How to: Convert to a 5-Speed Gearbox

[andeep]

Hey guys,

Thought I would write a thread about how to convert your 6-Speed transmission to a 5-Speed that is found in the S14s. The reason why I am doing a thread on this as when I was doing the conversion there was a lot of different information going around saying exactly what parts you do and don't need, so I thought it would be a good idea to clear it all up.

Why would you change to a 5-Speed from a 6-Speed?!
There's a lot of speculation about the 6-Speed gearbox being weaker than the 5-Speed, but I'm not going to go into this as they're a lot of different views about this, search for more information about it.

The reason why I'm putting a 5-Speed in is because I drift the car. I needed a paddle clutch for drifting and these clutches WILL eventually kill the transmission due to their harsh engagement. Therefore it would not be sensible to use a harsh clamping paddle clutch on a 6-Speed and kill it as they are very expensive to replace, whereas the 5-Speed is a fair bit cheaper and would cost less to replace when it breaks.

Another reason is the dual mass flywheel that the 6-Speed has. Again, harsh clutch engagement will kill the dual mass flywheel, so this will need to be changed if a paddle clutch is fitted. Problem is that you need a 6-Speed specific single mass flywheel and these are quite expensive, whereas the 5-Speed ones are a lot cheaper.

What bits are needed for the conversion:
1. 5-Speed Gearbox
Well this is the most obvious part of the conversion The 5-Speed gearbox from an SR will work as they are all the same. You can get the gearbox from a Jap S14/a Silvia, a Jap PS13, a UK S14/a 200sx etc, just make sure that it's an SR gearbox, the redtop and blacktop 5-Speeds are all the same.

2. 5-Speed Flywheel
You will need the a 5-Speed flywheel as the dual mass is a lot thicker and won't work with the conversion. You can use a stock 5-Speed flywheel, but I used a Driftworks Lightened Chromoly Flywheel. If you are using a 2nd hand flywheel, make sure that you have it skimmed - do not use it unless it is skimmed.

3. Clutch
You can use an S15 clutch or an S14 clutch. Again there is a lot of misleading information saying that the S15 and S14 have different clutches, but in fact they are exactly the same. You can use your current S15 clutch, but be careful as it has been run in and mated to your 6-Speed flywheel, and you will be changing the flywheel. If you are getting a clutch and a flywheel that have been previously used together, this usually is okay since they were run in together and therefore are mated. I personally used a new ACT HD Paddle clutch.

4. Front half of a 5-Speed prop shaft
The prop shafts in these cars are made in 2 sections that are bolted together and can be split. You will need the front half (closest to the gearbox) from a 5-Speed. You will need to the whole prop shaft balanced once the two halves are together.

5. 5-Speed Flywheel bolts
These are shorter than the 6-Speed flywheel bolts, so you will need all 8 of these. A lot of people say never to re-use flywheel bolts as they are stretch bolts and need to be replaced if they are taken off. Use your own discretion here and decide if you should buy new ones.

6. 5-Speed Bell housing and Starter Motor Bolts
You need all 9 Bell housing bolts (that bolt the gearbox to the engine) and both starter motor bolts as they are different to the 6-Speed ones.

7. Rubber boots
You will need the 2 5-Speed rubber boots, the one that goes from the shifter to the shifter control on the gearbox, and the one that goes from the cabin to the shifter (has a metal place with 4 bolts on it).

8. 5-Speed Shift Knob
You will need the shift knob off a 5-Speed as the 6-Speed one won't fit.

Points to Note:

Electrical Connections
The 5-Speed box has 3 electrical connections: neutral switch, reverse switch, and speedo. If you are using the stock S15 diff casing, you don't need to worry about the speedo as its reading is taken from the ABS sensor in the diff. Neutral you don't really need to worry about, but wire it up if you want. Obviously you will need reverse. The connectors are different, so you can't plug the S15 loom into it, but just chop the connectors off and it's just two wires per connection that you need to solder. Polarity doesn't matter as these are just simple switches.

Spigot Bushing
With the S15s the spigot bushing goes into the dual mass flywheel, but with the conversion the spigot bearing is installed into the end of the crack as seen with the S14s. The S15 and S14 spigot bushes are identical.

Trim
You will need to cut a bit of the trim. You need to separate the leather gaiter from the grey plastic and trim some of the plastic on the backside off. If you don't the shifter won't engage the rear gears (2, 4, R) as it hits this bit of the trim. It makes no cosmetic difference as you won't be able to see it.


And that's it! Those are all the bits that you will need to convert the gearbox over. Installation is exactly the same as a 6-Speed box.

If you are putting a 6-Speed into an S14, the parts are just the opposite of the above, but you will need a signal for the speedo.

[XTension]

Outstanding work and description.

I´m about to start the convertion on my S15, so this should be very helpful indeed.

Thank you!

Cheers
XT

[Keisu]

You can leave the trim untouched if you have a short shifter, leaves you more clearance