Limited Slip Diff? December 31, 2014, 12:15:27 PM Hi Folks,I have a 1984 Cougar LS and I'd like to first off, see if I have a limited slip diff and if not, determine the easiest way to change to one. Any advice is appreciated. I might even like switching to a 5-lug rear wheels if that's not a bridge to far.Thanks,Gart Quote Selected
Limited Slip Diff? Reply #1 – December 31, 2014, 12:44:48 PM With the back wheels off the ground, but still in park, a car with open diff will spin the left wheel in the opposite direction as the right if you turn one by hand. If you have limited slip, the wheels will resist movement. If you apply a lot of strength, they will turn opposite one another like an open, but it will take a lot of effort. You almost certainly have a 7.5" rear, so the chances of having limited slip are thin. That doesn't mean you're stuck, because they made limited slip 7.5's, mostly in Rangers with 4 cylinders or the smaller V6's (4.0L trucks will have an 8.8" axle). You're looking for a rear end that looks like yours, and has a diff tag that says 3L55 or something like that. That would signify a 3.55:1 gear ratio with a limited slip. An open diff tag would simply have 3 55. Swapping the unit is fairly easy, but rather involved. If you search the forum, you'll probably find a thread about how to do it. Quote Selected
Limited Slip Diff? Reply #2 – December 31, 2014, 12:57:03 PM Great. Thanks for the info. Quote Selected
Limited Slip Diff? Reply #3 – January 02, 2015, 10:04:32 AM If you want to go five lug then find a complete rear end from a 94-98 GT Mustang if you want an 8.8 which will have the Ford Trac-lok. I helped pull one out of a GT a couple months back and it was $200 brake to brake. These rear ends will bolt into your car and with some minimal brake line work you will have rear disc brakes. If the rear end has a tag bolted to the rear differential cover take a picture of it and go to one of the local Ford dealers or post it here and someone can tell you what gears are in it. From there you will want to change the differential oil and remember the additive for the limited slip with the new oil. You will also need to change the driven gear on the speedo cable to match the rear gears with your speedo. This is a good site to figure that out:http://www.angelfire.com/mb/mustangsrule/speedogear.htmlDo some searches on here and you will find several five lug conversion threads.Darren Quote Selected
Limited Slip Diff? Reply #4 – January 04, 2015, 09:19:42 PM I wonder how many 86 and older birds/cats have factory posi besides the turbos????It has to be a small percentage....1%??Travis Quote Selected
Limited Slip Diff? Reply #5 – January 04, 2015, 10:22:38 PM My 87 3.8 had it as part of a towing package.None of my other 86-88's had posi. One 88xr7 did. Quote Selected
Limited Slip Diff? Reply #6 – January 04, 2015, 11:06:19 PM Quote from: turbotrav;442459I wonder how many 86 and older birds/cats have factory posi besides the turbos????It has to be a small percentage....1%??TravisI'd put it closer to 10-15% Quote Selected
Limited Slip Diff? Reply #7 – January 21, 2015, 08:47:29 PM My 88 Sport has a limited slip 7.5in rear. Not sure if that helps figure anything out. Quote Selected
Limited Slip Diff? Reply #8 – January 24, 2015, 09:10:36 PM Percentage of ThunderCats with a posi: 0%But...some of them, TCs and Sports especially...did have Trac Loc. Quote Selected
Limited Slip Diff? Reply #9 – January 25, 2015, 12:52:54 AM So would a 86 turbo coupe have a limited slip 7.5? Quote Selected
Limited Slip Diff? Reply #11 – January 26, 2015, 07:39:47 AM I have 58 Cougar and 99 Thunderbird door tags in the database. Most of them junked or wrecked.Here are the engine/axle/trans combos that I have seen so far on the tags:19803.3L/2.73 open/auto4.2L/2.26 open/auto5.0L/2.26 open/auto5.0L/3.08 open/auto19813.3L/2.73 open/auto5.0L/3.08 open/auto19823.3L/3.08 open/auto4.2L/3.08 open/auto19832.3T/3.45 Trac-Lok/5-sp3.8L/3.08 open/auto5.0L/3.08 open/auto19843.8L/2.73 open/auto3.8L/3.08 open/auto5.0L/3.08 open/auto19852.3T/3.45 Trac-Lok/5-sp3.8L/2.73 open/auto5.0L/2.73 open/auto5.0L/3.08 open/auto19862.3T/3.45 Trac-Lok/5-sp3.8L/3.27 open/auto3.8L/2.73 open/auto5.0L/2.73 open/auto19872.3T/3.55 Trac-Lok/5-sp2.3T/3.73 Trac-Lok/auto3.8L/3.27 open/auto3.8L/3.45 open/auto5.0L/2.73 open/auto5.0L/2.73 Trac-Lok/auto19882.3T/3.55 Trac-Lok/5-Sp2.3T/3.73 Trac-Lok/auto3.8L/3.08 open/auto5.0L/2.73 open/auto5.0L/2.73 Trac-Lok/auto5.0L/3.08 Trac-Lok/auto Quote Selected
Limited Slip Diff? Reply #12 – March 20, 2015, 11:43:36 AM I think I have the towing package in my 1984 LS Cougar. It has a 7.5" 3.08 rear and I think there are transmission cooler lines to the radiator. I did see that the 3L08 tag is needed for a trac-lok rear and I don't have that.The Mustang conversion for rear discs is good info.Thanks to everyone for the comments and suggestions here.-GT Quote Selected
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