Limited Slip Rear End Questions - Vintage Mustang Forums
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post #1 of 39 (permalink) Old 11-30-2017, 08:33 AM Thread Starter
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Limited Slip Rear End Questions

I know there are a ton of random questions here, so any input would be greatly appreciated. Really wasn't expecting to have to do this on this car.

It seems to me there is a major misconception as to what a limited slip rear is. Previous owner told me the car had a limited slip rear. Great! I now realize the car has an open rear. Everybody I know says that I have a limited slip because I only spin one tire sometimes. No, I don't have a limited slip, I have an open rear and there is a difference. When the rear is jacked up the tires spin in different directions. I don't want the open rear. I bought a hot rod to have a HOT ROD! My stepfather has been griping on me for a couple months now because I haven't laid tread in front of his barn yet. So last weekend I pulled up and some of his buddies were there so I dropped it and laid one hell of a black line. Yes, one black line. Not impressive. I turned around and did it again and it laid two lines. Sometimes it will put two down but conditions have to be ideal.

Can the 8" open rear be converted to a limited slip, or do I have to replace the whole rear? Assuming I have to replace the whole rear, what can I expect to get $$$ for a good complete 8" open rear with 3.80 gears?

What is the easiest (to find and put in) and cheapest way to get a good limited slip rear in my car?

Should I go with a 9"? I would think an 8" would be fine since I don't have too much hp, but would it be harder to find a limited slip 8"?

My buddy has a 1st generation Bronco 9" he said he would be willing to sell me. From what I can tell the most notable differences are the width is 3/4" wider on the Bronco and the wheel bolt pattern in different. What is the process to make that work? Cut the axle down 3/8" on each side? How do I get the same wheel bolt pattern? What is this 9" rear worth assuming it doesn't have the gears I want? A guy has a whole 9" rear on Craigslist and wants $1,000 saying not to waste his time with lower offers. Are they really worth that much? It's not a Rockcrusher or anything.

What else?

1965 Coupe
351W - ~400 Engine hp
Edelbrock Performer RPM Top End Kit
Holley 670 Street Avenger
Bored .30 over
Hooker Headers
MSD Box/Distributor
4 Speed Toploader
3.55 Limited Slip Detroit TrueTrac
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post #2 of 39 (permalink) Old 11-30-2017, 08:45 AM
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I recently sold a 9" posi center section only from a Bronco, 3:50 gears, for $350. Your least expensive option (and easiest) is to buy a used or new center section and swap it in. You'll only need it, a tube of RTV, and some oil. If you go with a 9" swap, you're looking at the possibility of different wheel offset, so cut the axle or different wheels; different axle diameter, so new spring perches, U-bolts, brake line changes, etc; driveshaft length may be affected, and exhaust interference is another. It sounds like an 8" swap is your best option given your current set-up and needs imo. You could also buy the new posi unit, reuse your current gears (although they might not be super desirable) and just rebuild it. Loads of options for you, loads of threads. Lastly, we all know what the word 'posi' refers to, so no need to start the whole 'it's a GM thing' here please...

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post #3 of 39 (permalink) Old 11-30-2017, 08:58 AM
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Limited Slip Rear End Questions

You only need to change the existing differential to a locker of some sort. A Tru Trac is a very good option which will require zero maintenance after installation. No need for new gears if they are ok. You can buy new or used. You could also look for complete 8Ē center chunks with a locker. All depends on you skills and depth of wallet.
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post #4 of 39 (permalink) Old 11-30-2017, 09:25 AM Thread Starter
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From a quick internet search, is the link below what you are referring to? Is this the only part that I need or do I also need additional parts of the center chunk? With this setup, when I want to spin the tires is it going to spin both mostly every time?


Eaton Detroit Truetrac Differentials 912A616 Ford 8" 28 Spline - QuickPerformance.com

1965 Coupe
351W - ~400 Engine hp
Edelbrock Performer RPM Top End Kit
Holley 670 Street Avenger
Bored .30 over
Hooker Headers
MSD Box/Distributor
4 Speed Toploader
3.55 Limited Slip Detroit TrueTrac
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post #5 of 39 (permalink) Old 11-30-2017, 09:38 AM
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or one of these...
https://www.speedwaymotors.com/Richm...tial,1951.html

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post #6 of 39 (permalink) Old 11-30-2017, 09:44 AM
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The traction loc differentials require different side bearings or at least mine did. Since you have to pull it apart, you will need a new pinion seal too.

The link you have is for the modern iteration of the Detroit locker which uses helix gears instead of clutches. It is a hefty piece of hardware. If you are on a decent, flat piece of pavement it should consistently lay down rubber from both tires.


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post #7 of 39 (permalink) Old 11-30-2017, 10:01 AM Thread Starter
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I think after the great info you guys have already provided I am leaning heavily towards just swapping out the differential. I am not educated at all with these. You guys have already posted two differential options. For those and any more mentioned, please let me know why I might want one compared to another. I think you guys know what I want, to spin both tires but not be locked during normal driving conditions. I'm not worried about a $100 difference, so cost is not a factor unless one is extremely more than the others. If one unit is $200 more than another one, I'm willing to spend the extra $200 if there is a good reason to.

1965 Coupe
351W - ~400 Engine hp
Edelbrock Performer RPM Top End Kit
Holley 670 Street Avenger
Bored .30 over
Hooker Headers
MSD Box/Distributor
4 Speed Toploader
3.55 Limited Slip Detroit TrueTrac
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post #8 of 39 (permalink) Old 11-30-2017, 10:04 AM
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Just information and names you may hear.
In the 60's, Ford called their "limited slip" rear ends as "Equa-Loc", then believe '69 a slightly newer, stronger design (stronger center section casting) they called them "traction Loc". These are Ford names.
Either will fit in the housings.
If you go get a used housing, depending on how hard and much you'll use your car, maybe worth getting it rebuilt. Last thing you want from a used housing is a new whine sound.
My 67 was a complete rebuild so I bought a used '69 Taction Loc and had it rebuilt.

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post #9 of 39 (permalink) Old 11-30-2017, 10:32 AM
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My experience is with the truetrac. It is the only part on my car to be trouble free after 13 years of street driving, autocross, track days and vintage road racing. It will lay a double black strip as long as I mat the go pedal.
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post #10 of 39 (permalink) Old 11-30-2017, 10:35 AM
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I purchased one of these: https://m.ebay.com/itm/FORD-8-INCH-P...YAAOSw-0xYaFFm

Called him Tuesday. Arriving today. If you call him direct he will discount $75.00 for the core.

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post #11 of 39 (permalink) Old 11-30-2017, 11:09 AM Thread Starter
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Quote:
Originally Posted by patrickstapler View Post
I purchased one of these: https://m.ebay.com/itm/FORD-8-INCH-P...YAAOSw-0xYaFFm

Called him Tuesday. Arriving today. If you call him direct he will discount $75.00 for the core.
If I like my gears, is there any reason why I would buy a whole center section rather than just swap the differential? Is it just simply knowing that every part has been replaced/remanufactured? I'm leaning more towards just a differential swap to save a couple hundred but maybe there is a reason to spend the extra cash. Possibly I could save on mechanic bill by installing the center chunk myself.

1965 Coupe
351W - ~400 Engine hp
Edelbrock Performer RPM Top End Kit
Holley 670 Street Avenger
Bored .30 over
Hooker Headers
MSD Box/Distributor
4 Speed Toploader
3.55 Limited Slip Detroit TrueTrac
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post #12 of 39 (permalink) Old 11-30-2017, 11:34 AM
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Quote:
Originally Posted by silverblueBP View Post
My experience is with the truetrac. It is the only part on my car to be trouble free after 13 years of street driving, autocross, track days and vintage road racing. It will lay a double black strip as long as I mat the go pedal.

Ever had it lay a single or partial double when feathering the throttle?

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post #13 of 39 (permalink) Old 11-30-2017, 11:36 AM
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Quote:
Originally Posted by Israel View Post
Ever had it lay a single or partial double when feathering the throttle?


No, itís always left a double. Not that I do that very often anymore.
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post #14 of 39 (permalink) Old 11-30-2017, 11:50 AM
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I bought a 9" TruTrac for my build.
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post #15 of 39 (permalink) Old 11-30-2017, 11:58 AM
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Originally Posted by patrickstapler View Post
As long as you made it clear what year your car is, that should work well for you. 65-66 used a smaller pinion yoke than 67-73.

What gear ratio did you order?

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