I now have real-world feedback from my experience of the PTW replacement path on my 1.4 Tdi 75 (now on 138k). The car is mostly used for local commuting, but in normal times I have regular holiday drives Scotland to Plymouth overnight (grandparent visits with my daughter) so I have got used to sitting for hours at an indicated 2900rpm - the idea of something a little more relaxed has been appealing. I also know the fuel use from experience. For a long while I was thinking about the longer 5th option offered by
@depronman, but over the past couple of months the stars aligned in terms of parts and mechanic costs so I ended up going with the box swap approach instead.
Found the box on Ebay from a 50k 1.6tdi Bluemotion for £180 (£230 delivered on a pallet - made offer £50 under asking price, then added a completesavings 10% Ebay discount) - (pure luck - other codes of similar gearbox ie MYP / PTU were ~400-500 quid mostly). Picked up various replacement nuts and bolts as well as a Febi Polo diesel dogbone bushing which I managed to separate from the un-necessary gearbox end. New B&B clutch kit for around £60 with savings and an Ebay promotion). Based on
@depronman's recommendations picked up a JR driveshaft for the really noisy CV joint, and then a JR CV joint for the other side after the mechanic found the lock-tite on the splines to be about the toughest part of the whole job. I can also recommend JR as they have decent prices on Ebay (driveshafts, joints, boots etc.) and normally get your parts delivered in 24 hours if you order in a timely manner. I printed out the two photo guides from A2oc indicating the adaptor brackets to support the gearchange mechanism, and he knocked these up
in situ without issue and transferred the needed parts (gearchange cable connections, cable bracket, driveshaft flanges). As noted above, the lower mount only uses two bolts into the gearbox casing instead of the original 3.
Refilled the PTW with Bluemotion oil, and put it all back together. The original starter from my A2 and a 2017 CAYC/CRKB starter (
02Z911024L) I picked up just in case were compared, and the new starter seemed to offer up slightly better in terms of the pinion position and depth so we went with that option - there is a wire connector (
1K0973751) that needs to be substituted onto the loom to replace the original connector - mine is currently cobbled together with a cable connector under the starter motor cover. There was also a complete replacement of the rear suspension and handbrake using my supplied parts which confounds the numbers a bit, but if we divide the approx total labour costs 2/3 to 1/3, the whole swap has cost around £600-700 including parts, fluids and fixings.
My GPK always had a quite meaty shift (compared to both our 1.4i and my other AMF-engined A2), and this initially felt like a heavier but shorter shift front to rear - it was quite 'snicky' on the first drive, and occasionally baulked at the 2nd to 3rd transition even after warming up when trying to shift quickly. Looser on the right hand side of the gate (3rd to 4th to 5th to 6th were fine). The mechanic also said it felt a bit tight. As I was paying for fitting only rather than a 6-speed conversion
per se getting the rest right was my prerogative. I drove it for a couple of days adjusting my technique to match the new shift (slower / more deliberate movements to begin with, feeling for the gate instead of trying to push it where it used to be) and then decided last Sunday to try a cable adjustment in case they were a fraction out. Released the cable end that shifts the selector vertically between the planes of 1/2, 3/4 and 5/6. Within a few seconds, heavy rain started to fall, so I gave up and relatched it, replaced the bonnet and retreated to the garage. When the rain showed no signs of abating I decided to return the car to its normal position on the drive (I was using my other half's space as it allows access from both sides) - and found that the change into 1st and reverse felt markedly smoother reversing and driving back in. Having now used the car over a week the shift has loosened up considerably to the point that it feels barely different to my previous box (similar weight but slightly shorter shifting distance), so it is entirely plausible that the new box just needed some use as well as maybe a minute movement of the cable.
The next question is about the gearing and effect on economy given the seemingly interstellar gearing numbers of a PTW. On the latter, I won't know for a few tanks as I have only had it a week. Pulling away, my clutch point is obviously different (new compared to 138k clutch so hardly surprising), but the car takes off normally (12.2mph for 2000rpm vs 11.3 is negligible). I can quite happily tool around at 10-15mph in the supermarket carpark in 2nd gear at 12-1300rpm without issue - it isn't a case of needing to rev the nuts off in 1st to shift into 2nd - feels no different. Town speed roads (30mph / 40mph) are comfortable in both 3rd and 4th hovering around 1400-1500rpm respectively.
5th is a little longer than 5th in my original box (59.6mph vs 56.8 for 2000rpm, not quite as high as the Tdi90 at 61.3mph), and I have found that this works well on cruise at 40mph on flat backroads, and is good on the local dual carriageway (not that I use this a lot as there are quieter country roads to go home). However, on my single current experience up to around 70 - 5th is fine as a motorway gear, and putting it into 6th at 2100rpm and then activating cruise sounds like the engine has been stolen which bodes well for long distance motorway journeys. If 6th proves too high, putting the final drive from my spare GPK across into the PTW would be an option (drop from 73.7 to 68.7 mph at 2000rpm).
Finally - the new starter has also proved to be an improvement - elimination of the over-run squeal was one benefit, and it seems to spin the engine slightly quicker (reminiscent of a stop-start system) so it fires almost immediately. Will report back with fuel use comments after more experience and hopefully a long motorway run.