How To Make Your Gtir Rwd

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Thought I would post up the detail of my GTIR RWD conversion. It only cost me a carton plus quite a few hour of my life in labour so hopefully this will save someone some heartache!Mine was a bit of a backyard job but having been driven pretty hard in RWD for a couple of months now, all seems to have worked. I actually think you are less likely to destroy your gearbox with this mod, given that the car is now capable of generating far less grip. You can also get away with a pretty sedate clutch setup for the same reason.

First point is figuring out how the 4wd system works and finding a free workshop manual.

This Japanese site has some trannie layout pictures:

http://www.niji.or.jp/home/g0873537/attesa.htm

While this website has a very useful online manual:

http://www.gtirworkshopmanual.com/

I would stay away from Nissan4U.com as I found their transmission drawings to be more confusing (and wrong) rather than usful.

Basically the mods involve:

• Lock (by welding) up the Centre diff

• Removing the front drive shafts

• Optionally removing the front diff/ input shaft, which I did to save weight and the effort of getting it to go back in.

• Install 40mm Welch plugs to seal gearbox/ transfer casing where front drive shafts originally exited.

I also put in a new clutch from Clutch and Brake Australia, apparently Exceedy brand, Single plate organic with heavier clamping than stock. Was about $300-350 and was delivered to my door at home within 2 hours for about $7 extra.

How the gearbox/Tranny works:

• The GTIR gearbox is basically the same as any FWD transverse gearbox setup however what would conventionally be the front diff driven off the gearbox is in this case the centre diff. this centre diff is also located to the front left as opposed to closer to the centre in a FWD car.

• The centre diff is basically a standard open diff with torsion LSD bolted in parallel to the open diff. Because of this you only need to weld up the open diff section to lock the diff. you can leave the torsion LSD where it is, it just becomes redundant.

• The transfer case is bolted to the side of the gearbox, this houses 2 independent circuits. At the front right it houses the front diff which is a simple open diff. The rest is the transfer which uses 2 perpendicular shafts to transfer drive by 90 degrees. The output from this drives the prop shaft.

• The Centre diff and Front diff are parallel to each other. 3 drive shafts run within each other to transfer drive.

• The 2 hollow shafts are the output shafts from the centre diff. The outer shaft is for the rear drive, the other hollow shaft in side of it is the drive to the front diff. The inside shaft id the drift shaft for the left front wheel, coming from the front diff.

• To complicate things further the outer hollow shaft that transfers the rear drive actually splits in 2 when you separate the transfer case from the gearbox. One half stays located in the transfer case by 2 bearings the other half stays attached to the centre diff in the gearbox.

• The other hollow shaft for transferring drive to the front diff is one piece and is permanently attached to the front diff. when you pull the front diff out this shaft comes with it.

• The front left drive shaft pull straight out like on a normal fwd car.

Gearbox/Trannie removal:

• The final aim here is to lock the centre diff by welding it

• The gearbox and trannie will both have to come off the first time. After that you should be able to only remove the gearbox should you have to change a clutch or do a gearbox rebuild.

• Some helpful info on removing the box/trannie can be found here.

http://www.sr20-forum.com/gtir/713-how-gti...ngine-situ.html

as well as in the workshop manual. Study the manual don't wing it like I tend to.

• Pull out the front drive shafts

• Undo the little bracket on the end of the transfer case that connects it to the engine block.

• Undo the end casing and pull it off, pull out the front diff/input shaft. You can do this later but u may as well do it at the start. If that's too hard stop now.

• Put the end casing back on to stop dust getting in. Undo all the transfer case and gearbox bolts. Some are a pain in the ass, ok the whole ordeal is a pain in the ass. Undo the engine mounts, they are easy and shift the engine forward if you need to get extra room behind the engine. See article above for more info.

• There are 1 or 2 bolts behind the engine hidden by the transfer case. You will have to drop the transfer case off first before you can get to the last 2 bolts and get the gearbox off. Leaving these to bolt off when it all goes together again will mean the gearbox can come off on its own.

• The transfer case can stay attached to the prop shaft but u will need to undo one of the prop shaft mounts. I did it this way as I was only going to strip the prop shaft nuts if I tried to undo them. Slop the trannie onto the ground.

• Pull the gearbox off it has heaps of clearance from the chassis rails etc. It will never come off with the 2 mystery bolts still attached, believe me I unknowingly tried.

Removing the diff from the gearbox:

• Unfortunately unlike the easy to get to front diff the getting to the centre diff means pulling the gearbox apart.

• Read the manual… and follow it..

• Get the gearbox on the bench undo all the bolts including the spring and ball retainers. Collect all the balls/ springs. Pull the casing apart and try not to smash the plastic oil guide, good luck, I doubt it is needed anyway : )

• With the case off have a look at everything. There is a ball bearing in the reverse selector just waiting to fall out. The manual shows where it goes back in.

• As per the manual you will need circlip removers to remove most of the selector folks off their rods and remove the reverse selector. The 3 selector arms drive 3 selector rods that drive the selector forks.

• The selector arms are driven by rod controlled by the shifter input.

• Have a play and try to understand how the gear selector works before undo circlips. This is a pain with no standard shift lever attached.

• There are 3 arms next to each other that go up and down to drive the different selector forks. A sliding and rotating rod selects the arms one at a time, depending which gear you want to pull.

• You want all the arms to line up, this is neutral. U should be able to slide the selector rod freely across all 3 selector arms. Jam the selector rod between 2 arms if you want to help keep the box in neutral, which you do.

• Undo the circlips as per the manual. There is a retaining pin on one folk but this can be left in, ignore the manual.

• There are a series of ball bearings that limit the movement of the selector rods. By pulling neutral these balls are out of the way and all rods are free to move. If not perfectly in neutral certain balls will lock and you will have endless trouble. With the circlips removed and in neutral you can pall the whole of the gearbox internals out momentarily and at the same time remove the diff. replace the gearbox internals.

• You can not remove the Diff on its own I have tried and failed.

• Installation is the exact reverse. Make sure u have neutral else the rod wont go in properly and you will have dramas. Took me about 10 hours looking at the inside of the gearbox to get this all right.

• When you go to put the case back on make sure the shims are aligned properly. If they are not you wont be able to shift cleanly or at all.

• Don't freak out if you put the whole car back together and cant shift gears. You can pull the gearbox casing off the gearbox when it is installed in the car and have a fiddle. Not ideal but relatively easy and saves the heartache of pulling everything apart again.

Locking the diff and reassembly:

• Once out the whole centre diff just unbolts.

• I contemplated a number of options. Besides machining a whole new assembly the best option is to weld the 4 inner of the open diff to each other and their shafts. This is more than sufficient, Avoid welding the output gears (especially the rear drive one) to the housing. This might seem stronger. Unwelded it has some play. Welded it wont and may distort, you may end up having bearing failure/ binding when you put everything back together.

• Only welding the 4 inner gears mean you don't have to remove any of the bearings or risk problematic distortion of the outer housing.

• Get as much oil off as you can. Its cas metal so use Stainless Steel tig rods, or specific rods for cast metals. Only takes 10 mins to weld.

• Test the alignment of the diff splines using the input shaft of the front diff. The torsion diff splines need to align with the welded diff splines. If they are slightly misaligned when back in the car the front diff will not go back in and you will have to leave it out. I say just leave it out either way.

• Bolt it all back together and put it back in the gearbox and in the car. Follow the workshop manual for doing up bolts etc.

• Leaving the front diff out means the gearbox oil and transfer oil will be shared. This may or may not matter to you. According to the manual they take different oils but in reality these days you can use the same oil on both.

• Make sure you seal up all the interfaces of the gearbox and trannie good and proper else they will leak. The interface between the transfer case and gearbox will now be full of oil now too where as originally it is not as far as I am aware.

• Put two 38 or 40?mm Welch plugs in the holes where the driveshafts were. These press in perfectly into the seals and don't really even need gluing or further retaining.

• You will need to keep the front hubs but pull the drive shafts out of them.

• The trannie is as much of a pain to install onto the gearbox as the gearbox is to install onto the engine. Leave the Y bracket etc off. From now on the transfer case can stay on, whenever the gearbox has to come off.

Hopefully this is of use. I will try and get some pictures up so that it makes a bit more sense.

At this point you will have a car pushing 300hp through the back wheels and what is apparently a torsion LSD in the back will act as an open diff. I have had no breakages. Car will spin up 4th gear in the wet and no longer has any understeer.