The LuK technical team looks at the Toyota Aygo, which was launched in 2005, and advises independent garages undertaking the four hour clutch repair, tackling the semi automatic transmission in this article.
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In this era of near-ubiquitous (at least here in America) automatic transmissions and desperate defenders of the glorious manual experience, the semi-automatic seems to exist in a strange. A modern-day semi-automatic transmission is like a manual transmission. The biggest difference is that there’s no clutch on the floor for disengaging the engine from the vehicle’s drive wheels. Semi-automatics have electronic processors and sensors which assist in this process.
If the vehicle has alloy wheels then it is a good possibility that they are secured with anti theft bolts so make sure the locking tool key is available before starting the repair. Before removing the gearbox the first thing to do is to set the clutch actuator into a default mode which will release the preload. To do this install the diagnostic tool and set to the clutch clamp position which will release the clutch fully. Failure to do this can result in damage to the adjustment mechanism.
We used a two post ramp an engine support beam and two transmission jacks to assist with the repair.
Disconnect the battery terminals and stow safely. Remove the battery support clamp and battery. Release five bolts that hold in place the battery tray and remove.
fig 1
Disconnect the three gear shift connector switches positioned on the gear selector unit (fig1). Disconnect the clutch cable from the release lever. Remove the bolt that holds in place the wiring loom bracket. Disconnect the switch found at the front bottom of the gearbox and the switch found at the rear of the gearbox and stow the wiring loom aside. Completely remove the gear selector unit by removing the three securing bolts. It is a good idea to mark the positioning of the bolts to ensure the correct position when reinstalling the unit as (fig2). Once removed this will expose a connector switch underneath that can be disconnected, stow safely to the side.
fig 3
Remove the earth lead bracket that is held in place with two bolts and remove the oxygen sensor connection and bracket (fig3) and stow. While the vehicle is still at ground level it is a good idea at this point to remove the top two accessible bell housing bolts and one starter motor bolt (fig4). Remove engine top mount bolts and support the engine with the support beam. Raise the vehicle and drain the gearbox oil. Remove both front wheels and on the nearside release the inside wheel arch liner by removing three bolts. Only the front section needs to be released for better access when lowering the gearbox.
fig 5
Unbolt the bottom ball joints and release from the lower suspension arms on both sides. Remove the drive shafts from the gearbox and the wheel hubs. Remove bottom gearbox stabiliser (fig5) which is held by three bolts two at the front and one that secures from the rear through the sub frame, slide the stabiliser out from the sub frame. Remove the back plate from the gearbox held by three bolts and remove the starter motor bolt from the rear (fig6). Support the gearbox using the transmission jacks and remove the remaining three bell housing bolts.
Carefully lower the gearbox to the floor and remove the worn clutch cover, drive plate and release bearing. With the clutch removed, check the flywheel for signs of heat stress. Clean the first motion shaft splines and any debris from the bell housing (especially important when a release bearing has failed).
Put a small dab of high melting point grease (not a copper based product) on the first motion shaft splines and make sure the new driven plate slides freely back and forth. This not only spreads the grease evenly but also makes sure you have the correct kit. Wipe any excess grease off the shaft and driven plate hub. Using a universal alignment tool and checking the driven plate is the correct way round (note ‘getriebe seite’ is German for ‘gearbox side’) the clutch can be bolted to the flywheel evenly and sequentially.
Before fitting the gearbox make sure the locating dowels are in place and not damaged. Refit any that have become dislodged and refit the gearbox. Make sure the gearbox bell housing bolts are secured and the gearbox stabiliser is installed before removing the transmission jacks. Refitting is the reverse of the removal not forgetting to reset the clutch actuator and gears using your diagnostic equipment.
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Over the years, Citroën have found several different ways to spare the clutch foot yet leave the driver in control of which gear is actually selected.
Sensaud de Lavaud
Little is known about the Sensaud de Lavaud transmission which was intended for the Traction Avant, beyond it having played a substantial role in the Traction’s development bankrupting Citroën. It is believed that it may have been an early example of what is now a reasonably conventional torque-convertor automatic gearbox, but it is also understood that Adolphe Kégresse (also behind the half-tracks based on RWD Citroëns, as used to explore much of Africa and Asia in the ’20s) also designed a transmission for the Traction. An ingenious design, based around dual clutches and shafts, the concept was not developed due to the arrival of WW2 – but appears very similar to the dual-shaft design best known through VW’s DSG (developed and manufactured by Borg-Warner) and Porsche’s PDK (from ZF). Porsche also used a double-clutch transmission for racing in the mid ’80s.
It is not known how Kégresse planned to control the design, without the complicated electronics and hydraulics used by the modern systems.
Embrayage Centrifuge (Trafficlutch)
Falling a little short, perhaps, of qualifying as a fully-fledged semi-automatic gearbox, the centrifugal clutch fitted to many 2cvs, Dyanes and Amis cannot go unmentioned here.
In addition to the normal clutch, the flywheel contained a secondary clutch not dissimilar to a very large diameter but thin drum brake. When engaged, the friction material gripped the clutch drum, transmitting drive. However, when revs fell to idle, the clutch was automatically disengaged, separating drive.
As a result, cars equipped with this clutch design were virtually impossible to stall – ideal for a car that was intended to be the first car owned by most buyers. Equally importantly for a car with so little performance, there was no loss of efficiency or hit on performance or fuel economy. Normal use of the clutch was still required to change gear whilst underway, however.
The biggest drawbacks to the system – apart from a small extra maintenance penalty when the clutch needed replacing – were that the car could not be bump-started (but, since it had a starting handle, that wasn’t a problem), and that parking on a hill relied on the handbrake alone. With earlier A-series, fitted with front drum brakes, this was similarly not an issue, but the much less efficient handbrakes on later cars with front disk brakes marked the end of the concept, with some early ’70s Amis being the only cars to mix disk & Trafficlutch.
BVH
The DS brought perhaps the best known semi-automatic gearbox, with the BVH – Boîte de Vitesses Hydraulique. Apart from the control of the gears and clutch, the BVH was exactly the same transmission as the “normal” manual gearbox fitted to the lower-spec ID.
Control of gear selection was achieved through a system of hydraulic valves and servos built into the lid of the gearbox, in place of the conventional linkage, and operated by the fingertips on a lever on the steering column. To ensure that the car was not started in gear, the lever doubled as control of the starter motor.
Any movement of the lever also controlled the clutch. A set process of events followed selection of a different gear – clutch disengagement, gear deselection, gear selection, re-engagement of the clutch. A number of adjustments could be made to the speed at which these were carried out, so whilst it was possible to have a D which changed gear imperceptibly, it was equally possible for a badly maintained car to lurch and judder.
The clutch control was also linked to the brake pedal, with the idle speed reduced when the brake was pressed. Properly set up, the clutch would be engaged at the higher idle speed, but disengaged at the lower, so that “creep” could be easily achieved by simply removing the driver’s foot from the brake.
By the end of DS production, a conventional Borg Warner automatic box was also available, although very few were built.
Cone Drive Gearbox Lube
C-Matic
For the GS and, later, the CX, Citroen headed off down yet another tack with the C-Matic. The concept of “automating” a manual ‘box was continued from the DS, but simplified slightly. Rather than use a conventional clutch, with the sophisticated control required to move away from rest smoothly, a torque converter was used, as on normal automatic gearboxes. However, that didn’t help change between gears, so an electronic microswitch was used to detect movement of the gearlever, which then, via an electrovalve, cut fluid pressure to the torque converter, smoothing the change. Whilst the ‘box was based on the four-speed CX & GS manual transmissions, both lost a gear to become three-speed in C-Matic form (in line with then-common automatic boxes). Both GS & CX C-Matics require a particular fluid – sold by Total as Fluide T. This is no longer available generally, as Total donated their entire UK stock some years ago to the club, who are now the UK’s only source.
C-Matic was discontinued in both CX & GSA in the early 1980s. For the CX, it was replaced by a conventional ZF 3-speed automatic box, but the G became available only with a clutch pedal.
Sensodrive
In 2003, the C3 became available with a semi-auto termed Sensodrive. In an echo of the DS’s BVH, it comprised a conventional manual ‘box and clutch, and traded both clutch pedal and conventional gear selector for a set of “F1-style” paddles and a simple up-down manual selector. Computer controlled, the biggest step forward of Sensodrive over the BVH was that it didn’t need you to change gear. If you couldn’t be bothered, it’d do it for you.
Semi Automatic Gearbox Explained
EGS
Semi Automatic Gearbox Problems
In a further refinement of the concept, the C4 saw EGS take over from the previous Sensodrive system. Conceptually very similar, with a six-speed manual controlled by computer, improvements in computer technology mean that the EGS box is smoother and more refined than it’s immediate predecessor.