I have noticed on vehicles that have leaf springs it also has crossmembers that attach to the frame close to the area where the springs mount,the reason I am concerned is I have a 37 Chevy p/u and if I decide to put a newer motor and automatic trans in it the crossmember where the bellhousing mounts attach will have to be removed so will that affect the strength of the frame in that area if I retain the original front suspension.
I've seen parallel spring frames without crossmembers in that area, so my thought is that the crossmember is mainly to support the engine. Having said that, yes you will obviously lose some strength. The question is, will loosing that strength in that location eventually show itself as an issue like cracking or buckling in the main rails. You would need to post some pictures to get a clearer idea on that. A lot will depend on how the springs mount to the rails.
Tying left to right with a frame crossmember is the most straight forward way of doing this. A diagonal cross member will help even more, since a triangle is the strongest shape. A reinforced body bolted to the frame will provide a great deal of support also.
If you use the common tubular, dropped crossmembers to support the engine and transmission, then you should be fine if you remove the bellhousing crossmember.
Jim makes a good point there. The big problem with removing that crossmember on Chevy trucks is that the weight of the cab pushes down on the brackets for the cab mounts and twists the top of the frame rails outward until the cab sags to the point it rests on the top of the frame rails. I think that is more prevalent on AD trucks rather than Deco or earlier trucks but it still may be a problem if you have brackets outboard of the frame to mount the cab. If you have the cab off the frame I'd box the rails back to close to where the trans crossmember hooks on to add some strength back.
I never thought of the cab putting pressure on the frame too and if I ever do put another motor in it I was never planning on taking the cab off the frame where it would be easier to box,I think it would be better to start over with another frame and get it boxed if I do decide to go with a newer V8 and automatic trans. The V8 I really want to use is a 49 to 58 Olds rocket and they mount similar to the stovebolt so I can retain that crossmember and be in good shape but my daily driver that would most likely be the donor would probably be ready to give up the motor before I can find a rocket that is good enough to drop in.
A simple vertical load has to go thru the "shear center" of a beam (or frame rail) to avoid twisting in addition to the expected bending. C channels have really poor torsional stiffness. AND their shear center is (not very intuitively) located off in space from the closed side. http://****ysischamp.com/StressBook/fig0217.GIF So a vertical load will likely make them bend AND twist. So C channel frames often need some help. One is boxing, which boosts bending strength some, but increases torsional stiffness A LOT (like 10 X or more) Second is attach a deep crossmember that picks up both flanges close to where the load is applied, so the crossmember can resist the induced twisting. Third is Apply the load with a bracket cantilevered a bit off the C channel face. It is pretty common to combine 2 and 3. http://www.customcl***ictrucks.com/...rear_leaf_spring_conversion_kit/photo_02.html Adding a bunch of crossmembers does not really improve the ch***is' torsional stiffness ( one wheel bump) much. http://weldingdesign.com/blodgett/no_twisters_*******s_allowed_0501
You don't really need or want to increase the overall ch***is torsional stiffness. You do want to keep the frame rails from twisting somewhat where the load is concentrated, such as the end of the spring, and the cab and engine mounts. The cab mount is usually just a little bit outboard of the frame, so it's not a big deal. The front leaf springs are mounted under the frame, so they're not a big deal either. As long as you use the tubular crossmembers to support the engine/trans from the web of the frame channel, you are putting that load in a good place. In real life, the only issue I've seen with an old chevy truck channel frame, with the bellhousing crossmember removed, was one that had cantilevered engine mounts, which twisted the top flange of the frame and cracked it.
Lawman here put a v8 into his grandsons truck with no boxing plates. I believe he has no issues. You can contact him. Here are some pics.... http://www.jalopyjournal.com/forum/showthread.php?t=645905
Your 37 should have no problems. The frame on these is quite strong, and the crossmember can be removed without issue. I did box the frame on my '38 but I'm confident you could get away without if you wanted. To mount my small block I boxed the engine area then used the side mounts with donuts and used a tubular 4 inch drop for the trans mount. The cab mounts direct on top of the frame on these so no issues with torsion should be seen there. If you can box it you should, at least partially if possible. The original 216 was a pretty heavy engine, so a SBC would work good.... Good luck Tom Posted using the Full Custom H.A.M.B. App!
If it does not get a IFS when it gets a V8 I will try to keep a crossmember there,modify it and drop it down to clear the trans and make it removable for trans service. My Ford trucks with the twin I beams have a crossmember near where the radius arms attach and is removable (maybe a rivet or two needs to be removed first) so that is what I would try to duplicate to keep the frame from twisting in that area.
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