PDX.Zs wrote:
The truck is a beast. stout frame... but the frame does need to be clearanced in a couple spots. No big deal, the modification are obvious and can be handled with a grinder and sawzall in a few minutes.
I want to stare at it for a long time before cutting anything.
Good for you for staring for a while. They always say measure twice, cut once.
While you are staring, I urge you to think very carefully before "clearancing" your frame, especially in the manner shown in the second thread that APT linked to, and that you found in your own research.
From the pics in that thread, it appears to me that the downturned edge of the lower frame flange was trimmed off. But the problem is, that downturned edge is the very feature that strengthens the frame, making up for the significant reduction in material thickness that the frame steel has, when compared to the 2500HD pickup of the same generation, or the 2500 Suburban and pickup of previous generations, especially the GMT400 and earlier, by comparison.
Since on the 2500 Suburban platform, the GMT900 chassis is largely carryover from the previous GMT800 series (unlike the 1500), I am hesitant to say whether or not the material thickness of the rear frame section is thinner on the 900 over the 800, so that's why I say 400 and earlier.
I can tell you, as an owner of the GMT800 Suburban, the frame material is substantially thinner than the previous 400. In otherwords, the frame material on BenK's 3/4 ton Suburban is much thicker than the frame material on my 3/4 ton Suburban, despite both vehicles having the same GVWR, and nearly the same tow rating as equipped. I have measured these thickness differences in several equivalent locations along the length of the frame with a caliper, between a 1999 2500 Suburban and a 2005 2500 Suburban, with both vehicles at my disposal, sitting side by side simultaneously.
If lightening the vehicle for fuel economy, and reducing the production costs of the vehicle to keep the price to consumers in line of sight with inflation, then GM is to be applauded for applying clever engineering to the problem of vehicle towing and hauling capacity, rather than just throwing more metal (material thickness) toward the solution.
An example of one such engineering application in the evolvement of the 2500 Suburban frame from the 400 to the 800 was to introduce up turns and downturns to the open edges of the C channel frame, in targeted areas, so that instead of the frame cross section being in the shape of a C, it is instead the shape of an upper case G, or a lower case zeta in the Greek alphabet, or what is often referred to as a "lipped C" channel.
In places along the frame where ductility is needed, the flanges of the C channel are open and flat. But in places where the frame needs localized strength, or more resistance to deformation, rather than make the entire frame thicker and thus weigh more, GM instead formed a directional change in the flat frame flange formation, adding an up turned or down turned lip in order to increase strength.
And people cut this off?
For the purpose of making their tow rig hitch platform "stronger"?
This doesn't make any sense to me. The key word in "hitch platform" is "platform". And what is the platform for the hitch? Obviously, it is the frame.
It doesn't matter if the hitch added is a Reese Super Titan with twin 3" receiver holes and 25,000 lbs trailer weight capacity... it will still be limited by the platform upon which it is attached. And the capacity of the platform is determined by more than just the capabilities of the drive train. The 14 bolt rear end is meaningless if the already lightened and thin frame flange is yet further weakened by cutting of the lip that was engineered to make up for the thinner material the frame was formed by.
We see the same thing in fully boxed frames. The full box dimension, by virtue of it's shape, provides the resistance to bending that previous open C frames had to rely on material thickness to achieve. That material thickness is then thrifted out, once the frame itself becomes a box. The frame on an equivalent year 1500 Suburban offers a like kind example to compare.
While I don't see any harm in adding a secondary hitch that is rated stronger than the OEM hitch in the 2500 GMT900, perhaps some more staring and thinking is in order before the sawzall and grinder come out.
Meditate twice. Maybe not cut at all.
Try to find a hitch that will fit without shaving off the strengthening lips to the frame, if that is indeed what is required to fit the Curt 15324. Like APT says, 1,400 lbs tongue weight is plenty of capacity for what the rest of the Suburban can handle. Unlike the days of yore, the 2500 Suburban does not share the same frame as the pickups, especially in the rear where the hitch mounts. The 2500HD pickup frames are thicker, have significantly taller frame web height, have slighter wider frame flanges, and have longer directionally changing lips, where formed.
There doesn't seem to be a valid case for compromising the existing engineered frame strength by shaving it, in order to fit a hitch that has 2,500 lbs tongue weight capacity, that in and of itself is still not determinant of the capacity of the hitch platform. Far better to find a hitch that fits without cutting the strengthening lips from the frame flanges.
Have you researched the Reese Titan V aka Towbeast for the GMT800 application? Reese Part number 45013? The upper mounting flange of this hitch's side plates appears narrower across the top, and might be able to nest within whatever downturned flange that people are shaving off the lower part of their GMT900 frame. That might be worth looking into.
