Adding 3.73 gears to 95 Tbird 3.8L LX: what can I salvage from an Explorer? - TCCoA Forums
 
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post #1 of 23 (permalink) Old 05-17-2011, 09:20 AM Thread Starter
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Adding 3.73 gears to 95 Tbird 3.8L LX: what can I salvage from an Explorer?

Hi:
One of the next projects I'm considering tackling on my 24 Hours of Lemons car is to upgrade the gear set to a 3.73 gears on the cheap. Right now, I believe it's a 8.8" 3.27 open diff.

I read recently here that I could possibly salvage the ring and pinion gear set ("the gear set") from an Explorer.

I believe trying to salvage the Posilock or whatever traction lock would NOT be worth the additional effort & cost for my application.

Q: Do you guys have a summary of what years and what models I should be looking to salvage the gear ratio from? I know that if it says its a posilock, I should skip it. Any other suggestions? If you give me ONE model/year of explorer that had 3.73 gears, I'm sure I can dig out of rockauto the other ones and reply back here.

Q: What else can I salvage from the explorer rear end? I think the Explorers use 31 vs 28 axle splines so i can't just exchange the entire pumpkins as one would do with a Mark VIII's rear diff, right?

Thanks in advance for your replies.
Thanks,
-g

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post #2 of 23 (permalink) Old 05-17-2011, 10:51 AM
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http://www.tccoa.com/articles/gears/gears.html

You cannot use the explorer rear diff, but you can swap gears out.

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post #3 of 23 (permalink) Old 05-17-2011, 11:55 AM
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The problem with using the explorer diff is that it is a solid rear axle, so the side gears aren't beveled to allow the circlip to compress and slide out. If you put a diff from a solid axle into an IRS car, once you slide your axles in you will never get them out, so even if the spline count is the same, you still can't use it. If you want a trak-lok diff, the best bet is get one out of a SC, then rebuild that with the explorer gears, and you'll be good to go.

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post #4 of 23 (permalink) Old 05-17-2011, 12:14 PM Thread Starter
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Thanks for the explanation on why I cannot use an explorer diff.

So, if I just want to swap out the gearset for 3.73 open gears, can you guys point me to cars/trucks/ranges that had this model?

Dorman apparently only makes 3.55 differential ring and pinion gearsets
Looking at the Motive catalog, I found TWO part numbers: one for the standard gears (crosses with OEM) and one for their premium line (crosses with Ford Racing).

Motive# F8.8-373
OEM# E4TZ4209A

Motive# F888373
Ford Racing# M4209F373

I'm still using google fu to figure out which cars came with the E4TZ4209A by [B]FROM THE FACTORY[B]. Any suggestions/leads here?
-g


MOTIVE Says these are the possible compatible vehicles.
AEROSTAR W/4.0L 90-97
BRONCO 83-96
CAPRI V8 86
COUGAR 80-97
E150-E250 83-99
EXPEDITION 97-ON
EXPLORER 91-ON
F100 81-90
F150-250 81-2002
F150 (F) 97-2002
FORDŽ 1/2 TON (F) 97-ON
FORDŽ 1/2 TON (R) 83-ON
FORDŽ 3/4 TON (R) 83-89
FULL SIZE CAR 80-ON
MUSTANG V8 86-ON
RANGER W/ 4.0L 83-ON
THUNDERBIRD 87-97

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post #5 of 23 (permalink) Old 05-17-2011, 12:27 PM
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At the yards you can just check the axle code and compare to the list above.

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post #6 of 23 (permalink) Old 05-17-2011, 12:35 PM Thread Starter
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Quote:
Originally Posted by machausta View Post
At the yards you can just check the axle code and compare to the list above.
Yes I could but I'm trying to narrow down the list PRIOR to wandering all over a yard.
I'm sure SOMEONE has pulled some used 3.73 gears off a car that works in tbirds.
Can anyone let me know what car those gears came from?
Thanks,
-g

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post #7 of 23 (permalink) Old 05-17-2011, 12:44 PM
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I thought V6 cars had 7.5" rears?

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post #8 of 23 (permalink) Old 05-17-2011, 12:54 PM Thread Starter
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Originally Posted by JeffTBird93 View Post
I thought V6 cars had 7.5" rears?
Nope. I confirmed this morning.
8.8" rear end on my 1995 V6.
It's squarish vs. oval and has 8.8" stamped on the diff cover.
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post #9 of 23 (permalink) Old 05-17-2011, 12:55 PM
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Not all V6 cars has 7.5s IIRC, I think that mostly applies to older ones.

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post #10 of 23 (permalink) Old 05-17-2011, 02:55 PM
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Could be...I remember some of them do...not sure of when they changed it.

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post #11 of 23 (permalink) Old 05-17-2011, 05:44 PM
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The gearset and the differential are separate parts, and can be swapped independent of each other. If you are sure you already have an 8.8 diff and you want 3.73s, go ahead and pull them from an explorer. Double check that though because most V6N/A birds came with a 7.5" diff, and if that is the case, you will need a complete 8.8 pumpkin, or you will need to get a set of gears and a trak-lok unit for a 7.5, which would mean looking for either 83-86 tbird turbo coupes, or late 80s/early 90s ford rangers. If you want a trak-lok unit, the only ones that are going to be a direct bolt-in swap are ones from another MN12, or from a 99 Cobra Mustang if you happen to find one of those laying in the junkyard. There were no cars out of the factory with 3.73s and a trak-lok and IRS, so as far as finding a complete pumpkin to drop out of one car and reinstall in another, it pretty much isn't going to happen. However, with all that being said, the easiest and cheapest way to accomplish 3.73s and a trak-lok would be to pull a set of gears from a low mileage explorer, and a complete pumpkin from an SC, preferably from a manual trans car because they had 2.73 gears, which only one guy in Georgia wants, and he apparently already has one, so you can generally pick them up cheaper, then you swap the explorer gears onto the SC trak-lok unit and into the SC housing, and swap the whole housing into your car, and once completed, nobody will be able to tell you've done anything.

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post #12 of 23 (permalink) Old 05-17-2011, 07:09 PM
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Quote:
Originally Posted by MadMikeyL View Post
preferably from a manual trans car because they had 2.73 gears, which nobody wants
Don't say that, I keep a 2.73 pumpkin on my shelf for road trips. Couple of hours to swap out the pumpkin as a whole, a few bucks worth of gear oil, and bam, instant 30mpg's, lol.

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post #13 of 23 (permalink) Old 05-17-2011, 08:50 PM
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There, fixed.

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post #14 of 23 (permalink) Old 05-18-2011, 12:40 AM Thread Starter
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Well, I think I'm going the cheapest route to begin with and will forgo trying to add traction lock for now and am just considering the 3.73 gears. Yes, I'm positive i have an 8.8" rear end vs. a 7.5" one.

I did find something else interesting in my research

3.73 Ratio gearset
41 teeth on ring gear
11 teeth on pinion gear

3.27 ratio gearset
36 teeth on ring gear
11 teeth on pinion gear

Q: Does this mean that the pinion gears are identical between the two ratio gearsets and I can just pick the one in best condition to keep in my car? Or, are the pinion gears different sizes/diameters but just happen to have the same number of teeth?

-g

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post #15 of 23 (permalink) Old 05-18-2011, 10:19 AM
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Quote:
Originally Posted by MadMikeyL View Post
preferably from a manual trans car because they had 2.73 gears, which only one guy in Georgia wants, and he apparently already has one
Aww come on now man thats just mean lol. I thought it was a great idea personally, you guys can laugh at me if you like, I'm ok with that.

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post #16 of 23 (permalink) Old 05-18-2011, 12:06 PM
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Quote:
Originally Posted by CableguyJJS3 View Post
Aww come on now man thats just mean lol. I thought it was a great idea personally, you guys can laugh at me if you like, I'm ok with that.
Hey, whatever you have to do. I loved my 2.73s in my 89 XR7, I just wouldn't consider it worth it to swap TO a set of them. But yeah, for long drives, there is definitely something to be said for cruising at 80mph and 2100rpms getting 31mpg.

Quote:
Originally Posted by S4gunn View Post
Well, I think I'm going the cheapest route to begin with and will forgo trying to add traction lock for now and am just considering the 3.73 gears. Yes, I'm positive i have an 8.8" rear end vs. a 7.5" one.

I did find something else interesting in my research

3.73 Ratio gearset
41 teeth on ring gear
11 teeth on pinion gear

3.27 ratio gearset
36 teeth on ring gear
11 teeth on pinion gear

Q: Does this mean that the pinion gears are identical between the two ratio gearsets and I can just pick the one in best condition to keep in my car? Or, are the pinion gears different sizes/diameters but just happen to have the same number of teeth?

-g

No, the gears are completely different. The tooth pitch will not be the same, and if you put a 3.73 ring gear in with a 3.27 pinion, you will probably destroy both gears. Not only that, but even within a gearset, they are matched together, so if you take a 3.73 pinion gear from one set and a ring gear from another, it will probably go together, but it will also probably make a lot of noise and not last very long.

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Originally Posted by MadMikeyL View Post
Hey, whatever you have to do. I loved my 2.73s in my 89 XR7, I just wouldn't consider it worth it to swap TO a set of them. But yeah, for long drives, there is definitely something to be said for cruising at 80mph and 2100rpms getting 31mpg.




No, the gears are completely different. The tooth pitch will not be the same, and if you put a 3.73 ring gear in with a 3.27 pinion, you will probably destroy both gears. Not only that, but even within a gearset, they are matched together, so if you take a 3.73 pinion gear from one set and a ring gear from another, it will probably go together, but it will also probably make a lot of noise and not last very long.
Mike:
Thanks for the explanation. I was hoping I could mix and match here but oh well. So I need to confirm that the donor gear set a friend is allowing me to potentially swap with is for an open diff (vs. Posilock or whatever fancy LSD name there is). That should be as easy as cracking open the rear diff and seeing how complicated it is inside


-g

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post #18 of 23 (permalink) Old 05-18-2011, 12:51 PM
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Whether its trrac lok or not doesnt matter. The gears will work as long as its from a 8.8

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Quote:
Originally Posted by MadMikeyL View Post
Hey, whatever you have to do. I loved my 2.73s in my 89 XR7, I just wouldn't consider it worth it to swap TO a set of them. But yeah, for long drives, there is definitely something to be said for cruising at 80mph and 2100rpms getting 31mpg.
Oh I agree, I wouldn't ever intentionally build a rear with 2.73's on purpose, no. But keeping one around for the infrequent and long road trips I take from time to time, seems like a good idea to me. Like you said, 80mph and 31mpg's is nothing to sneeze at especially in today's $4 a gallon gas market. And for the OP, like they all said, you can grab any 8.8 gear set and build your rear from that. But they have to remain a set, mixing and matching pinions and ring gears won't get you far. You might could do that if you had a bunch of brand new never run sets laying around, but not with used ones. When they wear in, they are mated for life. I mistakenly bought an Explorer IRS rear thinking I could swap in the diff and gears, well I learned that wasnt possible, so I ended up with an expensive gear set and nothing else I could use. But the gears worked just fine, and are currently in my car working great and making no noise.

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Quote:
Originally Posted by Roadrunnner View Post
Whether its trrac lok or not doesnt matter. The gears will work as long as its from a 8.8
Hrm, I thought the pinion gear looked different in a TL set. I guess I'll figure that out after I tear into this spare differential I've been offered.

One more question, if you folks don't mind:
One Info site recommended that I go ahead and replace the bearings since the set I will be installing was USED and my original bearings+gears have been used for ~130K mi.


When I looked at Motive Product's 8.8" master install kit vs. the standard kit, it lists the front pinion bearing, the rear pinion bearing, and the differential bearing.

Q: For my application (1-2 track days plus the 24 hours of Lemons and a few shakedown ~50mi commutes = call it 2K-3K of mileage total), do I even care about re-using the bearings? If I should buy new ones, do I need to swap out just the pinion bearings, just the diff bearings, or the full set?


Thanks in advance for your tips.
-g

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post #21 of 23 (permalink) Old 05-18-2011, 05:10 PM
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There are 2 sets of bearings in the rear diff, the pinion bearings and the carrier bearings. The carrier bearings get pressed onto the carrier, and the pinion bearings get pressed onto the pinion. If you are changing either the carrier, or the pinion, then in order to re-use the bearings they would have to be pressed off your current part and pressed onto the replacement part. If you are keeping your current open differential and only swapping gears, and if the current diff does not make any noise or have any issues, then the carrier bearings can stay, just make sure you keep the right race with the right side. What I usually do is as soon as I take it apart I use a zip tie to hold the race and the shim onto the carrier on the side that they are used for, that way you can't knock them off the table or something stupid like that and screw them up. As far as the pinion bearings are concerned, the only way to re-use them would be to press your old bearing off your old pinion gear and onto your new one. At that point, considering how easy it would be to damage the bearing in the process and how cheap a new bearing is, I would just replace it. Also, remember once you get your old pinion bearing off, there will be a shim under there that you need to transfer over to the replacement pinion gear. That sets pinion depth, and it is case specific, so whatever thickness that shim is, no matter what gear ratio you put into that housing, that is the shim that you will need. If you lose it, it is possible to determine what thickness you need, but it requires special tools and a lot of time, so do yourself a favor and don't take the bearing off the 3.27 pinion until you have the 3.73 pinion and the new bearing in front of you, and then do it all at once, and remember to remove the old shim from the 3.73 pinion first if it is a used gearset.

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Originally Posted by MadMikeyL View Post
There are 2 sets of bearings in the rear diff, the pinion bearings and the carrier bearings. The carrier bearings get pressed onto the carrier, and the pinion bearings get pressed onto the pinion. If you are changing either the carrier, or the pinion, then in order to re-use the bearings they would have to be pressed off your current part and pressed onto the replacement part. If you are keeping your current open differential and only swapping gears, and if the current diff does not make any noise or have any issues, then the carrier bearings can stay, just make sure you keep the right race with the right side. What I usually do is as soon as I take it apart I use a zip tie to hold the race and the shim onto the carrier on the side that they are used for, that way you can't knock them off the table or something stupid like that and screw them up. As far as the pinion bearings are concerned, the only way to re-use them would be to press your old bearing off your old pinion gear and onto your new one. At that point, considering how easy it would be to damage the bearing in the process and how cheap a new bearing is, I would just replace it. Also, remember once you get your old pinion bearing off, there will be a shim under there that you need to transfer over to the replacement pinion gear. That sets pinion depth, and it is case specific, so whatever thickness that shim is, no matter what gear ratio you put into that housing, that is the shim that you will need. If you lose it, it is possible to determine what thickness you need, but it requires special tools and a lot of time, so do yourself a favor and don't take the bearing off the 3.27 pinion until you have the 3.73 pinion and the new bearing in front of you, and then do it all at once, and remember to remove the old shim from the 3.73 pinion first if it is a used gearset.
Mike:
I read your notes a few more times and reviewed the following DIYs and I think I understand what needs to be done.

http://www.corral.net/tech/drivetrain/gears.html
http://www.cartechbooks.com/vstore/s...=2557&CATID=21
http://www.americanmuscle.com/differ...r-install.html



If I understand you correctly,
1) it sounds like I don't need to do the shimming if I'm going to re-use the carrier AND the pinion shims. I will also re-use the carrier bearings.
2) For my application, I only need to replace the pinion bearing that's attached to pinion gear itself or ???

Planned Shopping List
1) Basic 8.8" install kit
http://www.summitracing.com/parts/RAT-405K/

Looking at the deltra between this RATECH kit and the basic MOTIVE F8.8IK kit, it appears to be carrier shims (not needed) and the pinion nut.

What are the chances that I'll chew up the pinion nut?

2) Pinion Bearings.

Q: Which one of these two cup+cone sets is the one actually attached to the pinion gear?

According to http://www.corral.net/tech/drivetrain/gears.html, I think it's the M802048 & M802011 aka "Rear Inner pinion bearing cup & cone" according to Rockauto.com. Please confirm.

Rear Inner diff pinion bearing cone part number M802048 $10.42
Rear Inner diff pinion bearing cup part number M802011 $5.10

Rear Outer diff pinion bearing cone part number M88048 $7.30
Rear Outer diff pinion bearing cup part number M88010 $3.71


Q: Just to clarify, should replace BOTH pinion bearings or just the inner one? The outer pinion bearing is relatively cheap and doesn't require any special tools (like a hydraulic press.) It's one more thing to screw up though so if I don't have to replace it by your recommendation, I won't.

Q: Lastly, since I'm planning to use used gears but a new pinion bearing(s), do I need to break in the differential?

Thanks again for all the replies. I've really learned a lot today.
-g

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Only the inner bearing is pressed on, so that is the only one that absolutely should be replaced. But at that point, you are already there so replacing the outer pinion bearing is cheap insurance. As far as breaking in the gears, no if you are using used gears, there will be no break-in period. However even if you were using new gears, the break-in procedure is a lot of hard acceleration and deceleration, so the race would do the break-in just fine. Also, the main reason for breaking in a gearset is to keep them quiet, so that probably isn't your main concern anyway.

-91 Cougar LS, coming soon, complete overhaul with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
-98 Mark VIII LSC, Procharger P600b, TR3650 swap and 3.73s.
-90 SC Automatic rustbucket winter beater
-97 Tbird Sport 4.6 Nice weather daily driver
-"Your buddy Mike is INSANE!" -ClintD's dad
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