1999 Tahoe w/ 3.42 rear end vs. 3.73?

lindeman23 · **Posted:** Thu Jun 02, 2016 2:39 pm

I bought a 1999 Tahoe last year to pull my 1999 Four Winns Sundowner. It did a great job and I have really gotten the Tahoe running great and everything working as it should. I sold the Sundowner this year and bought a bigger boat, a 2000 Four Winns Horizon 230. From looking at the manual it weighs about 6100 lbs. I see two different towing capacities on the Tahoe's owner’s manual, one is 5500 lbs w/ the 3.42 gears and the other is around 7000 (I think) w/ the 3.73 rear end. I really don't want to sell my Tahoe and as I have put a lot of money into it in the last year and it runs really good. We have one 3.5 hour trip this year down to lake Cumberland in KY. I always tow with it in 3rd not 4th and it does a decent job, slow and steady. Also I rarely go over 60 MPH with it as to keep the RPM's down. Is it going to destroy my Tahoe by using it to tow my boat for the 3.5 trip in three weeks? I also tow it to the river about 4-5 miles away from the house. Any insight would be great, I have no idea about gear ratios and the effects they have on towing. Thanks!

LouC · **Posted:** Thu Jun 02, 2016 3:24 pm

The main issue is if the torque converter has to unlock often to allow the engine to stay in its optimal rpm range. That causes heating of the trans fluid. The problem is no one can tell you when its getting too hot unless you have a trans temp gauge, or you get an IR temp gun and pull the dip stick after towing it a while and take a reading of the trans fluid manually. Does it have the factory tow package? Aux trans cooler? It may be OK, if you can install a larger than factory cooler to keep the fluid below 200*F.

RotaryRacer · **Posted:** Thu Jun 02, 2016 3:49 pm

Look up the RPO codes and then look at the sticker in the glove box to determine what packages it has and gear ratio.

http://www.sierragear.com/gm-rpo-axle-r ... n-codes-3/

lindeman23 · **Posted:** Thu Jun 02, 2016 3:53 pm

LouC wrote:

The main issue is if the torque converter has to unlock often to allow the engine to stay in its optimal rpm range. That causes heating of the trans fluid. The problem is no one can tell you when its getting too hot unless you have a trans temp gauge, or you get an IR temp gun and pull the dip stick after towing it a while and take a reading of the trans fluid manually. Does it have the factory tow package? Aux trans cooler? It may be OK, if you can install a larger than factory cooler to keep the fluid below 200*F.

It does have the factory tow package and I'm sure as part of that it has the trans cooler. But I guess my biggest question is regarding the gear ratio in the rear end, how does that determine the towing capacity. If the ratio that I have causes the RPM's to be higher, wouldn't I be ok just driving slower? Thanks!

GottWhat · **Posted:** Thu Jun 02, 2016 4:03 pm

lindeman23 wrote:

LouC wrote:

The main issue is if the torque converter has to unlock often to allow the engine to stay in its optimal rpm range. That causes heating of the trans fluid. The problem is no one can tell you when its getting too hot unless you have a trans temp gauge, or you get an IR temp gun and pull the dip stick after towing it a while and take a reading of the trans fluid manually. Does it have the factory tow package? Aux trans cooler? It may be OK, if you can install a larger than factory cooler to keep the fluid below 200*F.

It does have the factory tow package and I'm sure as part of that it has the trans cooler. But I guess my biggest question is regarding the gear ratio in the rear end, how does that determine the towing capacity. If the ratio that I have causes the RPM's to be higher, wouldn't I be ok just driving slower? Thanks!

The gearing you have (3.42) actually makes the RPM's LOWER than 3.73 gears.

Vintage Beauty · **Posted:** Fri Jun 03, 2016 6:37 am

I have a 2011 suburban. When we shopped for it there were a couple of original build options to sort through. Look up the actual build codes on your Tahoe to be sure.
In my case, the standard suburbans came with a "tow package" that included a hitch and trailer wiring. That standard had the 3.73 axle and no trans cooler. I believe capacity was around 5K lbs. We found a truck with a "true" towing package- 3.43 rear axle ratio and trans cooler. Capacity on that is in the neighborhood of 8000 lbs. The onboard computer also shows trans temp.

You can add a trans cooler if you don't have one, but changing the axle ratio isn't a simple aftermarket add.
Also, keep in mind:
1. Your boat weight is probably a dry weight- not including any fuel, water, or gear weight
2. True towing capacity is a dynamic number. You should subtract the weight of any gear and passengers in the truck itself.
3. Top end capacity usually includes a weight distributing hitch set-up. The manual should show a capacity with and without the weight distributing hitch.

RotaryRacer · **Posted:** Fri Jun 03, 2016 7:21 am

Vintage Beauty wrote:

I have a 2011 suburban. That standard had the 3.73 axle and no trans cooler. I believe capacity was around 5K lbs. We found a truck with a "true" towing package- 3.43 rear axle ratio and trans cooler. Capacity on that is in the neighborhood of 8000 lbs.

On the newer GM SUVs like your 2011 (I also have a 2011) have a 6 speed trans.

The "standard" gear ratio is 3.08. The K5L package (heavy duty towing) gives you the trans cooler, etc and also gives you the 3.42 gear ratio.

On the older GM trucks and SUVs you had either a 3.42 or 3.73 or in some cases a 4.10 to choose from.

The HIGHER numerical number is better for towing. It gets the RPMs up a bit and keeps the engine in the powerband. ALSO it helps create more torque at the wheels for accelerating.

Vintage Beauty · **Posted:** Fri Jun 03, 2016 9:48 am

RotaryRacer wrote:

Vintage Beauty wrote:

I have a 2011 suburban. That standard had the 3.73 axle and no trans cooler. I believe capacity was around 5K lbs. We found a truck with a "true" towing package- 3.43 rear axle ratio and trans cooler. Capacity on that is in the neighborhood of 8000 lbs.

On the newer GM SUVs like your 2011 (I also have a 2011) have a 6 speed trans.

The "standard" gear ratio is 3.08. The K5L package (heavy duty towing) gives you the trans cooler, etc and also gives you the 3.42 gear ratio.

On the older GM trucks and SUVs you had either a 3.42 or 3.73 or in some cases a 4.10 to choose from.

The HIGHER numerical number is better for towing. It gets the RPMs up a bit and keeps the engine in the powerband. ALSO it helps create more torque at the wheels for accelerating.

You are correct! I had my numbers mixed up.
I do remember having to explain to many dealers that I wanted the K5L. All the sales guys would tell me it had a towing package... No, please review the build sheet and tell me if it has the K5L code or not!

GottWhat · **Posted:** Fri Jun 03, 2016 10:29 am

Gearing makes a huge difference. The tow rating on our 2011 Silverado 5.3 4x4 with HD towing, 3.42 gears and 6-speed transmission is about 1500 lbs superior to our 2016 Ram Hemi 4x4 with 3.08 gears and 8-speed trans even though the Hemi has a LOT more power. The trans cooler with the HD towing package on the Silverado works really well too - trans temps are significantly cooler on the Silverado.

lindeman23 · **Posted:** Fri Jun 03, 2016 2:40 pm

RotaryRacer wrote:

Look up the RPO codes and then look at the sticker in the glove box to determine what packages it has and gear ratio.

http://www.sierragear.com/gm-rpo-axle-r ... n-codes-3/

I had to replace the front differential so I am 100% certain it is the 3.42. Also it has the factory hitch on the back b/c I can see the factory sticker.

RotaryRacer wrote:

Vintage Beauty wrote:

I have a 2011 suburban. That standard had the 3.73 axle and no trans cooler. I believe capacity was around 5K lbs. We found a truck with a "true" towing package- 3.43 rear axle ratio and trans cooler. Capacity on that is in the neighborhood of 8000 lbs.

On the newer GM SUVs like your 2011 (I also have a 2011) have a 6 speed trans.

The "standard" gear ratio is 3.08. The K5L package (heavy duty towing) gives you the trans cooler, etc and also gives you the 3.42 gear ratio.

On the older GM trucks and SUVs you had either a 3.42 or 3.73 or in some cases a 4.10 to choose from.

The HIGHER numerical number is better for towing. It gets the RPMs up a bit and keeps the engine in the powerband. ALSO it helps create more torque at the wheels for accelerating.

With mine since it has the lower of the two gear ratios, 3.42 vs. 3.73 I should be ok to tow it a couple hours to the lake? I just don't understand why the huge different in maximum towing capacity with different ratios.

rpengr · **Posted:** Fri Jun 03, 2016 3:21 pm

lindeman23 wrote:

With mine since it has the lower of the two gear ratios, 3.42 vs. 3.73 I should be ok to tow it a couple hours to the lake? I just don't understand why the huge different in maximum towing capacity with different ratios.

True, it's only a 9% difference in gear ratio. As others have pointed out, there may be another difference besides the gear ratio. The 3.42 may not have the transmission cooler (which is easy to add aftermarket). And I don't know if there were different options in the trucks brakes.

I think you are fine with your "60mph or under in D3 gear" plan. You may be OK using D4 sometimes, but as LouC said, you don't want to use D4 if the torque converter won't stay "locked up" most of the time. Sometimes more speed will actually encourage it to lock up. Otherwise stick with D3.

Ray

lindeman23 · **Posted:** Fri Jun 03, 2016 3:27 pm

rpengr wrote:

lindeman23 wrote:

With mine since it has the lower of the two gear ratios, 3.42 vs. 3.73 I should be ok to tow it a couple hours to the lake? I just don't understand why the huge different in maximum towing capacity with different ratios.

True, it's only a 9% difference in gear ratio. As others have pointed out, there may be another difference besides the gear ratio. The 3.42 may not have the transmission cooler (which is easy to add aftermarket). And I don't know if there were different options in the trucks brakes.

I think you are fine with your "60mph or under in D3 gear" plan. You may be OK using D4 sometimes, but as LouC said, you don't want to use D4 if the torque converter won't stay "locked up" most of the time. Sometimes more speed will actually encourage it to lock up. Otherwise stick with D3.

Ray

Thanks Ray, that is my plan. D3 and just try to stick with the 60 ish MPH. The Tahoe is really a trooper, it might not be the nicest thing but for 210k its really pulls the boat well.

Vintage Beauty · **Posted:** Fri Jun 03, 2016 3:28 pm

lindeman23 wrote:

I bought a 1999 Tahoe last year to pull my 1999 Four Winns Sundowner. It did a great job and I have really gotten the Tahoe running great and everything working as it should. I sold the Sundowner this year and bought a bigger boat, a 2000 Four Winns Horizon 230. From looking at the manual it weighs about 6100 lbs. I see two different towing capacities on the Tahoe's owner’s manual, one is 5500 lbs w/ the 3.42 gears and the other is around 7000 (I think) w/ the 3.73 rear end. I really don't want to sell my Tahoe and as I have put a lot of money into it in the last year and it runs really good. We have one 3.5 hour trip this year down to lake Cumberland in KY. I always tow with it in 3rd not 4th and it does a decent job, slow and steady. Also I rarely go over 60 MPH with it as to keep the RPM's down. Is it going to destroy my Tahoe by using it to tow my boat for the 3.5 trip in three weeks? I also tow it to the river about 4-5 miles away from the house. Any insight would be great, I have no idea about gear ratios and the effects they have on towing. Thanks!

6100 lbs sounds high... I couldn't find the specs on the Four Winns site for the 230, but the 240 maxes out at 4060 lbs (boat and engine) with a trailer weight of 1180 lbs. Total of 5240 lbs without fuel. A full tank of fuel (65 gal) adds around 420 lbs, but you could probably plan to keep that at a minimum before your trip.
http://www.fourwinns.com/upload/Documents/OwnersManuals/2000/205-245Sundowner.pdf

Food for thought.

lindeman23 · **Posted:** Fri Jun 03, 2016 3:40 pm

Vintage Beauty wrote:

lindeman23 wrote:

I bought a 1999 Tahoe last year to pull my 1999 Four Winns Sundowner. It did a great job and I have really gotten the Tahoe running great and everything working as it should. I sold the Sundowner this year and bought a bigger boat, a 2000 Four Winns Horizon 230. From looking at the manual it weighs about 6100 lbs. I see two different towing capacities on the Tahoe's owner’s manual, one is 5500 lbs w/ the 3.42 gears and the other is around 7000 (I think) w/ the 3.73 rear end. I really don't want to sell my Tahoe and as I have put a lot of money into it in the last year and it runs really good. We have one 3.5 hour trip this year down to lake Cumberland in KY. I always tow with it in 3rd not 4th and it does a decent job, slow and steady. Also I rarely go over 60 MPH with it as to keep the RPM's down. Is it going to destroy my Tahoe by using it to tow my boat for the 3.5 trip in three weeks? I also tow it to the river about 4-5 miles away from the house. Any insight would be great, I have no idea about gear ratios and the effects they have on towing. Thanks!

6100 lbs sounds high... I couldn't find the specs on the Four Winns site for the 230, but the 240 maxes out at 4060 lbs (boat and engine) with a trailer weight of 1180 lbs. Total of 5240 lbs without fuel. A full tank of fuel (65 gal) adds around 420 lbs, but you could probably plan to keep that at a minimum before your trip.
http://www.fourwinns.com/upload/Documents/OwnersManuals/2000/205-245Sundowner.pdf

Food for thought.

This is what I used to determine the weight. 5.7 GSI/DP 4190 Boat/engine + 1054 trailer. But thank you, I stand corrected, I was looking at pg. 32 4190 for the boat and 1910 for the trailer, but the trailer is only 1054. Still pretty heavy at 5244 lbs.

http://www.fourwinns.com/upload/Documents/Catalogs/2000/FastFacts_2000.pdf

GottWhat · **Posted:** Fri Jun 03, 2016 3:44 pm

Vintage Beauty wrote:

6100 lbs sounds high... I couldn't find the specs on the Four Winns site for the 230, but the 240 maxes out at 4060 lbs (boat and engine) with a trailer weight of 1180 lbs. Total of 5240 lbs without fuel. A full tank of fuel (65 gal) adds around 420 lbs, but you could probably plan to keep that at a minimum before your trip.
http://www.fourwinns.com/upload/Documents/OwnersManuals/2000/205-245Sundowner.pdf

Food for thought.

The fast facts for 2000 indicate a 230 with a 5.7GSi/SX weighs 4170 lbs (add 20lbs for DP). Add 60 lbs for batteries, 390 lbs for fuel, 150 for accessories and 1054 lbs for trailer weight and you are at 5824 lbs (+20 for DP). Throw in some coolers will with ice, food and beverages and you are pushing over 6,000 lbs...

www.iFourWinns.com

1999 Tahoe w/ 3.42 rear end vs. 3.73?

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