We just got back from a 2500 mile route through NM, CO, AZ in my 5.3L Tahoe with 3.42 gears pulling a 23 foot, 3700# dry, 4700# GVWR trailer (see sig. pic). Average MPG was 10.1 for the trip, and the combination made it through the mountains OK, we had a great time. I'm OK with the fuel economy (bucked some really tough headwinds).
My issue is that I kept the Tahoe in 3rd gear much of the time, and it dropped down to 2nd on long grades. So, at 60mph, we're looking at 1600rpm in 4th, 2300rpm in 3rd, and a whopping 3800rpm in 2nd (kinda screams). I only could use 4th on long flat runs with no head winds. And in 4th, it felt like it really bogged before it made the decision to shift into 3rd, which is why I just put the shifter into 3rd.
So, it seems that if I re-geared to 3.73, or even 4.10 gears, I'd be able to run better in 4th, and 3rd would be used on most grades, with 2nd called into duty only for the long 6% climbs.
So, questions...
Should I re-gear (Tahoe is a paid-up 2007 model I'd like to keep 6-7 years)?
Which ratio should I go with (might upgrade to a 27' ultralight in a year or two)?
Where can I go for the re-gear work (I'm in DFW TX).
According to the Trailer Life 08 Tow Rating Guide, you axle ratio is is not correct for your engine rating. A Tahoe with a 5.3L V8 2WD with a 3.73 rear axle ratio is rated for towing 7500 lbs. This would give you less strain on your engine and still give you about 10MPG while towing. The 4.1 or 4.3 axle ratio will only eat up you gas mileage. Where you go to get regeared, I don't know.
Happy Camping
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The 3800 rpm might sound like it was screaming,but in reality it was just loafing along.
The 5.3 doesn't even get to peak torque until 4400 rpm and peak hp is at 5200. The 5.3 is like all of todays small blocks,it NEEDS to rev to make power.
For the weight your pulling,and the description of how it pulled,I don't think I'd change a thing.
If you do want to change gears,I'd go right past 3.73s to 4.10. There isn't enough difference between 3.42s and 3.73s to make that change IMO.
If that were my Tahoe, I'd be looking into doing some good engine mods over gearing it. Let's face it, you're not rock crawling, you're pulling a camper on a highway. 3:73's would have been nice from the factory, but that's a whole nother animal.
Did that model come with a towing package? I thought all the towing packages came stock with 3:73's. Those 3:42's are really not the thing for towing.
Is that the "flex-fuel" motor? Maybe when you say it's "bogging" it's cutting off to 6-4cyl mode. When you downshift they come back to life.
I can't believe you're only getting 10mpg!! We get 9-11 with our 6.0L 30ft Class C MH pulling a 3100lb car!
Or if you really want to gear it, go with the 4:10's. The 3:42 to 3:73's is not a big difference to make it worth doing. You may pull the camper good, but you won't want to look at the gas bill at the end of the month.
Maybe you can get a good trade for it and buy a bigger truck before they are all gone. Prices sure came down a lot.
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This Tahoe was purchased in May 2006, when the "2007" model came out early. They all came with the 5.3L, and the 4-speed auto. Not sure about the axles, as I didn't even think about the ratio. It came with the "tow" button on the shift lever and the 7-pin connector on the hitch. Hooking up the brake controller was easy, as the two wires needed were taped-off and easy to connect to threaded studs on the power panel. So, I guess it has the two package.
Does anybody know which GM axle this vehicle would have?
I would assume the axle would be the AAM 10-bolt that GM normally puts in 1/2-tons, or maybe the heavier duty 12-bolt. Count the bolts around the differential cover.
I would re-gear it. Re-gearing is the quickest, easiest, most cost-effective way to increase towing power in any vehicle that is obviously under-geared or under-powered for the intended use. I would likely go with 4.10's, considering your trailer is not THAT heavy, assuming your tires are still the stock size. If your tires are over-size, that will play havoc with the gearing, effectively making your truck act like the ratio is even higher (numericaly lower) than it already is. If you have aspirations of towing a heavier trailer or swapping to taller tires, then gear it lower than 4.10, like 4.30 or 4.56.
My thoughts are that the manufacturers are messing up by spec'ing engines that make power at such a high rpm range and then offering such high (numericaly low)ratio gears that never put the engine up into it's powerband at a useable road speed. They need to drop the usable powerband of the engines back down to the 2500-3500 rpm range of the old gas engines, like my truck's 351W or the 350 Chevy or 360 Dodge. There is no excuse for an engine in a pickup or utility vehicle to be developing it's power in the 5000 rpm range. These are trucks, we are not racing on the oval track here! Save the 5000 rpm motors for the Corvettes, Mustangs and Camaros. Give us the low rpm torque!
Either that, or if they absolutely MUST use racing motors in trucks, then spec axle ratios in the 4.10 to 4.88 range instead of 3.23 to 3.73 so we can spin that motor right up there into the stratosphere at road speeds that are safe to move a load with. Lugging an engine at wide open throttle, at an rpm way below it's powerband, to get up a hill uses ALOT more gas and puts alot more strain on both the engine and the transmission, as well as the driver, than holding the rpms firmly in the range of peak torque output, in a lower ratio gear, at part throttle, to climb the same hill.
The engineers need to go back to school...
* This post was
edited 06/14/08 11:44pm by SoCalDesertRider *
HighCover wrote: This Tahoe was purchased in May 2006, when the "2007" model came out early. They all came with the 5.3L, and the 4-speed auto. Not sure about the axles, as I didn't even think about the ratio. It came with the "tow" button on the shift lever and the 7-pin connector on the hitch. Hooking up the brake controller was easy, as the two wires needed were taped-off and easy to connect to threaded studs on the power panel. So, I guess it has the two package.
Does anybody know which GM axle this vehicle would have?
Your first post you said you had 3:42 gears which I find very hard to believe since the tahoe came with a choice of 3:73's or 4:10's.
You need to check your RPO codes...
The following Regular Production Option (RPO) codes identify the rear axle and transaxle overall final drive gear Ratios. These codes can be located on the RPO sticker in the glove box or in the trunk on most GM vehicles. Axle codes typically begin with the letter D, F, G, H, or Numerical.
I still vote for a bigger truck with a heavier duty tranny. That 4l60E isn't known for it's guts.
The swap to 4.10 puts you at 1900 in OD, 2750 in 3rd, and 4500 in second all at 60 mph. That seems reasonable to me. To keep the second gear rpm down you may need to slow a bit on the 6%+ grades. Nothing wrong with 50 up those and likewise nothing wrong with running peak torque rpm of 4400 for an extended period. I would go 4.10 as 3.73 is not enough to pay for the change.
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"Lugging an engine at wide open throttle, at an rpm way below it's powerband, to get up a hill uses ALOT more gas .....than holding the rpms firmly in the range of peak torque output."
Not true.
For those of you that has the instant mpg readout, put your rig at the speed you want to check, Say 55 mph. Look at instant mpg in the display, driving in overdrive, press the tow/haul button and the transmission will most likely shift in to 3rd gear. Watch the MPG take a serius drop as the rpm increase and tha load of the engine is reduced.
The reason for higher fuel consumtion during light load/high Rpm driving is
higher internal friction and pumping losses in the engine compared with wide open throttle and low rpm.
It was the same physics at work say 20+ years ago, but then the gains in friction and pump loss were often more than offset by the poor fuel delivery systems, the carburettors of yester year.
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A Tahoe with a 5.3L V8 2WD with a 3.73 rear axle ratio is rated for towing 7500 lbs.
This would give you less strain on your engine and still give you about 10MPG while towing.
The 4.1 or 4.3 axle ratio will only eat up you gas mileage.
Where you go to get regeared, I don't know.
