first69 19 Report post Posted August 9, 2015 Thinking of keeping my eight inch but would like a 350 limited slip diff. What all is needed in parts for this? Is it a easy swap of parts? Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted August 10, 2015 I've been thinking about doing the same thing. I don't feel like rebuilding the whole thing myself and thought a 3rd member swap sounds like a good way to go. I'm looking into a couple options. The two I like right now are http://www.ebay.com/itm/8-INCH-FORD-MUSTANG-COUGAR-STREET-ROD-REAR-TRAC-LOC-POSI-9-550hp-9-/331622046091?hash=item4d3636d98b&vxp=mtr or http://www2.cougarpartscatalog.com/8intracloc.html I haven't done one yet but replacing a 3rd member sound like the easiest option. There are a ton of videos and tutorials online. Essentially you take your wheels off, pull your axles out a few inches, drain the fluid, unbolt the old member, pull it out, put a new gear set in with a new gasket, refill the fluid, and reinstall the axles and wheels. I would also love to hear other members perspectives on changing a 3rd member. Quote Share this post Link to post Share on other sites
bryonbush 85 Report post Posted August 10, 2015 going through this right now. 69 mustang with 2.79 open but with an AODE trans. I just ordered this http://www.ebay.com/itm/8-Ford-Trac-Lock-Posi-Gear-Bearing-Kit-Package-3-55-Ratio-8-Inch-NEW-/371341869546?hash=item5675b341ea&vxp=mtr they have other gear ratios as well. local shop can put it together for under $100 bucks which is still cheaper than the other posts Quote Share this post Link to post Share on other sites
1969_Mach1 334 Report post Posted August 10, 2015 I haven't done one yet but replacing a 3rd member sound like the easiest option. There are a ton of videos and tutorials online. Essentially you take your wheels off, pull your axles out a few inches, drain the fluid, unbolt the old member, pull it out, put a new gear set in with a new gasket, refill the fluid, and reinstall the axles and wheels. I would also love to hear other members perspectives on changing a 3rd member. It's simple like you mentioned. But, completely remove the axles. Just pulling them out a few inches and letting them rest on the axle seal might damage the axle seal. Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted August 10, 2015 It's simple like you mentioned. But, completely remove the axles. Just pulling them out a few inches and letting them rest on the axle seal might damage the axle seal. Yeah I was thinking about that. Also probably a good time to replace said seals and check the 47 year old bearings?... Quote Share this post Link to post Share on other sites
rwcstang 210 Report post Posted August 10, 2015 I've been thinking about doing the same thing. I don't feel like rebuilding the whole thing myself and thought a 3rd member swap sounds like a good way to go. I'm looking into a couple options. The two I like right now are http://www.ebay.com/itm/8-INCH-FORD-MUSTANG-COUGAR-STREET-ROD-REAR-TRAC-LOC-POSI-9-550hp-9-/331622046091?hash=item4d3636d98b&vxp=mtr or http://www2.cougarpartscatalog.com/8intracloc.html I haven't done one yet but replacing a 3rd member sound like the easiest option. There are a ton of videos and tutorials online. Essentially you take your wheels off, pull your axles out a few inches, drain the fluid, unbolt the old member, pull it out, put a new gear set in with a new gasket, refill the fluid, and reinstall the axles and wheels. I would also love to hear other members perspectives on changing a 3rd member. I've been on the fence about buying the ebay ford 8" as well, I was thinking 3:55's if i still kept my c4 or 3:80s if I went 5 speed, the builder swears it can handle 550hp... I have read about ppl buying from him but I have yet to hear if it does handle that kind of power. Quote Share this post Link to post Share on other sites
cavboy78 28 Report post Posted August 12, 2015 I bought an 8" 3rd member from tj1141, your first link. It was a 3.89 with a trutrac. Very easy install and has worked great with no issues for the past 3 years. He is out of PA and is great to deal with. He will also take your old 8" with a core refund if you so choose. It was a helluva lot easier than buying the parts and putting together. Quote Share this post Link to post Share on other sites
rwcstang 210 Report post Posted August 12, 2015 I bought an 8" 3rd member from tj1141, your first link. It was a 3.89 with a trutrac. Very easy install and has worked great with no issues for the past 3 years. He is out of PA and is great to deal with. He will also take your old 8" with a core refund if you so choose. It was a helluva lot easier than buying the parts and putting together. couple of questions for you: have you been spirited with the car? if so, how does handle? Do you feel confident that it can take punishment, i noticed you have a stroker motor aswell, so im kinda curious if his ford 8" can handle our kind of power. I've been on the fence with him for about 1yr now lol Quote Share this post Link to post Share on other sites
Rsanter 158 Report post Posted August 12, 2015 I have an 8" posi in my convertable. I have been putting 340hp to it for a number of years with no troubles. I have always heard they are good for about 400 hp. One difference is how you are applying the horsepower. If you have a 500hp stroker engine and you play with the car, take it on a road course once in a while and some streetlight to streetlight racing. I do not see how you will have a problem. If on the other hand you are drag racing and dumping the clutch at 3000rpms, you will have a much shorter lived rearend Bob Quote Share this post Link to post Share on other sites
Ridge Runner 1,154 Report post Posted August 12, 2015 9 inch and 8 inch share the same axles ,the 8 inch is about as strong as a base 9 inch except for the spiders ,that is the weak point of the 8 inch .The true track should take care of that . The swap is as simple as pulling the axles ,all the way out as stated ,and dropping the complete third member .The new third member simply slips back in place . Replacing the axle seals at this time is a no brainer but be sure you grease the seals before replacing the axles or they will burn up instantly from friction . Make sure to use gear oil made for limited slip diff . Also replace the copper washers on the third member studs to prevent oil leaks .If you have the new third member on hand the swap from removal to install of the new one can very easily be done in an afternoon . Quote Share this post Link to post Share on other sites
rwcstang 210 Report post Posted August 12, 2015 thanks for tips! Due to my recent work schedule and other priorities this car will probably never see a track and I probably won't be running slicks either, lol. she'll be mainly on the streets and I rarely drive aggressively since the streets in my area have potholes, gotta love the bay area... Quote Share this post Link to post Share on other sites
cavboy78 28 Report post Posted August 12, 2015 i don't have have a stroker, but i do have a stout 351w that puts out about 440/430 at the flywheel. Like Rsanter stated, I have done plenty of spirited driving and had some fun with no issues. I mainly drive on the streets and hope to increase the autocross and like events in the future. I don't ever plan on putting slicks on it...but may do a couple of 1/4 mile runs for sh*ts and grins. I know an 8" is not optimal for my car, but I'll drive it til it breaks. I also think internet folklore has people believing the 8" is a lot weaker than it actually is. Are you running an auto or manual? I know manuals can have a tendancy to break 8"s more than autos... Quote Share this post Link to post Share on other sites
cavboy78 28 Report post Posted August 12, 2015 Also, TJ1141 will give you the proper additive for the diff if you order through him. Quote Share this post Link to post Share on other sites
rwcstang 210 Report post Posted August 12, 2015 i don't have have a stroker, but i do have a stout 351w that puts out about 440/430 at the flywheel. Like Rsanter stated, I have done plenty of spirited driving and had some fun with no issues. I mainly drive on the streets and hope to increase the autocross and like events in the future. I don't ever plan on putting slicks on it...but may do a couple of 1/4 mile runs for sh*ts and grins. I know an 8" is not optimal for my car, but I'll drive it til it breaks. I also think internet folklore has people believing the 8" is a lot weaker than it actually is. Are you running an auto or manual? I know manuals can have a tendancy to break 8"s more than autos... Currently it's an Auto so I know for sure it'll prolly be safe im probably around the same Hp/Tq Rating as you. I was going to go with a manual conversion but the car got hit on the side and currently the whole car is getting repainted due to blending issues. if it wasn't for that accident I'd prolly be driving my stang with a tKO conversion from MDL, but even with that conversion i still feel that the 8 would handle it unless your dropping the clutch and doing burns outs every where you go. Quote Share this post Link to post Share on other sites
