Buying a LSD ? You better read this.

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The purpose of this article is acquisition of basic knowledge about buying used self locking differentials

 

What is LSD ?
It stands for Limited Slip Differential, avoid using that acronym when talking with mom or non car guys.

Why i need it in my life ?
– It’s really useful in mud and snow.
– It makes the car really easy to control while sliding or drifting.
– It makes the U-turns fun and spectacular.
– On a drag race, during power starts and up-shiftings one of the wheels might slip. LSD will prevent this so you won’t lose time.
– By buying and installing a LSD, you are adding “S209A LIMITED SLIP DIFFERENTIAL” to your car’s options list. That Increases the car value.
– DONUTS !
– Massive burnouts with both rear wheels (and/or clutch if you’re not experienced enough)

Attention : Everything on that article except the testing and recognizing of a LSD is valid only for the EU market.
There is a difference between EURO and US diff lockers.

What diff should i use ?
Common diff used on e28 is typ188 a.k.a. Medium case used on 518,520,525,528e,528i,
and large case typ210 for 535i and M5.

e28 shares same diff case with e34 and e30.

If you are going to use e34 or e30 diff on e28, you need to make sure the new diff is the same type (188 or 210) as your current.
Most of the e30s are with small case – typ168 (left – 6 bolts on the back plate) and very few of them are with type188 (Right – 8 bolts of the back plate).
None with 210.

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Most of the e34s are with medium case – typ188 (upper) 518, 520, 525 and 530 (m30) . The v8 powered e34s and m5s are with typ210(lower).
Picture is used only for visual representation of the flange bolt count difference for EURO (and maybe US) typ188 and typ210 diffs. 

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A same type diff from another e28 is a straight bolt on, except the difference in the back cover.  (Both covers are interchangeable.)
– before 84′ – for center mounted round bushing.

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– After 84′ – square bushing, it’s mounting point is shifted slightly to the left

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A same type diff from e30/e34 needs couple changes to fit:

– Replacing the back cover with your current
– Replacing the drive flanges with your current ( pop them out using a flat screwdriver)

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Gear ratios?

The possibility of using differentials from different cars offers a ton of gear ratio options
Find the one that suits you best by using our gear calculator.

We did a brief research over the web, about some popular ratios and where they might be found.
We cannot confirm if that’s 100% true, but it might give you some head ups. Also there are few other gear ratios. Here are the results:

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How you can recognize a LSD just by blink of an eye?
There are couple signs:
– There is a big “S” stamp ( Sperrdifferential ) somewhere on the case – usually on the top (shown on an e32 casing).
Picture is used only for visual representation of the look of the “S” stamp on BMW LSD.

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– There is a small gear ratio tag attached to one of the bolts of the back plate which should contain the leter “S” before the gear ratio.

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If the differential is still on the car there are also two options:

(Not recommended, because of reasons)
– Find wide and open space, full lock (left or right) , put on 1st gear, hold the clutch, 5k rpm, release the clutch and you should do an instant donut.
Make sure you are making difference between a smokey donut (LSD) or pathethic understeer accompanied by tyre squeeking (open diff).

(Recommended)
– Put on neutral, disengage the handbrake, lift one of the rear wheels off the ground and try to spin it.
It should be really hard to do this with the tyre on and almost impossible if you are trying to spin just the brake disk/drum.

Field testing.
In my case i got a differential on a killer price. I was looking for typ188 S2.65 out of a diesel e34 and found it just few kms away from work.
The deal sounds too good to be true, but i went prepared with tools.

For a proper testing you need the following:
– Ratchet with 17mm socket
– flat screw driver
– 2 metal rods (~ 500 mm long)
– 4 bolts M10X40-60 and socket for them
– sandpaper 60-80 grid ( to clean the ratio tag, if there is any)

So the seller presented me this.
(You will be able to replace your e28 diff with e34 one ONLY if it looks like this – 4 mounting holes on the top.)

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Dirty, muddy and rusty diff case. If you got the same – don’t worry. Sandblast it and spray it. It will do the work.
Don’t powdercoat it, because that will bake off the flange seals.

I’ve tried to rub the dirt off the top just to see the “S” stamp, but it was faded away.The ratio tag was missing.

The first thing you need to do is to try spinning the wheel flanges in opposite directions with your hands.
On a normal, open diff, the wheel flanges will be able to spin in opposite directions of each other with ease.
On a LSD they should only be able to spin in the same direction.

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There shouldn’t be any noises coming off it.
Diff shouldn’t stuck or become harder or softer to spin at some point. It should rotate smoothly.
Then shake all of the three flanges, just to see if there is play in the bearings. Should be close to none.
Observe for leakages around them (or the whole case looking ‘moist’) – a clear sign for a shot seal/s.

Since the ratio tag was missing i wasn’t sure if this is a 2.65 diff so i had to “count it” by myself.
How the whole thing work.
The gear ratio simply explained is how many turns of the driveshaft are equal to one turn of the wheels.
So in my case 2.65 turns of the driveshaft flange should be equal to 1 turn of the wheel flange.
And to be more precise, 26.5 turns of the driveshaft are equal to 10 turns of the wheels.
For example if you are buying 3.25 diff, driveshaft flange will spin 32.5 times on 10 wheel turns. etc.
Mark the drive flange and one of the wheel’s (piece of chalk works great) , and start to spin and count.
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Put two bolts on each side of the wheel flanges, so they could lock the metal rods.
Push one of them forward while trying to pull the second one backward making the differential to slip.

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It should be really hard to do so.If it’s easy, the friction discs are more likely to be worn out.
We’re having some sets in stock, but this is a major reason to negotiate over the diff price.

Remove the cover (17 mm socket) and inspect inside.

Oil has to be clear.
Silver shavings or oil reminding of a metallic silver paint are really bad signs of worn out pinion or crown (or both) gears. Whole metal chunks are the worst.
Deal breaker for sure, since the metal residue is damaging the gears and the friction discs and that sounds like complete and expensive rebuild.
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Inside walls of the case should be black and clean, there shouldn’t be any rust.

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Put the diff straight up the driveshaft flange, and start rotating the whole case.

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You will see pinion gear (underneath) and crown gear (left) spinning. Observe the teeth on both of them for damages, scratches, parts missing or wear. Although any irregularities on the gear surfaces will not necessarily hinder the diff’s function, they will make noise at greater speeds that some people may find irritating.

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If everything looks good it’s a done deal. Pay the man, order a new cover gasket and some Castrol Syntrax limited slip 75w-140 (oem applied) – 1.7 liters for typ188, 1.9 liters for typ210.

Congratulations – you are ready to become a boy racer.

P.S/N.B!  –  If both wheel flanges are spinning only in the same direction and you find it impossible to slip the diff with the rods, make sure the diff guts inside don’t look like that !!!
It’s not a LSD , it’s dogshit.
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We’ve sourced some of the pictures from Google.
We really appreciate the effort of their authors.

Credits to Shawn Doughtie & Michael Burroughs for letting us know US e34 diff might fit e28 only under some circumstances.

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