2wd SM465 Crossmember

[WamboJambo]

Would like to start with an apology, as I'm certain this answer exists somewhere on the internet (or even this forum) but I just can't seem to find it.

I am almost finished with a 3 speed column-shifted manual (saginaw?) swap to an SM465, last thing to do is bolt the crossmember up to the frame. Unfortunately the old crossmember frame mount holes are just about an inch too far forward, and there aren't any existing holes that I can use; before I drill six new holes in the frame just an inch away from existing holes, I want to make sure I'm not doing something wrong and can avoid this issue.

After a good bit of research, I think I've found that 700r4s and SM465s are the same length and can be swapped re-using the crossmember, but every picture I've found of an SM465 crossmember has been for a 4x4 and so is the "W" style that clearances the transfer case and is not applicable for my use-case.

Another thing I understand is that the crossmember I currently have (pictured below) is shared between the 3-speed manual and the TH350, and those two can be interchanged without issue. I really thought this crossmember would line up with existing holes on the frame, but there simply aren't any there; some of them are just barely overlapped by the crossmember holes, but enough that I'll still need to drill into them, and then will be left with an oval-shaped hole to mount to.

I also think it's a decently safe assumption to say that most frames should have holes drilled to accommodate different configurations from the factory, so I can't imagine that I need to drill all new holes; I just need the right part? In summation, I guess my real question is does there exist a crossmember that will allow me to reuse existing holes in my frame, or was my frame just not drilled with certain holes from factory because of its configuration?

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[PrairieDrifter]

My 77 c30 has the w crossmember. I've never seen one like you've pictured.

 

[WamboJambo]

Well that's super interesting, for some reason I thought the W ones were only 4x4 crossmembers. I've seen a few other ones like mine in looking on the internet but they were all on 73-81 half ton pickups/suburbans; no idea what the full applications of this one would have been.

 

[WamboJambo]

One other thought I just had - I do know trucks under a certain GVWR after 1975 had to have a catalytic converter, and mine used to be right on the driver's side where the muffler is (you can kind of see the heat shield above it) so that may have been by this particular crossmember was used in this application, since it has that odd dip.

 

[bucket]

There were a couple variations of 2wd crossmembers.

Your trans mount should have a minor offset fore or aft. If it's offset to the rear, unbolt it and flip it around. That would gain about 1/2". Then just slot the trans mount holes in the crossmember. On many other GM cars and trucks, the mount holes in the crossmember are slotted about 1" anyway. So don't think of it as hacking, but rather, applying factory engineering elsewhere lol.

 

[WamboJambo]

There were a couple variations of 2wd crossmembers.

Your trans mount should have a minor offset fore or aft. If it's offset to the rear, unbolt it and flip it around. That would gain about 1/2". Then just slot the trans mount holes in the crossmember. On many other GM cars and trucks, the mount holes in the crossmember are slotted about 1" anyway. So don't think of it as hacking, but rather, applying factory engineering elsewhere lol.

Yep, is offset to the rear; can't believe I didn't think of flipping it around, but I'll try that tomorrow when I've got enough light to drop the other half of the exhaust and see what it gives me. And that's a good idea to just notch the hole out, I was a bit worried about drilling more holes since a) there's already a lot of holes right there for some reason, and b) they would be overlapping, but just widening it out should definitely work better in that case. Thanks for the info

 

[bucket]

Just to clarify, you should only have to slot the two holes in the crossmember, where the trans mount bolts up. Shouldn't have to slot any other holes.

 

[WamboJambo]

OH. Yeah, that's an excellent clarification; I misunderstood and thought you meant slot the frame holes, not the crossmember holes, but that's so much easier. Sorry, brain clearly isn't firing on all cylinders right now

 

[pduffyd]

Here is a picture of my cross member on a 76 C20.

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Its a W mount as you can see. 2 dozen bolts hold it together too!

 

[Catbox]

This is what is under my 1979 C20 with the SM465.

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We also have this one that my kid pulled out of another 2wd truck from the junkyard.

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[pduffyd]

Yeah, I have the one that's sitting on your tailgate

The are two other brackets that bolt on, one each side, as in this photo, more strength to support the chassis, off the top and bottom of the rails.

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No filing of holes needed, this was the one that came with my truck with a stock sm465, I swapped out the motor from a 292, to a 454. It all fits! Just had to change motor mounts and R/H frame tower, up front. Rear trans mount stayed the same. Also easy access to the exhaust!!

 

[WamboJambo]

This is what is under my 1979 C20 with the SM465.

Wow, that's actually super neat; that looks a lot like the one that I have currently, I'm surprised I couldn't get it to work as it was.

Went ahead and went with @bucket's suggestion and slotted out the transmission mount holes in the crossmember and it fits great; also had to grind a little notch out of the front of it to accommodate the back half of the tailshaft, but not too big of a deal. Transmission is in and was able to drive it around the block so I'd say we're good. Thanks all for the pics though, great to have those as a reference, maybe I'll find a better one at a junkyard and pick it up one day.

 

[Raider L]

@WamboJambo,

Did you check out any of the after market frame companies, like Posies? There are others I can't think of right off.

 

[WamboJambo]

No, I definitely didn't look into or even know about companies like that; great idea to keep in mind for future projects like this. I looked at some of the usual aftermarket places like Summit, Jegs, and RockAuto, but if they sold them the crossmembers were mostly just generic that would fit multiple models, and only included 4 bolt holes to the frame instead of the 8 bolts plus reinforcing bracket my factory crossmember had. I was really looking to pick one up in a junkyard rather than use a lesser-quality aftermarket one, but it all turned out fine anyways. Thanks for the suggestion though!