Rear differential upgrade - who's done it?

[TN_Ryan]

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.

I have a Whipple and 3.73’s…guess that makes me the exception ?

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[The_Auto_Tech]

I have a Whipple and 3.73’s…guess that makes me the exception ?

It was different back in the day when we only had like 3 or 4 gears in an automatic. Nowadays there's no reason for those high ratios with a 10 speed transmission. Even 4.10's in my Raptor with 37's and a 6R80 is perfectly fine.

 

[Davidwnuc]

I have a Whipple and 3.73’s…guess that makes me the exception ?

i have a roush with 3.73s
And 4wd
I always thought that you wanted more gear to help these pigs get off the line. As long as you can get traction, why wouldn't you want more gear? Especially with 10 gears in the transmission.
admittedly, i am not an expert by any means.

 

[The_Auto_Tech]

i have a roush with 3.73s
And 4wd
I always thought that you wanted more gear to help these pigs get off the line. As long as you can get traction, why wouldn't you want more gear? Especially with 10 gears in the transmission.
admittedly, i am not an expert by any means.

If you're foot braking it into boost, you ain't gonna have a problem launching it besides traction.

 

[The_Auto_Tech]

The B&M cover is expensive, but it's the one I'm leaning towards. It has a fill and drain plug, as well as the bolts for supporting the bearing caps. It also looks the least gaudy out of the aftermarket options compared to Mag-Hytec, PPE, aFe, etc.

https://www.jegs.com/i/B-M/130/4129...tIl8rP7vMJOU8YrGzOFlVf_iFDSdsTo1Lpf88YNVNP04p

 

[The_Auto_Tech]

Went ahead and ordered the B&M rear cover. I know it's bling and won't really "do" much, but it looks nice and provides some extra support for the carrier. Got about 60 miles in now on the break in. Been driving it very lightly and at lower speeds, as well as letting it cool down completely before another trip to give the gears time to heat cycle every 15-20 miles. Plan is to do that until 100 miles, then normal driving/no towing until 500. At 500 miles I'm going to pull the cover, clean it out and inspect it, put fresh fluid in, and install the B&M cover.

 

[v8440]

Keep in mind that all else being equal, numerically higher gears are easier on the transmission as they present less mechanical load to the transmission.

 

[TexasTruck]

I have a 5.0, FP/Whipple, 3.31 Super 8. I swapped the OEM diff for a Ford Performance clutch style LSD. Like others mentioned, the install is not terrible. The pattern was spot on and backlash was 10, same as OEM. The Eaton True Trac was not available at the time, but when they did finally release it, I swapped the clutch style out for the Eaton.

I have to agree that the 3.31 works very well with the FP/Whipple. The truck drives very normal, smooth shifting, no weird shift flares or jerking.

 

[The_Auto_Tech]

I have a 5.0, FP/Whipple, 3.31 Super 8. I swapped the OEM diff for a Ford Performance clutch style LSD. Like others mentioned, the install is not terrible. The pattern was spot on and backlash was 10, same as OEM. The Eaton True Trac was not available at the time, but when they did finally release it, I swapped the clutch style out for the Eaton.

I have to agree that the 3.31 works very well with the FP/Whipple. The truck drives very normal, smooth shifting, no weird shift flares or jerking.

I think some people may not be driving these trucks on long trips, or that they are running some really tall tires. If I'm driving the truck on a 3 hour trip, I don't want it running an extra 500 RPM for no reason. I can't say I've heard anyone with a 5.0/Whipple and 3.31's complain that the truck isn't fast enough, because they have always been traction limited, and going to a 3.73 or higher ain't gonna help that. If they can run a mid 9 on a 3.31, what's the point of a higher ratio?

 

[The_Auto_Tech]

Over 100 miles into the break in and all seems good. The diff whine that I used to have with the factory setup is gone. Looking forward to pulling the cover at 500 miles to get the fresh oil in it and install the B&M cover!

 

[The_Auto_Tech]

Just made it over 500 miles after a trip this last weekend. Nice and quiet from the rear the entire drive and everything worked perfectly. On larger hills it will downshift more often into 8th gear compared to the 3.55's, but I'm also running the 3.3 V6 engine still, and I don't expect it to be a powerhouse either, but it does run extremely well. Upside is that once it's out of powertrain warranty I'll have the 5.0 engine built and ready to drop in, unless for some reason I decide to run a 7.3 for some reason instead.

If I get time this weekend I'll be pulling the diff cover to inspect, clean, install the B&M diff cover, and add flesh fluid.

 

[The_Auto_Tech]

Just to update the full setup at this point:

OEM Super 8.8 axle housing and axles (minus brake dust shields)
OEM 3.31 ring and pinion gear set (includes bearings, shims, and seals)
Eaton Detroit TrueTrac LSD
B&M Hi-Tek aluminum rear differential cover kit (sealed with Permatex Ultra Black)
MasterPro conventional 80W-90 GL5 gear oil

Everything has worked excellent thus far with no complaints. Rear end is nice and quiet and the Eaton LSD works excellent. B&M diff cover is a nice piece and not necessary, but I'd say if you really want an aftermarket cover it's the way to go.

 

[The_Auto_Tech]

Picture of the diff cover installed! Everything looked perfect inside with very minimal wear material.

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