Gear Ratio Change?

[SteveH]

I'm currently towing a 23' tandem Safari with an '07 GMC pickup equipped with the towing package, 5.3 liter engine, and 3.73:1 rear end gears. I am wondering if anyone has first-hand knowledge of the improvement in a simular truck after switching to a 4:10:1 rear end gear?

The truck does a great job towing on the flat at up to 75 or so, but who wouldn't want more power on the hills?

[69AmbassFl]

You may notice an improvement on the hills but you will also notice fuel mileage decrease as you will be turning more rpms with the higher gear ratio. I would have to toss around how often I went to the hills versus flat land driving. Especially since fuel costs here are 3.36 per gal for reg unleaded

[safari 28]

It looks like you have a good set up for the application and trading to a lower ratio will impact your mileage when not towing, not so much around town but if you drive interstate I would guess a drop of 3 to as much as 4mpg depending on the speed you travel. Also, if you have 4 wheel drive, I think you would have to change the front ratio as well. Big bucks. On such a new truck the 3.73 is a nice mix and work well on our half ton for nationwide towing a 28.

[jayray5]

Your truck has a 4 speed auto with tow haul, correct? I have the same setup
and I STILL tow in 3rd gear. Save your transmission! The difference is about 500 rpms and overdrive isn't involved. Your power band is 2000 to 3500 rpm which translates to 60 to 75 mph. plenty of power and no constant up and down shifting ( from overdrive (4th) and back to third). You still have the economy of 373 gearing when not towing.

[Wayward]

Steve, I studied this and my experience is that a gearing change can make a significant difference in a small block 1/2 ton. Factory gearing is a compromise.

I went to 4:30 gears and wish I had done it a long time ago. It is a completely different towing experience! The biggest problem it solved was "gear hunting" at interstate speeds. The rig just always seemed to be wanting me to upshift or downshift. Acceleration improved noticeably when towing.

The big surprise was that towing mpg went up 2 mpg! No significant mileage change around town so long as I do not get heavy footed. Just a broader more usable power spread now.

I used Ford Racing gears which were only a small bit more expensive and designed to take abuse.

..................Scott

btw: I built a spread sheet which put me at about 4:10's but I went with 4:30's, allowing me to to install larger diameter load-range D and E tires. The spreadsheet, combined with my engine's hp/torque curve let me find an optimal engine/road speeds in various gears for towing.

[markjoandall]

Steve,

I did the gear change to my 2001 GMC Yukon. I went from the 3:73 to the 4:10. The difference is extremely noticeable towing. It is very easy to do with a 2wd truck because there is on one diff. I have over 30,000 miles towing with the rig. There is a little drop in mileage not towing, and towing I had no change in gas mileage. Before the change the rig was always seeking a different gear on the slightest incline. with the change, I can tow all day long in OD. The sweet spot is about 62 mph. Uphill it will tow at 2800 rpm and the engine will never overheat. I search for the gear that will gives me 2800 rpm.

I ramble, because I'm trying to do too many things at once.

PM if you want more info

Mark Wegman

[SteveH]

My truck is two wheel drive. I understand there will be sacrifices in mileage when not towing, and that sort of information is what I'm after. I checked today, and at 70 MPH, the truck is turning 2000 RPM in OD, and if I drop down to 3rd, the RPM goes up to 2800, and I do tow in 3rd if there are a significant number of grades, and/or winds to deal with. I'm dissapointed with my current towing mileage (10 on my last trip to Big Bend Park), and that was at an average speed of 65. We were, however, unlucky to have head winds both ways. Scott, I am surprized to hear your mileage went up with the gear change. I wonder if my GMC would do the same as I see you are driving a Ford. Mark, your information is sort of what I was expecting to hear. I did notice you are towing a thirty footer, and so now I need to figure out if the change would be best for me towing the smaller 23'. Thanks for everyone's input.

[markjoandall]

Originally Posted by SteveH

My truck is two wheel drive. I understand there will be sacrifices in mileage when not towing, and that sort of information is what I'm after. I checked today, and at 70 MPH, the truck is turning 2000 RPM in OD,

Steve, With a 4:10 rear end, your speado will read 65 at 2000. The additional torque to the road is substantial. I couldn't believe the difference.

I bought the gear and pinion online.

Mark

[hshovic]

I got the 2007 Silverado 3/4 gas with the 4.10 rear end.
I never run out of power, and I live and travel in the mountains.

As you get above 6,000 feet, power always goes down, but
though it gears down, I never am slowed down.

Though you could put a 4.10 in, I was advised that is very expensive,
since it is not just the rear end that needs mod...

Gas mileage is 11 over 1000 miles for summer and 10 over 2000 miles
in the winter. 16 w/o trailer on the road.

[Wayward]

Originally Posted by SteveH

I am surprized to hear your mileage went up with the gear change. I wonder if my GMC would do the same as I see you are driving a Ford.

I suspect the towing mpg increased because my truck was just overgeared for towing the Safari. So the engine was never in the optimal power band at highway speeds (i.e. needed too much throttle or being over reved). The mpg jump would be not a Ford/Chevy difference- just more significant because of my smaller motor.

Does your tranny have a "towing switch" to disengage the torque converter lockup? If so, that would give you a very usable 4th gear for towing and really let you take advantage of the 4:10 gears. If not, you could call someone like Troyer Performance for a chip with 2-4 different shift patterns. That would give you an optimal towing pattern and the abilty to switch to an optimal non-towing pattern for mileage or one for high altitude towing etc.

I think that a chip and 4:10 gears would really make the Chevy's power available, increase mpg, and make you a very happy tow'er

.................Scott

[SteveH]

Scott,

Yes, my transmission has a "tow/haul" mode, but it just adjusts the shift points and the down shift points....it does not eliminate operation in overdrive. I too believe the towing would be much better with 4.10's, but I'm just trying to figure if it's the best move for me as the truck is also my "daily driver", and the unloaded mileage is part of the equasion for me. At minimum, I think I'll wait and drive the rig as is on our planned trip this summer to Alaska and see how it goes. I did learn the "feel" of the down shift points in the throttle pedal on our trip last week to the Big Bend Nat. Park, a trip of about 900 miles towing. We came back on IH10, and there are lots of grades out West of San Antonio that are pretty steep, but fortunately, not too long.

[BillTex]

FWIW; we had 2 indentical Burbs, one had 3:73 the other 4:10. No difference in mpg at all. Towing was always done in TH mode and sometimes in 3rd.

Bill

[Wayward]

Originally Posted by SteveH

Yes, my transmission has a "tow/haul" mode, but it just adjusts the shift points and the down shift points....it does not eliminate operation in overdrive. .

Overdrive and torque converter lockup are two different aspects of your tranny. Overdrive is simply your top gear (usually a bit higher than 1:1, hence the name "overdrive"). Whether or not you can get practical use of OD for towing depends upon your overall gearing and engine power. The torque converter lockup feature "locks" the torque converter from slipping at highway speeds for mileage but is not recommended to use when towing. However, in some vehicles the only way to disengage the torque converter lockup is to drop down one gear, effectively eliminating one gear and forcing you into a less usable gear spread.

I do not know about your tranny's mode switch, but if it has a configuration to disengage the lock up and still run in top (OD) gear, you can make the top gear usable for towing with 4:10 or 4:30 rearend gears. Having 4 usable gears instead of 3 would greatly increase your gear spread, usable power and terrain options. You may want to call Troyer Performance they really know this stuff!

.................Scott

[SteveH]

Scott,

Yes, I'm aware of the different gears, and the torque converter lockup. My transmission goes into OD, and the torque converter locks up in Tow/Haul mode. I've watched the tachometer and it's the same in T/H, or out. It just goes higher in the gears, and down shifts quicker. While towing on grades, you can watch the tach, and see it first shift out of lockup, and then down shift to third gear. And, by the way, the TC will lockup in third gear also. As far as what's "recommended" by the GMC, I have searched the book and all they say is to tow in "Tow/Haul" mode.

[Andrew T]

Hi Steve

The 4:10 gears will slightly improve your fuel economy towing and they will fairly substantially improve performance. However you can get the same performance improvement easier just by changing the tire size.

Most new SUV's and trucks have tires that are very large on them. Not only do these tires make the gear ratio artificially tall they also have substantial rolling resistance and sidewall sway. We have change the tires on hundreds of trucks. What size does your truck have on it now?

Andy

[BillTex]

From GM owners manual;
If You Do Decide To Pull A Trailer
Notice: Pulling a fifth-wheel trailer with a vehicle
that is equipped with the SS trim package could
damage the vehicle. Do not pull a fifth-wheel trailer
with a vehicle equipped with the SS trim package.
If you do, here are some important points:
• There are many different laws, including speed limit
restrictions, having to do with trailering. Make sure
your rig will be legal, not only where you live
but also where you’ll be driving. A good source for
this information can be state or provincial police.
• Consider using a sway control. See “Hitches” later
in this section.
• Don’t tow a trailer at all during the first 500 miles
(800 km) your new vehicle is driven. Your engine,
axle or other parts could be damaged.
• Then, during the first 500 miles (800 km) that you
tow a trailer, don’t drive over 50 mph (80 km/h)
and don’t make starts at full throttle. This helps your
engine and other parts of your vehicle wear in at
the heavier loads.
• If you have an automatic transmission, you can tow
in DRIVE (D). You may want to shift the
transmission to THIRD (3) or, if necessary, a lower
gear selection if the transmission shifts too often,
such as under heavy loads and/or hilly conditions. If
you have a manual transmission and you are
towing a trailer, it’s better not to use the highest
gear. See Tow/Haul Mode Light on page 3-49.
Three important considerations have to do with weight:
• The weight of the trailer
• The weight of the trailer tongue
• The weight on your vehicle’s tires

If You Do Decide To Pull A Trailer
Notice: Pulling a fifth-wheel trailer with a vehicle
that is equipped with the SS trim package could
damage the vehicle. Do not pull a fifth-wheel trailer
with a vehicle equipped with the SS trim package.
If you do, here are some important points:
• There are many different laws, including speed limit
restrictions, having to do with trailering. Make sure
your rig will be legal, not only where you live
but also where you’ll be driving. A good source for
this information can be state or provincial police.
• Consider using a sway control. See “Hitches” later
in this section.
• Don’t tow a trailer at all during the first 500 miles
(800 km) your new vehicle is driven. Your engine,
axle or other parts could be damaged.
• Then, during the first 500 miles (800 km) that you
tow a trailer, don’t drive over 50 mph (80 km/h)
and don’t make starts at full throttle. This helps your
engine and other parts of your vehicle wear in at
the heavier loads.
• If you have an automatic transmission, you can tow
in DRIVE (D). You may want to shift the
transmission to THIRD (3) or, if necessary, a lower
gear selection if the transmission shifts too often,
such as under heavy loads and/or hilly conditions. If
you have a manual transmission and you are
towing a trailer, it’s better not to use the highest
gear. See Tow/Haul Mode Light on page 3-49.
Three important considerations have to do with weight:
• The weight of the trailer
• The weight of the trailer tongue
• The weight on your vehicle’s tires

[SteveH]

"What size does your truck have on it now?"

The tire/wheel size is 275/55R20. Yes, they are tall at 31", but I won't be changing them.

[shantz]

I have a 1997 F150 with 4.6 l engine. stock it had 3.55 gears. when I added 3 inch body lift and 35" tires I changed gears both front and rear to 4:56's.
Towing my 28' AS I am getting 9 or 10 mpg. The 4:56's with what I have are definitely worth it... However my next TV is definitely a Dodge Cummins or a Chevy Duramax. Even though these TT's were designed to be pulled by a car I find I limit my camping to mainly on mostly flat land or slight hills because of my current TV. next year game on as I will pick up teh Chevy or Dodge and go EVERYWHERE
I did all this to my truck BEFORE i had a TT and now wish I hadn't touched a thing. I did the lift and tires mostly for getting through the mud at the hunt club.
I am now waiting for teh car dealerships to get real on 3/4 ton diesel pricing before I buy the next TV

[Silvertwinkie]

Originally Posted by 69AmbassFl

You may notice an improvement on the hills but you will also notice fuel mileage decrease as you will be turning more rpms with the higher gear ratio.

This is not entirely true. I was on a caravan with my Suburban (4.10s) and a Suburban (3.73s), both filled up at the station, both towed similar weight Airstreams and both got nearly exact, if not exact MPG via the DIC and the fuel g.

In the end, moving to 4.10s will increase towability, but 3.73s are pretty darn good. You really, really, really don't want to mess with the rear end unless you have to. Most folks don't know what they are really doing and you can get wining, shuddering, etc. I would say that unless you plan many mountain tows regularly, stay with the 3.73s and if you want, upgrade your TV next time it's due and get 4.10s.

I have been pleased with my 4.10s, but having gone through the rear gear changes on my Impala from 3.08s to 3.73s, it's a lot of work. ABS reluctor, PCM re-programming, gears, seals, ABS sensors. It's not that easy with electronic cars in some ways, while in others it's easier.

**edit** I just saw you are towing a 23' vintage. I would NOT mess with it with that size and weight. You are more than fine with what you have, even if you tow in the mountains.

[shantz]

I got rambling there. The 4:10' swill not hurt your fuel economy much. Normally they recommend making a jump TWO gear ssizes as going from 3:73 to 4:10's will not feel that much power. and check around for pricing. I bought Yukon gears and checked out a bunch of local shops and I paid around $500 for gears and $1500 for install and haven't had any issues.
Pick a good shop as most dealers will not put in after market gears due to warranty