4 to 5 Speed Conversion
Table of Contents
It is possible to convert a manual 4 speed vehicle to 5 speed.
This wiki page is for converting a factory motor. If you are intending to convert your 4 speed vehicle to 5 speed whilst also doing an engine conversion (such as a V8), please refer to this wiki page for additional considerations.
The 5th gear in the MQ is in an extension housing between the main housing and the transfer case. The main housing and transfer are the same on the 4 and 5 speed gearboxes, making parts interchangeable. The extension housing is 100mm long. This causes the transfer case to be moved further towards the rear of the vehicle, which has 2 effects;
- The front drive-shaft needs to be longer and the rear shorter.
- The transfer mounts are further towards the rear of the chassis.
These 2 differences must be addressed to complete the conversion.
If you want to see the difference, go to gearbox length wiki page.
The different drive-shaft lengths can be addressed in 3 ways.
- Source correct length drive-shafts from another MQ. Please refer to this wiki page for information.
- Modify the length of the current drive-shafts (recommend to take to a professional workshop, as an un-balanced drive-shaft can cause damaging vibrations).
- Have new drive-shafts made to suit.
Solving Transfer Mounts
The different location of the transfer mounts can be addressed in 2 ways.
- Cut the old mounts from the chassis and weld on new ones in the correct location. It may be possible to re-use the cut-off mounts if they were not damaged, or replacements will need to be fabricated.
- Make adapter plates between the existing chassis mounts and the transfer case.
|Left side (Australian passenger side)||Right side (Australian drivers side)|
Using Gearbox from Different MQ Engine
It is also possible to use gearboxes from different engines, such as a L28 5 speed on a SD33. There are a few differences that require addressing though;
- The 3 motors all have different bell-housings. The connection of the bell-housing to the main gearbox housing is the same, so they can be interchanged.
- The L28 motor is not as long as the P40 and SD33, which causes the gearbox to be located further forward). Because of this, each type has a unique top-plate on the gearbox, which locates the sticks correctly through the floor (SD33 and P40 are the same). The top-plates can be exchanged between the gearboxes to suit.
- There are 3 different input shaft lengths, L28 = 210, SD33 and P40 pre ‘84 = 185, SD33 and P40 post ‘84 = 195. It is possible to interchange the input shafts. It may also be possible to make a modified spigot bush, however most people opt for the first option.