to get some more cornering acceleration out of your BMW? Do you want to add
a limited slip differential to your car? In both cases, the differential
must be replaced. In this article I will go over the steps involved in
swapping out differentials in the BMW E30 3 Series from 1984-91. Keep in
mind that this tech article covers all 3 series models, including the BMW
E36 318ti from 1995-99, as it uses the same rear end setup.
a limited slip differential? Simply put, a limited slip differential or
L.S.D. is a differential that distributes power evenly to both rear wheels.
Regular differentials only distribute power to one wheel. The real advantage
of an L.S.D. is felt during cornering, as power distribution is split
between both wheels. Basically, the wheel with less resistance will receive
more power then the other. A good way to explain this is when a car goes
into a turn; the outboard wheel will be spinning faster than the inboard
wheel. More resistance is placed on the inboard wheel, making it spin
slower. Though a series of clutches or weights, the L.S.D. mechanically
sends less power to the inboard wheel and more power to the outboard wheels.
This helps to increase the stability of the car when coming out of turns at
high speed, such as freeway on ramps or that high-banked turn at the track.
BMW E30 3 Series cars have an excellent reputation for handling and control,
however if you wanted to go one step further, you would get an ďisĒ
model. The ďisĒ models featured the L.S.D. as well as other handling
upgrades. The nice thing about the design of these cars is that the L.S.D.
can be easily swapped into cars that did not originally come with it.
first step is to get a hold of a L.S.D. These can usually be picked up on
EBay in good shape for around $250-300. I would be cautious if buying off
EBay, as there is no guarantee of the age or condition of the diff. Your
best bet might be going to the junkyard to find one. Most major junkyards
offer a limited warranty on items such as engines, transmissions and rear
ends. So you have a little piece of mind. They are easy to spot, as there is
a large ďSĒ stamped on the outside cover. (For all of you out there
interested in doing this, and you are not sure if itís L.S.D. or not, I
can always check part numbers for you)
If you are looking to have your current differential upgraded to an
L.S.D., there are several companies out there, such as Quaife, that can
convert your standard differential into an L.S.D. many times with custom
lock-up rates far beyond what was offered stock on the ďisĒ models.
While these are great for track use, they donít apply very much for the
street. So, in this article we will be assuming that the unit in question is
a low-mile, stock used unit picked up from the local junkyard.
letís jack the car up. First, chock the front wheels to keep them from
rolling while you have the rear wheels jacked up. Next, loosen (but do not
remove) the rear lug bolts. Now, use a floor jack and jack up the rear of
the car. Be sure to jack the car up on a re-inforced part of the body, such
as a crossmember or chassis beam. Be sure not to jack the car up on any
other part, as you could put a hole right through the bottom of the car. I
have seen Porsches in the past where jacks have punctured the floorboards. A
handy reference is Wayneís article on jacking up your BMW. This article is
specific to the E36 series, however, the same principles apply to the E30 as
the car is firmly secured on jack stands, the next step is to remove the lug
bolts on the rear wheels and take the wheels off. Now, look at where the
drive axles are bolted onto the differential. We will need to separate the
axle shafts from the differential in order to remove the differential. There
are six internal Allen head bolts that hold each axle to the differential.
Before you remove them, itís a really good idea to clean them off to get
any dirt of grease out of the bolt heads. Any good brake cleaner should work
perfectly. We donít have to get them spotless, however just enough to
where we wonít have the Allen key from popping out. Itís also a good
idea to hit the bolts with WD-40 or good penetrating oil. Typically, I like
to let the spray sit overnight, to let the oil work itself into the threads.
This will make it much easier to remove the bolts, not to mention preventing
stripping and seizing when you hit them with the wrench. Put the car in gear
if itís a manual gearbox. This will lock the rear end and allow you to
loosen the bolts. Now remove all the bolts. The drive axles will now be free
of the differential. Use a piece of rope or stiff wire to hang the drive
axles to the car and keep them from crashing downward.
look at the front of the differential. You will see the mounting flange for
the driveshaft. There are four bolts that hold the driveshaft to the
mounting flange. Put the car in gear to lock the driveshaft in place, and
then use and open-end wrench to hold the nut on the end of each bolt. Now
remove the bolt. Put the car in
neutral and rotate the driveshaft so that you have enough clearance to
remove the next bolt. Now put the car in gear again and repeat the
procedure. Repeat these steps until all the bolts are removed. Now use some
wire or rope to suspend the driveshaft in place to prevent stress on the
move towards the rear of the differential and remove the electrical
connector from the speedometer sensor. I forgot to do this one time and
ended up ripping the wires off the ends of the connector. Nothing was
damaged to badly, but I did end up having to splice the wires back together.
we have to remove the mounting bolts for the differential. Iíve found that
using WD-40 or another good penetrant spray on the bolt will help loosen
things up. Iíd recommend that you spray it on all the differential
mounting bolts and let it sit overnight to soak in. The next morning, it
should be a lot easier to get these loose. I have found that in some cases,
using a torch to heat up the bolts also helps to get the bolts turning. If
you decide to do this, use EXTREME caution as you are directly in front of
the fuel tank. Gas vapors and a torch = explosion. Just use enough flame to
heat the bolt up slightly. This will cause the threads inside to expand and
put a jack under the differential to support itís weight. Trust me, you
donít want the differential falling on you while you are under the car.
Now we have to remove the two rear upper mounting bolts. These are located
at the top of the differential. You will need to use an open end wrench to
get these off. You may also need to use a ďcheater barĒ to loosen the
bolts. A cheater bar is essentially a large piece of pipe fitted over the
wrench. The extended length of the wrench provides you more leverage. Just
like you learned in basic physics. A longer lever equals less force required
to move it.
remove the two front mounting bolts. They are located at the very front of
the differential on either side of the driveshaft. Once again, you may have
to use the cheater bar in order to get them loose. Now remove these bolts.
Lastly, remove the nut and bolt for the rubber mounting bushing. Use an
open-end wrench on the nut to hold it in place while you loosen the bolt.
we will be able to lower and remove the differential. Keep in mind that the
differential is very heavy, so use caution and while pulling the
differential back, lower the jack. The differential will come out of the
out, take the old differential off the jack and place the new L.S.D.
differential on the jack. Now position the new diff in roughly the position
it would fit in the car, but slightly to the rear. We will need to do this
in order to angle the diff into position. Now start to raise the jack. As
you bring the diff into position, push it slightly forward to line the
driveshaft up with the input flange on the front of the differential. Once,
there, slide a bolt through to hold it in place.
use the jack to carefully lift or lower the diff until the mounting holes
line up. This may take a few tries, as the diff is very heavy. Once you have
it correctly positioned, slide the front mounting bolts through the mounting
holes and torque the bolts to 59ft/lbs. each. Now re-install the rear upper
mounting bolts and torque them to 59 ft./lbs.
now need to re-install the driveshaft mounting bolts. Take the car out of
gear and rotate the driveshaft til the mounting holes line up. Now
re-install the rest of the bolts. Itís a good idea to use new self-locking
nuts on the ends of these bolts. These nuts will not come off once torqued.
Use an open-end wrench to hold the nut in place and torque all the mounting
bolts to 53ft./lbs. Now attach the sender for the speedometer on the rear of
we need to re-install the axle shafts to the new differential. Before you
start, make sure to clean the mounting bolts. They must be clean and free of
grease before you install them. Now, make sure the car is out of gear and
rotate the flanges on the side of the differential until the bolt holes line
up with the ends of the drive axles. Thread the 6 bolts into the flanges and
put the car back in gear. Having the car in gear will lock the diff and help
you torque the mounting bolts. There are two different sizes of bolts used
on these cars, M8 and M10 Torx. If you have M8 bolts, torque them to 47
ft./lbs. If you have M10 bolts, torque them to 74 ft./lbs.
a good idea to change the diff oil while you are under the car. Look under
the diff, you will see a hex-head plug. This is the differential drain plug.
In order to drain the old oil, we will need to remove this plug. Slide a
drain tray under this plug. Now, look at the back of the diff. You will see
a similar plug on the rear face of the differential. This plug is the fill
port for the new differential oil.
remove the fill plug first. Use a 14mm Allen key or socket to remove the two
plugs. This will help relieve any vacuum built up inside the diff and make
it easier to drain the old fluid out. Next, remove the drain plug from the
differential oil will pour out. It should take a few minutes for all the
fluid to drain out.
all the old fluid is out, re-install the drain plug and tighten. Next you
will want to measure out the correct amount of fluid for the differential.
For 4 cylinder cars, you will want to measure out 1.2 quarts of oil. For 6
Cylinder models, you will want to measure out 1.8 quarts of oil. BMW
recommends you use BMW SAF-XO Synthetic Oil for differentials without
limited slip, or use BMW SAF-XLS Synthetic Oil for differentials with
limited slip. I just use Swepco products, as they seem to work wonderfully
in the differential.
use a siphon or pump to get the new fluid into the fill port on the rear of
the differential. When the fluid starts to pour out of the top of the fill
port, the differential is full. Remove the pump/siphon, and re-install the
fill port plug and tighten using a 14mm Allen key.
re-mount the tires and snug up the lug bolts. Now lower the car and tighten
the lug bolts using a criss-cross pattern.
Well, there you have it - it's
really not too difficult at all. If you would like
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