Suburban 2500 (GMT900) towing build - 11th gen -

Unintentional double post while trying to post pictures. Getting rusty at this... been a while since I'v been on RVnet. Please see next post below for final version with both photos.

BenK wrote:
Reslly good info.

Thank you much for the info Ben.

So I like that Curt hitch as well. The problem is that is seems to interfere with the added C channel on the Suburban frame. So the channel would need to be relieved. I agree this is suboptimal.

Without access to GMs design, I note that the factory hitch/bumper terminates very early. Meaning it does not reach very far forward on the frame, which as you noted is not desirable. And it seems the C channel under the frame rail is positioned at the terminus of the factory hitch to support it.

My theory is that a longer, real aftermarket hitch wouldn't need these. Who knows?

Anyway, draw.tite makes a hitch that is narrower in the top section that may fit in between the channel and actually reaches further forward than even the Curt unit. But it is only rated to 1200lbs. Even so it is clearly more robust than the stock unit.

Any input greatly appreciated. Aftermarket hitch, reinforce the stock unit.

I would also very much appreciate your best recommendation.

Thanks in advance.

First rule of thumb in designing an after market add on to any structural 'C' channel member is to NOT touch the flange...that is where their main strength is...in conjunction with the web

The holes you see in structures (mainly where weight is an issue), there are large holes in the web. Yup, but designed in AFTER they calculate the increased box section of the whole 'minus' those holes

Any of the upset/bends/ribs/coining/etc to increase the sheet or flat is to increase the box section dimension.

Most after market receivers of traditional design us the OEM frame "C" channel's bottom flange holes. Those holes are designed in and are there BEFORE any hardening/strengthening/etc process(s).

Also note that OEMs now employ much better material science and production science. Meaning that frames today are no longer one piece, but sections that they put together for whichever platform it will end up being

Even though the front and middle sections of the frame are from a pickup, the Suburban's rear section many NOT come from it's pickup cousin

Apologize for the previous short comment on the need for a side plate, or gusset to move (spread) the stresses over onto the Sub's frame.

More detail is that it should tie into the frame web in addition to any OEM flange holes

Farther forward and maybe into the axle arch of the frame

Remember...the OEM receiver is now part of the NHSTA's crumple zone mandate...so I'd guess that rear portion of the frame rail is NOT as stout as before they made it part of the bumper

Leave the OEM receiver alone and it will continue to meet mandated bumper duty...

This is the Curt 15324 you are considering


Love that design and note that the end plate has three components that increase it's box section.

Upper bend is to mate with the bottom of the TV's frame rail's OEM holes, and is the main component to handle side to side moments

Just below it is a triangular gusset at about where the receiver cross tube (a torque tube) is welded to the side plate. Assume there is a higher stress point because of that torque tube's transference force

Bottom has a slight bend. Looks like about 15* or so.

Those along with what looks like 1/4" plate...this guy is STOUT !!!!

Here are some pictures Jbarca took when the GMT900's first came out and shows that crumple zone receiver to frame gusset...and the bottom of the Sub frame rail flange






There appears to be something bolted to the bottom of frame rail just where the Curt receiver would bolt to and that frame flange bendback...all in the way...gotta figure out HOW2 work around them...and do NOT remove that bendback...also shows the notches on the receiver to frame rail bracket (crumple stress raisers)...also, is there room to make a three threaded hole nut-bar for the bolts coming up from the Curt flange?

BigToe wrote:
Lots of great info

Thank you much certainly much to consider.

I am still trying to figure out exactly the week point of these hitches.

I have not been able to locate a pic of a failure of the factory hitch. But that would be appreciated.

The failures I have seen on the GM hitched seem to be related to the actual receiver ripping away from the crossmember. If that is the week point, that can be easily fixed by gusseting or plating.

I hear your points on cutting the reinforcing channel. Seems very sensible. I am however stumped as to why the frame in that area has the unused weldnuts in the frame. My assumption was that it was because the GMT900 Suburbans share a frame with the trucks which use those nuts for their hitch.

And so the questions continue.

I did not that there are hitches that, unlike the Curt, seem to be more knife edge in that area and may be able to clear. The DrawTite 41930, which is rated to 1200lb tounge in clearly more robust than stock.

Still need to do some height measurements and understand if being lower with the hitch would help. I tow both a travel trailer and a car hauler.

Thanks all for the input. The best thing I can say is that there does not seem to be a rash of these hitches failing on the 900 series Suburbans, so I am not super concerned. But I will address it.

We owned a 2001 k2500 4x4 Burb. FANTASTIC tow Beast. We actually named it Beasty! I put a class 4 hitch on it from etrailer.com. No fussin bolted right up. Towed thousands and thousands of miles without any issues. We even hit a huge bump on the BQE trying to escape NY and went airborn. Burb and Trailer were one. We tookit on the shin and kept rolling.

We couldnt find another one so now we have an F250 quad cab and Luv it.

PS I did put a K&N on it so it could breath and tuned it with a programmer. Made a big difference.

Happy trails

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.

Thanks for the kind words and info. I should have been more specific.

The factory hitches on both the 800 and 900 series are not awesome. My plan is to use an aftermarket hitch such as the Curt class v unit from a gmt800 on my 900 series truck as it is a close fit.

CONGRATULATIONS !!!! and know how rare a 8,600 GVWR Suburban is. A big block rarer. In mint condition like what you found is rarer than finding a needle in a haystack...

But...by going to the GMT800 receiver will have you downgrade from the GMT900 receiver

The GMT900 receiver was integrated into the bumper...so it then had to have bumper crash crumple zone duties. They notched the transition bracket to the frame so that it will crumple during a rear end crash

The GMT800 receiver is one of the worst mechanical designs I've seen. Would have fired any of my engineers for designing that thing...heck wouldn't have hired that kind of engineer in the first place...

There were also production quality issues and GM said they fixed it...I'm not going to trust that and here is one failure mode...among many modes of failure. Plus it derives much of it's strength or how it works...is to transfer or depend on those two bolts to the bumper (GM had a cross bar bolted to the bumper inside) in an attempt to turn a torsional loading into a beam loading & torsion (a very bad idea, unless they beefed up both, but am assuming cost reduction...so management wouldn't have approved beefing it up)




Image from this thread: Need advice from the experts, Posted: 03/06/13 12:56pm


The Curt receiver you are contemplating is what I'd get for my GMT800 K3500 Suburban some day. Mine is okay for now and has served me well over the +21 years since ordered it

The modifications for yours will need to have a 1/4" or so plate made up to transition from the Curt side plates to the 'outside' of the Suburban Frame Rail.

Yes, it will be lower, but that is what good shanks will take care with their multi-hole adjustment

Good luck !!!!

APT wrote:
Great find! We love our Suburban 2500. We just rolled 90k miles last week. I would love a receiver rated to about 1400 pounds. The second thread bellow should really help you.

Reference Thread 1.
Reference Thread 2

Thank you sir!

I had actually found those threads as I was doing my research. Great info!

My intent. And I see it's working. Is to compile everything related directly to these vehicles (and mods) in an easy to find and use thread.

Great find! We love our Suburban 2500. We just rolled 90k miles last week. I would love a receiver rated to about 1400 pounds. The second thread bellow should really help you.

Reference Thread 1.
Reference Thread 2