Thursday, November 6, 2008

Information On The AL4 Gearbox

This gearbox first appeared in Peugeot 306 and 406 models, and Citroën's Xantia and Xsara at the same time. It's mated to four cylinder engines, and is typically identified by a "wriggly" pattern for the shift lever. Installation carried over to the Citroën C5, Peugeot 206 and 307. It's also fitted in slightly different form to other marques including Fiat.

The earlier auto box is quite different, and is characterised by a straight slot for the shift lever to slide along. This commentary doesn't really apply to that unit, aside from generalities.

One point frequently raised with the AL4 is poor reliability. What I'm trying to do here, is address both rumours and facts. It's not actually a technical "how to" but may serve as a guide for prolonging enjoyment of a car.

  • Installation: Make sure that perceived transmission faults are not in fact other deficiencies, such as irregularities in the engine operation or failing motor mounts. This latter detail is coming to a head as vehicles age, especially given the original softness of their mount rubber. Also make sure the vehicle cooling system is healthy - free of scale and bled of air pockets.
  • Fluid Level: There being no dipstick, the level is checked via the overflow plug with motor running and transmission in Park, at operating temperature. It's quite well covered elsewhere on the 'net. Checking it with engine off, may result in oil running out of the overflow as the internal fluid pump is not keeping a volume of fluid in circulation. Low fluid level may result in a fault being indicated as the internal pump picks up a little air now and then - dropping internal fluid pressures.
  • Transmission Cooling: There is no external cooling for the gearbox oil. It circulates from the internal pump, through a heat exchanger that looks like a beefed up cigarette packet on the back of the gearbox (near the left front wheel). This heat exchanger is plumbed into the car's cooling system with hoses of about 16mm internal diameter. Three different heat exchangers have been used. The smallest was fitted only to gearboxes with the 1.6 litre petrol engines, while the largest came on turbo diesels. Rebuilders here only use the larger two sizes, and a rebuilt trans will typically have a new heat exchanger fitted for best efficiency. It's my personal opinion that auto transmissions in mainland Australia cannot be overcooled.
  • Adaptive Behaviour: The gearbox is rumoured to understand intimately your moods, intentions, know the road ahead and generally behave as experienced valet to your French magic carpet. Truth is somewhat less stunning. It simply looks at how you are driving it and attempts to help based on past "learning" events. One comment made by a transmission rebuilder, is that it responds well to an assertive driving style. In other words - let the gearbox know your intentions clearly. Accelerate smartly and it will kick down; feather the throttle off as you approach cruising speed and it will soon upshift. Brake firmly and it will downshift.
  • Alternative Modes: Most come with a three way switch panel allowing choice of Sport, Snow or low gear operation. For all intents and purposes, I have not noticed any benefits in the "Sport" setting - other than pulling hard out of an intersection into fast-moving traffic, and am yet to experience either snow or a need for creeping along in first gear. Don't drive with the car in "1" mode unless you have a clear understanding of when this is to be used (refer owner's manual).
  • Fault Lights: Infamously, when the two dash symbols for Snow and Sport flash (a little asterisk, and a stylised "S") there is an internal fault being recognised. This fault may be transient or somewhat more long term. The transmission has its own ECU; it does not have shifts controlled by the engine ECU. The default or limp home mode puts the trans into second gear without much subtlety in shifting.
  • Internal Components: The basic guts of an auto haven't changed much for years. The big differences are working tolerances, and how shifts are actuated (electronically, rather than purely hydro-mechanical). Often referred to in AL4 tales of woe, are "the solenoids". There are in fact a good deal of solenoids or electrovalves in the transmission, but the two problem ones are atop the valve body ("hydraulic block" in Franglais) - this is all behind the black pressed metal cover on the transmission front.

    Some years ago, the top two solenoids were recognised as a weakness, and revised. These are driven by a pulsed current to avoid permanently magnetising or overheating. Old solenoids were pulsed at 50 Hz, while the newer type are pulsed at 100Hz. Solenoid failure here, causes the default into "limp home" mode. When these are changed, the transmission ECU is supposed to be updated with a computer download. The update can be done without changing solenoids - old ones will operate on a 100Hz pulse, but newer units won't function satisfactorily on 50Hz.
  • Fluid Condition: Remembering that trans fluid has to do its job in a wide range of categories - cooling, cleaning and lubricating - it's a big ask. Over time the fluid will age and effectiveness is blunted. The transmission ECU includes a "oil wear counter" that adds in appropriate details based on operating temperature, fault events and accrued hours. When the counter is full (rather like putting coins in a jar) the unit needs a service and the wear counter resetting. A simple fluid drain/top up as mentioned earlier is calculated to allow a partial reset of the wear counter, by subtracting 2750 (presently this is a non-verified number) wear units per half litre of oil. Internet sources put the wear counter total at 32768 units.
  • Rebuilding: At present, rebuilt transmission in Australia, are only supplied by A&B Automatic Transmissions in Victoria. Due to arrangements in place with PSA, they will only supply the units to accredited dealers. Rebuilt tansmissions come with fluid (Esso) already filled to correct volume. I am not certain if the original ECU is changed over to the rebuilt transmission but consider it likely.
  • Perspective: The AL4 probably deserved its poor reputation at the outset - however, like bias against other aspects of the European makers this has lingered beyond fairness. Matters may have been aggavated by lack of customer liaison here; there perhaps could have been superior handling of drivetrain issues arising when cars were still under warranty, in some instances. It's a fine line between admitting fault and trying to improve customer confidence.


1 comment:

Ethan said...

Stick shift rocks...