Chassis Stiffening J-Bars (Truck)

[JGC403]

Its for my Ram, but I think I can get more help on here. I wan't to stiffen the frame on my '85 Ram. I could box the front frame rails but I think that will add a lot of weight. So I was thinking of making some J-bars for the truck. The bar would be welded to the firewall then bolted to the frame and in-between would be a polyurethane bushing, so the cab could be removed from the frame.

The only concern I have is that using the J-bar would turn the cab into more of a structural component of the truck, instead of being just bolted on top of the frame. So is this going to be a lot of extra strain on the cab that it could cause damage to the cab?

 

[72bluNblu]

Interesting.

The cab on your truck was never intended to be incorporated into the frame structure. I'm not saying that it can't be, but unlike our unibody cars where the "cab" is a structural part of the chassis, your truck cab is totally separate. Basically just "along for the ride" as far as the chassis is concerned.

I suppose that adding J-bars as you describe would stiffen the frame, but I'd be concerned about what it would do to the cab. The reason open channel is used for truck frames is so that it CAN flex, and twist to some extent. I'm not sure the cab by itself would be enough resistance to keep it from doing that. And I would definitely be concerned that the cab might not hold up well to the extra stress. I mean, driving around town it wouldn't matter at all. But I assume you want to do this because you don't just drive around town.

I would look at boxing the frame rails first. Might be a little heavier, but it's known to work. I don't think I'd just add J bars to the cab by themselves. If you were tying them into a roll hoop or something it would be a whole different story, but I don't think I would just tie them into the cab structure without additional reinforcements.

 

[ntsqd]

Search around the off road forums and you'll find that this is a bad idea. It doesn't go far enough. As soon as you add structure to the frame you need to consider the load paths and transfer those loads to the rest of the frame. Transferring them just to the cab itself will just serve to break the cab as it was not designed to have those loads put on it.

So if you want a stiffer frame you'll need to look into adding structure from end to end. Boxing the frame does make it stiffer and that can be good or bad depending on what you're doing with the truck and what else you've done to the truck.

 

[JGC403]

Yea that is what it was figuring that just using J bars wouldn't work so well. Thanks for the help.

 

[ntsqd]

Pure speculation on my part, but I'll guess that the diesel frame will be stiffer up front. It should be if it isn't. Might be worth looking at.