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1996 Thunderbird LX
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Discussion Starter · #21 · (Edited)
Okay, so to recap what is going on in my head. Door jam says I have TL, the rear brakes are discs, the wheels spin in opposite directions while off the ground, the tag is missing from the diff. It is driving me nuts. I cant wait to buy a rebuild kit only to find out someone was cheap and replaced the whole thing with an open diff. I am going to go ahead and take the cover off today. I will update what I see afterwards. I can deal with smell.

One question though. Is the smell so bad that it will bother others? I am working in an apartment parking lot.
 

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The wheels spin in opposite directions with the trans in park or in neutral? Even a TL will spin in opposite directions with the trans in park, because if the pinion gear cant turn, there is no other way for either wheel to turn but to make the opposite wheel turn the opposite way. Also, if you only tested with it in park, did the wheel turn easily, or was there some resistance to it? A TL rear will have resistance, whereas an open rear you can spin either wheel with little to no resistance.
 

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1994 Cougar XR7 DOHC/5-Speed
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Are you spinning them with the trans in park? Open or TL they will spin opposite directions as the pinion is effectively locked, that’s the limited “slip”, it’s just more resistance than an open. If it’s really easy to do the clutches are probably worn out.

The smell is bad in enclosed spaces, but not THAT bad. Outside it’s not even close to the intensity of a skunk or a dead animal you might encounter outdoors
 

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The Parts Guy
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Gear lube isn't that bad. If it is to you, you don't work on rear ends often enough. :p
 

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This is the tag you're looking for, if it's still on it. I found mine at the top of the cover.

41741
 

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Here is the article on gears and axle codes.


If it's an aluminum pumpkin on an MN12 it's not factory, and the axle code on the door jamb sticker means little at that point. One thing to keep in mind though is the rear cover is aluminum for aluminum and iron pumpkins alike, so to be sure, check whether the rest of the housing is aluminum or iron.

If it is aluminum, it's possible someone swapped in an aluminum pumpkin from an FN10 which will have either a 3.07 or 3.27 open. Given your observation that the wheels spin in opposite directions it's an open diff (or the trac-loc clutches are completely shot).
Not to hijack the thread, but that page you linked now has me wondering what I have as a differential. I have a '97 Sport with an Axle code of W5, which means 3.27 'Conventional' rear-end. What is a Conventional rear-end? Also, on this page, it says '97 Sports have a "Traction Lok limited-slip 3.27:1 rear differential".

So do I have TL or not? And what's a Conventional?

Thanks
 

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Conventional means an open rear. Not all Sport's had a trak-lok, and based on your axle code, unless someone has swapped it out in the past, you don't have a trak-lok.
 
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Conventional means an open rear. Not all Sport's had a trak-lok, and based on your axle code, unless someone has swapped it out in the past, you don't have a trak-lok.
Thank you for the info. My Sport is all factory original still, so no rear-end swap happened. If I understand correctly, an open rear-end allows one wheel to spin on slippery ground, like in the rain...which mine does.
 

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The tag in the pic above says 3L27; that is a locking diff. the non locker does not have the "L"
 

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If I understand correctly, an open rear-end allows one wheel to spin on slippery ground, like in the rain...which mine does.
An open (conventional) differential transfers torque to the wheel with least resistance / traction.

A Limited slip diff transfers torque to the wheel with the most traction.

Locking differential distributes torque equally between both wheels when engaged (auto or manual).

These cars were never equipped with lockers .. Its open or limited slip.
 

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1997 Thunderbird LX
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The differential might have been swapped.

Joe
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I left dual skids with my old 3.8 open diff Cougar on several occasions. Those few occasions where I could break traction with that car, anyway. lol

What do your wheels do when you have both rear tires off the ground? Can you spin either; if you can, does the other wheel spin backwards? What's the tag on the pumpkin say?
 

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You can get an open diff to go side to side while burning out by steering slightly, a locker or LSD will burn both regardless
 

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I left dual skids with my old 3.8 open diff Cougar on several occasions. Those few occasions where I could break traction with that car, anyway. lol

What do your wheels do when you have both rear tires off the ground? Can you spin either; if you can, does the other wheel spin backwards? What's the tag on the pumpkin say?
Cool, but unless I do somehow have a trac-lok, or something I can't think of is locking the axles together beforehand that doesn't really explain how I can on dry pavement going straight just by stomping on the gas peddle or by starting off using the brakes like I did in the picture.. Again, this is consistent, not a freak one time thing.. :)

I haven't had the rear of the car up to check the direction the wheels spin since this post. When I looked on the tag on the pumpkin a while back (couldn't get a picture) it said 3 27 on it with no "L" between the 3 and the 27 that I was expecting.. I'm baffled.

You can get an open diff to go side to side while burning out by steering slightly, a locker or LSD will burn both regardless
I realize that. Like I mentioned in my previous posts, I wasn't trying to induce a drift or do this on wet or dirty pavement. I started going straight, with the steering wheel straight. I'm not ready to do the diff service yet, otherwise I'd know right there and then if I did somehow have a trac-lok or something else unusual that I can't explain is going on..
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Cool, but unless I do somehow have a trac-lok, or something I can't think of is locking the axles together beforehand that doesn't really explain how I can on dry pavement going straight just by stomping on the gas peddle or by starting off using the brakes like I did in the picture.. Again, this is consistent, not a freak one time thing.. :)

I haven't had the rear of the car up to check the direction the wheels spin since this post. When I looked on the tag on the pumpkin a while back (couldn't get a picture) it said 3 27 on it with no "L" between the 3 and the 27 that I was expecting.. I'm baffled.
Cool, but you're not alone in this. Going straight is where you'll be most likely to do that. Going in a turn at low speed is where it's most likely to do a one-wheel-peel since the weight of the car is transferred to one side; if the inside wheel loses traction, then that indicates an open diff or worn out clutches.

If you're not willinng to take our word for it, you're going to have to yank the cover and look inside the pumpkin - no other way around it. The tag, door code etc. all point to an open rear.
 
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