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Diy:diff Shimming For R33 Gtst

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Hey all.I have recently wanted to buy an lsd for my 33 but found the prices a little bit to high.so i pondered and pondered and pondered some more,could i do anything to my stock item to give it better lock.thats when i found out about "diff shimming".

Its a process which puts extra preload on the stock viscious lsd centre,(dependant on how thick it is shimmed),whereby exherting quicker,sharper and more lock than the old worn out stock unit could ever provide.thus giving more torque to both wheels simultainiously.

Step 1:

Jack the rear up nice and high so you have plenty of room to move around.You have to undo the half shafts,tailshaft and diff housing nuts and bolts yet.

Step 2:

Drain the diff oil (make sure you undo the filler plug at the mid way point of the diff).And clean everything up.Ie:The metallic sludge that has formed on the drain plug.Then put it back in place.Tighten it up.You most lilkely wont be un-doing this again.But leave the filler plug loose for the time being.You will use it at the end.

Step 3:

Put the gearbox in neutral and make sure the handbrake is on.Loosen the 4 bolts holding the tailshaft to the diff flange.You can't reach them all.Remove the handbrake and rotate driveshaft to gain access then repeat.(loosen dont remove yet)


Step 4:

Its now time for the half shaft flanges.On either side of the diff there will be a stub with a 5-bolt pattern (gts-t, factory turbo a31/c33) or a 6-bolt pattern (3 lots of 2, regular a31/c33 etc etc).Once again,remove the handbrake and the rotate wheel etc. Some WD-40/CRC/WURTH won't go astray either if this is the first time the diff's ever been disturbed.The reason you do this last and the driveshaft first is that if you unbolted the 2 halfshafts first you couldn't utilise the handbrake to hold the driveshaft still while you undo the bolts.


Step 5:

Now we're ready to remove everything.Before you do this make sure all the nuts & bolts are removed that were loosened off.Lever the driveshaft out of the way with a screwdriver the driveshafts are 5 stud flanges that are just 2 flat faces and are easy to slide out the way. Check (if you live in usa): Publix Weekly Ad, or Big W toy catalogue.

Remove the hics bolts and lever the hicas out of the way.


Now there are 2 holes & 3 nuts,(the reason there is 3 and not 4 nuts is because one of the nuts holds down an earth strap),remove these first(you may have to lower the diff cradle to gain sufficient access).


Now remove the 4 bolts that hold the swaybar to the floor pan,(this will give you room to manuver the diff out).There are still the 2 bolts at the front of the diff housing by the driveshaft flange,remove these and the diff will fall on the swaybar and sit there.Then it just takes a bit of dicking around to get it out.Utilise a trolley jack to help lower it down easily.


Step 6:

Remove the rear diff cover.


Now,before you do anything else tap the half shafts out of the diff housing.They need a good whack in the right spot(id recomend after every whack or 2 that you turn the half shafts arround to make everything exit evenly).Make sure u mark them left and right.


Now there are 2 bolts either side,undo these and remove the bearing caps (again remember which way around and what side these go on.it is so easy to forget).


You will then see some bearings and spacers and things beside the diff head on either side.Lever the crownwheel & diff centre out with a big bar and make sure u keep all the bearings and shims etc in the correct order and sides.


Step 7:

Now there are 10 large bolts holding the crown wheel on.They are F$$KING tight!!!!! I'd recommend a decent vice and large powerbar or powerbar & 5pound hammer and possibly some WD-40 (dont root the bolt heads) - alternatively a pneumatic gun will work(Dont try to lever off the bearings they arnt in the way.just dont get sand or grit in or on them).


Once the crownwheel's off, you'l see 2 large phillips screws.Remove these and off comes the viscous center.pry these apart with a flathead.


You'll see once u pull it off a washer sitting on a flat surface.That's your original preload shim.



Now if you want to shim up the other side also (i did) you will have to take the spider gears and the smaller centre out of the hat(Housing) and you will find that there is another shim.


Step 8:

Do everything in reverse.


Before you screw the diff center back together,after inserting shim and the centre,take the 'longer' of the 2 stub axles and insert it through the center of the diff all the way(in the same side it came out of).This splines the 2 different splined parts of the diff center together so that when you go to insert the diff stubs at the end they'll actually fit (easiest way to explain it).Otherwise you'll be screamin' your head off wondering what you did wrong.

Also when reinserting the lsd and crown wheel back into the housing you can use the caps to push it back into the the housing make sure they are the right way arround.Saves u beating unessisarily on the lsd.

Pour the diff oil in before you put the diff back into the car.

In conclusion:

-Now,ive heard allot of different stories about shims and their results and how long they last.some say that they have added 1 standard 0.8mm shims to the existing shim and it wasnt what they were expecting performance wise.

-others have added 2 extra 0.8mm shims and say that it has lasted them for a long time others not so long but both say that there was a noticeable increase in lock/performance.

-I am the the only person i know of to shim it up to 3.3mm of preload.of course there are crazier.The results were excellent for drifting.both wheels locked consistantly and predictably.I will repost if it ever gives up the ghost.I have never driven or been in a car with either a 1.5way or 2way lsd though i have been passenger in a car with a welded diff.

Side notes:

*There is a little breather plug at the rear top back position of the diff housing dont forget to unplug it before you lower the diff.

*Try to get not dirt,sand,grit etc in the diff or lsd whilst doing this job.keep a cover over things you arnt working with like the diff housing.which now has the cover off etc..

*A bit of WD-40 wont go astray anywhyere it feels to tight to undo

*It is so easy to forget.so mark everthing!

*Clean all your parts before reinstallation.A little smear of clean diff oil wont go astray when putting the lsd centre back together.i also lubed up the shims before i put them back in.The teeth of the half shafts dont need lube.just dont wipe what they have on there off.

Shim Sizes & Prices (@tradeprice):

0.80mm = 3842440f60 price = $10.12

0.85mm = 3842440f62 price = $14.67

0.90mm = 3842440f63 price = $9.97

1.01mm = 3842440f67 price = $9.79

1.05mm = 3842440f68 price = $14.40

1.10mm = 3842440f70 price = $6.37

1.20mm = 3842440f73 price = $6.37

1.30mm = 3842440f76 price = $10.89

1.40mm = 3842440f80 price = $6.37

1.49mm = 3842440f83 price = $6.37

There is nearly allways a wait on these shims so i am told.no-one has them in australia so they have to be ordered from japland.and they have a wait of 1.5-3wks.<<From Nissan Spare Parts.

Attempt this mod at your own risk.I am not a mechanic.this is only a guideline.

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Nice work/pics etc. :pwned:

How do you find the locking action?

I used a single 0.8mm shim and turning around sharp bends the inside wheel would chirp, it gave the same shudder feeling a mechanical would on sharp turns when accelerating.

There was one small annoyance, I could essentially feel the spider gears binding and then turning, this gave the feeling of understeer/push then turn, understeer/push then turn BUT ONLY on small round abouts when turning right.

The rest of the time it felt fine.

Corner exit was awesome, twin wheel's all the time every time. However I found straight line acceleration still had one wheel spinning up but not as bad as before the shim. It would lunge a little better but then single leg it through first, I should have threw a little more preload in to it.

The shudder mechanical feel on sharp slow corners dissapeared after ~2weeks BUT the twin wheel action was still there, so it simply became nicer to drive without loss of twin wheel drive on corner exit.

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It locked great and worked well at the recent sau/initial drift drift day.The ass felt predictable it's still locking good and straight off the line it locks up 2 whels pretty good.:thumbsup:.

Power needs to be fed into it arround corners.otherwise it's drift time.

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How is yours if you take off slowly, cruise at say 10km/h and simply nail the throttle?

Thats when mine would open wheel, launching with a few rev's it appeared to twin up.

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I gave it some in 1st coming out of the toll gates,from a rolling start,last night.And the stockers just chirped their way to redline,no one legging.

Definently better on the launch than the old worn out diff.

I can tell you the behaviour of the car arround corners is allot [email protected] low speeds the ass tends to want to stick and it's a bit easier on the steering inputs.But like i said before.the throttle can only be fed on if i get to aggressive on the acc and i tighten the turning circle it's drft time.

Id like to try it out at the circuit and see how it behaves.Prolly some time this winter.:bunny:

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Its all good.. I really think I needed a bit thicker than a 0.8mm shim to bind those spider gears up a little more.

I now have a mechanical that when rolling on the throttle in first spins the rears up, only difference is now when its spinning it accelerates much quicker than the old one legger spinning. Second gear is much nicer also, holds on well with a little squirming around 4000rpm but depending on the road surface it can still let go. :bunny:

Biggest difference I've found is its much easier to get out of corners in second and third without it going sideways and spinning up. Its improved throttle control 10 fold.

Will definitely be throwing a set of sticky tyres on the rear.

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Nice.I will have to get out there and try a car with a locker if someone will let me do it.

I think i know why the mechanical lsd are better than a shimmed lsd.That is an investment for the future.

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Cubes, what do you feel you should have put in rather than the one 0.80mm shim?

I'm currently looking at carrying out this mod and was wondering what would be a good compromise regarding shim sizing/number of shims for daily driving and some track/spirited power over-steer. I really don't want something that's going to bound around when driving and screech every time I go into BP on their nice shinny concrete floors.

Also what does the shim on spider gear side do? why couldn't you just put a thicker shim on the one side? Does it help give more even lock or something...

Big cheers to Trust33 for writing this comprehensive DIY ;) .

Edited by BAMR33
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If I were to do it again yes I would definitely run the bigger shim.

Even with a 0.8mm it chirps the inside wheel and clunks around a little.

The local diff place down here (Boss Automotive) sets them up with a given breakaway, they almost always settle on a 1.2mm shim and he said he hasn't had any one report back stating they single leg it.

It doesn't matter what side the shim is placed on as its placing preload on the whole spider gear assembly. 99% of people throw it on the spidergear side.

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I'll have to give the 1.2mm shim a go. Thanks.

So you just order the shims at Nissan dealers right?

If you add 1.2mm extra to the lsd you will end up haveing 2.0mm of preload on one side and on the other if you dont change it there will be 0.8mm which all up=2.8mm.

If you are going to attempt this mod you should buy some cheap "supercheap" plastic verneer callipers.I found they came in handy.As when i pulled the lsd apart to my suprise the stock shim had allready been replaced with a 1.1mm shim.Having them there and seeing the thickness gave me the idea of replacing the other 0.8mm side with the 1.1mm shim and buddying up the 0.8mm shim with my new 1.4mm shim.

BTW:Cubes i see what you mean by the extra preload binding and unbinding feeling.If i am going slow and am in 2nd gear turning a corner and i dont have enough momentum,as i put my foot down the car starts to bunny hop till i straighten out. :P

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i have a shimmed diff but doesnt seem to have any of these characteristics you describe. perhaps, other mods on my car contribute to it this. my car sticks to the road like glue and it requires giving it some stick before it will kick out.

Edited by Nozila
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i have a shimmed diff but doesnt seem to have any of these characteristics you describe. perhaps, other mods on my car contribute to it this. my car sticks to the road like glue and it requires giving it some stick before it will kick out.

If you ever get a mechanical in to it you will say wow.. How much easier is it to get the power down out of a corner without it getting all crossed up. :P

BUT saying that.. It does depend how much power your making and the transition of power. Mine comes on really hard with little throttle so it does make throttle control a touch difficult.

+ once the diff wears in with its shim its much softer so to speak.

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Yeah the diff has calmed down allot just from regular daily street driving.But is still much,much better than before.

I found that the car will go arround the corner with allot more grip from the rear end now.In grip situations Instead of getting straight on the pedal as i am exiting the apex,i feed it,and the resulting speed is greater than before.

Thats if im not slipping the clutch or if it doesnt break traction.Once traction breaks i have to be easy and not stomp on it.

Its not like i have masive power.185rwkw @13psi.It still binds/unbinds and hops in 2nd when turning a corner and locks on medium and tight turns.

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I've heard before that as a rule of thumb for nissan viscous LSD's that you add 50% of the original shim thickness for a good result. Don't quote me on it just something I was "told" by a diff shop!

Edited by ellie
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If you have the tools (rattle gun) give your self a day on your first attempt.

Lock it good as you don't want to be pissed you wasted a day + skinned knuckles only to have it open wheel still.

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