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71 Chevelle TH350 to T56 Magnum Conversion: Step-by-step with pictures

10K views 74 replies 10 participants last post by  Portagee 
#1 ·
Hi All,

Wanted to post some pictures and descriptions of my automatic to manual transmission conversion in my 1971 Chevelle, in case it was useful. This process should be roughly the same for all 68-72 GM A-bodies, but YMMV.

I'm going to gloss over the TH350 removal, as it is pretty straightforward, and focus more on the issues relating to stuffing the T56 Magnum into the car.

So the plan is to cut the tunnel out, insert larger patch with opening for shifter, design custom center console to fit over new transmission tunnel, then reinstall.


Here's the victim: 1971 Chevelle with a Dart 427ci SBC, 12 bolt rear, truetrac diff with 4.11's, aftermarket front and rear suspension from SC&C.
 
#9 ·
Got this patch panel from a guy on ebay - fit over the area perfectly! Was shipped to me flat, so I just bear hugged it around a pole until it was generally in the right shape, then I bent the edges of the floor at the solid orange line up to mate with the face of the tunnel patch. Seems like it's going to work well.

(not sure why the image rotated sideways)
 

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#13 ·
In the meantime, I've also been working on the design for the new center console. Feedback and suggestions definitely appreciated, as I've never made one before.

Plan is to wrap the black surfaces in black microsuede to match the corbeau seats, and the grey faces on the top and around the shifter/buttons in a black madrid grain leather to match the dash.
 

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#53 ·
First, awesome work. Car looks awesome, love the build. I really wanted this trans some years back but it was out of my price range then and now a young family precludes the time and money. Someday....




What CAD program are you using? I like the overall design, perhaps post what some of the features are meant for.

I presume the CAD drawing is just conceptual at this point, but I share what I see as opportunities to dial it in. Presuming you'll make it from sheet metal the material thickness looks far thicker than you'd need. If you'd be welding sides to it, 1/16" should be lots with the exception of the mounting points where reinforcement might be needed for which a small 1/8" pad ought to be lots. IIRC, the stock mount points are more central - if you are lik me and like to lean on the console a bit, consider moint points at the corners for stability/rigidity.

Plan out the number of pcs you'll make it out of, the CAD looks like the base is all one pc right now, which is fine for concept, but redraw it in the way that you'd actually make it and you will have less rework. Advance plan the bends you will use - a cardboard template can be a great tool for ironing out the order of operations/bends that way. With lots of planning, you might be able to make most of it from once pc with the sides attached to the base and folded up.

Pre -plan what foam you might use under the leather or other material wrap. Use dense stuff for the top side - it'll be heavier and more expensive but worth it not have permanent deflection marks from where your arm/hand rest often and it will improve the tactile feel. If you will have foam near gauges or switches, plan how you want it to look (bezels recessed slightly or proud of the wrap material) as the foam may not be rigid enough to hold the items securely. So removal of the foam may need to be offset by a spacer if you want the item to sit proud of the wrap for example. Or perhaps you apply very thin/no foam to this area. Foam/wrap do not like sharp edges, round off everything if possible.

The wrap is the finishing touch and what most people will actually see so this is the area to spend a lot of time planning. It is harder than it looks I believe. Contour changes may be easier to apply the wrap like wrapping a Christmas present but stitching it will look better. A contrast thread colour stitch adds a professional look, I'd suggest silver or grey since your car is white if you like the contrast idea. I have not done stitching, I am just suggesting based on what I have seen in pics and shows.

Love the project, keep us updated.:thumbsup:
 
#15 ·
Thanks, Chris. You're right - the tunnel patch was spot on. Although I needed to extend the shifter opening farther back than I would've liked to allow the rear shift rail to clear (since the patch set so low there).

But I checked out your T56 install, and I had been thinking about doing the same thing with a shifter access box to cover the hole and seal around the shifter. Your car looks awesome!
 
#16 ·
Thanks. The access box has worked well for me, but looking at your console idea you may want to have that built before building/installing an access box.

Also if you go with 1350 U joints, you will likely have clearance issues as the U joint locates directly under the floor cross brace. Clearancing with a hammer is what I did, but some cutting/welding would be a better solution IMO.
 
#17 ·
Great points - I plan on making the access box as low profile as possible, and then to have the flat part of the console near the shifter opening rest/mount directly to that box. Hopefully will add some rigidity to the console.

As for the 1350 U-joints, my current driveshaft has 1350 joints, and I'll just need to get it shortened. I didn't even consider clearance issues, but I'll definitely make sure to look for that.

Did you have issues after you swapped out the original body mounts for the poly ones? Mine aren't too bad, but I'm anticipating that the body will raise up maybe 1/4" or so after I swap mine out...
 
#18 ·
Got the pilot bushing installed tonight. Had to hit it harder than I would've liked to get it to seat, but looks good now.

Going to use the Ram billet clutch alignment tool, since I will be using a McLeod dual clutch, and I've read the plastic alignment tools are garbage.
 

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#19 ·
After I put the poly body and trans mount in, I haven't had any contact since. So I think it's fixed.

I used a billet alignment tool and it still didnt work. I was pissed since it was like $35. I had to use to an old input shaft to get mine to line up nicely.
 
#20 ·
Aww crap, yeah this one wasn't cheap either. Well hopefully I can make it work, because I don't have an old input shaft lying around!

Glad to hear the body mounts made a difference. My passenger side frame rail also has a slight tweak to it (soon to be fixed), which I'm sure will make something contact (driveshaft, trans crossmember, who knows...)
 
#21 ·
Testing out engine block off plate for the QuickTime bellhousing, looks great!

Except.... milodon oil pan drain plug is definitely in the way. Super lame, because I can't drop the oil pan and swap it out without pulling the engine - don't wanna do that again.

Plan is to plug this hole with some flush NPT plug or something, and carefully cut/weld new drain plug on the bottom.

Anyone else run into this problem?
 

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#29 ·
Testing out engine block off plate for the QuickTime bellhousing, looks great!

Except.... milodon oil pan drain plug is definitely in the way. Super lame, because I can't drop the oil pan and swap it out without pulling the engine - don't wanna do that again.

Plan is to plug this hole with some flush NPT plug or something, and carefully cut/weld new drain plug on the bottom.

Anyone else run into this problem?
yes I had the same exact problem. the threads are just nation course threads, it is not a NPT thread. This is the reason for the brass crush washer. initially I ground down the end of the nut and just tighten it up. Oil change was done via 'suck pump' through the dip stick. then when I had more time I got a weld in -8AN bung and welded it to the pan and used a cap.


You will also run ito problems with the bellhousing to block plate bolts. They will hit the pan as it shifts back quit a bit. I just re-arrange the bolt pattern so that all worked.


that cross member looks incredible heavy duty...
 
#22 ·
Hoping to work on the cross member mount tomorrow, but will need to address this first.

The T56 is obviously longer than the TH350, so the cross member is gonna have to move back. This tweaked section of the frame rail was never an issue until now.

Hoping to use a harbor freight pneumatic tool to at least make the bottom portion of the rail flat again, so the cross member will sit correctly.

Fingers crossed...
 

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#23 ·
Used the hydraulic jaw to open up the frame closer to where it's supposed to be - worked great! That support under the body mount was garbage, and wasn't supporting anything anymore. Will eventually remove and weld a new piece, but good enough for now.
 

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