How to: Convert Automatic to #Manual

This is one of the most requested tutorials, especially on Nissan Skyline forums and facebook pages.
This scenario tends to happen a lot: Someone sees a car for sale at a great price and they decide to buy it. Then they either realise its an automatic, or they knew it was auto and planned to convert it.
Now it’s time to stop saying and start doing.

Parts you need:

1. Manual Gearbox
2. Manual Flywheel
3. Clutch and Pressure Plate
4. Manual Starter Motor
5. Sandwich Plate
6. Release Bearing
7. Spigot Bushing
8. Clutch Master Cylinder and Slave
9. Manual Driveshaft/Propshaft
10. Manual Bellhousing Bolts
11. Flywheel Bolts
12. Clutch and Brake Pedals
13. Manual Wiring Loom
14. Manual Gearbox Crossmember

Tools you need:

1. Vehicle Jack
2. Jackstands
3. Drill with 35mm Holesaw
4. Dremel
5. Toolkit (preferably metric)
6. Transmission Lift
7. Clutch Alignment Tool

Step 1: Remove the driver seat

At the front are two bolts that hold the rail into the floor.
At the rear there are two more bolts - one in the floor, the other in the tunnel for the drivetrain.
The front are different length from the rear, so don’t get them mixed up.
Fold the seat all the way forwards, then tilt it back - there should be a wire running out from the floor and into the seat. This is the seatbelt sensor and can be unclipped at the middle where it is ziptied to the seat.
Lift the seat up and pull it out through the driver’s door - be careful that the rails don’t touch anything since they are metal and scratch the plastic trim very easily.

Step 2: Remove the Pedals

You do not need to replace the accelerator, but the brake pedal on an automatic is usually a lot wider than on a manual. Therefore it should be replaced by a manual brake pedal as it may get in the way of the clutch pedal.
Marked in red are the bolts to hold in the brake pedal (there may be another bolt at the very top).
Marked in orange is the pin that connects the pedal to the master cylinder (and the hidden bolt at the very top).
Marked in yellow are the bolts that hold the accelerator pedal.
There are two sensors on the automatic’s brake pedal - one that tells when the brake is pressed, and one tells the auto transmission that you can put the car into gear. These can both be unplugged, but the brake light sensor must be plugged back into the new brake pedal, and not the clutch pedal.

For better access, you can remove the bottom of the dashboard, and drop the steering rack.
The image above shows the locations of the screws holding the dashboard in.

If you are replacing the accelerator pedal, then you can unhook the cable from the throttle body. Pull on the throttle and slide the stud out through the side. Unbolt the accelerator pedal and pull the throttle cable through the firewall.
To install the new accelerator, run the throttle cable through the firewall then bolt in the pedal. Connect the throttle cable to the throttle body after.

Step 3: Drill the holes for the Clutch Pedal

The easiest way is to do it from the inside.
In the photo above, there are two studs marked in red, and the master cylinder marked in orange.
In a Nissan Skyline, there is a blank cut out of the insulation shaped perfectly, and the perfect place, for the clutch master cylinder (refer to picture below).
Note that there should be an air condition vent in the way - it is screwed into the dashboard via a strip of metal that is very hard to access. I cut mine to pieces with a dremel and took it out in parts.

If possible, try to only remove the centre by cutting the joins with a craft knife. As you can see in the photo above, I removed the whole piece and marked the area on the firewall, using the centre as a template.
Place the clutch pedal in the space and mark the areas to be drilled for the studs, and the area to cut with the holesaw.
The brake and accelerator pedals will fit straight into the existing holes.

Step 4: Fitting the pedals

If the master cylinder doesn’t fit, sand back the hole using a dremel.
The clutch master has two holes where the studs from the pedal fit through - the pedal and master clamp onto the firewall.
Bolt the master into place, then attach the pushrod from the inside.

The picture above shows how to do it on the brake pedal. It is basically the same as the clutch pedal.
Bolt it into place and connect to the brake master.
The steering rack will often get in the way, making the job difficult, however you can get through without dismantling the rack.

Step 5: Drop the Auto Gearbox

The image above shows my RB25DET manual big-box, but the automatic is basically the same.
First, you need to drain the fluid out - there is a bung at the bottom which should get most of the fluid out. It is not right at the bottom, so there will be a bit of auto fluid still inside. The orange arrow points to the bung where you fill the gearbox.

Inside the car, remove the centre console and auto-shift shroud. There are two screws near the top, while the rest is held in by plastic clips.
Unplug any electrical wires - in this case, the steering wheel’s control switch, the cigarette lighter, and the park sensor.
The auto-shifter will come out through the bottom with the gearbox.

With the transmission firmly in place, undo the mid-section of the driveshaft. The automatic driveshaft has a smaller diameter than a manual driveshaft, so will not fit into a manual gearbox.
Remember to unplug the wires on top of the auto box, and remove the hydraulic lines and dipstick.
Place a transmission lift (or a jack with a block of wood) under the transmission and undo the ten bolts around the bellhousing, and four bolts holding the crossmember in place.
Pull out the front half of the driveshaft and lower the auto gearbox (might have to pull backwards while doing this).

Step 6: Attach the Flywheel

The flywheel is attached to the crankshaft. When the motor is running the crankshaft turns and, being attached to it, the flywheel turns.
Remember to clean the flywheel with brake cleaner before use, then wipe off with a dry cloth. This will get rid of any microscopic dust and dirt, and remove any clearcoat.
If the gearbox uses a one-piece sandwich plate like a skyline, you probably want to hold it in place between the flywheel and motor before you attach the flywheel. If the sandwich plate is in two parts, you can add it after (or so I’ve heard).
There are three studs around the outside of the flywheel - these are guide pins that allow you to correctly attach the pressure plate.
Line up the six bolt-holes in the centre with the bolt holes in the crank and tighten them in at about 128nm.

Step 7: Attach the Clutch

In the photo above, you can see that the centre of the clutch is raised on one side, and flat on the other. The flat side presses against the flywheel.
When the teeth on the pressure plate are pressed, they act like a pivot to lift the clutch away from the flywheel.

In the image above, the clutch alignment tool has been pressed through the clutch, and the spigot bearing placed on the end - the spigot should go into the crank first, as is may need to be hammered in.
Remember to grease the spigot bearing as it acts as a guide for the shaft in the gearbox.

Using the clutch alignment tool, guide the clutch and spigot into place.

After the clutch has been placed onto the flywheel, attach the pressure plate over the top of it.
In the step about the flywheel I mentioned the guide pins - in the photo above, I have pointed out the guide holes. They are a bit smaller than the bolt holes.
If the clutch does not line up properly the first time, rotate it and try the next guide pin.
Once you have it lined up, and it sits flat against the flywheel, bolt it in place with the nine bolts around the perimeter.
Torque them down to about 40nm.

Remove the clutch alignment tool as the pressure plate will hold the clutch in place.

Step 8: Perare the gearbox

Before attaching the gearbox to the vehicle, we must attach the release bearing and clutch slave cylinder to the bellhousing. The yellow arrow points to the release bearing - a metal ring that presses against the teeth of the pressure plate.
The red arrows point to the clutch fork inside and outside - the clutch slave pushes on this which in turn pushes on the release bearing.
The orange arrow shows the mounting bolts for the slave cylinder.
Before you connect the clutch slave to the bellhousing, screw in the clutch line, connect the other end to the bottom of the clutch master cylinder, fill with brake fluid and bleed the system.
Also, before placing the release bearing, give it a good coating of grease so it does not stick.

Next, we have the fun part with the wiring.
While you can use an R32 gearbox in an R34, vice versa, the wiring loom is different - even for an R33 and R34.
If possible, try to get the loom from the exact same car as yours. The same applies to the driveshaft. Each generation of Skyline uses a different length, but they can still be cut, welded and balanced.
I have labelled the plugs on the gearbox to the best of my knowledge.
If you don’t have the correct wiring loom, you can still use the automatic loom, and bridge the inhibitor (sensor to tell when the auto is in park). If this is the case, the best option is to go to an auto electrician - I searched for months and tried tracing back the loom and in the end an electrician got it working in a couple hours, including the reverse lights and reverse beeps.
On a Skyline, the gearbox loom ends on the side of the fusebox and most engine components plug straight in.

Step 9: Lift the gearbox into place

Using a transmission lift or trolley jack, move the gearbox into position and lift it into place. This can be difficult as the shaft in the gearbox must line up exactly with the clutch, and the bellhousing must line up with the sandwich plate and engine block.
I found that on my gearbox, the sandwich plate could sit almost perfectly along the groove of the bellhousing.

The automatic and manual gearboxes have different bellhousings so make sure you get the bolts for a manual bellhousing. As far as I can remember, the longest bolts were at the top and the shortest bolts at the bottom.
Do not lower the transmission lift until you have bolted in the crossmember.

Once the gearbox is in place, you can insert the manual driveshaft into the gearbox and connect the other end to the rear driveshaft.
As previously stated, you can get the driveshaft cut and welded if it is not the correct length.
Once the driveshaft is in place, you can fill the gearbox with gearbox oil. The bung is near the top of the gearbox, so you will need a pump.

You can also add the starter motor if you haven’t already - you will see a circle cut-out on top of the gearbox where the starter motor lines up with the teeth of the flywheel.

Step 10: Finish the Interior

On my R34, I was not able to add the gearstick surround or gear boot as they were off an R33.
However I was able to add the docking ring and rubber insulation.
If you haven’t replaced the driver’s seat or the bottom of the dashboard, now is a good time to - and don’t forget the seatbelt sensor.
You can use the automatic ECU and dash cluster as long and everything is wired properly.
Congratulations! You now drive a proper car.

This was a big post, and I did this 6 months ago, so feel free to let me know if I’ve forgotten anything.

This content was originally posted by a Car Throttle user on our Community platform and was not commissioned or created by the CT editorial team.