Is it worth regearing my tow rig?

[SnowSTi]

I recently bought a new travel trailer and a used truck to use as the tow vehicle. When I bought the truck I was told it had a 3.73 rear diff... anyhow after some investigation it has the 3.42. That drops the tow capacity down to 6700lbs from 7700lbs which is cutting it close for my rig ( Here are the details )

2008 GMC Sierra 1500 Crew Cab Shortbed
5.3L / 4L60e / 3.42 diff / 2WD / G80 locker
Trailer package
Heavy Duty rear suspension
Upgraded Transcooler to 24,000 GVWR (Hayden 678)

Jayco 267BHS
5690Lbs dry / 6200Lbs loaded
Equalizer WDH

The truck tows the trailer well in 3rd gear on the highway at 2400 - 2500rpm. Never downshifts unless it's a very steep hill. Acceleration is slow but acceptable. Transmission temps hover between 70C - 80C while towing during the summer.

I've done some smaller 2-3 hour trips already with the rig and it will cruise along quite happily on the highway. However I've got a longer 4000km trip later this year which has me thinking a bit.

Would going to a 4.10 from the 3.42 be worthwhile? It would move my cruise rpm up to 3000 in 3rd which seems unnecessarily high, but I assume would make accelerating a bit better.

It would cost me about $1000 to get the rear diff swapped, plus I would then need to get a programmer to correct the speed/transmission shift points.

The rig in question

[blt2ski]

A 4l60 can be built up with larger diam cooling holes inside trans. Also you can get heavier duty clutches. Now one is talking $1000 for rear end work, another $2000-3000 for a better built trans......
Not saying it is not worth it! But, one does or should question the "Is it worth it?"
At the end of the day, only OP can answer if it is worth it! Vs going with a need version.

Marty

[Grit_dog]

Blt2ski and your mech are right. Stuffing 4.88s in a 10 bolt (if they even make that low of gears for them) and running in OD towing heavy with a 4l60 are both not so great ideas.
Besides, all you'd be doing is gaining more low speed grunt. Which is good, but you're not racing or doing anything extreme with an older 1/2 ton and a big trailer anyway.
Don't be too fixated on rpms. LS engines spin up fine. You could run in 2nd gear all day down the highway if you wanted to, barring the screaming engine.

[danrclem]

In your original post you stated that it is acceptable as it is. If it's acceptable then why change it or maybe go to 3:73 gears for just a little bit more take off power.

[dodge_guy]

ib516 wrote:

dodge guy wrote:
If you have 3.42 then going to 4.10 will allow you to tow in OD. Best thing I’ve done. I’ve even heard of people going to 4.20 4.30 ratios. I went from 3.73 to 4.30. Best thing I have done. It let me use OD when towing.

The OD clutches in a 4L60E are tiny. I wouldn't suggest putting that load on them.

With the proper ratio the load would’ve less. So it would actually be easier in the clutches.

[ib516]

dodge guy wrote:
If you have 3.42 then going to 4.10 will allow you to tow in OD. Best thing I’ve done. I’ve even heard of people going to 4.20 4.30 ratios. I went from 3.73 to 4.30. Best thing I have done. It let me use OD when towing.

The OD clutches in a 4L60E are tiny. I wouldn't suggest putting that load on them.

[Skidus1]

I know it’s kind of apples to oranges. I bought a 1987 Chevy 3/4 ton first year tbi then wanted to pull with it and found out it had 3.42, I upgraded to 4.10 and it made a world of difference. Now with the new transmissions it might work well for you for me no. If you are keeping the truck for a while I would do it. Way too high to do proper towing but these new transmissions alter that. Chevy/Gm had the 2.73
/3.08/3.42/3.73/4.10/4.56/4.56/5.13/5.88 If keeping regrear.

[mountainkowboy]

BenK wrote:
Not a complete comparison...

Like folks who compare a racer/dragster/etc vs towing with the same ICE, diff, etc is out of context

The hours at high throttle at +60MPH and heavy loads...going up inclines has a much higher duty requirement than racing and 4x4'ing out there.

I've pulled 4x4's out that twisted axle splines and/or broken axles...so much depends...

You can break anything if you try, and I know rigs that have over 50K on them...just crawling, and NOTHING puts more stress on a drivetrain than racing. Ask any racer

[BenK]

Not a complete comparison...

Like folks who compare a racer/dragster/etc vs towing with the same ICE, diff, etc is out of context

The hours at high throttle at +60MPH and heavy loads...going up inclines has a much higher duty requirement than racing and 4x4'ing out there.

I've pulled 4x4's out that twisted axle splines and/or broken axles...so much depends...

[mountainkowboy]

blt2ski wrote:
Not to be a buster on this idea.......Depending upon the gear ring size, going lower than a 4.10 to 4.56 or even a 4.88, may put the teeth too small. So yes, you get use of OD towing. BUT, if you stomp on the go pedal in 1st gear, you may break the R&P teeth! If you have an 8.5" or smaller setup. I would not go smaller than a 4.10. If you have at least a 9.5, then a 4.56 may be the largest you want to go. I really doubt you have one of the 10.5 or larger ring gear setups with a 1500, those, into the 5.xx would be doable.
Also going lower, you may need to change out the axel shaft itself, as the current setup may not handle lower gear sets too! A new 9.5 or larger RP from a 2500 may be in order. Now you have to change out the 8 lug to a 6......any way, I'm going to quit typing, as some of this may be an issue, or it may not!

Just throwing another monkey wrench or 2 or 3 into the thought pattern here!

Marty

I don't think that it would be an issue really. In the offroad world a Dana 44 can take 35" tires and a crawl ratio of over 100:1 and not break teeth...being stomped on to climb something all the time. That's WAY more torque than a street driven truck towing, and the D44 is a lighter axle than a half ton has.

[BenK]

Oh...most all GM full sized half ton trucks has the 9.5" ring gear...4.1's would just make it with that trailer

8.5's would be pushing it and would likely fail sooner than later

You have found a GREAT, honest and truthful mechanic

[4x4ord]

For a 6200 lb trailer I would want 3.42 gears.

[SnowSTi]

blt2ski wrote:
Not to be a buster on this idea.......Depending upon the gear ring size, going lower than a 4.10 to 4.56 or even a 4.88, may put the teeth too small. So yes, you get use of OD towing. BUT, if you stomp on the go pedal in 1st gear, you may break the R&P teeth! If you have an 8.5" or smaller setup. I would not go smaller than a 4.10. If you have at least a 9.5, then a 4.56 may be the largest you want to go. I really doubt you have one of the 10.5 or larger ring gear setups with a 1500, those, into the 5.xx would be doable.
Also going lower, you may need to change out the axel shaft itself, as the current setup may not handle lower gear sets too! A new 9.5 or larger RP from a 2500 may be in order. Now you have to change out the 8 lug to a 6......any way, I'm going to quit typing, as some of this may be an issue, or it may not!

Just throwing another monkey wrench or 2 or 3 into the thought pattern here!

Marty

The truck has the GM 8.6" 10 bolt diff which I guess makes this a bit of a weak point.

This is very similar to what the shop told me when I called them this morning. They strongly recommended against it due to durability and heat. He mentioned that the 4L60e shouldn't tow in OD even with a very low ratio as the clutches are weak in OD.

They would do the work, but the owner told me he wouldn't do it if it were his truck. He also tows frequently and his advice was just to leave it alone for now, and if I run out of towing capacity in the future it would make more sense to upgrade the truck to a 3/4 ton over doing the diff.

Seems odd to turn away work so I guess he's being honest.

[BenK]

Agree with Kevin and Marty...but gotta take these 'system' things in context...as Kevin points out...

Also, a good mechanic 'should' discuss this with their customer

Half ton's weigh less than higher class TV's, so less mass to move (yes, know their MTWR's are way up there, but the OEMs play that King of the Hill marketing game by deriving that MTWR using a stripper model, most use a 10% tongue, etc, etc)

Lots of stuff that comes with the higher class TV...like bigger frame (sheetmetal gauge, box sections, cross members, etc), bigger suspension (components, sub-systems, brakes, higher class tires, etc, etc), bigger power train, software that manages those bigger stuff, etc, etc

Then the final component in this food chain down to pavement...tire traction. Street tires (even higher class LT) has better traction on pavement than AT/off-road/mudder/etc...so that makes a huge difference on this topic.

Since the OP has a middle level half ton (not the fake half ton with higher rated RGAWR) and their trailer isn't too big...going 4.1's should be doable...but...dependent on how they drive and where they drive...IMHO

[dodge_guy]

blt2ski wrote:
Not to be a buster on this idea.......Depending upon the gear ring size, going lower than a 4.10 to 4.56 or even a 4.88, may put the teeth too small. So yes, you get use of OD towing. BUT, if you stomp on the go pedal in 1st gear, you may break the R&P teeth! If you have an 8.5" or smaller setup. I would not go smaller than a 4.10. If you have at least a 9.5, then a 4.56 may be the largest you want to go. I really doubt you have one of the 10.5 or larger ring gear setups with a 1500, those, into the 5.xx would be doable.
Also going lower, you may need to change out the axel shaft itself, as the current setup may not handle lower gear sets too! A new 9.5 or larger RP from a 2500 may be in order. Now you have to change out the 8 lug to a 6......any way, I'm going to quit typing, as some of this may be an issue, or it may not!

Just throwing another monkey wrench or 2 or 3 into the thought pattern here!

Marty

Good point! Especially on a 1/2 ton axle. I have heard of the pinion shearing teeth, but it isn’t common. Also when going that low it would be wise to upgrade to a finned aluminum cover for cooling.