Review of the AL4 automatic gearbox

If you have a Tip or Trick, some advice or you just want others to know something that is specific to the a Citroen C3 with an automatic gear-box , please, post it here. Includes the 4 speed AL4 with PRND and the 5 speed semi-automatic (SensoDrive) with '+ and -' controls.
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Think: Auto not changing up or down, snowflake and sport flashing, flappy paddles and sensodrive not changing gear.
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My Name: Ozvtr

Posts: 1043
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Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
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This review turned out to be a bit long and wordy. If you just want my thoughts on the AL4 gearbox skip to the review part.

The AL4 gearbox is an "automatic" gearbox used by Citroen in the C3.
An automatic gearbox simply means that the driver does not have to worry about manipulating a clutch during the operation of the cars controls.
There are a number of different types of automatic gearboxes but suffice to say the AL4 is a "classic automatic transmission". Sometimes referred to as a PRND transmission, as this refers to the modes of operation. Park, Reverse, Neutral and Drive. Other types of automatic gearboxes include Constant Velocity Transmission, duel clutch and piloted manual gearboxes, But I'm not going to talk about them.
The classic automatic has a number of major components. The torque converter, bands, clutches, epicyclic gears, hydraulic actuators and an electronic control unit. By comparison to a manual gearbox, an auto is very complicated.
Both a standard gearbox and a 'classic' automatic gearbox match the engine revs for the road speed and demand by changing gear ratios (changing gears). Of course the driver performs this in a manual gearbox but an auto does it "automatically"!
In a manual gearbox the driver needs to manipulate the clutch to disconnect the engine from the drive wheels during gear changes and to stop the engine being overloaded (or "stalled") by the car being stopped.

The 'classic' automatic has a device called a torque converter which indirectly couples the engine to the gearbox. It is roughly doughnut shaped and is filled with hydraulic fluid which couples the engine to the gearbox when the engine revs climb but uncouples the engine when the engine revs fall. As you can see this unit basically replaces the clutch.

The hydraulic power for the gearbox comes from the hydraulic pump. This is connected directly to the engine by the spinning casing on the outside of the torque converter. Effectively the entire torque converter spins around at the speed of the engine!

Manual gearboxes and automatic gearboxes use very different types of gears to select gear ratios. Manual gearboxes have one set of gears which mesh another set of gears. Classic automatics use epicyclic or planetary gears. Effectively, gears inside gears! I wont go in to why or how, but basically, if you stop one set of gears rotating or allow a set of gears to rotate, you can change the output gear speed with respect to the input gear speed. As a benefit you don't need to uncouple the engine to "change" gears.
The automatic controls these locking and unlocking of gears by hydraulic actuators. They are no more than pistons that push (or pull) onto bands or clutch packs by using the pressure of the hydraulic fluid.

In the "old days" the shift points (gear changes) of the automatic gearbox were controlled by engine revs, manifold vacuum and hydraulic pressure (totally old school). Today, the gearboxes have a brain! An Electronic Control Unit that co-ordinates all the things the gearbox needs to do and 'talks' with the rest of the car (engine and braking system). To better manage the operation of "changing gears" and adapt to the car and driver.

Back in the day, the price of fuel was the last thing you were concerned about and automatics were not fuel efficient! Typically they only had 2 or 3 gear ratios, allowing the torque converter to "take up the slack". Automatics today can have up to 6 forward gears. The AL4 has 4 forward gears.

A review of the AL4 automatic

Well if you have a first generation C3, it's between 15 and 20 years old. Its probably done between 100 and 200 thousand miles!!! This may effect the performance of the gearbox. So don't expect an old gearbox to perform as well as a new one.
The AL4 has been in production for (in my estimation as I don't know when it started production) more than 20 years now and is manufactured by two different companies. It has proven to be adequate for the job by a number of different car manufacturers. It seems the gearbox has not changed mechanically over the years and upgrades have only been slight. For example different types of shift levers and software upgrades.
Actually there isn't much to say about the AL4 auto. When it works, it's seamless. That means you don't notice the gearbox change gears. The power is always there when the gearbox is doing it's job. It needs to change up to conserve the engine economy and change down when you need the power.

I have the little 1.4 petrol engine in a pre-facelift C3 and IMHO the car is under powered. This means that the autobox spends more time changing gears than average. Unfortunately for the gearbox this means that you tend to notice it more. The 1.4 would do better with a manual transmission. I think the AL4 would do fine in the 16 valve 1.6 engine. It tends to be the engine that lets the gearbox down and not vice versa.
I'm not saying it does a bad job, it's just that the gearbox is working a little harder to get the best performance for the car with the smaller engine sizes. You need to separate the performance of the engine from the performance of the gearbox.
I have driven two virtually identical C3's. Same engine size and AL4 gearbox. The driving experience was different between the two cars.
One has engine problems I have yet to figure out. The throttle response at low revs is lacking a bit and the over-all power is down a bit. Both had gearbox problems that were solved by replacing the electro valves (I'll get to that in a minute). The car with the "good" engine performed well. Most notably more power up hill, quicker response at low revs and more importantly to this review, less gear-shifting. My point is, again, The AL4 gearbox is more than up to the task, it's the engine that lets the car down (in the case of the 1.4 at least).

Now I mentioned before about the torque converter and how it disconnects the engine from the drive line. Well this action of coupling the engine to the gearbox by hydraulic fluid is inefficient. Power and energy are wasted by the fluid "slipping". The AL4 has what's known as a "lock up converter". That means that the input and output of the torque converter can be locked together to directly couple the engine to the gearbox. It reduces power loss and makes the car more fuel efficient. The 'converter is locked in 2nd, 3rd and 4th gears.
The locked converter also gives you engine braking. This means you can use the compression of the engine to slow the car down reducing brake component wear. Older auto boxes 'coast' when you release the accelerator, usually then requiring more use of the brake peddle.
I have found I use very little brake force at all. But I'm not a very aggressive driver.

The shifter control gives you a "manual mode". By moving the selector lever across to the left of the drive (D) position, the driver can sequentially shift up or down through the gears. This is handy on occasions when you want a bit more control over the shift points.
shifter 001.jpg
One last note. When driving at highway speeds (about 100KMH) the engine revs are about 2800RPM (just under 3000) This is quite low for this capacity engine (1.4). Generally speaking you need to get the revs up to gain horsepower. However the 1.4 still has enough 'poke' at this point to overtake. What I'm getting at is the engineers actually did there homework for the best economy and power for highway speeds from this gearbox. So, if nothing else, the AL4 and 1.4 combination give you excellent highway performance!

Ok, so the bad news.

Most of the bad news is to do with the longevity and mechanical failures of the auto, not really it's operation. But...

I mentioned that by moving the selector lever across to the left of the drive position, the driver can sequentially shift up or down through the gears. However being an automatic (the whole reason why the owner decided to buy an auto in the first place) the driver tends to forget that they put the gearbox in manual. YES, in manual mode the instrument cluster now tells you the gear number instead of the 'PRND' mode. But you still don't tend to pay attention to it. This is not a problem for most of the journey as, for the most part, you don't change gears. The gearbox will still automatically shift down (in manual mode) if you are coming to a stop or slowing down, BUT it doesn't warn you that IT has changed gears and not YOU. It just quietly does it in the background. However, in manual mode, it will not shift UP gears (Duh)! Meaning that when you take off from the lights, or just speed up, you wind up reving the (expletive) out of the engine before you realize the gearbox is not shifting and you are still in manual mode!! So really you need to move the lever across to manual, do whatever you need to do, and then put it back in 'D'...every time. That's not very intuitive!!

Dash indication in auto. Shows mode (PRND). Park in this case.
dash 001.jpg

Dash indication in manual. Shows selected gear (1234). Second gear in this case.
dash 002.jpg

If the gearbox is not in top condition the 'slip' of the torque converter can be felt in 2nd gear. Then you can feel the torque converter 'lock up'. This can feel like the gearbox has 5 gears! Considering the whole point of an auto is to give a seamless, smooth and unobtrusive gear change. feeling 5 'gear changes' is not good!

Connecting the mechanical parts of the gearbox to the electronic "brain", are the 'electro valves'. These are valves that are powered by the computer but control the flow and pressure of the hydraulic fluid to the actuators. These valves can get clogged or ware out and stop functioning correctly.

A bad decision was for the manufacturer to say that the gearbox is "sealed for life". This is non-sense. The hydraulic fluid powering and lubricating the gearbox wares out and should be changed!
Failure to change the fluid can result in excessive metal-on-metal ware and clutch and brake material failure. This generally causes the gearbox to "slip" and not drive. It can also cause bad gear shifts, clogging of the electro valves and a number of other problems.

The major actual physical damage to the gearbox is typically wearing of the clutch and brake band material. Once the pad material is gone you get metal parts rubbing on metal parts, destroying them in the process.
Unfortunately it's hard tell if this is a design or operational problem.
I believe with correct maintenance the AL4 should last the life of the car without 'major' repairs.

In summation.

I guess the AL4 is no better or worse than any other modern auto gearbox. Older auto boxes tended to last longer because they were simpler. But they were also noisy, inefficient and consequently gave bad fuel economy.
When running correctly, the AL4 gives satisfactory results, everything you could expect I guess. To be frank what are we talking about here? A little buzz-box with a little engine! The performance is never going to be spectacular! So 'satisfactory' is all you need.
The only piece of advice I could give is; change the gearbox fluid regularly!!!
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