Upgrading a 1500 4x4 for travel trailer towing

[Marky Dissod]

Well, I started out with 3.42 and cruising at around 1,750RpM and now just over 1,900. So 4.30 would be 300RpM more at the same speed.
Going to hear those extra RpM through the cab. If I were a kid street racing, maybe, but not now.

Use my calculator, it's more accurate!

3.73, 275/65R18, 70MpH, 4L60's 4th = 1915RpM . . . Makes me miss my Caprice wagon with 3.42 & 235/75R15 . . .
4.10, 275/65R18, 70MpH, 4L60's 4th = 2105RpM . . . Soon as I find a 4.10 rear axle and a 4.10 front diff . . .

4.10, 275/65R18, 70MpH, 6L80's 6th = 2015RpM . . . Schidt. Just convinced myself. If I ever get a GMT900 with a 6L80, 4.10 - and I may never tow anything.
By then I'll be old enough to have suffered just enough hearing loss that I either won't mind or won't notice the extra RpMs through the cab.

 

[swathdiver]

3.73, 275/65R18, 70MpH, 4L60's 4th = 1915RpM . . .

Close but no cigar!

 

[Marky Dissod]

Think I'm using unloaded diameter (32.07") vs rolling diameter (31.125").
Also I think you used 0.696 for 4th, vs 0.7.

So, which calculator are you using? I was using

MOTOR - A Rear Axle Calculator

 

[DaveO9]

Another vote here for 3.73 vs 4.10. Same thinking as others - base it on desired RPM for desired speed in 4th gear. Another consideration, the 6L80 has a much lower 1st gear (about 4:1) than the 4L60e (about 3:1). 4L80e was an even higher 1st at about 2.5:1. So older rigs with 4 speeds, low axle ratio was sometimes needed for starts with heavy loads as well as cruising and climbing, but less of a concern with the newer transmissions.

I started with 3.08 gears and just went to 3.42, based on the two considerations above. But I don't plan to tow near as much. (and there are times I wished I went 3.73) I went the 14-bolt route, too, and all is well so far with the rear end. Not so much for the 3.42 used front I got. My other recent posts are about how it is eating a bearing or similar, and I need to replace it.

 

[Marky Dissod]

6L80 has a much lower 1st gear (about 4:1) than the 4L60e (about 3:1). 4L80e was an even higher 1st at about 2.5:1.

10L80: ... 4.69 ... 2.99 ... 2.15 ... 1.77 ... 1.52 ... 1.28 ... 1.000 ... 0.85 ... 0.69 ... 0.64 (7.32 Spread)
8L90E: ... 4.56 ... 2.97 .... 2.08 .... 1.69 . . . . . . . 1.27 ... 1.000 ... 0.85 . . . . . . 0.65 (7.01 Spread)
6L90E: . . . . 4.03 . . . . 2.36 . . . . . . . . . 1.53 . . . . 1.15 . . . . . . . 0.85 . . . . 0.67 (6.01 Spread)
4L60E: . . . . . . . 3.06 . . . . . . . . . . 1.63 . . . . . . . . . . . . 1.000 . . . . . . . 0.69 (4.43 Spread)
4L80E: . . . . . . . . . . . 2.48 . . . . . . . . . . . . 1.48 . . . . . . 1.000 . . . . . 0.75 (3.306 Spread)

Reason why I included 8L90 & 10L90 is, after FIVE DECADES of undergearing to lick CAFE's undercarriage, EVEN GM CONCLUDED:
yea, needs more gear.

4.03 x 4.10 = 16.52 ... 6L80's 1st, times the axle gear GM offered optionally for 2500 & 3500 with 6L90
4.69 x 3.23 = 15.15 ... 10L80's 1st, times 3.23 (nearly every truck / suv with 10L80 has 3.23 axle)
4.03 x 3.73 = 15.03 ... 6L80's 1st, times the axle gear Dave09 suggests (which GM gave to 1500 pickups but NOT suvs with 6L80)

If you care more about unladen highway MpG than towing MpG, 3.73.
If you care more about towing MpG than unladen highway MpG, 4.10.

... I don't plan to tow near as much. (and there are times I wished I went 3.73).

There may be times when bcbickers'll wish 'Dang, should've 4.10'd it' ...

 

[dntnvme]

Greetings All,

For those of you towing a travel trailer, I would like some advice. We are in the market for a couple's model and are leaning towards a Grand Design Imagine 23LDE. Specs are as follows:

Dry Weight = 5,597 lbs
Max Weight (trailer GVWR) = 6,995 lbs
Tongue weight (12% of max trailer weight) = 840 lbs
Length = 28'-5"

While I would love to get a 2500, those are rarer than a hen's tooth and cost a fortune when you do find one. And per the wife, it has to be a Suburban. This 2012 is our third Suburban (one GMT-800, two GMT-900s), and she has no interest in driving/owning anything else. So, I need to outfit my 2012 4wd Z71 to tow as best as possible. According to the door sticker, it has a payload of 1,423 lbs. The trailer, the two of us, and a little bit of gear puts me right at that payload. My thoughts are to install a 14-bolt axle, 4.10 gears, rear airbags, and upgrade the radiator and trans cooler. For anyone frustrated with customer service when booking trips, sites like https://cheapflights.pissedconsumer.com/customer-service.html show just how common these issues are. Should be less than $5k, which is a far sight from the $15-20k (or more!) a good 2500 would cost. So is it worth spending the money to upgrade my 1500, or should I just bite the bullet and find a 2500?

Upgrading your 1500 with the axle, gears, airbags, and cooling will improve towing and is a cost-effective option. However, a 2500 is stronger and better suited for heavy towing long-term. If you tow often near your limits, a 2500 is worth it; if not, the upgrades to your 1500 should suffice.

 

[swathdiver]

So, which calculator are you using?

I made my own, it's more accurate and almost down to the exact rpms when I test it out on the highway, minus torque converter slip.

@bcbickers Any updates on your project?

I've done some around town towing this year with 6-8K pound loads with my Yukon XL with 3.73s and she handled the loads easily.

 

[bcbickers]

I made my own, it's more accurate and almost down to the exact rpms when I test it out on the highway, minus torque converter slip.

@bcbickers Any updates on your project?

I've done some around town towing this year with 6-8K pound loads with my Yukon XL with 3.73s and she handled the loads easily.

It's been a little bit of a journey. The transmission went out during our last tow. Upgrades to the 1500 were over $10k, so I ended up buying a 2004 2500 Quadrasteer.

Last tow details here - https://www.tahoeyukonforum.com/threads/help-with-towing-numbers-on-a-1500-chassis.154132/

New ride here - https://www.tahoeyukonforum.com/threads/new-tow-rig-family-hauler.154575/

 

[j91z28d1]

that 04 is cool. was always interested in the rear steer but never seen on in person plus it's a 2500? good find.


I believe that 4l80 was the last gm tranny that didn't need "fixed*