Project Leyland Mini Clubman
The Mini is our second project car to get wrapped up this issue, and we finish with a visit to AP2 gearbox specialist Martin Altria of Northampton to check and service our automatic gearbox.
Another long-term project is wrapped up, this time with an inspection and service for the Mini’s AP2 automatic gearbox.
The AP2 automatic gearbox was developed for the Mini by Automotive Products and BMC. It was a very compact design that packed four forward speeds into the Mini’s sump at a time when other automatics were much bulkier but still only had three gears. The AP2 was designed to run on engine oil, too.
Many enthusiasts will turn their noses up at the thought of an automatic, and it is true that having a self-shifter changes the nature of the Mini. However, that is not necessarily for the worse, because it encourages a more relaxed and laidback driving style – the gearbox will still hustle if you have a heavy right foot, but that is really not its natural element and automatics tend to live a much easier life than manual cars. However, if you are thinking of buying a parts car, be warned that a manual box cannot be simply fitted to an engine from an automatic car.
Just like a manual Mini, the gearing on the AP2 is low to make the most of the modest power available to cope with heavy loads in hilly terrain. That means it changes rapidly up through the ratios, and unless you have your foot to the floor, it will be in top gear by 22mph. That low gearing is partly what made it suitable for use with such a small engine at a time when automatics were generally the preserve of luxurious cars. It is also unusual for autos of this era in providing engine braking on the overrun on the top three ratios.
Our Mini was driving very well, but we wanted to have its gearbox checked out and serviced by specialist Martin Altria, who runs AP2 World in Northampton. Martin learned all about these units in the 1990s, while working for Michael Leach (one of the engineers who worked on the design of the AP gearbox originally) alongside somebody who had worked for Automotive Products in manufacturing and rectification back in the day.
Martin also owns VL Churchill, and is putting a lot of their special tools back into production, as closely as possible to the old drawings. He started making some of the
Churchill tools around 15 years ago for the AP boxes because there is no getting away from the fact that you do need special tools to work on them. However, although Martin very kindly showed me around his workshop so I can get a better idea of what goes on inside the AP gearbox, our aims for the Clubman were hopefully less invasive: we would carry out a road test, check the selector cable adjustment is correct, check the kickdown cable too, make sure there are no leaks, check the pressure and change the oil and filter.
Martin advises that on the road we are looking for change points, roll out points, any flare and clonks. Change points are the road speeds at which the gearbox moves up to the next gear, and ours are pretty much according to the book. Roll- out is the change down point when you take your foot off the throttle and let it coast down through the gears. As mentioned earlier, there is engine braking on all except first gear, and you want the change down to be smooth and not thump – again, ours passes this test fine. If it had been harsh,
that would have suggested the pressure regulator and valve body were a little sticky, or the springs a bit weak. Those can be changed in the car if you drain the oil and take the front cover off.
Flare is essentially the clutch pack slipping and causing the engine to rev between gears on upchanges. This is a bigger problem if it occurs between first and second or between second and third than if it is between third and fourth. ‘I can feel that the revs are picking up ever so slightly more quickly than the road speed when accelerating,’ says Martin. ‘ That is nothing to worry about, it is just a design characteristic of the unit. Modern torque converters have a lock-up mechanism, but ones from this era will always exhibit this slight slip if the torque overcomes the oil’s ability to transmit drive until the revs pick up to increase the amount of oil being pumped. You won’t notice that when accelerating hard, more so when you are just cruising on a light throttle and then want to accelerate.
‘ There is a little flare from third to fourth, but it is barely noticeable. If it was at a level that was damaging the unit, you’d really notice it as the car would feel like a manual when you have put one foot on the clutch while keeping the other on the throttle. If you have that, then you should lift off the throttle and push through the problem gently. Other potential problems are that if you have to really strain a leg on the brake pedal to stop it pulling away from rest, then either the engine revs are too high or the stator in the torque converter is starting to seize. If it is the latter, then you will need a new converter. This unit feels in all-round good shape, though.’
When it comes to an oil change on these units, Martin recommends that you should always inspect the old oil that has been drained. ‘ You will invariably get a little bit of aluminium debris,’ he says, ‘but the danger signs you are looking for are a lot of aluminium wear, a little bit of bronze or brass flecks, or any bits of steel. The big killer is what looks like black carbon flakes, but is actually the friction material on the bands breaking down.
‘It costs a lot of money to put one of these gearboxes right,’ Martin continues, ‘so a decent oil is usually a lot cheaper in the long run. If you don’t know what oil is in there, then changing it once should be fine on a car that is not being thrashed, but if you want to push it hard then I would recommend running it for a couple of weeks with the new oil, then changing it again. The only way to fully drain things like the torque converter is a full strip down, but changing the oil twice helps you get out as much as you can without going that far. And talking of oil, never use 20W50 in one of these. The specification is for 10W40 as it needs to be thin enough to get in between all the valves in the valve body and to get pushed out of the clutch packs through the grooves in the friction plates.’
While the oil is draining out, Martin
takes care of any adjustments – these are all detailed in the workshop manual. The oil itself is very clean, and we take this opportunity of checking the magnetic drain plug, which also shows no sign of swarf or metallic debris. The oil filter is a paper element type inside a reusable bowl. There is a blanking bolt on the top of the filter housing which is there to enable people to fill the new filter with oil, but nobody does. Martin manufactures a Churchill tool for reading the pressure that attaches to this point, with a hose that is long enough to reach the cabin so an assistant can read it while on the move.
First though, we need to clean the filter assembly and fit a new element. All the components clean up nicely, but Martin advises that you should check the end of the filter bowl carefully to make sure it has not become distorted. ‘ There is a rubber seal under the metal washer at this end of the canister,’ he explains. ‘If that seal goes hard and starts leaking, people then crank the bolt up more and more tightly in an effort to stop the leak and end up distorting the metal canister.’
With everything cleaned and reassembled, Martin removes the spark plugs, explaining that he doesn’t want any load on the crankshaft bearings until oil is fully circulated. You only need to spin the engine over like this for 10 seconds or so – time enough to see if there are any oil leaks and that you have some oil pressure building. With those checks passed, he refits the plugs and starts the engine.
He runs it gently initially, leaving it in neutral and not revving it. Then, with one foot firmly planted on the brake, he selects reverse, and then neutral. The gauge records 110-120psi in reverse which is exactly where it should be, and 90psi in Drive which is very good. There is no fluctuation at idle either, which is great.
With the gearbox given a clean bill of health, Martin completes the oil level check according to the book – warm the engine up, run through the gears, then turn it off and wait exactly 60 seconds before checking the dip stick. All figures are really good. ‘ That 60 second wait is important,’ he concludes, ‘and you should keep it consistent to get the right level. If you are consistent, you will be able to notice any changes right away and investigate them before things go seriously wrong.’
And with those words of advice ringing in our ears, our Mini Clubman adventure draws to a close – we hope you have enjoyed it as much as we have.