Topfuel67

I hate automatics. I really hate the 4L80e. It has a 2.48 first gear ratio. That is ancient technology. It is ridiculous that GM used this all the way into the 2000s. The 60s Muncie 4 speeds even used a 2.5 first gear. My 01 8.1L suburban tows great. But with the power of the 8.1L is a dog off the line. I blame the 2.48 first gear ratio. I have the 3.73 rear end. I have researched swapping a zf6 from the same year trucks, but think they went too far the opposite direction on that trans with a 5.79 first gear ratio and still only .72 for the o/d. I would prefer having a .6 or lower o/d to save fuel on the highway. Also I have read that the zf6 is so big it requires 2-3" of body lift on the subs. My sub is 2wd and I'd rather not lift it. I do tow with my sub. I have a 24' car hauler and a 5000 lb rv trailer. So I am wondering if any of the other transmissions out there are capable of handling this power. I've seen the tremec and other 6 speeds advertise that they can handle 700lb+ of torque which is far above the 8.1, but that's not the towing load. I am in California so I don't have to worry about smog. I don't care if I have to disconnect the trans controller. I have looked at the 6L80 and that seems like I would need to change the engine to a 07+ 6.0l which I'm not willing to do. Plus, I still hate automatics. Has anyone used any other 6 speeds to tow and how much weight?

Bgbldodge

Nv4500 or 5600 would handle the load. Don’t know what it would take though.

Topfuel67

The 4500 is another one that went too far. It is around a 5.2 ratio in its first gear basically making it a 4 speed with a granny gear. Also too big for the sub. Needs body lift. I think the 5600 is the code for the zf6. I may consider the zf6 and dropping the rear end to a 3.21, but would prefer to just put a better ratio geared 6 speed in. I have even toyed with the idea of putting a zf from the early 90s Corvette. A lot of people call that a diesel transmission that was overkill for the Corvette. It has a .5 o/d, but only a 2.68 first gear. That would help the final drive a lot, but doesn't do much for the off the line response.

Bgbldodge

Just about any truck manual transmission is going to have a granny first gear. That’s why everyone starts off in second unless they have a load and even then depending on the load folks start out in second. The 4500 has a 3.04 second so that gives you much better off the line and a .73 final which is a little better than the 4L80e. There aren’t a whole lot of options out there for what you are wanting that can handle the abuse. The nv3500 is about perfect but it’s only rated at 340ftlbs of input torque.

Topfuel67

I have the nv3500 in my 01 Silverado with a 4.8l. I really like the ratios, 4.0 in first and .68 o/d. From what I've heard on it is it can't take much abuse at all. I think that's why it's only available on the 4.8l. It never came with a 5.3 and as far as I know the 6.0s got the nv4500.

Fullpower

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....................... " All that hate's gonna burn you up, kid "
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Towing with 3.73 axle ratio is NOT ideal.

I put 4.56 gears in my Tahoe, and it made EVERYTHING better.

RDF1

What tire size and what all is done to the truck?
Thats not too crazy of a load but Im not sure of your expectations.

ive never had a complaint on towing heavy with my 2500hd with a 6.0 and 4l80. Heck I even hauled 39,000# with it 130 miles. It got 8.6mpg, it wasnt going to outrun anything but I wasn't expecting a 2000ft/lb diesel either.

Topfuel67

I just really like that 3rd pedal. As far as the 4L80e goes I just think GM really dropped the ball on using the same trans for so many years.
She actually tows just fine. I start off slow. She gets about the same gas mileage towing or not. I get 11 mpg not towing with mostly freeway driving. I towed a 5500+ lb expedition on a 1800 lb trailer plus tools, floor jack and extra parts from San Diego to LA and got 11 mpg. The majority of my towing is the rv trailer that is under 5000 lbs. She tows up steep hills doing 65 effortlessly.
She is completely factory 2wd and I run 275/75 16s. I am planning on doing the intake manifold mod and upgrading to electric fans. I'd just really like to have better gear ratios for starting and highway. Changing the rear to 4.11s won't improve towing for my needs as she already does just fine. That will just hurt my mpg. I have looked into the Allison trans and the issue with that is the same as the zf6, it is too tall for the SUVs. If I'm going to have to body lift her I might as well go with the zf6.

_zebra

iTrader: (5)

i'm in the same boat & would've bought a Escalade or Denali to stick-swap if we hadn't found our H3. they've all got the same cut-out spots for the clutch master & shifter as the pick-ups & can easily swap interior pieces to look like a factory job.

first-off, i'll clear up some misconceptions before giving my opinions on the matter:

• the ZF S6-650 and NV5600 are completely different transmissions; the former was made by ZF and was a factory offering behind the 8.1 & Duramax pickups, while the latter was made by New Venture Gear and never offered in GM trucks (because they chose the ZF over it).
• you mention the NV4500 basically being a 4spd + a granny (technically more like a 3spd + granny + overdrive [since 4sps usually ended in 1:1])... but this ZF is the same way. "first" is a deep granny (because it was designed for diesels using a high 3.42 axle ratio), so it's normally driven as 2-6 (with 5th being your direct gear, i.e., single overdrive).
• all the truck transmissions of this era have almost the same overdrive ratio (even ones with a couple application-specific gear set options throughout their runs).
  • 4L60/65 = .70
  • 4L80/85 = .75
  • Allison 1000 = .71 (2006+ added .61 double OD)
  • NV3500 = .73
  • NV4500 = .73
  • ZF S6-650 = .72
  • NV5600 = .73
• using a Corvette ZF S6-40... just NO! it was designed for a 3400lb car & would burn right up in a 1/2ton Suburban by itself, let alone trying to tow with a 2500 (just like every guy who tries a T56 in that kind of application).

as for my own thoughts: had the 2500 SUVs been offered with an Allison instead of the 4L85, it would've already had the 2" body lift (only the Allison & ZF physically needed it)... so if you were to do a lift, the factory bumpers, brackets, & filler plates to make it less obvious would be a relatively-easy swap from a pickup.

the NV3500 from your 4.8 truck could take the 8.1's power... it'd just quickly die under the loads discussed here (i added my thoughts/experiences to your other thread about that truck). to quickly address the NV5600 idea: never heard of anybody trying it, but you might could swap a NV4500 bellousing over & make it work, but no clue on comparing the hydraulics, mounting modifications, or driveshaft length needed to make it happen = proceed at your own risk after a ton of thorough study.

given the data you've provided, my recommendation would be to still do a 4.11 swap (or at least leave the 3.73s). the few hundred RPM difference in OD will be offset by better mechanical advantage (less load on the engine), so the highway mileage shouldn't change much while increasing performance (especially with the 32" tires and driving around town in the lower gears). for a towing rig, you don't want to gear the axle for a DD-able granny - that just leads to lugging around in OD & straining everything more in a 3-3.5 ton truck (now, if this was an RCSB will all that torque, i'd sing a different tune).

that said, since what you described towing above (~14k gross) wouldn't require the 26k of the ZF, i'd recommend the NV4500 (14.5k GVWR). the Suburbans & Avalanches never had the Allison or ZF, so they ran the same body height as the 1500s over the frame... which is as simple as using the GMT400 transmission case lid instead of the 01-06 version that accommodated the 2500's body lift. just make sure you also get the correct shifter for the lid (personal suggestion is forking over the cash for Core's Hurst remake - totally worth it!).

if you're worried about heat when loaded up, the NV4500 can use the same trans-cooling PTO cover extensions as the ZF & 5600, too.

_zebra

iTrader: (5)

sounds like a fun truck, so good luck with the build!