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[General] [VP - VZ] How To Put Together An IRS Diff DIY Style + How To Identify An LSD

WazzaVN

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So I've been reading a few books, speaking to a few diff shops and mucking around with some diffs lately and thought i'd make a bit of a guide on how to put an irs diff together. I'll be using an irs diff out of a vz (m80) as an example. Now there will be a few pieces of information i will tell you to get from other sources. I don't want to risk giving you bad information that will ruin your diff! This is just a rough guide not a complete course! also it might be a good idea to buy a second hand diff and use the housing to build your new diff in. just so if something goes wrong you're not risking your current diff that you use in your car. (apologies in advance for the lack of photo's, my phones been really crap lately)

Tools Needed -
a 30mm, deep socket
a dial gauge
some general spanners and sockets
a couple of home made specials
A torque wrench wouldn't hurt
some lapping paste

Always wear some crap clothes when you're working with diffs as it get pretty messy. Wouldn't want to ruin your tuxedo!

Firstly you need to take out the axles. Just use a pry bar and they should pop out. Next you need to take the cover plate off the back of your diff. with an m80 diff the 15mm bolt at the bottom is a drain plug. so look out! Then undo the rest of the 13mm bolts then take a moment to enjoy the aroma of the lovely smelling diff oil. once your cover is off it will look something like this. (see below)



What you see here is your crown wheel (ring gear) bolted on to your diff centre (carrier). Now if you have never opened up an irs diff before you will be thinking "how da hell do i get dis out?!?!?!?) like I was. It's quite easy. In fact, even easier than taking out live axle centres with the c clamps. all you have to do is make up a tool (see below) and spin out those things on the side of your diff. They are holding the centre in!


and your diff should look like this.



Now time to take of your crown wheel. Put it in a vice with the bolts facing upright. there are two ribs sticking out on the side of your diff centre oposite eachother. when you put it in the vice place it so these ribs are just next to where the vice clamps it so it wont spin. now these bolts are done up pretty tight so you may want to get a long socket wrench or breaker bar. They are also Left Hand Thread! so you need to spin the bolts an clockwise to get them out and anti clockwise to tighten them. now with a bit of gentle tapping with a hammer and a block of wood just on the back of the crown wheel where it sticks out from the carrier it should come off pretty easily. tap a bit at a time on oposite sides.



Now there's a dounut looking rubber on the outside of your pinion gear making it really difficult to get to your pinion nut. and it's attached with some weird looking bolts. a 9/16 ring spanner will fit these bolts perfectly. make sure it's a star patter ring spanner and not a hex one though. you can also use another socket on another nut to stop your yoke from spinning. (see bellow) Now you can take off your pinion nut. a rattle gun is the easiest way otherwise use a deep 30mm socket or a bent 30mm ring spanner. and make something like a long bit of steel you can bolt to the holes to stop the yoke from spinning. (not needed with a rattle gun) of coarse its easy to take off while the diff is in the car. this is just the diff i bought and it came with it still attached.



Now get a few cans of degreaser or some prepsole and give everything you're going to re use a mighty good clean! now you can breath easy without the smell of diff oil everywhere. Now do what you planned on doing, wheather it grabbing your new diff centre, new diff gears or both and it's time to do what we just did in reverse with a few extra bits!

Ok so it's time to put in your pinion gear. when you took it out there might have been a shim (thin metal washer) and there will be a crush sleave/washer. if you are using new gears there will be a certain size shim you will need. it varies from brand to brand. don't ask a performance shop, mechanic or you're mate wazza what size shim you need. ask the manufacturer of your diff gears or a diff shop. if you're re using your existing gears then you can re use your shim or get one the same size Genuine gears might not have/need a shim. there's somtimes shim kits for sale on ebay otherwise a diff shop should have some they can sell you. if you're using a new gear then you will have to put a new bearing on. it's a bit of a tight fit so you might want to find a piece of pipe the same diameter as the inside ring of the bearing and tap it onto the gear. don't hit the outside of the bearing or you will break it. have fun trying to get the bearing off the old pinion. i tried and gave up! if you're re using your pinion gear and the bearing on it is stuffed or you want a new one then you might want to take it to a diff shop for them to get it off. you can try but i'm telling you it's not fun!



Put your pinion gear in the same way you took it out. The easy way of doing it is to just get a rattle gun and tighten your pinion nut just a little bit at a time till you feel some resistence when you spin the yoke by hand. you can just use a breaker bar and make little adjustments as it starts to get tight (like a quarter of a turn then check). if you over tighten it you will ruin your crush washer and have to start over with a new one.

Once your pinion gear is in it's time to put in your diff centre. Puting your crown wheel on you centre is pretty easy. just lay a few blocks of wood on either side of your vice. then put the crown wheel teeth down on the wood. then put the diff centre through the crown wheel (the right way up) and make sure your holes are lined up. then put a block of wood on top of your diff centre and gently tap it down. the crown wheel should quite easily slide through. There is probably a certain torque setting you need to put your bolts on with. but generaly just do them up TIGHT. use some stud lock on each bolt and do them up one bolt then it's oposite bolt. like putting a wheel on your car. i used a torque wrench when doing up my crown wheel and just did them super tight and took note of the reading so that all the bolts were the same. and remeber that they're left hand thread :spot on:

Now put your centre back into your diff and tighten up those carrier holding bits that go into the side of your diff (still don't know what they are called) to the same as they were before. Now here is were it gets a little technical but it's not all that hard.

Backlash -

Backlash is the freeplay between the gears. Basically how much one gear can move without the other gear moving. it's always a tiny amount but it's important to get it right! Again the best place to find out the recommended backlash setting is from your gear manufacturer, the shop that sold you the gears or a diff mechanic. you can get a dial indicator gauge off ebay for pretty cheap. just make sure you get one with a magnetic base! a better place to put your gauge is to the side of your gear with the needle side on. unlike the picture i took below (oops). i tried asking holden what the backlash setting was but the guy at the desk didn't seem to know what i was on about. if you get it as close as you can to how it came from factory it would be less likely to make any noises.



(Obviously your diff will be clean during this step. this photo is a re-enactment because my phone didn't feel like taking photo's when i was setting my lash.)

Now try and get your gauge needle perpendicular with your gear tooth. The gauge with be behind the zero mark. after you have put the base down try and set it so it is at zero. This can get fiddly but you will eventually get it. now make sure your pinion is locked and cant move, so either have it on the ground or clamp it somehow. now rock your crown wheel backwards and forwards and you should get a reading. if it is higher than the recommended reading you have to move the crown wheel closer to the pinion gear. so slightly loosen the carier holder on the side of the diff where your crown wheel teeth point and slightly tighten the other side. or do the oposite if your reading is lower than the recommended backlash. now check it again and ajust it until it's right. Hope you understand what i'm talking about there!

Diff Patern -

Now it's time to make sure your diff has a good pattern. get some lapping paste. it shouldn't be too hard to find, diff shops will have it. A good diff pattern means that your pinion gear is making contact with your crown wheel right in the middle of the crown wheel teeth.



(my phone didn't feel like taking photo's while i was doing this either so i found a photo. different diff but same principle see how the contact area is right in the middle of the teeth)

Paint about 4 of your crown wheel teeth with some lapping paste and give it a revolution (spin) in the direction your wheels will drive. now seeing as you used the recommended pinion shim your patern should be nice and in the middle. if you have a bad patern you will have to adjust your pinion with new shims.


If your patern is too high you will have to add another small shim or replace your existing shim with a thicker one. if your patern is too low then you will have to replace your shim with a smaller one. there should be a few different sizes in the kit you brought.

once have checked your pattern double check your backlash.

Put the cover back on, pop in your axles fill her with some oil and enjoy!

Bearings -

I replaced the bearings on my diff centre but it was extremely difficult. if you're going to replace your bearings get ready for some fun trying to get them off. they are stuck on pretty tight. the side winding centre holder bearings where your axles go into require a certain tool and can't be diy'd as far as i know.

Hope this guide makes sense and i havn't missed too much information!



Do I have an lsd????
How To Identify A Limited Slip Diff!

A quick guide on how to find out if you have an lsd or not. Here's a few ways to check.

1. check your filler plug for a tag. if it says lsd then it's most likely an lsd.

2. jack up the rear of your car and spin a wheel. if the opposite wheel spins in the same direction it's an lsd if the opposite wheel goes in the opposite dirrection then it's an open diff.

3. Now here is what an lsd centre looks like as opposed to an open. take note of where the split is.



4. You could always just do a skid (not on a public road, no no thaz illegal yo!) if it slides out the rear or it's most likely an lsd. rember though on the rare occasion an open diff will spin 2 wheels. either when allot of power is put through it, when the road is really slippery or when you havn't changed the oil for 25 years and there's metal shavings and crappy old oil clogging your spider gears.

happy skidding!
 
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Geek2.0

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Nice write up mate! Good to see someone is giving it a shot themselves, everything I read says "Don't bother, take it to a specialist"
+ rep :)
 

WazzaVN

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Yeah all I could find was "You cnt do it iz too hard!!!!!" Granted, you can't do everything. If you do enough research though, you can give most things a go.
 

WazzaVN

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I have a single spinner, if I want a LSD, can I just swap the gears and centre, or is it more extensive?
You can get and lsd centre and put your old crown wheel on it and put it in. But you will have to set your backlash. if you want to change your gears though it's pretty much a rebuild.

Sorry about the late reply, didn't see your post.
 

immortality

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Hey Mate,

It's a good write up. Just a few small corrections.

When it comes to tightening the pinion nut, there is not set torque, it is all about getting the correct bearing pre-load. If you check in any car manual it will show 2 values, 1 for new bearing and one for old bearings. Bearing pre-load is really a measure of how much torque it takes to turn the pinion. Unfortunately doing these types of measurements is very difficult for the average back yard mechanic. The same goes for the carries bearing pre-load. Ideally you would fit the carrier without the pinion fitted to measure the carrier bearing pre-load but again it's not really within the ability of the average back yard mechanic.

The other thing is the pinion shim. If you have a look at the old pinion that came out it will have something like + 1 or -1 or 0 written on it and refers to the shim (yours is +1 in the picture by the looks of it). This would have been worked out when the diff was first assembled on the production line. If you can't get the proper depth of the gear mesh pattern it may need to be adjusted although all those that I have ever spoken to, when using used gears, as long as you use the original shim with that gear set it generally works out ok and then you just need to adjust the carrier to get the proper back lash.

The other thing to be aware off, when you re-build a diff or change diff gears using a 2nd hand set of gears that unless you get the backlash and wear pattern exactly the same as when they were originally fitted (almost impossible) the gears may be a little noisy. Generally more noticeable when reversing or possibly engine braking.
 

WazzaVN

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Hey Mate,

It's a good write up. Just a few small corrections.

When it comes to tightening the pinion nut, there is not set torque, it is all about getting the correct bearing pre-load. If you check in any car manual it will show 2 values, 1 for new bearing and one for old bearings. Bearing pre-load is really a measure of how much torque it takes to turn the pinion. Unfortunately doing these types of measurements is very difficult for the average back yard mechanic. The same goes for the carries bearing pre-load. Ideally you would fit the carrier without the pinion fitted to measure the carrier bearing pre-load but again it's not really within the ability of the average back yard mechanic.

The other thing is the pinion shim. If you have a look at the old pinion that came out it will have something like + 1 or -1 or 0 written on it and refers to the shim (yours is +1 in the picture by the looks of it). This would have been worked out when the diff was first assembled on the production line. If you can't get the proper depth of the gear mesh pattern it may need to be adjusted although all those that I have ever spoken to, when using used gears, as long as you use the original shim with that gear set it generally works out ok and then you just need to adjust the carrier to get the proper back lash.

The other thing to be aware off, when you re-build a diff or change diff gears using a 2nd hand set of gears that unless you get the backlash and wear pattern exactly the same as when they were originally fitted (almost impossible) the gears may be a little noisy. Generally more noticeable when reversing or possibly engine braking.
Cheers mate

Yeah i will update the setting preload part because trying to torque it to a setting like you said is a waste. i have used a new and an old crush washer and there"s a big difference in the torque needed. i found the easiest way is to just get a rattle gun and do a little big at a time till you get the resistance you need. the diff shop did say there was a rating but i think its easier to just disregard it because its too tight to do up by hand and i don't think anyone has a wrench that would go that high! lol

I had pulled genuine gears out of my 2 diffs one was 3.45 the other was 3.08 both m80 and neither of them had pinion shims. i think they are probably built to suite the housing like you said and might be hard to get them %100 in another diff. i got aftermarket 3.9's and the seller told me they generally shim the pinion 12 thou. the only shim set i could find had a 20, 10 and 5 though shims. so i rounded it down to 10 and it made a decent pattern. does have a bit of an offload whine though so i might have another play with it if i can find smaller shims. i don't mind the whine too much, proof that it was a backyard special built by me haha! also my calais diff whines a bit at certain speeds, which was built by a diff shop a few years back.

also mate if you know a good way or have any tricks/tips for changing the bearings that would be awesome. i managed with great difficulty to change my diff centre bearings but it took allot hammers, chisels and rage to get the old once off. anyway if you do i'll chuck them in the guide courtesy of immortality.

Will put in updates cheers for the input!
 

immortality

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Getting the bearing of the pinion is a PITA. although it's a little easier with the proper bearing pullers/attachments.
 
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