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Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 09-14-2011   #1 (permalink)
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Default 8" rear end in 66 mustang

I bought my car from the original owner, he told me when he was in the army he brother was driving the car and had to change out the rear end. i know from counting the gears it has 3.0 gears but what i want to know was if its limited slip. I have know idea how to tell, i swore when i was a kid that remember leaving two tire mark when spinning tires. Im about done know with rebuild and just want to figure out i i need to start planning for another rear end. not worry about breaking from power (ill only be pushing maybe 300hp) but if its not at least limited slip then back on the stands it will go. I have some pics here just wanted to see if anyone could tell by pics.
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8" rear end in 66 mustang-img_0427.jpg  8" rear end in 66 mustang-img_0428.jpg  8" rear end in 66 mustang-img_0429.jpg  8" rear end in 66 mustang-img_0426.jpg  
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Unread 09-14-2011   #2 (permalink)
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Look at the edges where the bolts go in. If it's flat, it's a trac loc. If it has a canyon look, I guess you can say it deepens, it's an open differential. To me, this is vital to know so when you buy one online especially used, you know exactly how to tell. Check this link out and go to the bottom. I used it and it was handy. Kevinstang's Ford Nine Inch Differential Page +
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Unread 09-14-2011   #3 (permalink)
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alternatively, with the differential installed, if you spin the axle on say, the drivers side, to the left, the axle on the other side should spin forward in the same direction if it's limited slip. If it's not, the axle on the passenger's side will spin in the opposite direction.
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Unread 09-14-2011   #4 (permalink)
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Quote:
Originally Posted by SDMustangRider View Post
Look at the edges where the bolts go in. If it's flat, it's a trac loc. If it has a canyon look, I guess you can say it deepens, it's an open differential. To me, this is vital to know so when you buy one online especially used, you know exactly how to tell. Check this link out and go to the bottom. I used it and it was handy. Kevinstang's Ford Nine Inch Differential Page +
Im gonna look at that site now and see what bolts your talking about.

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alternatively, with the differential installed, if you spin the axle on say, the drivers side, to the left, the axle on the other side should spin forward in the same direction if it's limited slip. If it's not, the axle on the passenger's side will spin in the opposite direction.
i have spun the left and i do know when i spin it does turn the drive shaft but not sure about right side direction. I also know when i turn right side that the left turn opposite way, but at same time i believe have had them spinning same way before. I was told only true possi would turn them same way but that limited split wouldnt. Ill try this again tonight, its all back together now. i really only pulled it down to look at it (make sure teeth all look good) and get pics. hope its limited slip cause i just put 50 bucks worth of royal purple in it, definitely wouldnt have put that in if i knew it was peg legging. But if not then ill just chalk it up to lesson learned.

Funny thing is bunch of my friends said they'd know when they came over to look at it, hell even i said that. but know no one has any idea including me. Im sure this is just being over thought.
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Unread 09-14-2011   #5 (permalink)
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It does look like a trac loc btw.
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Unread 09-15-2011   #6 (permalink)
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Looks like an open diff from a '66 to me. If its really a '66 it cannot be a Trac-Lok. Trac-Lok was a Dana trademarked name that came in 1968 by which time I don't know that the 8" was still around. The 8" limited slip was called Equa-Lok and did not actually lock but added 100 ft-lb of friction instead. BTW, the non-limited slip internals of an 8" are the same as a 9".

I don't know exactly what a Trac-Lok looks like since I have never owned one. But the Equa-Lok is the one with the recessed ring gear bolts since the cover needed to be stronger with the big springs inside. The '66 open 8" diff bolts sat on a flat flange surface just like the ones in your picture #3. I have more than one of each and am holding that flat plate with bolt holes from an open 8" in my hand.

If you have the innards on the bench as your pictures indicate there is no need to put it in the car to tell. Stick an axle in each side and try turning one axle while holding the other one. If its not a limited slip then you can easily turn one side while holding the other stationary; only the input shaft will turn. To meet spec, an Equa-Lok will require 100 ft-lbs of torque to turn one side WRT the other. If its was an Equa-Lok and has never had new clutch plates installed then those clutches are likely worn out and the 100 ft-lbs may well now be ZERO. Even if it were an Equa-Lok you could turn one axle WRT the other if the clutches were worn out.

A 'rebuild' that means more than paint. Pull the axle apart and make sure its not worn out internally. You already have it out of the car; take it apart and see whats in there. Even a non-limited slip axle can wear out inside - why do you think I own more than one?? Mine had all the internal thrust washers trashed along with the shafts. You can't see any of that worn out stuff without some more disassembly.
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Unread 09-15-2011   #7 (permalink)
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I can hold left side when i spin right but its not easy at all. I have to really put the strong arm on it to hold.

i have know idea at all anymore, it seems like half info points to open half to some type limited slip. i should have the drive shaft in tonight, car is on jack stand so ill just start her up and see what happens. if they both spin ill be happy, if not ill start to rethink this. thanks for all the help.
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Unread 09-15-2011   #8 (permalink)
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ill also post what i find, maybe this will help someone else.
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Unread 09-16-2011   #9 (permalink)
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Looks like an open differential.

Good Luck and Be Safe
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Unread 09-16-2011   #10 (permalink)
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Quote:
Originally Posted by 66 restomod View Post
Looks like an open differential.

Good Luck and Be Safe
Ron
Thanks, i really praying its not but my luck im sure it is. Hopefully ill know tonight if my dang u-joints would ever come in.
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Unread 09-17-2011   #11 (permalink)
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well looks like it may be trac lock because left tire is spinning when i put it in gear and spinning fast when i hit the gas.
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Unread 09-20-2011   #12 (permalink)
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ok. im still waiting on rims and tires to come in to sit car down. I thought because left wheel was spinning when on jack stands that it would be trac-lok but now i have people telling me that left will spin when not under a load even with open diff. Anyone know if this is true?
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Unread 09-20-2011   #13 (permalink)
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Hi

Comparing your pic (showing ring bolts with no recess) with those on the Kevinstang site, it looks like you have an open rear to me.
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