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post #1 of 27 (permalink) Old 08-26-2014, 10:22 PM Thread Starter
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Swappable rear differentials

If one has a 96/97 TBird and wants to upgrade gears to 3.73 what year/model stock 3.73 pumpkin can be swapped into the bird?

I see a ton of 96+ Explorer rear ends out there for pretty cheap. Would be nice to pick one up and have it rebuilt.

Thank you!
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post #2 of 27 (permalink) Old 08-27-2014, 07:09 AM
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Your answers will vary on what Differential to use..Everybody has their own preference..

Between the Aluminum 8.8 IRS Differential found in the 93-98 Lincoln Mark VIII..To the Iron 8.8 IRS Differential found in all 89-97 Thunderbirds/Cougars..

Just make it easy on yourself, and grab an Iron 8.8 Differential from the junkyard..Make sure to find one with a Trac-Lok already in it..

That will save you some $$$$..

Unless you're rebuilding the Differential yourself (which I don't recommend)..

The cost to have the Aluminum Differential built may be slightly more than that of the Iron since you need a case spreader to install the guts..

Buy some Ford Racing 3.73 gears, and find a shop to put it all together for you..That's what I would do in your shoes..

No 8.8 IRS equipped car ever came stock with 3.73 gears..

Explorer rear ends will not work..You need a rear end from a 93-98 Lincoln Mark VIII or a 89-97 Thunderbird/Cougar..






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post #3 of 27 (permalink) Old 08-27-2014, 09:45 AM Thread Starter
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Since removing the one on my car to have it rebuilt is not an option, what is needed to build a new one from scratch?

Having a hard time finding TBird or Mark VIII pumpkins online.
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post #4 of 27 (permalink) Old 08-27-2014, 09:49 AM
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The only pumpkin you can use is one from an MN12 or FN10. No other cars will "swap". If you can't remove the one from your car to have worked on, you're going to need to find another one from a donor vehicle.

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post #5 of 27 (permalink) Old 08-27-2014, 11:33 AM
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I thought the explorer and mustang rear ends work its just once you put your axles in you will have a hellva time taking them out again.

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post #6 of 27 (permalink) Old 08-27-2014, 12:03 PM
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Do the V6,SC, and V8 all have the same differentials for all years 89-97?
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post #7 of 27 (permalink) Old 08-27-2014, 12:07 PM
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I have a 3.73 differential for sale. With the '00 trans you bought from me, you would need to use a SpeedCal to get the speedo right though.

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post #8 of 27 (permalink) Old 08-27-2014, 01:20 PM
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Quote:
Originally Posted by KEVIN8989 View Post
Do the V6,SC, and V8 all have the same differentials for all years 89-97?
Yes and no. All SC and V8 cars came with an 8.8 and some V6s had them also. Any pumpkin from any year will work, even a 7.5!

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post #9 of 27 (permalink) Old 08-27-2014, 01:39 PM
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So some V6's have 7.5 or 8.8. Can I see the difference by looking at it, is one pumpkin bigger and one smaller. Does the 8.8 last longer?
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post #10 of 27 (permalink) Old 08-27-2014, 04:20 PM
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Quote:
Originally Posted by Rayo View Post

Unless you're rebuilding the Differential yourself (which I don't recommend)..
Cmon .. they are easy if you have the correct tools.


Quote:
Originally Posted by Tbird1997 View Post
I thought the explorer and mustang rear ends work its just once you put your axles in you will have a hellva time taking them out again.
No Mustang .. not sure about Explorer. The Cobras from 99 and maybe 01, had the 28 spline side gears that will work direct swap. The 03/04 are 31 spline. and need to be machined to match.


Quote:
Originally Posted by KEVIN8989 View Post
So some V6's have 7.5 or 8.8. Can I see the difference by looking at it, is one pumpkin bigger and one smaller. Does the 8.8 last longer?
You have a 7.5. Its stamped on the rear cover. The larger ones are capable of handling more power in the drivetrain.
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post #11 of 27 (permalink) Old 08-27-2014, 06:18 PM
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Originally Posted by KEVIN8989 View Post
So some V6's have 7.5 or 8.8. Can I see the difference by looking at it, is one pumpkin bigger and one smaller. Does the 8.8 last longer?
IIRC, The 8.8 was added to keep from breaking from the added torque from the 4.6l engine. And the SC, of course. Yeah, I know the SC came first.

The 8.8 rear cover is more oval, and says 8.8 at about the 4 o'clock position on the back face; you may need to rub dirt, but it's raised in the casting, on the passenger side of the bracket.

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post #12 of 27 (permalink) Old 08-27-2014, 06:35 PM
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Quote:
Originally Posted by Grog6 View Post
IIRC, The 8.8 was added to keep from breaking from the added torque from the 4.6l engine. And the SC, of course. Yeah, I know the SC came first.
The stock 4.6L in the MN12 has never been known as much of a "torque monster"..

Don't forget the 5.0L MN12 came before the later modular MN12's..and...All 5.0L MN12's got the 8.8 rear end..


Here are the 8.8 and 7.5 side by side, for comparisons sake:
8.8 vs 7.5 Differential.JPG







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Last edited by Rayo; 07-30-2017 at 04:33 PM. Reason: update pic..
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post #13 of 27 (permalink) Old 08-27-2014, 07:38 PM
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Originally Posted by Rayo View Post
Don't forget the 5.0L MN12 came before the later modular MN12's..and...All 5.0L MN12's got the 8.8 rear end..

Rayo..
I have a 7.5 laying here, as a spare, because it was free.
I won't be running it unless I have to; it's not as beefy, regardless of pix. It does have a 3.55, according to the code.

I haven't forgotten anything about a 5.0 pushrod motor at all. OHC iz way More Roxors, tho.

I seem to remember something about 5.0 engines ripping themselves in half over 500 hp or thereabouts, tho... No, that was my buddy's Mustang, lol

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post #14 of 27 (permalink) Old 08-27-2014, 08:16 PM
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Originally Posted by Grog6 View Post
I seem to remember something about 5.0 engines ripping themselves in half over 500 hp or thereabouts
Hmmm..

So what your saying is..As long as I stay at the power levels that you are at in your MN12's..I won't have to worry about that then huh?..

Besides..This thread isn't about how much power a stock Iron MN12 modular block will take before it splits vs its pushrod counterpart..

Back on topic.. Swappable rear differentials






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post #15 of 27 (permalink) Old 08-27-2014, 08:19 PM
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I can think of two stock power 5.0s that split in half just from passing someone. Must be that monster torque!

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post #16 of 27 (permalink) Old 08-27-2014, 08:23 PM
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I see I struck a nerve with the modular folks..







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post #17 of 27 (permalink) Old 08-27-2014, 09:28 PM
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Here's the thread.. I thought they were talking about mustang differentials..
http://forums.tccoa.com/showthread.php?t=108693

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post #18 of 27 (permalink) Old 08-27-2014, 09:45 PM
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I don't know how the 7.5 and the 8.8 compare in real world torque ratings and such, but I just rebuilt a 7.5 for a Ranger guy and I have to say...... I did a lot of snickering just looking at that ring gear. I couldn't help it! It may or may not have been deserved, but when you're used to doing 8.25, 8.75, 8.8, 9.25, 9.75 rears the 7.5 just looks like a toy. lol

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post #19 of 27 (permalink) Old 08-27-2014, 10:21 PM
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I've run both

Hello

I've run both in my race car.
3.73's & 4.10's in a 7.5
3.90's in the 8.8


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post #20 of 27 (permalink) Old 08-28-2014, 06:37 PM
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Quote:
Originally Posted by Rayo View Post
Hmmm..

So what your saying is..As long as I stay at the power levels that you are at in your MN12's..I won't have to worry about that then huh?..
I do know the fox body my Dad had was a 5.0 with a 7.5, and it wasn't near the car my MN12s are.

And I just posted that to annoy you, not 5.0 owners.

Quote:
Originally Posted by XR7-4.6 View Post
I can think of two stock power 5.0s that split in half just from passing someone. Must be that monster torque!
My buddy makes that three, lol.

Quote:
Originally Posted by 94 Thunderbird XX View Post
...the 7.5 just looks like a toy. lol
Yeah, that's my impression as well. I keep it as a backup.

You never know what you're going to break...

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post #21 of 27 (permalink) Old 08-28-2014, 07:26 PM
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How much power would it take to break a 7.5??? I'm sure that I'm no where near the breaking point in my V6, but I am curious...

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post #22 of 27 (permalink) Old 08-28-2014, 08:15 PM
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Quote:
Originally Posted by '93MN12 View Post
How much power would it take to break a 7.5??? I'm sure that I'm no where near the breaking point in my V6, but I am curious...
Have you checked under you car to see what size you have? You might have an 8.8 already.

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post #23 of 27 (permalink) Old 08-28-2014, 08:40 PM
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Originally Posted by '93MN12 View Post
How much power would it take to break a 7.5??? I'm sure that I'm no where near the breaking point in my V6, but I am curious...
I'm willing to bet that it's not just a question of HP.. it's a question of how the HP & torque is applied.

If you are subjecting your driveline to hard jolts (i.e.: high revs+clutch drops, drag strip launches, and power shifts), you are probably going to break a diff more quickly than if you were easier on your launches and gear changes.

Given the smaller size, such shocks would more easily kill a 7.5" diff vs. an 8.8" one.

If you already have a 7.5" rear end, I'd just use it until it breaks and then replace it.
If you have some $$ burning a hole in your pocket, I'm not sure why you (as a tbird owner) would ever invest in a 7.5" rear end when 8.8" are direct swaps and readily available.

Of course, if you find someone who wants a 7.5" rear end locally, sell it off.
-g
PS. Mustang/Explorers and other non-IRS 8.8" rear ends have one big benefit for a tbird owner: even if you cannot use the rest of their pumpkin, you can use their ring+pinion gears. You'll often find mustang owners swapping in shorter gears so it's an excellent opp for you to buy used gears on the cheap (I've paid from $35-60 for sets of used 3.73 gears).

Used Gears + rebuild kit + 8.8" TL IRS diff = cheap way to a "built" rear end.

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post #24 of 27 (permalink) Old 08-28-2014, 09:04 PM
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Quote:
Originally Posted by Rayo View Post
I see I struck a nerve with the modular folks..



Thats okay .. we all know the SC's makes more power and way more torque than either of those V8's.


On the subect of differentials .. I have never actually seen a Ring and pinion break. I have seen the rear cover break, I have personally broken the rear mount to the subframe on my SC, seen broken half shafts, etc .. weakest link.

I worked on a Ford ranger with the 8.8 solid axle. The pin in the carrier snapped in near the bolt. When I called the dealership to order the part, the guy was confusing it with the pinion and said he wanted me to bring in the original because Ford needed to verify it was broken for some reason, said it was unheard of. When I explained it further, and that it was the pin in the center of the carrier, he said Oh, yeah we have those in stock, they break all the time.
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post #25 of 27 (permalink) Old 08-28-2014, 10:46 PM
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I have a 7.5" limited slip differential, and I'm not very hard on it I don't think. I don't race it or rev up the engine above 3500 rpm's, just street driving. I think it should be okay

1993 Thunderbird LX. 3.8L with Underdrive Pulleys, Ford Racing Limited-Slip Differential, Intake & Dual Exhaust, and I like to run advanced timing
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post #26 of 27 (permalink) Old 08-29-2014, 09:27 AM
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While I'm in here, it may be worth noting that there is a severe difference in the rear mounts as far as quality. The stock 7.5 from my 94 v6 had a very wimpy looking mount compared to the one from an 8.8 out of an 89 SC.

Guess which one is which


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post #27 of 27 (permalink) Old 08-29-2014, 01:28 PM
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That's the same mount the late model 8.8s come with as well. I'm sure Ford saved $0.08 per car redesigning that piece

-Matt
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