Installing a 3.46 limited
slip differential
Replace the factory installed 2.93 LSD, to see
what kind of performance improvement is actually obtained, along with the effect on fuel mileage and interior noise.
The 3.46 was purchased from a source in California, who sells quite a few BMW differentials.
I chose the 3.46 ratio based on the best mix of adding some additional power,
not impacting fuel economy significantly and not adding too much engine noise. There are many articles that have been written
about choosing a proper final drive (differential) ratio, but an older one by Richard Nott pertaining to the E28
is perhaps the best for an E28 owner making such a decision. This document has vanished from the Internet, but you can download
a PDF copy of it that I've made, from the link below, "Choosing a Performance Differential".
An additional article by Mike Miller may also be helpful, even though he is talking about differentials in an E30.
Lastly, if you want to really get into the nitty-gritty of diff ratios, including
the effects of tire size on engine RPM, look at John G. Burns Unix Nerds Domain, which includes a calculator for such things, along with other info about BMWs.
Choosing a Performance Differential
The diff arrived from California and appears in good
shape. Note the "center mount" rear cover (below), which was obtained and installed by the seller, so that the diff can be
installed in my early E28. I'll comment later about different rear cover configurations, used by BMW on the E28 models, during
various years of production. It's something you have to pay attention to, if you want to install a diff with a different ratio,
from a different year and model E28 such as I am doing.
Additional parts (all original) are being renewed along with the differential installation,
such as the half shafts, (one of which has developed a light knocking sound) the rubber rear differential mount and corroded/damaged
original hardware.
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| Center mount rear cover on E28 differential. |
Below is a close-up of the "Info Tag" which is on most differentials,
so that you can identify the ratio and if the diff is "open" or a "limited slip differential" (LSD). The tag may be attached
to any of the rear cover bolts, but is usually found on the left or right side (such as this one) of the rear cover. It may
also be totally covered with dirt and baked on grease and be very hard to see under a car. The "S" indicates this is a LSD
model and the "3,46" is the ratio. In the US we use a decimal point (3.46) but in Europe it is a comma.
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| Tag showing this is a LSD with a ratio of 3.46 |
The used differential appears to be in very good condition.
No sign of cooked fluid on parts, excessive dirt or indications of worn ring gear teeth. The metal blades on the right (BMW
call this the Pulse Spider) is the speedometer sensor trigger for the sensor housed in the rear cover. Don't forget to check
the sensor terminals, including cleaning the terminals to insure good electrical contact. The signal is a simple on/off magnetic
switch but it travels a long way through some pretty small gauge wire, so clean connections are important, as is the condition
of the rubber boot cover.
Differential mounting bolt locations on the drivers side,
very easy to get to compared to the passenger side! Soak the bolts with PB Penetrating Catalyst a day or two before you start work, to make the bolts easier to remove.
Passenger side upper bolt location is difficult
because the Main fuel pump and fuel filter is in this area, greatly limiting the space available to work with wrenches.
The differential rear mount... This mount was replaced in
1983 under the NHTSA 82V-108 BMW recall campaign, replacing the mount and installing a new, longer center bolt. It is being
replaced again, with a new rubber mount due to the current age of the existing mount and signs of deterioration and shrinkage
of the rubber, although the mount is not allowing the differential to make any detectable movement noises, yet.
After removal of the rear mount, (which had lightly tightened
bracket bolts and no sign of Loctite having been used) you can see the access plug in the floor of the trunk, used on early
E28's to reach a lock nut on the back of the large thru-bolt.
New and old differential rear mount. Note the difference
between the two designs. I am not sure why the old one has the large rubber ring and large bolt retainer... to prevent the
diff from dropping down too far if the rubber fails?
June 22, 2007 Update -
On later model builds, from about mid 1984 and later, the differential rubber mount
design changed and became rectangular in shape, as shown above. You can see that it won't work in an earlier build model which requires
the square model.
The rebuilt CV joints/axle shafts shown above, require additional
work as received... the old end caps from the removed axle's are required, inorder to pack the CV joints with lubricant (supplied)
and reseal the assembly. Be very careful removing the end caps and clean them properly, getting all the old sealant out. Bentley
suggests several BMW spec'ed sealants which are not readily available, but you can use Permatex Aviation Form-A-Gasket No.
3 Sealant, which is a substitute for the Curil 2 Sealant that BMW specs. You're much better off obtaining complete rebuilt
axle shafts, which are fully lubricated, sealed and only require that you bolt them in.
10 of the 24 hexhead axle flange bolts are damaged!
More expense to replace damaged hardware caused by BMW and independent shop poor technical skills and/or poor tools. The more
work I do on this car, the more I find that I paid for sloppy workmanship, clearly exhibited by the damaged hardware and many
overtight fasteners. While nothing actually failed, thankfully, it was damaged and was not replaced, as it should have been!
Unfortunately, the organizations involved are no longer in business as I would certainly like to have some words with
them!
For those of you who took the time to write to me about my "preoccupation" with damaged
hardware, which I've called attention to several times here on my web site, I thank you for taking the time to contact me.
I also suggest you purchase a book published back in 1990 by the late Carroll Smith, titled "Nuts, Bolts, Fastners and Plumbing Handbook". I think you'll find after reading it, that my concern about damaged hardware is certainly warranted.
Resealed, fresh lubricant, carrier mount threaded bolt holes
chased with a tap, outside cleaned-up and the differential is ready to install.
When resealing the diff, if you don't have a differential oil
seal arbor tool like the ZDMAK BMW3000 (shown in the background above) or a large 3/4 or 1-inch drive socket that is 2-3/8 inches
in outside diameter, you can make-up an inexpensive tool to seat the new side seals by purchasing a 1-1/2 inch to 1-1/4 inch
pipe reducer fitting and a cap for the 1-1/4 inch end. This will properly fit the seal so that you can seat it in the diff.
Make sure you properly lube the seal before installing and install to the proper depth (note original seal depth before removing)
if you don't have an arbor tool, which has a shoulder to limit the depth that the seal will be seated at (see above photo).
The differential carrier rusty spots have been treated and
repainted and the new differential rubber mount has been installed. Note that the anti-sway bar and exhaust pipe heat shield
has been removed, to permit easier access during removal and replacement of the differential.
While under the car, take a look at the aluminum heat shields
attached to the floor and see if they are covered with gunk, which causes them to be poor reflectors of heat coming from the
exhaust system. I've noted that many E28 heat shields are covered with stuff. Use cheap paint thinner and scrub the stuff
off. You'll notice a difference in hot weather and slow traffic!
Update April 25, 2008
What's the condition of your Guibo disk?
And one other item you should look at is the Guibo disk at
the rear of your transmission. Look carefully for signs of deterioration of the disk as you rotate the drive shaft slowly
by hand. If it has cracks or shows signs of flaking particles of rubber, now might be a good time to replace it while you
can move the driveshaft rearward, before you put the differential in. A quality replacement is a Guibo from Lemforder and
if you're running a turbo or have made other major power modifications, consider using a Guibo for an E34 M5 which is thicker
and requires the longer associated E34 M5 mounting bolts.
Mine was replaced at 105,606 miles when I had a new clutch
installed. Now, 14 years later, but only 25,000 miles, the Guibo disk remains fresh and in excellent shape. Mine has
a semi-shiny surface because it has been coated with Gummi Pfledge every couple of years. This surface also shows imperfections,
quickly, versus a dirt caked surface.
A Guibo from a friends 528e with an automatic transmission and 180,000 miles on the
Guibo, which was replaced today, is shown below. You can see that the coupling is failing, with major cracks and tearing
around the bolt hole bushings. I've noticed that Guibos removed from an auto trans equipped E28, versus a 5-speed, are usually
in better shape, perhaps due to the auto's smoother shifts over the life of the Guibo.
UPDATE April 16, 2009
Modify Your Shift Linkage?
While
in this area, you may also want to think about modifying your 5-speed shift linkage, by involving a different shift linkage
assy., that will shorten the length of the shifter movement. A discussion about doing this is here. Additional info about doing maintenance/modifications on a 3-series shifter bushing replacement and using different throw shifter shafts are discussed at these links. An article named "The Short End of the Stick", is also a good reference. There are only minor differences in the 3-series linkage and these web pages will give you
a good sense of what is involved in doing these things.
Installing the Differential
Yes, it can be accomplished by yourself, without help, if you take your time and follow
my suggestions... but for safety sake, you should have a helper.
I've replaced three (3) E28 differentials, by myself, using
only a service jack and jackstands and two others with the assistance of the owners. What I describe works well, as long as
you take your time and work slowly. To make access a bit easier, remove the exhaust pipe shield and position the fuel lines
out of the way by wire wrapping them, as shown above. I have more to say about the fuel line arrangement, later.
To position the differential for installation, I use a piece
of 4x4 fence post under the diff, with the diff balanced so that it can be easily positioned by hand as it is raised into
position. This is not a stable platform for the diff and you want to keep a hand on it to keep
it stable during lifting, until you get the diff up inside the carrier near the bolt holes. I lay on my right side and use
my left leg to pump the floor jack handle, leaving my hands free to steady and position the differential. It'll wobble around
on the block, which is what you want it to do, so you can position the diff with reference to its mounting bolt
holes in the top of the carrier. A stable diff placement on the lifting jack will make the diff too difficult to position
for mounting bolt insertion... and you'll spend way too much time, to say nothing about frustration, trying to get these bolts
threaded!
Position the diff so that it can be attached to the drive
shaft flange first, using the old nuts which will go back on easily. New locking nuts will replace the old nuts before the
installation is complete. Trying to use new locking nuts now would be difficult because you can't hold the drive shaft firmly
enough to properly torque the new nuts and prevent from having the bolt threads screwed-up, because the mating parts aren't
together tight.
With the rear of the diff not yet attached to the rubber
diff mount bracket, there is sufficient room for you to get your hand in to install the upper bolts first, adjusting the position
of the diff as you work to line-up the bolt with the threaded upper bolt hole on each side. The trick is to have positioned
the diff on the jack so it can be easily moved within the area you are working in. Don't tighten the bolts all the way yet,
leave them backed off several turns to continue to allow movement of the diff in the carrier. Now, install the lower bolts,
adjusting the differential position on the jack, so that the bolts can be properly threaded.
With all the bolts installed, but not fully tightened, you
need to install the center bolt in the diff rubber mount bracket, positioning the diff as needed to allow easy insertion of
the center bolt. The amount of clearance shown above, between the diff rear cover bracket and the face of the rubber mount
bracket is about what you should also have in your installation at this point. With the diff rubber mount center bolt partially
threaded, raise the diff with the jack to mate with the rubber mount and torque the bolt and the other carrier mount bolts.
Later model E28s and diffs have different rear cover
mounting arrangements, of course.
Remove the old drive shaft nuts and install the new locking
drive shaft nuts. They have serrations around their top and are 16mm, not the 17mm size of the old nuts. If you have a Snap-On
meter torque wrench with short half-inch drive openend wrenches, they will fit on the passenger side of the diff nose which
is recessed... directly in front of the center nut shown above.
If you're installing rebuilt half-shaft axles and the CV
joints at the outer ends did not come pre-packed with greese and end caps (like mine did), make sure you use something like
Permatex Aviation Sealer No.3 to seal the end caps to the CV joint housing. Apply to both mating surfaces, including about
an 1/8-inch on the edges and let stand for about 10 minutes to become tacky and then put them together. I put nuts and bolts
through the ends and snug them up until I am ready to put them in the car.
When installing the half-shaft, it's easer to place the outer
end (wheel end) into its flange first and then place the inner end (differential) in its flange from above. Place a bolt in
each end at the bottom to hold the shaft in its flanges while you rotate and install the other bolts.
With everything back in place and tightened to torque specs,
make a final check of everything before you put the wheels back on and lower the car for its test drive.
And the results with this 3.46 differential?
After driving a 139 miles this lovely April 2nd, my opinion in the nutshell, is that
I think the 3.46 coupled to the 5-speed is a very good improvement over the original 2.93. Others have selected different
ratios, 3.25, 3.64 or a 3.73 and are also happy with their choice, given what they were looking for and the type of driving
they do. Since I do mostly long distance driving, I was looking for something to manage inclines better, not requiring a downshift
to 4th so much of the time and improved passing performance. I have driven a 5-speed with a 3.25 and couldn't tell
much difference at all and driving a 3.64 was just too much engine noise and rpm's.
Having spent four hours with this 3.46, I'll keep it! The first thing you notice
with my early 528e with its very light flywheel is that you won't kill the engine if you release the clutch too quickly. This
has been a problem for my wife as well as others who have driven this car. With the 3.46 ratio, you'll spin the tires if you
try to push it too hard around a right hand corner and merge into traffic. The old 2.93 was just too tall to do this.
Passing time in the 60-80 MPH range in 3rd gear is much improved, getting you out and
around the vehicle ahead of you much quicker. Remember I am running a Mark D'Sylva chip which gives me another 20 HP or more,
and 500 rpm more than a stock 528e. And getting up inclines without need to downshift to 4th, also works for me now... not
all inclines, of course, but the one I used as my incline to test on.
Lastly, I log my fuel mileage, so I'll know after a couple of tank fulls what the 3.46
is costing me in fuel mileage. More later.
Not a quality rebuild!
Oh boy, more work because somebody else didn't do their job right! All the CV boot to
flange joints were not sealed and are throwing grease everywhere. It sure messed up the underside of my 528e!
  The CV Joint boots were simply slipped on the flange
and clamped, no adhesive was used! Consiquently, all
four boot joints started throwing grease all over everything, because they were not properly installed!
The BMW Factory Service Manual (the big blue book) as well
as Bentley's, make it clear that the boot install process must include the proper adhesive, such as Bostik 1513 or Epple 4851.
Since neither is readily available here in the U.S., I use Permatex 80338 (RS-9) which has worked well in sealing the CV boot
to flange joint, on many vehicles that I've replaced CV boots on over the years. People who simply use a clamp and "hope"
it won't leak, are not taking care of business... they are lazy or stupid and their incompetence is going to cost more
time to correct it, after you may have already paid someone to do the job right.
Yes, I am really pissed about this and have told my supplier
to tell his source to get their act together, or find another source!
Apr. 12, 2007 Update
- The CV boot joint edges have been carefully rolled back, cleaned and Permatex 80338 (RS-9) adhesive applied
and new band clamps (double strapped and properly torqued) installed. Half-shafts will go back in the car after the thrown
CV grease mess is cleaned up.
With the CV grease cleaned up the half-shafts are ready to
go back in. I took this opportunity to rearrange the fuel pump and filter hose arrangement, using new hoses and clamps. The
factory hose routing had overly long hoses routed rather oddly, which you can see in the pictures further back up
this page. In looking at a friends later model 535i ("John in VA") the fuel lines were routed the same way I now have
mine routed, above.
Apr. 13, 2007 Update
- 93 miles of testing this morning, including some serious whoop-de-do's at speed to really flex the CV joints and everything
looks leak free at this point. I will be keeping track of my fuel consumption using the quantity pumped divided by the miles
driven calculation, not the OBC reading, and posting it at the bottom of the Home page, so that you'll find my latest MPG numbers there.
Modifications and Resources
Pg.5
(under construction, not yet complete)
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