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Old 06-10-2008, 07:01 PM   #1
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Default How much trouble to change rear end

I have an 07 Yukon with trailer towing package. It has the 3.72 ratio. Any ideas on ease and cost of switching to the 3.42 std. ratio? I get 17 MPG overall now and don't tow anything. Thanks
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Old 06-10-2008, 07:51 PM   #2
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I would be interested in this as well. I have a 6.0 Suburban with a 4.10 rearend...I am also curious if anyone has changed from the 4 speed tranny to the 6 speed avail in Denali/Escalade/2009s...
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Old 06-11-2008, 12:04 AM   #3
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As for switching the rear end what type of driving do you do mostly? If it is city stick with the 3.73. Highway 3.42 might help alittle I dont know if it is worth it as far a cost and reprograming the computer.

As for swaping the transmission im sure its possible dont know how expensive it is to do and what has to be swaped.
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Old 06-11-2008, 11:05 AM   #4
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This discussion was brought up on a diesel truck forum that I belong to, but the parts are the same regarding the Tahoe. The expert's opinions were that mechanically, it's an involved procedure for the average shadetree mechanic. It's not a transmission mod, but a differential mod, and the removal of the ring and pinion gear in the differential is involved. There is also the issue of shimming the new gears to insure correct amount of backlash. Then you need a speedometer re-cal, and possibly a reflash of the ECM. I would imagine a good shop could do it, but I'm guessing you figure in a day's labor with the cost of the parts.

One other thing. The difference in the 2 ratios you reference is fairly small, so I doubt the difference in mileage would be significant. I did some quick figuring, and I think your engine RPM at typical highway speeds would be less than 200 RPM. That's pretty insignificant.

Last edited by Hardin Thicke; 06-11-2008 at 11:17 AM.
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Old 06-13-2008, 02:07 PM   #5
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Yeah, going from 3.73 to 3.42 is not gonna get you much at all...and it would take a long time to pay for the parts and install, plus reflash of the computer, etc...is your truck 4x4? If so, you'd need to do all of this in the front at the same time as well. You'd want to use a quality ring and pinion set, cause if you go with a junk import cheapie, you'll likely experience gear whine and who wants that in a nice quiet Tahoe/Yukon? R&P set alone will cost you probably $300-400 for a quality set, plus the master install kit (bearings, shims, etc)...unless you know how to swap a ring and pinion, you're looking at several hours of labor charges. Then when the gears are done, you'll need to have the computer reprogrammed at a dealer or someone with the equipment.

If you're getting 17mpg combined, I'd be pretty happy with that...my average is 15mpg pretty constantly, unless I go on a long highway trip, which is usually about 17-18mpg if I drive smoothly...and I have the 3.73s.

Some quick math - if you somehow picked up 2mpg (which I doubt), that would get you basically 50 extra miles per tank (25 gallon tank). Let's just say 19mpg (in your hypothetical case) now. If you drive 12000 miles a year, at the 17mpg, using $4.00/gal, you'd pay $2823 in gas. At 19mpg, you'd pay $2526. So, you might save $300 a year if you were somehow able to increase your mpg by 2mpg with the gear swap, and I really doubt you will get anywhere near that going from 3.73 to 3.42. In fact, there is a chance that your mileage might actually go down, as many have shown that the 4.10 ratio might actually help mpg because of it's torque multiplication benefits in getting the vehicle moving.

In my view, you could spend your money much more wisely than going with this swap...it will take you several years to pay off the cost, and doubly so if you have 4wd!

Oh, and swapping in a new 6 speed auto would be WAY more expensive! I'm sure you could get someone to do it for you, if you can get your hands on one in the first place...but you're likely looking at big $$s for a swap like this, plus losing your warranty for the drivetrain...and I'm sure you'd need a new computer to get the engine/new tranny all talking together and working right...big headache I'm sure!

Last edited by kpanza; 06-13-2008 at 02:14 PM.
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Old 06-13-2008, 06:19 PM   #6
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Thats about what I figured. I have 2WD, but would have to have dealer or shop do the work. so no payout for me. Just keep it a while more and trade for an Arcadia. But Yukon sure rides great.
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