C3500 Chassis cab rollback project

[Steve Addy]

Ok, so I'm digging into the rollback aspect of this, currently the cab to axle length is 108" which is enough to do a 17' bed preferably in aluminum since the GVWR of this truck is 11k (why not 12k I have no idea...).

So I've been gleaning through some old rollback parts catalogs and prep guides and Challenger says (very old guide) that you have to cut the frame off at 34.5" aft of the axle centerline, which means trimming about 17.28" of length from the existing frame. This isn't something I'm keen to do ATM but it's out there. This due to the requirement for bed pivot.

Now, this is what I would like to do instead of cutting off the excess frame length. I would prefer to push the rear suspension (and axle) back 12-18", extending the WB and CA by that amount which would 1) make it possible to install a 19' carrier bed (if I could find one reasonably), or a 17' bed with a clear area between bed and cab for a toolbox etc. This would also require extending the driveshaft (3 piece) but that would be something let out to a drivetrain shop. Granted, moving the rear axle is a lot of work, but it's not out of the question I guess....looking for comments.

Further, I found today a GMT455 at the junk yard I frequent that has the frame reinforcement plates I'm interested in adapting to my C3500. The notes for the GMT455 indicate frame reinforcements were added under the cab area in the mid-90's due to problems with stress from rollback adaptations. These are bolted on, 12 bolts per side, and the integrate the rear cab mount that was otherwise welded to the frame. Here is a photo of what they look like. These might be overkill but I've seen GMT400 C3500 chassis cabs with problems in this area. Comments on this too....

Here's a photo of what they look like, you can see the reinforcement bolted up to the flanks (and over the top edge) with the rear cab mount as part of it. Since they're bolted on I see this as a pretty easy upgrade although it will mean adding some weight to the truck too. I'll be doing more research on this to make sure they fit to the GMT400 CC frame properly.

Steve

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[Sean Buick 76]

Yes I would add the reinforcement and I would also move the rear axle back

 

[Steve Addy]

Preliminarily it looks like the reinforcements won't work unless they're modified. The frame on the 3500HD doesn't drop as far as the GMT400 CC does as it goes under the cab, and if the measurements from that upfitter plow catalog I linked to above are to be believed the HD frame doesn't flare out as wide as the GMT400 CC does under the cab, which seems strange to me.

I could have the plates modified for the change in width, but adjusting for the drop is probably not possible without having some of the material cut away. But before I do that I'll crawl under the 3500HD and do some actual measurements myself to see if what's published is actually true.

There are some additional reinforcement pieces that were used on later GMT400 CC's, but they're welded in place and I'm pretty sure by now if they were shown in GM parts catalog as separate pieces they are likely NLA now.

Steve

 

[someotherguy]

The 3500HD frames are monsters compared to the 3500 - the plates definitely won't be direct swaps. But yes, you'd want to do some reinforcement in that area for your purposes. This is done even when converting the trucks to wheel lift wreckers, not just rollbacks.

The 17' carriers, aluminum, were the overwhelmingly common choice for 3500HD trucks back in the day. I don't know if that was based on the GVWR (15K) or other reasons, or likely a combination of them. On a 3500 non-HD I don't think I would aspire to installing a longer bed, because the potential to overload would be too great. You'd already be at a disadvantage with the extra weight of the longer bed.

I'll add that while I've seen plenty of 3500's built into wheel lift trucks, I can't recall seeing too many setup as rollbacks. 3500HD's, sure.. but not really remembering any 3500's. I'm sure some were made, but probably in backyards, or against the advice of wrecker builder shops. When it's -your- truck and you're keenly aware of the limitations, that's one thing, but a builder selling a truck spec'd that way to someone who will press it into commercial service is a whole different scenario.

Richard

 

[Sean Buick 76]

Richard makes a good point, if done right it will be safe to use over the GVW however never legal over the GVW. I built a ramp truck that was this way, it was never an issue but I promised myself if I ever did it again I would start with something that had a GVW higher than what I needed.

If it were mine I would simply build reinforcement plates for the frame, and I would make them very long with bolts to secure them and a few stitch welds.

 

[Steve Addy]

Thanks for the advice guys, certainly worth getting comments from people who've some experience with this.

I have thought a lot about it and the 17' aluminum bed makes the most sense really, given the GVWR of this truck. I would still consider moving the rear axle back to save frame length and that would allow for a tank or tool box install between the bed and cab. I could justify the change in driveshaft length for this reason.

I recently stumbled upon a 2000 GMT455 with a 7.4L in it. The truck is at a JY and would require a bunch of work but it's possible that it could be bought and the frame doesn't look bad at all. Also, it's the C31803 chassis at 183.5" WB without frame stretch or axle move, so it's the same wheelbase as my truck but has the 15k GVWR. The owner would likely not want to part with the 7.4 but I could work around that issue.

I'm getting too many things going at once....

Steve

 

[someotherguy]

Thanks for the advice guys, certainly worth getting comments from people who've some experience with this.

I have thought a lot about it and the 17' aluminum bed makes the most sense really, given the GVWR of this truck. I would still consider moving the rear axle back to save frame length and that would allow for a tank or tool box install between the bed and cab. I could justify the change in driveshaft length for this reason.

I recently stumbled upon a 2000 GMT455 with a 7.4L in it. The truck is at a JY and would require a bunch of work but it's possible that it could be bought and the frame doesn't look bad at all. Also, it's the C31803 chassis at 183.5" WB without frame stretch or axle move, so it's the same wheelbase as my truck but has the 15k GVWR. The owner would likely not want to part with the 7.4 but I could work around that issue.

I'm getting too many things going at once....

Steve

Looks hurt but saveable! I built a heck of a wrecker out of a $300 parts truck that didn't even have an engine, and all the body parts other than the cab were junk. It was worth far more than the price just for the rolling chassis and cab w/title.

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Not saying it was easy or cheap! LOL. But, having good bones to start with always helps.

Richard

 

[Steve Addy]

Looks hurt but saveable! I built a heck of a wrecker out of a $300 parts truck that didn't even have an engine, and all the body parts other than the cab were junk. It was worth far more than the price just for the rolling chassis and cab w/title.

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Not saying it was easy or cheap! LOL. But, having good bones to start with always helps.

Richard

That's a nice looking rig, and exactly what I'd like to have, and the GMT455 is the perfect foundation to build that up on. My biggest criticism today is overkill. I drove for a local JY for a year and everything we picked up I had to use the F650 V10 for, and that's just too big for most of what I picked up and it was horrible in town on narrow streets or especially in alleys. It also was horribly wasteful on gas, it just doesn't make sense to pickup a 3000 lbs car with a truck that can carry 12k and gets at best 5 mpg. I see the need for having large rigs because of the types of towing situations are varied, but today there's a tendency for overdoing it.

That's why I don't mind a 17' rollback on a 11k GVWR chassis cab. Not that much of what we drive today weighs all that much, so why push a class 6 truck around that just gulps down the fuel? The JY even had a class 5 but the powerstroke in it had a boost pressure problem so it just sat...all the time. I hated that F650 with a passion and I'm glad I don't have to drive it anymore.

Still trying to get the bed setup purchased...not having much luck, the seller is being kind of a dick about it. He posted it up FS with almost zero info and doesn't like it when people ask questions about it...even length, which he never listed it!

Wondering if I can find someone in WI close enough to go have a look at it before I make the 5+hr trip to retrieve.

Steve