Putting in 3.73s in a couple of weeks. Few questions...

[jchristena]

All the preload discussions aside...couple of questions about GT500 specific parts.

1. I see that the pinion bearing is a different part number (6L2Z-4625-AB) vs. standard 8.8 kits. Is this the only part that is different besides the torsen diff? Basically, can I buy the pinion bearing in conjunction with a standard gear install kit?
2. A couple of the wholesale Ford part sites say it's a different gear part number for torsen(DR3Z-4209-B) vs. non torsen(CR3Z-4209-B) cars. Those are Ford parts, not Ford Performance. I don't see that any of the vendors that sell FRPP gear sets specific for torsen vs. non torsen. Anyone know whats up here? Will a standard 3.73 FRPP gear set fit ok w/ a track pack car?

Thanks.

 

[07 Black Beauty]

I got my 3.73's from lethal, they sell an install kit minus the bearing for the 13/14s @ a reduced cost and you just purchase the bearing separately

 

[07 Black Beauty]

 

[biminiLX]

Yep should be all you need, gear is same for either diff, nothing special on the Torsen.
-J

 

[fearthesnake]

All the preload discussions aside...couple of questions about GT500 specific parts.

1. I see that the pinion bearing is a different part number (6L2Z-4625-AB) vs. standard 8.8 kits. Is this the only part that is different besides the torsen diff? Basically, can I buy the pinion bearing in conjunction with a standard gear install kit?
2. A couple of the wholesale Ford part sites say it's a different gear part number for torsen(DR3Z-4209-B) vs. non torsen(CR3Z-4209-B) cars. Those are Ford parts, not Ford Performance. I don't see that any of the vendors that sell FRPP gear sets specific for torsen vs. non torsen. Anyone know whats up here? Will a standard 3.73 FRPP gear set fit ok w/ a track pack car?

Thanks.

Sorry OP, I am not technical and can't provide any input other than you are going to love the new 3.73 Gear. Give us your feedback once you test it out!

 

[jchristena]

Yep should be all you need, gear is same for either diff, nothing special on the Torsen.
-J

Awesome. Saw another thread talking about carrier preload and then I saw the two different part numbers for the Ford gears(still not sure why) and the different pinion bearing.

I've done several 8.8's on other Mustangs including my 11 Shelby and all those came out great. No slop, no whine...just perfect. That other thread kind of planted the seed that this '14 8.8 is somehow different. Seems though, if you have the right parts, it should be exactly the same. If you get the pinion depth, backlash, preload and gear pattern correct, everything should be just fine.

I apprecite the info guys.

 

[jchristena]

Sorry OP, I am not technical and can't provide any input other than you are going to love the new 3.73 Gear. Give us your feedback once you test it out!

Yea, definitely will. Everytime I drive this car, with the ratios in this Tremec, it is obvious that the 3.31s are just not enough. I get that Ford wanted 200mph out of the car and also to avoid the gas tax...but I can't imagine 3.73s not making for a better all around experience in every way. It's not like gas mileage was ever good to start with. lol.

 

[biminiLX]

Yep, don't fear the gear you'll love it. The 6th 0.50 ratio and higher peak on the GT cams ('13-14 run Ford GT cam specs) make it pull up high quick and 80mph at 2000rpm is perfect to me.
-J

 

[biminiLX]

Awesome. Saw another thread talking about carrier preload and then I saw the two different part numbers for the Ford gears(still not sure why) and the different pinion bearing.

I've done several 8.8's on other Mustangs including my 11 Shelby and all those came out great. No slop, no whine...just perfect. That other thread kind of planted the seed that this '14 8.8 is somehow different. Seems though, if you have the right parts, it should be exactly the same. If you get the pinion depth, backlash, preload and gear pattern correct, everything should be just fine.

I apprecite the info guys.

Sounds like you will be good to go. My only advice is that if you ever intend to drag race you must have some sort of brace. Using a bias ply tire may also help.
-J

 

[07 Black Beauty]

The 3.73's definitely made the car easier and more fun to drive. The 3.31's made the car feel sluggish from a stop, w/ the 3.73's I can get the car going without any throttle @ all

 

[Drewsky65]

I'm actually a fan of the 331's, my only gripe is the sluggish 1st off a stoplight and very low 6th under 70mph on the freeway. But 2-5 is perfect really. It allows you to ride through the tq the motor has in these cars and use it to its potential. The 331's are believe it or not faster on freeway pulls and or even in town (and in dyno). I'm not aposed to the 3.73 at all but I think the 3.55 would be the "perfect gear" for the 13-14 Shelby but wouldn't notice a big enough difference to spend the money and make the change

 

[jchristena]

I'm actually a fan of the 331's, my only gripe is the sluggish 1st off a stoplight and very low 6th under 70mph on the freeway. But 2-5 is perfect really. It allows you to ride through the tq the motor has in these cars and use it to its potential. The 331's are believe it or not faster on freeway pulls and or even in town (and in dyno). I'm not aposed to the 3.73 at all but I think the 3.55 would be the "perfect gear" for the 13-14 Shelby but wouldn't notice a big enough difference to spend the money and make the change

Yea, first and sixth are my main gripes. I read as much as I could and it seems most people recommend 3.73s or even 4.10s. I had 3.73s in my SVTPP '11, and really loved them. Either way, the 3.73s have been ordered so it's a done deal now.

And yea, I wouldn't think 3.55s would be worth the switch.

 

[biminiLX]

I'm actually a fan of the 331's, my only gripe is the sluggish 1st off a stoplight and very low 6th under 70mph on the freeway. But 2-5 is perfect really. It allows you to ride through the tq the motor has in these cars and use it to its potential. The 331's are believe it or not faster on freeway pulls and or even in town (and in dyno). I'm not aposed to the 3.73 at all but I think the 3.55 would be the "perfect gear" for the 13-14 Shelby but wouldn't notice a big enough difference to spend the money and make the change

What tire do you run?
If you think your 3.31 car is faster on the street, you don't want to mess with a 4.10 drag radial car from 40-140mph.
Earlier cars had different trans gearing and cams, with our 2.66 first/0.50 6th and GT cams, you need to look at things differently.
If you have the traction, the car with more mechanical advantage will win every time.
I feared very few cars even when my car had just a tune, 4.10s, DRs.
Now that I've been in a built 6R car and own an A8 Hellcat, I can tell you very few stick drivers can hang, but it makes it more impressive when you can.
-J

 

[Drewsky65]

I believe a 3.73-4.10 trinity would prolly be more enjoyable to drive around 100% agree there, and the power band around town and certain freeway speeds possibly more suitable. In my old 06 gt 3V car I had 4.10s with a 5 speed and ran it that way for 4 years and didn't regret a single thing! I had a 2011 5.0 with 3.73s and wouldn't change a thing. When I got my 13 Shelby one year ago last May the very first thing I said was "I'm swapping out the gears." Then after a few months my mind changed. I remember I had a 67 mustang with a 351w in it fully built, it had a c4 tranny and 3.55 posi rear end I had built for it. The car was never as fast as it should have been. At a car show I talked to an old timer that was a engine builder that drag raced his whole life. We got into long conversations and and I was telling him it's just not running right, told him my set up and without hesitation he said " put a 3:00 in it" I thought he was crazy and blew it off. About a year later I just decided to go ahead and swap out the rear end just for kicks with a 3:00 non posi old dirty setup just to try it out. ( picked it up in a junkyard for like 30 bucks) took half a day to change it out and that car was faster in every single way across the board. Off the line and all the way through to 5k rpm. Now take this story with a grain of salt just because of the c4 auto and particular setup it was. But the motor had the tq to move the gear and ride it out like it should have, rather than shifting before the motor was in its tq curve.

The trinity cars have a similar situation though. They have an extreme ammount of tq and a great flat curve on the dyno. A longer gear allows the motor to stay in the tq curve a little longer and keep pulling all the way though. This would not be the same with a 5.0 or 3v car. For freeway pulls or even freeway racing I don't see a 3.73 or 4.10 edging out a 331, the 3.73 will be shifting while the 331 still pulling and using the tq the motor has. But it will definitely not "feel" as fast.
Trinity's like the 331 and are suited for it. I think the tranny should be very slightly changed, ( 1st and 6th) and or as I said in my last post a 3:55 would prolly be the "perfect gear"
I definitely don't fear the gear! I just grew on the 331 and the tq curve. Engineers didn't just design them that way for gas guzzler tax/ and 3.5 1st gear 0-60 time.

I'm running MPSS in the rear.

 

[Speedboosted]

I have an '11 with 3.55 gears from the factory. For the longest time I wanted 3.73 gears in there as I felt it would be faster. Then stopped drag racing as much and thought the 3.55 were awesome on the street. Now with a built motor, cams, and a ported tvs I am in love with the 3.55 for all kinds of driving. It's a sledgehammer on the highway, drives decently at low speeds, and gets good mileage all things considered.

I run a DR on the back pretty much all the time now, and there's a tiny part of me that thinks 3.73 would be fun since the car has a lot of traction and the cams took away some of the vicious TVS torque hit.

 

[jchristena]

Well, I'll report back on this with my results and a few questions in case anyone wants to chime in. I already PM'd Snoopy and BiminiLX. I also poured over the existing 3.73 gear noise thread. My main difference is I reused my bearings and factory shims to achieve .008 backlash...so my carrier bearing preload should be factory. Anyway...here's my findings.. And yea, I know this has been beat to death.

The 3.31s were quiet but just had a little slop. I measured about .014 backlash before I took them out. With these new gears, I have a whine on light acceleration after about 55mph+ in any gear.

-Reused the same bearings on everything as they looked perfect. Just cleaned them out real well before reinstalling.
-Pinion depth was pretty close w/ the factory shim. Factory was .032. I added .002 for a total of .034. Preload feels really good. No slop in the pinion at all. Near as I can tell, preload is around 22lbs which seems to be within Ford spec. If preload wasn't enough, I would THINK i'd be getting a whine on deceleration instead. New crush sleeve of course.
-Gear wear pattern looks perfect. Had a buddy of mine look at the wear pattern and he's been doing the racing thing for 55 years...countless 8.8s. Said it looks perfect to him.
-Backlash. I have it set at .008. With the factory shims, I was closer to .012-.014. The shim on each side were so close in thickness, I just swapped them and that closed it down to .008. I was pretty happy about this because this should maintain the identical carrier bearing preload on these used bearings as it was from my quiet factory rear end.

The gears were quiet as hell for the first 20 miles. I have about 30 miles on the gears now and the whine has just creeped in.

-I'm going to tear this down tomorrow again but can excessive backlash(and probably not a ton of it) cause noise?
-Would you replace the carrier bearings even if they look perfect? It was of course preferable to leave them as we had a known shim thickness to give the factory preload value. I guess better too much preload than too little from what I've read.
-After 30 miles, assuming that maybe it's backlash, would you replace these 3.73s w/ new ones? Or do you think that's few enough miles that they might be fine. There are no hard launches or anything. I think I stepped on it in second and third maybe 1 time w/ street tires...so no severe duty or anything.

Anything you can think of or offer I would greatly appreciate. I can't over emphasize how much I'm looking forward to tearing this down again tomorrow in the Texas heat. ...but definitely don't want to queue up for a 3rd or 4th time after this.

 

[tomshep]

I want to do 3.73s so bad but I FEAR THE WHINE!

Good luck with your efforts and please update.

tom

 

[Norton]

I want to do 3.73s so bad but I FEAR THE WHINE!

Good luck with your efforts and please update.

+1 to all of this!

 

[Dinosgt]

+1 to all of this!

+10


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[Mojo88]

Subscribing! I have 3.55's with a whine on light acceleration after 50mph, and I freakin' hate it. Gonna put new gears and whatever else it takes to get rid of the whine.

OP, please keep us all updated on your progress. And good luck!