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I have no personal, first-hand knowledge of this, but I've saved several messages from this Brickboard forum on this subject -- maybe something here can be of help to you:
1) "...The reportedly best thing for a 240 or 740 differential is the True-Trac made by Detroit Locker. This is a fairly new limited slip designed for the axles made by Dana Corp. The 240 has the Dana 30, 27-spline axle. This differential as it turns out, is also used in the front of a lot of Jeeps. So it's fairly common and popular, and the True trac is pretty cheap. I've seen it listed for under $400...."
2) "...Actually the axle manufacturer is Dana, and the rear end in your car is a Dana 30. Officially a 27-spline Dana 30 center.
This turns out to be a common axle for lightweight off-road use. The same differential is in Jeep CJ and Wranglers for the front axle. Detroit Locker makes a very effective torque-sensing limited slip differential called a True-Trac for this axle.
They run about $400 new. It's listed by virtually every 4wd supplier in the magazines that support that hobby, and may be sold locally if you have a 4wd shop, truck accessory shop, or hot rod shop in town...."
3) From "Dave's Spec Sheet:" http://personal.linkline.com/dbarton/SpecSheet.html
"Basically, TrueTrack (and also Dana) only make two limited slips each for the Dana 30, one part for 1030/1031 with 3.54's and below, and one part for 1030/1031 with 3.73's and above. It just happens that most 1031's we see come with the 3.73's because of the cars this axle came in -- mostly turbos, towing package cars, and seemingly some random 5 speed cars.
"UPDATE NOTE: (04-08-02) Derek Walker wrote that while in the process of examining different options for an LSD for his '89 745 GLE with a 5.0L Ford engine and 4.10:1 differential, he checked with Reider Racing regarding the TrueTrac per the recommendation here. Reider responded that his 1031 Volvo housing will NOT accept the TrueTrac LSD due to slight dimensional differences from the 1030. They've got a few returns from Volvo owners due to incompatibility issues. It's not clear if the issues are unique with the TrueTrac LSD or the 1031 housings.
"Also it does seem all 1031's have the "ears" on the right side of the pumpkin (they are not machined on 240's. They attach to the torque tubes on the 740 suspension). Justin's source for the info on the "ears" and the 1031 axle is Mike Knell at Jagsthatrun. Mike wrote the V8 engine swap book on the Volvo 240.
"From reading posts on 4x4 chat groups the TrueTrack sounds like a great LSD, especially for street performance. The Dana Powr-Loc (which I'm pretty sure is what Volvo offered for towing packages) is also supposed to be a good, long-lasting differential, although very expensive.
"UPDATE NOTE: (12-08-02) Stealthfti from the Turbobricks Forum wrote:
A 1030 is about 10.125 inches from the rear cover surface to the front of the pinion neck.
A 1031 is almost exactly .5 inches longer.
"Visual differences:
A 1030 has a single gusset on each side of the pinion neck, roughly centered along the pinion centerline...
A 1031 has 2 gussets on each side; with the larger gusset spreading back from the top of the pinion neck; and the smaller gusset following the pinion centerline...
"UPDATE NOTE: (02-12-04): tuff240 from the Turbobricks Forum wrote:
The differentials are all the same up until they changed for the speedo tone ring. The only difference between a 1030 and 1031 is the housing itself and the R&P (ring and pinion). The differentials can be swapped back and forth. The R&P's cannot.
"The later model cars (86 and up) with speedo tone rings are, I believe, all 1031's. The true trac units that will be put in a car that requires a speedo tone ring will be different only to fit the tone ring. You can still swap tone ring or no tone ring differentials from 1030 to 1031. Only problem will be that you won't have a working speedo if you need a tone ring and install a diff that does not have a tone ring.
"AGAIN, the major difference is the R&P.
"Also the differential units come in 2 sizes depending on what R&P you have/want. There are 3:73 and up, or 3:73 and down. Make sure you pick accordingly in case you ever want to change gears. For example, you cannot change from a 3:91 R&P to a 3:31 R&P w/o changing the diff. This goes for stock oem diffs and True Trac diffs as well.
"*EDIT The pinion bearings are also different from 1030 to 1031. So make sure you get the right pinion bearings for whatever rear end you have. "
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