LIMITED SLIP/LOCKER OPTIONS FOR 200 AND 700
by Stu Spencer
So you want to spin both tires, huh? Tired of that open differential
letting one tire spin itself into a slick? If your car was not lucky enough
to come from the factory with an "anti-spin" differential, you have 2 basic
differential options to allow you to better distribute power to both tires (short
of welding the spider gears); limited slip or locking. All 200 turbos
and most 700 turbos (with a live axle, sorry no multilink) came with a Dana
30 differential in either the 1030 or the 1031 rear end. This is the same
differential that came in many late model Jeeps. Because of this 'commonality',
any competent 4X4 or differential shop should be able to install a traction
aiding device for about 2-3 hours of labor depending if you have all bearings
and seals replaced too (recommended).
I personally have a NOS (new old stock) Volvo LSD in my 81' 245GLTi that I
got for a very good price. I think it was some of the best money I have
spent on the car. Now I can take a corner without lighting up the right
rear. It does take a bit of getting used to when you are in a fast corner,
under full power, and both tires start to break loose. Overall, it has
increased the smile factor when driving my car.
According to the SAM catalog for there LSDs they sell, the differentials break
down as listed below. The cars listed in the same column use the same
differential part number from SAM. (If you know the difference between
the LSD for ABS and non ABS, please drop me
a line) In the early late 80s and 90s, Volvo went to a locking rear that
locked the rear at about 25 MPH. There is no LSD listed for cars with
multilink rear suspensions (88-90 764 and some 900s)
With Volvo 'locking' rear
There are pros and cons to every style of traction aiding devices. For a
very good summary of each style, please read the Traction
Aiding Devices FAQ. Remember, this site is based on 4X4s, so not all the devices
mentioned are available or practical for our cars.
- Limited Slip Differential (LSD):
The 'positraction' or LSD is recommended for road driving and for moderate racing
applications. They are the most driver friendly. There are two basic styles
of LSD that can be put into the Volvo Dana 30; friction based and torque sensing.
- Friction based units such as a Dana "Powr-Lok" and OEM 'anti-spin'. These
units use clutches to allow some speed differences, like while turning, but
will 'bind' the wheels together starting with a specified amount of torque.
Typically you might get a 70/30 power split between wheels or a 60/40 with
a really tight LSD. One major drawback is that eventually the clutches
wear out and require replacement. The harder you use the LSD (more burnouts,
etc.) the shorter the life of the clutches. Usually a friction modifier
is added to the differential oil to extend the clutch life and reduce chattering.
This style of LSD is the most commonly used in Turbobricks member's cars.
- Torque sensing units such as a Tractech "TrueTrac". These units use
worm gears to 'bind' the wheels together before slip occurs but allow some
speed differences like while turning. They apply more torque to the
wheel that has the best grip. One drawback is that because the Dana
30 is a 'small' differential, these units must be very compact and therefore
small gears must be used. Some 4X4 shops I talked to said that under
high torque these smaller gears may fail. An advantage of these units
is that there are no clutches to wear out. Talk to your 4X4 shop for
their opinion. To my knowledge, no Turbobrick member has installed
a torque sensing differential.
Most 'locker' differentials basically have mechanical teeth which are meshed
together to lock the axles together. An advantage of a locker is that
they are tough as hell and don't 'wear out'. The locking differential
is recommended for heavy duty racing. There are two basic styles of locking
differentials; automatic and manual. Some lockers replace the entire carrier
and others only replace the spider gears. If only the spider gears are
replaced, the ring and pinion does not have to be reset.
Purchasing and Installing a LSD/Locker:
- Automatic 'locker' differentials are controlled by where the torque is
being applied, not necessarily by whether or not you are turning a corner
(although this is a good example). If the torque applied by the engine
to the differential via the driveshaft is greater than the torque applied
by the ground via the wheels, then the locker will lock and force both axle
shafts (and both tires) to rotate at the same speed. If the torque applied
by the ground to one of the wheels to the differential is greater than the
engine torque, that shaft will unlock and allow that wheel to rotate free.
Not all corners will elicit this unlocking action. If the road surface
is slippery and you are applying engine torque, the tires may very well spin
instead of unlock ('tires' because you can never spin just one tire with a
locker, it's both or none). An automatic locking differential may bang,
clunk, or hitch when going around corners and may cause some slippage when
turning in icy or slippery conditions.
Automatic lockers such as the Tractech "Detroit EZ-Locker" or a PowerTrax
"Lock Right" are available. There is a new "Detroit Geroter" from Tractech
that is advertise to have eliminated the noise and jerks associated with the
standard locking differentials. The Tractech are more expensive but
are reported to be more durable than the PowerTrax.
Turbobrick member Philip Bradley commented: "I just took the 242T on a
500 mile road trip. The EZ Locker works fine, just as it is supposed
to. It is not, however, just like a limited slip but with no clutches
to wear out, as it is sometimes advertised. The noise is heard only at very
low speeds, usually between 0 and 10 mph, when turning. Sometimes when
coasting on a very slow turn, the rear will snatch and grab, causing the car
to buck. There is not really anything to adjust to get rid of this.
In fact, the brochure and instructions warn to use light throttle rather than
coasting in slow turns. So one has to remember to use a little gas rather
than back off completely (or push in the clutch) and then you cannot really
tell the EZ Locker is there. In a straight line, there is a solid, 50/50
lock that sends equal power to each wheel. I have tested it so far only
on dirt roads. The car moves forward under power, however. When
I had the open differential, I could just spin a wheel on a dirt road without
increasing speed much. I should have the car at the drag strip soon
for a proper pavement test. I will obviously keep the EZ Locker, but
it is less streetable than a limited slip, although perhaps more durable.
To anyone who lets others regularly drive the car, or does not want any odd
sounds from the rear, or does not want to alter very low speed driving techniques
on turns, I would not recommend this style of rear. The 50/50 lock is
better than a limited slip, however, as those are often 25% TO 40% lock."
- Manual lockers lock by engaging a sleeve that connects both axles together
via an air valve (ARB "Air Locker") or an solenoid (PowerTrax "C-Locker").
This is the only type of differential that allows full control. You can choose
the predictability and handling of an open diff, or the ultimate lock of a
spool. Installation requires some extra wiring; either airlines and
an compressor (Air Locker), or electrical wires (C-Locker). To my knowledge,
no Turbobrick member has installed a manual locking differential.
Before shelling out your hard earned money, talk to a local 4X4 or differential
shop about your install. Unless you have lots of specialty tools, setting
up a rear end is not for the amateur. The average shop may look at you
weird when you ask about a Volvo but once you inform them that it is 'just a
Dana 30', they should calm down. If they want to charge you extra because
it is a Volvo or has disk brakes, go somewhere else. The disk brakes are
easier to remove than the locking hubs on the front of a Jeep! Most shops
can set up the differential with it still installed in the car, although the
rear sway bar will need to be removed. You can purchase the differential
from your local shop or try Reider
Racing or West
Coast Differentials on the web. Check to see if the unit comes assembled
or if you get a box of 'guts' and a 'carrier'. You can sometimes get a
pretty good price if you play one company against another; "So and so has that
differential for x$, can you beat that?"
You will need to specify the gear ratio when purchasing to insure that the
LSD/Locker is correct for your ring and pinion set. Differentials will
have different carriers for ranges of ratios. I have been told that
gears from the factory on a 240 Turbo are 3.73 with a manual and 3.91
with an auto. 740 Turbos had fuel economy gears of 3.54 for a manual and
3.73 for an auto. To verify the ratio, there is a label on the axle (picture
below). When viewed from the rear, it is on the driver's side just to
the right of the spring. If you can't find the label, "jack up one tire
if you have an open diff, or both tires if you have a working posi or locking
differential. Rotate the tire one full revolution for posis and lockers and
2 full revolutions for open diffs. Carefully count the number of full revolutions
the driveshaft makes. This is your gear ratio. In other words, if the drive
shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning
the tire for twice the number of full revolutions and dividing the drive shaft
revolutions by two will give you a more accurate reading." (quoted from West
If you have a car with an electronic speedometer, and your LSD replaces your
current carrier, you will need to replace the sensor wheel that signals the
speedometer impulse sender with the Volvo PN that corresponds with a stock Volvo
LSD for your year of car. Early model 700s use PN 1220844.
If you are installing a Dana "Powr-Lok", the new sensor wheel should fit correctly
because Dana made the OEM LSD too. If you are using a locker that only
replaces the spider gears, like a PowerTrax "Lock Right", your current
sensor wheel will stay as is. Any other style of LSD will require some
creative problem solving to attach the sensor wheel to the LSD carrier.
If you come up with a method that works (or does not) for a particular LSD,
please let me
Although you don't have to, it is recommended to replace the outer bearings,
outer seals, inner seals, and the carrier bearings. Replacing all of these
components will add about $200 to your install. At a minimum you should
replace the inner seals to keep the new differential fluid from washing the
grease out of your outer bearings. Check with wherever you buy/install
your differential to see if they can get the bearings and seals cheaper than
from Volvo. After the initial break in period (~500 miles) change the
differential oil. Red
Line has a 75W90 synthetic gear oil which already has a LSD friction modifier
in it. Check with your differential manufacturer to see if a friction
modifier is recommended.
Good luck and in the words of Turbobrick member Dave Barton, enjoy your "tire
If you have any questions, comments, testimonials, or found a
good supplier, please e-mail
Thanks to Paul Schuh, Dave Barton, Jarrod Pilone, Peter Linssen, and Philip
Bradley for input on this article.