit to reach the rubber line on the Allroad side, so I cut a section of the original line and flared it out a bit as well to bridge the distance.

The front section of the lines snaked in with no modifications, and I used the body clamps from the Passat donor. All the necessary studs were already present on the Allroad body.

For the pump, I first disassembled the Passat sending unit and removed the pump from the sending unit. The plastic line that is attached to the pump is quite difficult to pull off, so I ended up just slicing it with a razor blade to make sure the pump stayed intact. The Passat TDI pump has a built-in pressure regulator which returns excess fuel straight back to the sending unit with a short plastic line.

The main differences between the original Allroad pump and the diesel pump, are that the Allroad pump does not have a built-in regulator, and the Allroad pump's outlet makes a 90* turn, and the diesel pump output points straight up. Because I wanted to re-use the plastic hose from the Allroad sending unit, instead of cutting it off the pump, I crushed the nipple on the Allroad pump with some pliers and pulled it off intact.

The diesel pump slipped right in no issues into the Allroad sending unit and clipped into place. I reused the sock from the diesel even though I'm pretty sure either one could be used.

The line from the Allroad sending unit slipped nicely onto the diesel pump and I secured it with a zip tie.

The regulator return has a specific place to be secured in the diesel sending unit, but I simply snaked it through the Allroad sending unit to place it near the bottom. I don't see it being an issue in this position.

Reinstall was pretty straightforward. The original wiring fit right onto the diesel pump, and because the diesel pump points straight up, I had to take a little care to make sure the outlet line didn't get kinked with the lid reinstalled. There is enough room however, and this setup is confirmed to work perfectly with the original suction jet system as well. I have driven the car down to about 5L remaining in the tank with zero issues.

I also took the lid off the sending unit on the left side of the car to make sure there was minimal gasoline remaining, and soaked up a bit with some paper towels; there was almost nothing left.

Last thing to finish the fuel system modifications was to open up the filler neck to accept a diesel filler. I bought a truck-stop adapter from VW to be able to test that the opening was large enough. The fuel filler can be removed separate from the tank, so it was removed first before drilling it out. I ended up using a hole saw in order to get deep and large enough. The flap that's in there was completely removed through this process. The inside is mostly plastic so was really easy to do the drilling.

The filler neck has a line on it that goes to the charcoal canister under the spare wheel well, and the leak detection pump on the left side has this filter on its inlet line, so I took that filter and put it onto the line going to the charcoal canister, and removed the canister and all of its lines completely. I don't know if it is necessary to keep this line open, but I felt that it couldn't hurt to keep this as a way for the tank pressure to remain stable as it is filled and emptied.

Topped it all off with a diesel fuel cap from a Mk5 diesel in the yard. Direct fit.