home articles community multimedia register members about

Come say hello, or just browse through the forums and find what you're looking for


Come join our growing community and be a part of revolutionizing Volvo performance...

Register Now!


Get your Turbobricks apparel! Everything from shirts to stickers.

Turbobricks Store



by Stu Spencer

Differential Options:

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)

Without ABS
With ABS
With Volvo 'locking' rear
240  -1991
240  -1991
240  1992+
740  -1988
740  -1988
740  1989+
764  -1987
764  -1987
765  1988+
765  -1988
765  -1988

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.

  1. 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.
      typical friction based 'clutch' style LSD
    • 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.
      Internals of a TrueTrac
  2.   Locking 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.
    • 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.

    • Tractech Detroit Locker PowerTrax Lock-Right

      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.
Purchasing and Installing a LSD/Locker:

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 Coast Differentials)

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 know.

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 glue".

If you have any questions, comments, testimonials, or found a good supplier, please e-mail me.
Thanks to Paul Schuh, Dave Barton, Jarrod Pilone, Peter Linssen, and Philip Bradley for input on this article.


Home | Message Board | History | Members | Gallery | Classifieds | Maintenance | Modifications | Resources | Contact
©1996-2005 Turbobricks.org - All Rights Reserved Privacy