Will I need a new tune??

[Power Hungry]

Once the VSS gear is corrected, the shifts will all return to normal, at least based on MPH. However, they may still be a little high RPM-wise since you've now changed your RPM/MPH ratio. This isn't necessarily a bad thing, but might not exactly be what you're looking for... especially if you're looking for fuel economy.

If you can provide old gear/tire combo and new gear/tire combo, I can run it through the calculator and let you know just how much to expect your RPM to change. Of course, you've probably already noticed the difference.

[97xl]

Thanks Bill,

Old:

3.08 open diff 265/70r16 tires 30.61"

New:

3.73 LS 265/70r16 tires 30.61"

Update. I spoke with Eaton directly and they said 99.9% that the reason I've got the noise is because they used synthetic diff fluid. They said only use conventional. Was told it will make a small amount of noise when turning but other than that there should be no noise if the gears are setup properly. Also that its possible to take the exciter gear from the old rear diff and install it on the new one so the ABS will work. I called the shop today to make sure they still had my old parts, which they do, so this should be getting fixed tomorrow.

[Power Hungry]

The gear change with no tire size difference equates to a 21% difference.

I've attached a really neat calculator that will take tire size, rear gear ratio and transmission ratios to provide an RPM per MPH value for each gear. Hopefully it's useful.

Take care.

[97xl]

Thanks Bill, that gives me a better picture. Right now when the speedo says 120kph(74.5 mph) the tach is only at ~2000, with the old gears the tach would read ~1800-1900.

Update:

Took it back on Tuesday. Mechanic took it for a drive and said yeah its too loud and there is a clunk when it downshifts. Took it apart again, swapped over the exciter gear from my old carrier so now I have ABS again, put in the conventional 80w90 diff fluid and tightened things back up...what a difference now, no clunks and no noise, except if you turn a corner and get on the gas it clicks but thats normal for transferring power to the other wheel. I can now get the tires to squeal on dry pavement from a dead stop in a straight line, with the old setup I didn't get so much as a squeak. Feels like a new truck. The backlash is 0.010". Now I just need to get that new speedo gear and this mod is complete.

If the speedo gear doesn't fix the shift points I'll be calling you guys for some new tunes. I mean I love my Troyer tunes I just don't want to wait 13 weeks to get them.