Question on changing legal GCWR

[gmcman]

While looking for an 8.1 Burb, I come across some 3:73 models which have a factory GCWR of 16K. Since the only change to the GCWR of 19K with the 4:10 models was the gears, has anyone changed the gears to increase the legal GCWR? By doing this also with documentation changing the legal GCWR?

The GVWR is the same 8600 LBS with both axle ratios, only the GCWR changes.

I understand most agencies won't pay much attention to more than the tow vehicle GVWR, trailer GVWR, and tire ratings.

I'm only looking to maybe change the legal GCWR if it came down to this.

If anyone has gone through this successfully, please share your thoughts and experience.

Thanks.

[Grit_dog]

Or what Marty is saying in layman’s terms is your biggest limiting factor may be pulling your boat out of the hole, up a ramp. But you can do that calculation. However if you get a 4wd that point is moot.
That said you are worrying mostly about other things that matter to a lesser extent or not at all. Those things:
Cops, insurance, accident and gcvw bust. Not a real concern.
Lowering rpms for empty driving? Unless you want to cruise at 85-100mph, it ain’t gonna make any difference practically and very little in mileage. Never even get close to the expense of re gearing. But you’re looking at the higher geared ones anyway.
Your biggest issue is getting a 12k load rolling and that’s not an issue except on steep uphills.
No matter what gears you get, an old 4 speed trans with a high (comparatively) 1st gear ratio and only 2 more useable gears for towing is basically out classed by the trailer you want to tow if your looking for good (by today’s standards) performance.

ALL that aside, a 4x4 8.1 Burb, with 3.73s will get the job done.
And if I was only towing super short distances as you are and mostly daily driver, I would not worry about it. They’re nice rigs if you find a good one.
But I’d be hard pressed to pay a premium for any sort of tow rig that only has 3 or 4 effective gears. Too many other, better, options for towing.

[blt2ski]

Another to look and think about. Is actual gradability of your truck. A rig with 400 lb ft of torque, a 16-1 over all low ratio with stock 30.5" tires has a max starting ability of 15-17% at 20k lbs. Make the overall low 24-1, you can now pull a 30% grade. That's the difference in one of my trucks with the 14500 gcwr auto, lower ability. Vs the 12500 gcwr with a 5 sp manual, believe it or not, better performer. Back in 90s, GM lowered the gcwr by 2000 lbs with the nv4500, Dodge on the other hand, increased gcwr with the nv4500. Reality from a performance standpoint, the NV4500, kicked both auto transmissions ability's.
If you boat ramp is in the 15-20% tell like a few I know of here in puget sound region, having lower gears all around for slow speed stuffed good. With 4wd, you do have 4lo which can save you bacon, vs numbers I quoted in rwd/4hi. For youruseage, I can see how a 3.73 change out to 4.33/4.56 would be better than a 4.10. as you appear to be doing local stuff, vs over the road stuff like Don did, others on here.
Marty

[wilber1]

GCWR is a power train limitation as others have said. If you stay within it the truck shouldn't break down before the warranty is up. Going from 3:55 to 4:10 in my 2001 Dodge CTD increased the tow rating and GCWR by 2000 lbs. The auto transmission was the limiting factor. Manual transmission trucks had the same rating regardless of gear ratio. Of course that did nothing to change the truck GVWR which is a legal limit where I live.

[gmcman]

@BurbMan

BenK wrote:


Agree with Burbman about going to a GearVendors OD. It replaces the tranny tail housing and no driveshaft changes needed. Ditto if 4x4. GV

Thanks for the replies, sorry to reply so late, I'll try to touch on everything.

I did reach out to GV and they said there was no option for a 8.1 Burb with 4WD, only 2WD....but that option would be great with the 4:10.


My plan was for weights around 11-12K, it would be a boat. The haul would be short, less than 20 miles.

To correct my error in GCWR, it is 17K (not 16K) & 19K for the 3:73 & 4:10 respectively.

I guess my initial worry was if there was an accident, and I had the factory 3:73 gears and was towing 11K and still within the GAWR of both the TV and trailer, would I possibly be denied insurance coverage if they ran my VIN and saw the 17K GVWR.

So it seems that isn't really the case as it comes down more to GAWR, tire and wheel rating, and trailer rating with trailer tire and wheel rating.

I would prefer to find a 4:10 Burb and add the GV for unloaded highway travel if that option was possible. I guess the 3:73 would be fine for short trips.

I've found a few 8.1 Burbs but some of the prices have been crazy high. Been alot of flipping recently by a few outfits but hey, free enterprise.

I don't mind the logistics involved with locating one, as long as the body and undercarriage is good.

[Grit_dog]

OP, there’s nothing “legal” involved.
Regardless of what the sheeple think...

But absolutely, a lower gear ratio will help with towing.

[blt2ski]

Another to consider about gears. If you go from a stock 30.5" tire, to next generally speaking diam of 31.5 or 32.5" diam tire. Your 4.10 gear setup just went to an effective 3.95 or 3.73. So if you go to a say 285-75-16 @ 32.5", you would need to go to a 4.33 or there about to keep your effective ratio at 4.10....

More to this than tow rating per a gear ratio chart like Ben is showing. Tire diameter also needs to be taken I to account, along with what that bigger diam tire weighs, taking HP away from getting to the ground turning said bigger heavier diam tire....

Marty

[BenK]

The charts from GM has the GCWR change with only diff ratio...also their MTWR also increase with higher numeric diff ratios

Here is a RAM 2017 half ton ratings chart...all OEM's used to have these that shows or compares the GCCWR & MTWR vs diff ratio




For some,depending on the diff carrier, going from 3.73 to 4.55/4.88 might require a carrier change. The diff pumpkin remains the same.

That would also mean changing the G80 locker, if you have one. I'd go with a Detroit locker with no clutches.

Agree with Burbman about going to a GearVendors OD. It replaces the tranny tail housing and no driveshaft changes needed. Ditto if 4x4. GV has a 'splitter' option that will automatically shift in between each 4L80/4L80E gear. Turning a 4 speed automatic into an 8 speed automatic. Still noodling whether a GV 0.5 or 0.75 OD. Think an 0.5 is too close to the HP required to cruise at 65MPH and it might hunt...so leaning towards 0.75

Also, check your wheels to make sure they are +3,000 lb rated. Mine are 16x10 (bead to bead) rated 3,200 lbs. Get concentric if you can, otherwise they will be lug-centric. Both okay...just that concentric is better of the two.

That is in my list of things to do to my GMT400, 1996 K3500 Suburban.

Yes, still an older 'truck', but that is a personal choice thing.

[blt2ski]

BUT the springs are at 6400. If going with lower of ratings....keep this in mind too.

As far a axle ratios. If like me, more off the beaten path, lower gears are better. If you stay on main roads like the interstates, you can pull just fine the same load as a rig with lower gears.

Hence my I would prefer 4.33s in a previous post vs don saying 4.10s. personal choice for how he pulls etc vs me.

Marty

[BurbMan]

The RAWR on the GMT-800 2500 burb is 6084, exactly twice the 3042 rating of a factory 245/75-16E tire. The burbs got the same 14-bolt full floater as the HD trucks with 10.5" ring gear (3500's had 11.0"), which is said to be good for 10k lbs depending on what you read.

Factory wheels are 16x6.5 which limits tire choices, if you upgrade to 16x8 you have lots of tire choices to effectively increase your RAWR rating.

[mkirsch]

You put the gears in, and your GCWR is "legally changed." No paperwork involved.

As long as your Suburban and travel trailer are properly registered based on what your state laws say, there is nothing else you need to do.

In some states the Suburban can be registered as a passenger vehicle. Otherwise it is registered as a commercial vehicle based on expected gross weight of the vehicle itself. That can be the GVWR, or something less than the GVWR if you never expect to be loaded to the gills, or something more than the GVWR (such as the sum of front and rear GAWRs). You don't HAVE to register at any specific weight, because you will probably never get weighed. If things change you can always claim ignorance and get off of any ticket by upgrading to the proper registration.

Trailers are also registered by weight. Usually the RV dealer will fill out the form at the trailer's GVWR, but again, it doesn't HAVE to be the GVWR. At least not in any state that I'm aware of.

[BurbMan]

Yes the GCWR jumps from 16k to 19k because the tow rating jumps from 10,500 to 12,000 with the 4.10's. I wouldn't go higher than 4.10's because with the 4L80E 4-speed transmission you'll be screaming at highway speeds. IIRC, the next step after 4.10 is 4.56, I think the 4.30's is a Ford gear. Also anything higher requires a new housing I'm told, so between that and the GV overdrive you'd need to cruise comfortably, you'll have more invested in gears than the truck is worth.

How much trailer are you looking to tow?

[blt2ski]

If you're going to change out gears, go to a 4.33.
You're looking at $2g per pumpkin, you'll get more take off power which you lack with the trans in that rig.

Marty

[JRscooby]

In my state, you put passenger car plates on the 'burb. Then your only legal limit is tires. If the weight watcher sees you squatting real bad might stop you to look at them. With a RV, not likely to be heavy enough to be looked at.

[dodge_guy]

That a performance number, no legality behind it, only if it’s still under warranty and you were towing more than the 3.73 rating, hen they could’ve denied coverage.

I went from 3.73 on my V-10 Excursion to 4.30 (factory option). Best thing I did for towing.