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#1
10-05-2017, 04:33 PM
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4Speed Conversion
I'm perplexed! I'm changing from my Turbo 400 auto to an M 20 4 speed in my 67 GTO. I thought that it was a straight up bolt it change over but the rear trans mount is located about 6" forward than the auto. My car is a convertible with a boxed frame so I can't just move the cross member forward that easily. Also, my cross member has the rubber mounts and brackets so that is also a bit of a problem. The only solution I see at the moment is first lengthen the cross member a bit so it touches the inside of the frame rails and then weld another bracket to my existing bracket that extend forward 6" to accommodate the cross member. Does that make sense? I sure didn't want to weld to my freshly powder coated frame but if I have to......Has anyone else done a convertible (boxed frame) conversion that can give me some advice?
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#2
10-05-2017, 04:44 PM
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Search for squids Fab shop website. He has some good info showing how he worked that issue.
Sent from my XT1585 using Tapatalk |
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#3
10-05-2017, 05:03 PM
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Quote:
If you make a 1/8" steel flat plate that is long enough to bolt to the T-400 Cross-member frame mount and also go forward far enough to be in the correct position for the Muncie 4-speed trans, then adding a simple steel support at the front of the 1/8" steel plate and a single mounting bolt (or you could weld it to the frame) will give you a convertible trans mount for a Muncie. I helped a friend do this and we used ONE RIVNUT (on each side (mounted in a drilled hole in the frame). The rest of it was all simple "bolt on bracket stuff" once the frame support was welded to the 1/8" steel plate. Tom V. ps 99% of the people would never notice the rivnut if you put the T-400 back in and removed the muncie trans parts.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. Last edited by Tom Vaught; 10-05-2017 at 05:10 PM. |
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#4
10-05-2017, 06:55 PM
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Just talked to a rod builder friend of mine and he suggested fabbing a trans mount plate at the trans mounting holes and going forward. Duh, just one plate to fab and that could be gusseted to the cross member and welded strong, then mock up engine/trans to frame and drill mounting holes in plate at trans. This might be easier, but what did the factory do when using a 4 speed in a convertible? The frames are all the same, manual or auto so that wasn't the issue. They must have used a different cross member that bolts to the same frame welded brackets. If they have a ready made part, I'd rather buy one.
PS, I'll look on squibs site to see what he did. |
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#5
10-05-2017, 08:04 PM
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Quote:
2) The cross-member brackets on the frame are designed to support a downward load NOT A DIVING BOARD LOAD, which is what you would have without the front support, even on your Rod Builders Design. Good way to break the cross-member mount loose from the frame as there are only small welds holding that part to the convertible frame. A Rood Car with a "C" section frame has the whole lower section to the frame to support the cross-member. Now your buddies deal will work it you promise to never shift the muncie trans like a racer. 3) I have done this deal before, as posted on my convertible frame, I know what works and doesn't work. BUT IT IS YOUR CAR. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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#6
10-05-2017, 08:04 PM
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Just checked out Squibbs site and like how he added on to his frame mounted brackets. I may just bite the bullet and grind a little on my nice powder coated frame to do it right. I did some research and found out that GM did in fact have two different convertible frames. One was for the auto and one for manual. Location of the brackets being the only difference. Go figure. Thanks for the suggestions and for the reminder to check Squibbs.
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#7
10-05-2017, 08:07 PM
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Tom, you're right, and yes I know that I'll be using most of the power that my built up 455 will put out so, got to do it the right way. I figure I'm surely going to break something but don't want it to be this. LOL
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