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post #1 of 9 (permalink) Old 04-20-2012, 11:06 AM Thread Starter
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Complete Differential Swap

Its been a while since I've posted on here, but I have been visiting your forums and website alot due to the plethora of information.

Anyway, I am racing a 1997 Thunderbird Sport in the 24 Hours of Lemons, and I friggin love it. The car has been amazing in so many ways, and has gotten my rag-tag bunch of amateurs into the top 10 overall (and set hot laps in the top 5).

During the post-race inspection earlier this year, I noticed that our differential looked a little tired, so I think its time to buy a spare and keep it around (just in case it blows).

On our door code, it states the axle as being a W5, and the Suspension as JJJJ. The tag on the differential itself is gone, and I would like to not have to open it up again to identify it. How do I know what gear ratio I have (other than turning the driveshaft) and whether or not it is a Trac Lok? As for the replacement, how long is a Trac Lok going to last in a racing environment (keep in mind, our next race is a true 24 hour)? Should we look for a True Trac instead?

I want the replacement to be an entire, complete differential. If it blows, I want to be able to tow it into the pit, lift the car, and unbolt the whole thing from the driveshaft and CV's, and slap the new unit in as quickly as possible. Since this is a spare part, cost doesn't really enter into the equation (as long as it is reasonably close to stock, I don't want to put 4.10s and a super expensive LSD in it).

So what do you guys think? What are my options here?
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post #2 of 9 (permalink) Old 04-20-2012, 11:15 AM
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It's a 3.27 open.

If you want the cheapest TL route, hit the local yards and try to find a car with an axle code of E or XE (limited slip 3.27). Other traction lock codes you may find are Z (3.08) and M (2.73).

Also complete TL pumpkins do come up for sale on here every now and again, sometimes 3.27 but often 3.73 or 4.10. There are other options, but I'll let the more knowledgeable give the info on those since I'm not as familiar.

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post #3 of 9 (permalink) Old 04-20-2012, 11:47 AM
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We run a 3.73 gears in our rear diff for our lemons as our 3.8L engine needs all the help it can get in the acceleration dept. We had to correct our speedometer to not hit the governed speed (no budget for an aftermarket ECU) but our bottle neck appears to be our weenie engine and NOT the governer (never hit it on the track).

* There's another lemons Racer with a cougar, MadMikeyL, that also runs a V8. I'm not sure what gears he's using but he's rigged up this belt driven diff cooling system. He's cooked his diff before and his other problem (which sounds closer to yours if you were running top 10 in TX) was that he keeps chewing through brakes.

I have a spare 2.73 w/ traction lock that came with my supercoupe donor car. I briefly toyed with the idea of swapping parts with our on-car diff to create an LSD w/ TL but other Lemons veterans have told me that stock LSDs don't last very long in lemons under hard abuse. In fact, I think the open diff actually helped us in the rain at our last race so I'm in no hurry to do anything with the spare other than keep it around.

If you want to get slightly cheaty, a Mark VIII diff is all aluminum and will save you some weight at the rear end. Before I found my donor car, I was also looking for a spare. I did find though that these diffs weigh so much that you are better off finding one locally than trying to buy one and have it shipped to you.

Q: Are you running a 4r70w automatic or did you swap in a manual?

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post #4 of 9 (permalink) Old 04-20-2012, 12:15 PM Thread Starter
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We still have the stock 4r70W. I don't want to change the final drive ratio because we do have a serious problem of running into the speed limiter. Our brakes, however, are totally fine (in fact, we never once heat soaked them and we can consistently out-brake any car on the track)

I think I may stay with the 3.27 open, due to concerns from overheating. If I were to happen across a True Trac (thats the gear driven one, if I'm not mistaken) would that eliminate the overheating concern? Remember, this is Texas, and it is toasty.

In all honesty though, I am reluctant to do anything but replace it with a stock unit. The car has been so good, and we are just a handful of (mostly logistical) adjustments away from a podium finish.
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post #5 of 9 (permalink) Old 04-20-2012, 01:51 PM
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Quote:
Originally Posted by ProphecyG View Post
We still have the stock 4r70W. I don't want to change the final drive ratio because we do have a serious problem of running into the speed limiter. Our brakes, however, are totally fine (in fact, we never once heat soaked them and we can consistently out-brake any car on the track)

I think I may stay with the 3.27 open, due to concerns from overheating. If I were to happen across a True Trac (thats the gear driven one, if I'm not mistaken) would that eliminate the overheating concern? Remember, this is Texas, and it is toasty.

In all honesty though, I am reluctant to do anything but replace it with a stock unit. The car has been so good, and we are just a handful of (mostly logistical) adjustments away from a podium finish.
You can fix the speed limiter by upgrading the speedo gear. Best deal I found for the 23 tooth BLACK gear (for automatics -- apparently less likely to break than the white ones).
http://www.latemodelrestoration.com/...-Gear-Kit-Auto

Your odo and speedometer will be off but whatever... at least its consistent. Some people don't even bother with the speedometer as its one more thing to distract the driver (my friends gen 3 N/A Supra just has the tach).

I can't comment on the diff overheating. That's not been a problem for us yet even though our effective rear ratio is approx 4.3:1 (3.73 gears + 3" smaller tires).


I learned a lot after our first race to minimize our fuel stop times.

Q: Have to sized your fuel jugs hoses to the fuel filler neck (i.e.: wallowed out the fuel filler flap opening)? I learned that and it sped up our refuel times dramatically.
I'm from TX so I understand how toasty it can get -- racing most of the yr sounds like work vs. fun to me

I wonder if the brake wear differences between you and MadMikeyL have to do with track differences.

It's good to hear that your transmission hasn't given you any grief yet. Have you JMODDED it and put a monster transmission cooler? We used our A/C condenser and our temps never rose above 190F on the track and 150F on the street (it's still street legal)
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post #6 of 9 (permalink) Old 04-20-2012, 02:21 PM
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Quote:
Originally Posted by S4gunn View Post
You can fix the speed limiter by upgrading the speedo gear. Best deal I found for the 23 tooth BLACK gear (for automatics -- apparently less likely to break than the white ones).
http://www.latemodelrestoration.com/...-Gear-Kit-Auto
There's another limiter that will kick in even with the speedo gear. My 94 would hit it around 85mph before I had the chip made to remove it.

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post #7 of 9 (permalink) Old 04-20-2012, 02:41 PM
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I run an 89 Cougar in the 24 hours of lemons with a 5.0 out of an explorer and an M5R2 trans. We typically run 3.27s with the M5R2, which would be comparable to 3.73s with a 4R70 or T45. I highly reccomend converting to a T45 and getting a chip for the ECM to get rid of the speed limiter and deal with any issues with the trans swap. With the ECM mounted, and some duct tape over the chip, we have never once had an issue with the BS judges noticing it or taking issue with it. As far as a trak-lok goes, our trak-lok unit has held up just fine, and in fact it was still holding fairly well when we boiled the gear oil out of the rear diff. We rebuilt the diff and set up a cooler for it to stop that from happening again, and we used 3.08s this time just because we had them laying around, but we really lost speed from it, so we'll be going back to 3.27s for the next race, which is the Capitol Offense in June.

I would like to know what brakes you are running, since with my diff sorted out, that is now my major issue. We initially were wiping out front pads, so I put on some Hawk racing blues, and they almost made it the whole day, but were metal to metal by the end of the day on Sunday, and we also went through 3 sets of rear pads over the course of the weekend. We are also running 13" Cobra front brakes and 11" rear cobra rotors with stock 94+ tbird rear calipers relocated out to clear the rotors. Like you, we have no problem outbraking most cars on the track (though the little 190 benz's still outbrake the hell out of us), and with the 5.0 and 5-speed, we can out-run everyone on the straights no problem, and now that I finally put sticky tires on the car, we can out-corner most of them too, so at this point our only obstacle is keeping the car on the track instead of in the pits or penalty box.

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post #8 of 9 (permalink) Old 04-20-2012, 06:57 PM Thread Starter
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I would like to know what brakes you are running, since with my diff sorted out, that is now my major issue.
You didn't need to upgrade to cobra rotors, we run the stock sport setup (which is the same as a mark VIII). The real key is using the right pads and well ventilated rotors.

We found that Porterfield R4e pads (which operate ideally at around 700 degrees) and Powerslot rotors (which have cooling vanes big enough to stick my thumb in) are the best setup. Motul RBF 660 is the only thing that enters out reservoir. Our front pads have lasted 3 complete races, one of which was at the infamous Eagles Canyon (which EATS brakes).

We don't use any ducting, from what I have observed it does more hard than good.

Are you running drilled rotors? I have found that they eat up pads and don't do as good of a job evacuating debris/dust/water from the friction surface as just plain slotted rotors. Plus, the drilled holes are structural weak points and will allow tiny fractures from heat-checking to propagate into full grown cracks.
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post #9 of 9 (permalink) Old 04-20-2012, 09:12 PM
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What I would do - is haunt the boneyards for Mark VIII and Mark VIII LSC rear ends (LSC is 3.27, non-LSC is 3.07 or 3.08) - and while you're getting them, get the VSS.

Driveshaft should have non-greasable U-joints for durability during the race.

While getting the rear ends, get the half-shafts also (do it right, you can get the spindles, LCAs, and half-shafts - then sell the spindles and LCAs to reclaim the money!)

As long as you're cool about the speedo being off, I'd stick the 3.27 VSS on the car, and run it with either or both rear end ratios.

(Why Marks? Lighter, can run cooler due to the aluminum. Why LSCs? 3.27. But the 3.07/8 may be better for what you run. Also, open means you don't have to run the friction modifier -and if the opens work, that's less to heat up!)

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