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I have read quite a few threads on modifying fixed crossmembers (early C3) to be removable, but not much on swapping a fixed "manual" crossmember with a removable OEM "Auto" crossmember.
Can this be done ? I will be having the body off of the frame.
Anything is possible when it comes to welding and custom design. But it is so much easier to cut the fixed on either side and replace it with mild steel box tubing with bolt on flanges. Making the central section removable. It's a PITA to clean up and try and tap the two frame rails for a couple of bolts each like the automatic transmission cross member
You want to make it so that the exhaust passes under the transmission cross member. NOT through the cross member.
It makes it removable with out mucking around with the exhaust system. You don't need all the complicated pipe bends to fit through two holes. You keep the hot pipes away from the transmission and straight back from the header collectors
The problem with converting to an automatic is you don't have the weld nuts inside the frame for the bottom bolts. I suppose it would be possible to add them or some other work around, but much easier to cut it and use the plates.
It is possible but lot of work. I converted my ‘68 frame from a fixed 4 speed to a removable crossmember. I used a removable cross member and reworked the frame to accept it. Used the frame mounting bracket from a donor frame installed concealed nuts in the frame. Then you have to rework the transmission mounting area to accept the shifter mounting bracket. A lot of work but I really like the look and convenience when working on the transmission.
There are a bunch of different ways of designing a removable crossmember, with your body off you will have an easier time deciding which direction you go. I did the above with the body on, and it is not easy cutting the crossmember with traditional DIY tools. I like the idea of additional gussets for stiffness.
gkull has good point about the exhaust. I have found that I have been removing the exhaust quite often to address rear suspension/ differential issues. These exhaust band clamps have made exhaust removal easy.
Here's a pic showing my frame during re-assembly. I went the route of cutting the crossmember and inserting plates with bolt holes. Someone on the forum (David Howard as mentioned in post below) made the template and offered the for sale. Getting rid of the through holes for the exhaust is really a personal choice unless you want to have/need room for 3" exhaust or want to make dropping the exhaust easier.
Here is mine. I had my exhaust built so I can get it off in no time, even with the large pipes through the holes. I used the plates David Howard makes and couldn't be happier about the way it turned out.
Why are you wanting to do it? Is it to upgrade to a TKX 5-speed?
Ha ! Now that is insightful of you. I made my crossmember removable, but !! I find it ugly. That is the primary reason for me to want to make it more OEM in appearance, or at least more stock looking... and perhaps stiffer.
That being said, I have a T5 in there and I am considering swapping in a TKX.
Here is mine. I had my exhaust built so I can get it off in no time, even with the large pipes through the holes. I used the plates David Howard makes and couldn't be happier about the way it turned out.
DorianC3, Changing from a stock 4 speed crossover to a OEM removable crossmember is not a difficult job if you have the body off the frame. I made the change because I wanted a stock looking Crossover. At the same time I did the seam welds and enforcement per the Chevrolet Performance Manuel.
I don't have a before picture just the pictures after I removed the 4 speed crossover and did the change over.
DorianC3
I made my crossmember removable ages ago to install a Richmond ROD 6-speed. In 2022 when I installed a 200-4R I modified it to make the exhaust "pass-under" and that really works well, but it really looks like crap.
One of my "projects" is to either make my own crossmember, or purchase a bolt-in pass-under crossmember and modify it to fit my vehicle.
If I was starting over today I would make it pass-under to begin with...makes life a lot better and simpler. I'll go find some pictures.
OK, found some pics. It is plenty strong but it got a bit heavier, I used 3/8" channel(pretty sure it's 3/8") and welded it in but it really looks like garbage. Pretty sure the original wall thickness was only 1/10". I already have a new box-tube of 1/8" wall thickness but I am considering just ordering an aftermarket pass-under crossmember and modifying the ends to fit my existing mounts (or even modifying what I have). No hurry since it is fine but I don't like the way it looks. It is a lot better for dropping the exhaust though! My exhaust was fairly new from Corvette Central and I hacked it up but I'm quite happy with it overall.
Here is mine. I had my exhaust built so I can get it off in no time, even with the large pipes through the holes. I used the plates David Howard makes and couldn't be happier about the way it turned out.
Bill
Do the David Howard ALLC34Me removable crossmember kit, it is the best quality.
Many on the forum have used his kit and it’s a direct fit and those who have used it are all very happy.
If you plan to go with 3” exhaust tubing then look at the G Force aftermarket crossmembers.
Their design allows the exhaust to run under the crossmember rather than through it.
I bought one for my auto to manual conversion and I’ll be running 3” exhaust.
Can someone get the "Width" and "Height"of the Frame Stubs for the Automatic crossmember? I'm thinking it would be easy enough to get an aftemarket-pass-under crossmember and modify the ends so that single horizontal bolt would hold it up? Seems like that is holds most of the load anyway?
I understand that, however it would not be absolutely necessary to bolt in the aftermarket crossmember in the same manner. Could even add bolts/nuts to the pre-existing side stubs if someone wanted to do a similar setup.... all simple at that point.
Need to know the dimensions for the automatic side stubs to start with though.....
Originally Posted by Bandit54
On a automatic removable crossmember there is two bolts that come up under the frame for added strength.
Automatic crossmember swap
