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.