Several brands of this era have developed transmission controlled by a hydraulic system. Ferrari calls there’s F1, Lamborghini has the E-Gear and Maserati with its DuoSelect and Cambiocorsa. Other brands such as Alfa Romeo also have their own variants that are similar. The 4200 series is named Cambiocorsa so will refer to the system throughout as that. However, in most cases you can use the other names pretty interchangeably.
Effectively, what the Cambiocorsa system is built around a standard manual gearbox (it’s the exact same trans-axle as found on the 4200 GT’s with a traditional 3-pedal 6-speed transmission). However, instead of the transitional shiftier and pedal linkages going back to the passenger compartment, a hydraulic system is attached instead.
The system is built around several key components:
- Hydraulic Actuator – this component bolts to the side of the transmission and does the actual moving of the shift forks within the transmission. There are actually two actuators contained in this component, one controlling the linear (back and forth movement) and a second controlling the rotational (left and right movement).
- Clutch Actuator – this component replaces the movement of the traditional clutch pedal with a simple hydraulic actuator
- Solenoids – a series of solenoids that control the flow of high pressure hydraulic fluid to the correct areas of the actuator
- Hydraulic pump – a electric pump used to pressurize hydraulic fluid to give the actuators the power they need to perform their tasks. This pump drives the pressure of the system to 40-50 bar (588-735 psi)
- Accumulator – a mechanical device used to store the potential energy of the pressurized hydraulic fluid and later release its kinetic energy
- Power unit – a manifold that includes the accumulator and all the solenoids
- TCU – transmission control unit. A computer module that controls the pump motor and solenoids and monitors various sensors in the system
- Reservoir – a small tank that contains the hydraulic fluid
The principle of the system is quite simple. Basically when we want to mechanically move something, say change gear in the transmission, the TCU signals several of the solenoids to pass fluid pressure to the appropriate ends of the actuators. This causes the clutch actuate, and the two shift fork actuators to move to the correct position. Throughout this process there are a series of sensors on each of the actuators to tell the TCU what position they are in (e.g. to confirm the command action took place).
The most mysterious part of the system is the main actuator. This is a costly component (many thousands of dollars new) and has several points of potential failure.
The actuator pictured here came out of of 2006 Quattraporte DuoSelect but is the identical part from a 4200 series (248084). The only electrical connection goes to the two position sensors.
This is the face that mounts to the transmission itself. You can see in the opening the slides that fit into the forks on the transmission to actually move things in/out of gear.
Ontop of the actuator are all the hydraulic inputs. These feed into hoses that go back the solenoids/power unit.
On the back of the unit is this plastic dust cap. This is a common place for gearbox fluid to seep out of (as the seals of the actuators inside start to deteriorate). I’ve heard this cover easily cracks as well (luckily it’s available as a separate order-able part).
Here the cover is pulled off with 4 small T5 torx screws. There’s a gasket sitting in-between. It’s meant to seal dust out, but not fluids in.
With the cover off, we can see the ends of the two internal actuators. The smaller one imparts the rotation motion on the engagement selectors. The larger controls the linear engagement motion.
Here we can see the larger engagement actuator moving the selector in/out.
Here the smaller actuator imparts the rotational motion on the selector.
As you can see the overall concept is fairly simple. One thing that’s necessary in the system is some sort of feedback mechanism to tell the computer where both of the actuators (and hence the selector) is positioned to ensure a valid gear is selected/etc.
To do this, a pair of potentiometer are employed. They convert mechanical rotation to a variable electrical resistance that can be easily converted to a voltage that the computer to read.
The sensor plate is held on by five T5 torx screws. The part number labelled is CA.0015118.D.
Again, a gasket dust seals this plate to the actuator. The backside you can see the control arm connected to the potentiometers.
The potentiometers get moved by a shaft inside of its housing. This shaft moves in/out and rotates in sync with the selector.
The heart of the system are the actual actuators themselves. Opening the actuator housing is also fairly straight forward and involves separating the case in two. The case is held together by seven 7mm studs around the perimeter.
Before its possible to separate the two halves, there is a bit of a hidden bolt inside the larger diameter actuators (this took me a while to figure out!).
This bolt has a 5mm hex head. I had to cobble together a bit of tools to reach all the way to the bottom of the bore and get this one undone.
With that out, the whole body of the actuator easily splits. There’s a small gasket between the two halves that’s somewhat delicate.
Inside you can see the actuators and some of it’s seals.
The entire unit is now separated into the selector/sensor half and the hydraulic actuators themselves. The actuators are held into their body with a curclip on the end. After removing those, they should simply slide out.
The end of the actuator shafts ready to come out. I haven’t yet cleaned off any of the grease as I want to be cautious to not damage any of the seals along the way.
To be continued. In Part 2 we will continue to tear down the actuators and examine the seals and the rotational cam and the actuators themselves.
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