Rear differential upgrade - who's done it?

[The_Auto_Tech]

I just double checked on the truck and it's got a 3.55 open diff. Would it make sense to go down to a 3.31?

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[SALEEN961]

I just double checked on the truck and it's got a 3.55 open diff. Would it make sense to go down to a 3.31?

Depends on how much power you plan on making, what size tire you want to run, and if you want to leave in 1st or 2nd gear.

 

[The_Auto_Tech]

Depends on how much power you plan on making, what size tire you want to run, and if you want to leave in 1st or 2nd gear.

Well, the plan is 5.0 with a Whipple, and whatever tire will be needed to hook. lol

 

[SALEEN961]

Well, the plan is 5.0 with a Whipple, and whatever tire will be needed to hook. lol

Are we talking about a 700whp Whipple or a 1000whp Whipple?

 

[v8440]

Nothing wrong with a locker on the street in my opinion. I've had one in my dually since '06 or so, works fine. Probably not needed for the majority of folks, but it hasn't caused me any trouble.

 

[The_Auto_Tech]

Are we talking about a 700whp Whipple or a 1000whp Whipple?

I plan to shoot for 800 as I know it's pretty easily attainable. I know 1000 doesn't take a ton of work either.

 

[The_Auto_Tech]

Spoke to Quick Performance yesterday regarding this as well. They recommended going to a 3.31 and an Eaton TrueTrac, especially for a Whippled 5.0. They said they have had a lot of success with that setup as far as holding up to the power and it working very well, as well as retaining excellent street driven manners. Most likely that's the route I'll end up going. Most of the stock 5.0 trucks came with a 3.31 in them, and the lower 3.17 gear set will not work with the TrueTrac.

 

[Fuelin_Around]

I put a TrueTrac in my 3.31 geared Super 8.8. It was super easy. I checked the backlash before and after, and there was no adjustment needed. You'll have to go thru the whole rear end setup process if you swap to a different ratio and the pinion needs to come out of the housing.

The TrueTrac drives like an open diff when you're driving normally, and spins both when it's time to party.

 

[The_Auto_Tech]

I put a TrueTrac in my 3.31 geared Super 8.8. It was super easy. I checked the backlash before and after, and there was no adjustment needed. You'll have to go thru the whole rear end setup process if you swap to a different ratio and the pinion needs to come out of the housing.

The TrueTrac drives like an open diff when you're driving normally, and spins both when it's time to party.

Yeah, from what I read if you weren't changing gearsets you probably wouldn't need to adjust anything. I would like to go down to a 3.31 though because I know a Whipple'd 5.0 with a 10 speed will function better with a 3.31 than a 3.55 or 3.73.

 

[MonkeySpank]

I just installed a Yukon LSD after months of watching YouTube and other videos. I have a 3.31 super8. Coming from an open diff, I'm very happy with it, has great off-road capability and wont be doing any one wheel peels anymore should I choose to do so.

I did have to shave a few thousands of an inch off of the drive axle locking washers, assuming this was just machining. Backlash after install was exactly .010, exactly the same before install.

Other then that it was a very rewarding install.

 

[The_Auto_Tech]

Placed the order yesterday with Quick Performance (they are about 30 minutes away from me) for the 3.31 gearset, master rebuild kit, and the Eaton TrueTrac LSD. Should be installing it the weekend after Thanksgiving!

 

[The_Auto_Tech]

Got the parts in yesterday, looking forward to getting them installed!

 

[TN_Ryan]

I installed 3.73's in my truck...didn't care for the factory 3.31's honestly. But it also depends on the wheel setup you plan on running. I'm running heavy 22's...so the 3.73's help makeup for that. When the truck was stock, the difference between the stock 17's steel wheels and the heavy 22"s was night and day. The diameter was the same, so the loss in power was directly related to the increase in rotational mass.

 

[The_Auto_Tech]

I installed 3.73's in my truck...didn't care for the factory 3.31's honestly. But it also depends on the wheel setup you plan on running. I'm running heavy 22's...so the 3.73's help makeup for that. When the truck was stock, the difference between the stock 17's steel wheels and the heavy 22"s was night and day. The diameter was the same, so the loss in power was directly related to the increase in rotational mass.

I could see that, but with 850HP on the horizon in the next year or so, I want the 3.31's, especially with the 10R80. I had asked Quick Performance about the gear swap and they said that the guys running a 5.0 with a Whipple are using the 3.31's with an Eaton TrueTrac as the preferred choice of rear diff setup.

 

[The_Auto_Tech]

Got it all wrapped up yesterday. Most of the time spent was just double and triple checking everything to make sure everything was right. Before I tore all the old stuff out I measured the backlash which was 0.010", which is right in the middle of the spec. I also measured all the old shims with a micrometer from the carrier and pinion as well. I figured the backlash had to be pretty good, because the carrier was pretty tight in the housing and I had to work it out with a box end wrench on the ring gear bolts. Just for laughs I also paint marked and checked the teeth engagement on the old setup to see what it looked like to, and just as a I figured, it was spot on with the depth and centering. The only thing I hadn't checked was the rotating force. I pulled the brake dust shields for the TBM brake install as well.

Since I was putting in a new Ford ring gear and pinion I figured the shims probably were going to be pretty damn close as a starting guide, so the pinion and carrier shims were reinstalled from the locations they came from. I made sure the entire housing and axle tubes were spotless as well before installing the new pinion races. Getting the crush sleeve tightened down is definitely a chore as it takes some major oomph, otherwise the pinion setup was pretty easy. Ended up with a rotating force of about 21 inch/lbs, spec was 16-27, so right in the middle. Using the same carrier bearing shims gave me a backlash of 0.010", so identical to factory, and right in the middle of the 0.008"-0.012" spec. Lastly, I checked the tooth pattern engagement, which was right on the money too, same pattern as factory. I ended up just re-using the factory diff cover for now, but will change it out to something else when changing out the break in fluid. Nice thing is that Eaton recommends 80W90 non-synthetic oil with no friction modifiers, so fluid changes are cheap on it.

Took it on the initial drive, but can't really comment much yet because you have to baby it for the first 100 miles and let it warm up and cool down every 15-20 miles, as well as not run it on the highway. No noises or issues yet though!

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