Differentials

Torque Biasing (Quaife, TORSEN)

The Quaife differential uses helical cut gears as opposed to the Invex cut gears in the Gleason. On either side of the differential, each stub axle connects to its own large helical gear. There is no direct connection between these two large helical gears. Each of the large helical gears drives five smaller-diameter helical gears (for a total of ten). The smaller gears from one side of the differential mesh with their counterparts from the other side of the differential. In a corner, the outside wheel must turn faster than the inside wheel. The Quaife (and the Gleason) allows this speed differential. But because the axles are connected through the smaller planetary gears, both axles receive the proper amount of torque. In practice, the Quaife differential does increase the steering effort (in FWD cars) slightly in low-speed maneuvers. This stiffness is the result of the application of torque to both wheels, not because of any loss of differential action. And unlike detent, viscous, friction plate, and others, the Quaife limited slip does not "snatch" (slip a little and then catch). This makes it more pleasant to drive, and it is easier on tires and other drivetrain components. The design is the result of five years of development, with "test vehicles" provided by various police agencies and ambulance firms. Under these conditions, the differentials have gone more than 100,000 miles without wearing out. Either of these two torque sensing differentials can be used with ABS, which is not true for detent or locking differentials.

Friction Clutch
This is a traditional construction for a limited slip. An arrangement of plates (some with a smooth finish, some with a finish surface) are interleaved to obtain the desired amount of slip. Unlike a torque biasing differential, the friction clutch has the amount of torque transfer preset (for example, at 40 percent) so that when one drive wheel breaks loose, a preset amount of the otherwise lost torque is applied to the other wheel. Like most things that rely on friction to operate, the clutches wear out, necessitating replacement. In addition to replacing the clutch discs every 10,000 to 25,000 miles, you can vary the amount of slip by using shims of different thicknesses. The harder you set the differential and the harder you run it, the more often you will have to replace the clutch disks.

Viscous
The viscous differential also has interleaved plates, and in fact works because of the viscosity (internal friction) of the silicone fluid that fills the gaps between the plates. The plates therefore do not actually touch one another. The percentage of torque transfer varies with the difference in speed between the two wheels, partly as a result of the plate design and spacing, and partly because of a physical property of silicone fluid that it experiences virtually no change in viscosity when heated. If one wheel is rotating only a little faster than the other, only a little torque transfer occurs, when there is a big difference between the speeds of the two wheels, the viscous differential will transfer up to 95 percent of the torque to the wheel with traction. Because of the difficulties in handling the silicone fluid, servicing a viscous differential can be accomplished only with special equipment. The silicone fluid is under pressure, and there is an air bubble of known (and controlled) volume included in the differential casing. Any deviation from the correct amount of pressure or air bubble volume can radically change the characteristics of the differential.

XR Upgrade (thank Chris 'Kif' Anglin)

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:

http://www.asknik.co.uk/car.html
http://www.truechoice.com
http://www.redlineoil.com

Fluids:

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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