There in lies the problem

 

Update.

The 3.42 Gears have been installed. Everything seems to be working good. I have yet to drive it on the open road for a long distance. The front gear set did not require a spacer ring, it was a thicker ring gear to compensate for the off set pinion.

In short speed bursts the RPM's are similar to what SS MINNOW reported.

G56 Stock tires

75 mph 21-2200 rpm
80 mph 2300 rpm

I estimate a 300 rpm decrease with the gear install. I will definatly keep you posted as to the fuel economy I find. But after reading through the posts there are many variables that contribute to MPG. Thank you all for your input and research.

 

What about where you got them?

 

Yes, please do, I am very interested in how it turns out for you. I do know that the drop in RPM's, especialy 300 will give (or at least should give you) a pretty good jump in MPG on teh highway. Are you going to be doing any hauling with it??? This is a cool MOD, one off the beaten path.

 

There's talk over on the TDR that for the '08 models a 3.42 is offered with the G56.

MikeyB

 

I had the install done by Accurate Automotive in Logan, UT. The gear sets came from West Coast Differentials in California. After a short (500 mile) break in period, I do plan to continue using the truck for hauling. I have a 30ft. Wilson stock trailer(GVW 26,000 lbs), 6000 lb boat, and misc flatbed trailers.

As far as the drop in RPM, I'm goin out on a limb and guessing that an increase of 2-3 mpg is what I can expect. Based on traveling at lower speeds with the old 3.73 ratio. The truck on the highway feels like it runs alot smoother, and not so "wound up" in the rpms. Bottom line I feel like I've accomplished making this manual G56 have a similar ratio to the 3.73 geared Automatic in overdrive.

I'll keep you posted on the actual economy I'm getting. Thanks again.

 

MLB its been 2 weeks you got any updates for us?

How about what are you doing for speedo calibration?

what kind of mileage are you getting?

I really want to do this and figure worst case scenario I drop down a size in tires and if I have to run around in 5th gear in the hills who cares.

 

I wanted to subscribe to this thread to hear some results.

 

MLB the suspense is killing me! Make with the numbers.

 

ANYTHING?? This will be next on the list for me!!

 

I'm a 2nd gen so please bear with me, but I'm still very interested in the above reaults.

I'm seriously looking at a GV however most of my driving is town/freeway about 70/30 so the GV will only help the 30% area. With heavy towing I would expect to run 4th over and save the 5th gear. Cruising unloadedwith 5th over would be nice however. Cost justification is hard though.

I keep track of every dime I put in the truck and especially fuel as it is the highest cost per mile.

I have running debates with my son regarding speed vs mpg. I get considerably better mpg than his Suburban and absolutely demoralize him pulling the trailers. He keeps showing me his overhead at 20+ but coasting downhil with a tail wind doesn't count. I don't have an overhead but I'm sure some of you could probably get up to 80-90 mpg with these conditions. Still don't count.

I see that there are a lot of comments about conditions of the trip filling etc.

I fill at the same station, same pump, I even try to park within about a foot if possible to give some stability to the fills. I get some variance and a really high or really low mpg result I usually take with a grain of salt. Long term average is what really counts. I also drive pretty conservatively but I do blow smoke when someone needs a smoking..haha. Overal I try to be very consistant and I even drive the same routes frequently. Same,Same, Same ie I try to do only apples. haha

Here is some info from my speadsheets;

19.74 for 4085.9 miles town/freeway 40/60 full winter fuel no towing

19.33 for 2076.6 miles town/freeway 70/30, summer fuel. No towing. Completely different driving routes, different but new station but I used the new station all the time.

19.66 for 5130.3 miles 70/30 Same driving routes summer fuel but ULSD, same station as #2 but with Smarty on #3. 2 8000# open trailer tows 110 miles each.

I show 9 20+ mpg fills and 6 18+ mpg fills, none lower or higher.

Over all mpg is 19.63 mpg for 12,719 miles including above. Some is with LSD and about 3/4 is with ULSD. The amount of fuel recorded also included the volume of any additives. Overall cost per mile is $0.14314 per mile.

I add about 1 oz/gal of PS in the winter and 1 qt of 2 stroke in the summer. Our fuel in Minn is 2% bio and winter/summer conditioned. I also included in calculations 4 gallons of clean, new motor oil that burned rather than toss out. I can't claim any +/- gain from any additives.

As you can see I have radically different driving conditions but the mpg is about the same. The Smarty is a very big help towing from my previous observations. It helps around town too so I think this is an equalizer so far.

There is no doubt that going over 65 with 4.10 gear cost you mpg.

 

still waiting on mlb

 

hmmm he hasnt loged in since 9-22...?

 

Has anyone made the 3.42 gear change with American Axle's new set? I looking to make the change and want to know which gear set is the best.

 

I made some calls around yesterday and it sounds as if only oem stuff is available yukon is distributing them also but it was staed that it was just repackaged oem