XR4Ti Archived Tech Articles

    Installation of a Sierra XR4x4 Diff - A continually developing writeup on the installation of a European XR4x4 viscous limited slip differential into my 87 XR4Ti.

Post Date:    Mon, 05 Feb 2001
Subject:      Re: LSD just arrived today
List:         xr4-hardcore@yahoogroups.com, merkurowners@merkurowners.org

Mike wrote:

> The Sierra LSD arrived today, Yippee!

Great!  Mine came in Friday.  Someone mentioned sometime ago that 
there was a spacer required to install this smaller diff case, but 
failed to elaborate, as I recall.  Well, it looks like it's the 
upper most mount of the diff.  I measured the width of the mount 
on the US diff, and it's 7 9/16" across, and the Euro diff case is 
a tad under 7" across.

BTW, I'm speaking of the mount where the crossmember attaches by a 
large pass-through bolt at the top, front of the case.

I'm going to provide more accurate measurements as well as 
measurements relative to the centerline of the pinion, just to make 
sure I don't install the thing skewed.


Post Date:    Fri, 16 Mar 2001
Subject:      V6 XR4x4 LSD Install
List:         xr4-hardcore@yahoogroups.com, merkurowners@merkurowners.org

As I posted previously, the installation of a V6 Sierra XR4x4 
viscous LSD requires a spacer on the upper, forward most mounting 
point.  I was originally concenred about installing the 
differential in a skewed position, but it looks like I won't even 
have to worry about this.  Why, you ask?  Well, I pulled a spare 
rear crossmember out of my parts warehouse for the purpose of test 
fitting the smaller diff to the US beam.  Here's what I found.

The diff fit perfectly at 5 of the 6 connection points.  I bolted 
it in at those points to make sure I had a solid connection.  The 
only point where it didn't fit was the upper, forward most 
*driver side* flange of the crossmember.  This is where the spacer 

I stuck a 12mm stud through the hole in the crossmember into the 
diff so I could mark off, on the unthreaded body of the stud, how 
wide the spacer needed to be.  I then measured the marks that I 
made on the stud.  My measurements, with a ruler measuring to the 
1/100th, indicated that a 0.65 width spacer was needed.  Since the 
mounting ear on the crossmember is a little flexible, and I wasn't 
measuring on the crossmember that the differential was going to be 
installed in, I gave myself a small margin of error, opting to 
make the spacer 0.63 instead.

I used a 1/2" steel bolt spacer.  My fastener supplier doesn't 
currently carry any metric bolt spacers.  The spacer was originally 
1.5" in length, so I had plenty of room to play with.  I marked 
the body of the spacer and started cutting.  Since I used such a 
precise ruler, I had to use an equally precise machining tool.  I 
pulled out my angle grinder (with a coarse wheel, no less :-).  I 
was able to get the trimming within about 0.03 with that, and then 
I squared everything up.  I did the finish work with my Dremel.

The end result had a less than perfect average spacer length of 
about 0.64 (range: 0.63 to 0.65).  It fit right in the opening.

My next task is to dig up some appropriate differential fluid and 
some sockethead cap screws (aka Allen headed bolts) to replace the 
horrid Torx bolts that I'll be dealing with very soon.


Post Date:    Sun, 01 Apr 2001
Subject:      XR4x4 LSD Install Complete
List:         xr4-hardcore@yahoogroups.com, merkurowners@merkurowners.org

Hello all,

Well it's about time.  I've had the diff for almost two months and 
I've finally gotten it in the car.  It was hardly a trivial job, but 
it's all done.  Now it's time for my final write-up on this subject.

I spent a fair amount of time cleaning the differential, cleaning out 
threads, preparing the spacer for the mouting flange, etc.  See my 
article in my Archived Tech Articles section on the web page for info 
on the spacer I made.

First order of business is discussing spacers, bolts, and fluids.  
The XR4x4 differential has two mounting points that use through-bolts 
rather than the single through-bolt on the XR4Ti diff.

Important Tip #1:  The through-bolt for the lower mount on the XR4Ti 
diff will work fine in the upper through-bolt position on the XR4x4 
diff.  This means you'll need two idential through-bolts (with 
accompanying nylon insert locknut [aka nylock] and washer).  So a 
spare from a junkyard, easily removable, will work just fine.

This upper through-bolt is where the spacer goes, BTW.  I just put 
the upper bolt in the same orientation as the lower bolt (through from 
passenger side to driver side).

The other fasteners I replaced were the much-lamented T-40 Torx head 
bolts.  I found M8x1.25 x 50mm socket head cap screws (aka Allen head) 
at a local hardware store in 12.9 grade (using a 6mm socket head driver), 
with the proper phosphate coating (black).  I can't BEGIN to describe 
how much easier these are to install and remove.  It's amazing how 
little thought they require compared to the T-40 method (clean, spray-
with-penetrating-lube, apply-heavy-blows, pound-in-theT-40-bit, 
apply-heavy-pressure-toward-the-bolt-while-turning method).  I just 
wrenched them in.

I did a little research on the web regarding what fluid would be the 
best for the differential application.  I found that the XR4x4 requires a 
SAE 90 GL-5 hypoid fluid from the "AskNik" web page.  The best substitute 
in synthetic I could find from RedLine was their 75w90NS.  The "NS" is 
important as it stands for "non-slip", designed for viscous couplings 
like the XR4x4 LSD.  I ordered the fluid from TrueChoice in Columbus, OH, 
at about $8 per quart.  I purchased two quarts.

I completely prepared the differential before installation time, short of 
one item; differential fluid level.  I couldn't find reference to a correct 
fluid level in the XR4Ti shop manual.  The method that I chose was to 
compare fluid levels from the diff in the car to what I thought it should 
be.  I'm going to fast-forward to the fluid filling part for the sake of 
clarity and order.

I opened up the fill hole on the diff after I removed it from the car 
(10mm socket head).  The level appeared to be about 1" below the fill 
hole.  I felt like I needed to fill the fluid to the bottom of the fill 
hole (as is the case with the T-5 tranny), but wasn't completely confident 
in that decision.  I ended up filling the differential with fluid to about 
1/2" below the fill hole.  That's a pretty solid compromise.

Instead of creating a funnel and tube fill setup, I just stood the diff up 
on the pinion flange and poured the fluid in the hole.  I repeated this 
method until the fluid level was where I wanted it.  I took about 1 quart 
bottle plus 1/4 to 1/3 of the second bottle.

Now let's rewind to the removal and installation of the differential.

I jacked up the car and left the wheels on.  First thing to be removed was 
the halfshafts.  Same old Torx bit job.  Once I broke them loose (an 
amazing consumption of physical strength) I sped up the job by utilizing 
the tool that is:

Important Tip #2:  I used a cordless drill (the same one I use to run my 
lugnuts on and off when changing race and street tires at the track) to 
speed the Torx bolts out.  I just need a 1/4" hex to 3/8" square socket 
adapter.  There isn't a bunch of room to work with, but there was enough.

I utilized my wife (and later my racing teammate, Grayson) to press on the 
brake pedal, preventing the wheel from turning while I applied the force 
to the bolt.

The halfshafts are sided, but not ended.  In other words, you have to leave 
the driver side halfshaft on the driver side (because it's shorter) and the 
passenger side halfshaft on the passenger side.  However, it's not ended, 
as in, inboard end, outboard end.  You don't have to have any particular 
end of a haflshaft bolted to the diff or the stubshaft at the hub.

After the halfshafts were out I dropped the swaybar (13mm).  I supported the 
differential with the jack.  I thought it was possible, with the stock 10mm 
rear bar to unbolt the rubber differential-to-body mount without removing 
the bar, but with the 14mm XR4x4 rear bar on the car it was much harder.  
Okay, impossible without dropping the bar.

So I dropped the bar and then, with the jack supporting the diff, I unbolted 
the rubber diff mount from the body (13mm).  Then I unbolted the diff from 
the crossmember (19mm).  The diff is perfectly stable on the jack as long as 
it's surrounded by the crossmember.  It's a different ballgame once you lower 
the diff out of the crossmember.  Fortunately the assembly is light enough to 
reposition as needed.

I'm sure you are wondering about the driveshaft.  I didn't remove it.  This 
isn't going to work if you don't have a one piece driveshaft.  If you have 
the stock XR shaft you'll need to separate the driveshaft from differential, 
and you'll probably have to remove (part of) the exhaust from the car.  I have 
nothing but a downpipe on my racer, so it's no problem.

I had the rear of the car jacked up high enough that when I dropped the diff 
to the ground (and lifted it off the jack, setting it on the floor), and slid 
the driveshaft yoke out of the T-5 that no fluid leaked out.

Let me state that removing the differential with the driveshaft attached is 
HARDLY the prefered method.  It was not fun dragging the diff and driveshaft 
assembly under the car from the rear end all the way to the transmission 
tailshaft.  I chose to do it like this because I didn't have anyone around to 
put the car in gear and take it out of gear, allowing me to rotate the 
driveshaft to get to all the bolts connecting the shaft to the rearend (a 
little Freudian).

So the diff came out with the driveshaft attached.  It took a little work 
with correct placement of a screwdriver to prevent rotation of the diff 
while I unbolted the driveshaft and the adapter from the stock diff.

Once the diff was out I cleaned up the halfshafts and the locking plates.  I 
was amazed how much crud there was on both items.  I wired-brushed the 
locking plates.  I also repacked the CV joints with semi-synthetic grease.  I 
found that one of the CVs was a little sticky, but not bad.

It was all pretty much downhill from here.  I bolted the driveshaft up to the 
LSD and stuck the shaft into the transmission.  Then I lifted the diff onto 
the jack and raised it into place.  It was reasonably easy to get the diff 
to fit into the subframe.  With the jack holding the diff up, it was very 
easy to adjust height and placement to get the bolts into the diff.  
Installing the spacer (in the upper, driver side mount) was also gravy.

Don't forget to reconnect the vent tube to the vent.  I did and I need to 
get under there and reconnect it.  Duh.

I then attached the rear diff-to-body mount to the car, then the swaybar 
back to the body.  Then I torqued those bolts.

The last step was the installation of the halfshafts.  I preloaded each 
hole with a bolt and the locking plates before bringing the halfshaft 
near the car.  The hardest part about the halfshafts is getting the first
bolt on each end started.  Make sure to do one bolt on the diff end first.  
The other end of the halfshaft can just lay on the semi-trailing arm while 
you do that.

Again I used the cordless screwdriver to run the bolts into the stubshafts 
once I got them started.  This saves an amazing amount of time and 
physical effort.  Finally I torqued the halfshafts in.

That's it.  I lowered the car, then drove it about 8 miles to get it nice 
and warm before trying to use it at all.

I'll add some info here to sum up everything as a quick reference.  Here's 
all the basics:

Web Resources:



75w90NS RedLine gear oil
semi-synthetic CV grease

Tools (general, you'll need others):

13mm socket
19mm socket
15mm wrench for the driveshaft bolts (or what ever size you need)
T-40 Torx bit (preferably K-Mart brand, or other strong stuff)
10mm socket head driver (gear oil fill hole plug)
6mm socket head driver (for my socket head screws, Torx replacements)

Torque specs:

halfshaft bolts - 28-31 ft.lbs
rear mount to diff - 37-41 ft.lbs
rear mount to body - 37-50 ft.lbs
diff to crossmember - 51-66 ft.lbs
swaybar to body - 14-19 ft.lbs

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Published by Chris Anglin.