Heavy Towing questions

[thz71]

So when does the F/I came in no play? Haha

 

[Jesse82nc]

I think the C6 is more capable.

Haha, I just felt like posting a video of my other Chevy that just finished like $8k of engine work

But back to towing, pretty sure after looking at options, I will go with the 6L90E to replace my 4L60E when I do my swap in a few months.

 

[Jesse82nc]

So in thinking more about the 6L90E swap, what about the output shaft? It's a larger 1.5" 29 spline for 4wd applications I think. I have the NP246 (4x4 auto push button) transfer case I believe (27 spline?). So what is the best option there? Finding a different transfer case, or getting something custom made?

 

[Supercharged111]

Why not get the tcase with the trans? I wanna say it's a different spline count than 4L60 and 4L80.

 

[eluwak]

Most of the RV's we have been looking at would be around 7500-8000 lbs loaded with a hitch weight of between 650-800 lbs.

So 7500-8000 lbs RVs are no joke territory. Is that the brochure weight? If so they're usually on the low side of accurate. 650-800 lbs TW is not realistic for that weight range either, probably more like 900-1200 lbs, plus another 100 lbs or so for your hitch system. 12-15% TW is typical for a stable towing experience on the highway. These things tow way different than an open trailer too.

I currently tow a <6000 lbs ~32 ft travel trailer with my C2500 Suburban. I definitely feel it back there, and it's not just pulling power. We're looking to get a bigger unit in the future, but I want to do a DRW conversion for the added stability first. Having more sidewall with the bigger tires mean that you'll probably feel a little more movement than normal too.

 

[Supercharged111]

32ft is an awful lot for a bumper pull for anything. I'd be wanting a 5er at that length. That's likely the reason your truck feels the way it does.

 

[eluwak]

32ft is an awful lot for a bumper pull for anything. I'd be wanting a 5er at that length. That's likely the reason your truck feels the way it does.

it's ~32 ft LOA, with a 28 ft box. Don't get me wrong, it's pulls fine. You know it's there though.

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[column_shift]

The type of RV could affect things too, unless youre decided you might look into something like an Airstream if you don't need slideouts. For their length they are not only very light (relatively speaking) but also very stable in sidewinds, very stable weightwise (in general even in extreme maneuvers the tires will slide sideways before it tips over), and more aerodynamic than normal RV rigs. The 33 footers can come in around 7000lbs though the newer ones with heavier internal amenities get closer to 8500lbs. NOTE I don't own one I just have one on my future shopping list.

The axle ratio i'm a little hit and miss on, a 4.56 would be easier on towing and easier on the transmission, with overdrive the mpg hit isn't as much but the less transmission load would be a plus. I'd be mildly concerned about the 4L60 lifespan at stock HP's much over 7000lbs just because Chevy put 4L80's in the heaviest tow packages, an axle of 4.56 would reduce transmission stress. A combination of high engine power and heavy towing is especially hard on transmissions, for over 400hp (not a big deal in a quarter mile, becomes a big deal when youre pulling up the 7% grades with weight) i'd be pretty seriously wanting the 4L80 I would think.

NOTE I am not an expert and this is entirely based upon anecdote mining of lots of other people on lots of other boards whose brains I picked extensively for a future 10k towing Suburban where I was consistently warned off using lighter parts because lifespan will be uncertain, built or not.

I'll be spending about $10k when all said and done probably. A 4L60E with the right rebuild can easily handle over 800 lb ft of torque and can be specifically built for towing. A 6L90 would require a lot more changes, including custom shafts and custom shift linkages.

Yes but it cannot handle them at the same TIME. 800lb-ft is in drag trucks moving only themself for maybe 12 seconds at a bit. You can't ask hot rodders for advice on heavy towing, ask heavy towing guys, whose parts break at stock HP levels even sometimes despite being far heavier than hot rod parts.

I know of at least 2 guys running this setup with over 1000 lb ft of torque going through it - http://www.rpmtransmissions.com/page30.html

Both in C5 Vettes, it's the exact same transmission as the GMT400 minus the servo and bell housing. Most truck guys seem to forget that in drag racing, a lot of high HP guys use 4L60E transmissions.

And many hot rod guys seem to forget that guys have been putting heavy s___ behind their trucks for years and breaking even stock parts which is part of why every new generation of truck keeps upsizing everything. Why do you think dodges went from dana 70's to dana 80's to dana 110's? I asked many many people for every make on all the boards and finally accepted that what I originally wanted to do with 1/2 ton chassis and 12 bolt rear's and 4L60's would not last. Though I was aiming for another 2000lbs than you.

I would think that a mildly built 4L80 or even better 4L85 (stronger stock parts) would outlast even a very well built 4L60 simply for the towing reason and definately for the money. For high HP drag trucks moving only themself it's different, but design it first to tow reliably before listening to the performance guys. The 6 speed is cool but the extra money is an issue, even stock 4L85's could be put in and would outlast most built 4L60's in just a towing scenario. (though less sure about HP + weight without the buildup)


Even the venerable TH400's would break ENDLESSLY behind the 130hp Cummins 4bt's in the Chevy P30 chassis at low miles. Guys on the diesel swap forums can attest to this. The weight really does make a huge difference, it loads differently than just lots of power and lots of tire.

 

[90halfton]

Buy a diesel dually towpig and hook up whatever you want, probably save money in the long run too. Definitely save fuel pulling 8k lbs and over too.