OD Transmission
Thread Starter
Heel & Toe
Joined: Jul 2024
Posts: 16
Likes: 1
OD Transmission
My 1973 Convertible with a TH400 needs a tranny rebuild. Seems like the perfect time to upgrade to an overdrive automatic. I’m hearing folks are putting in 200’s, 700’s, 4L60, 4L80 even C-4 Fords. Any suggestions?
Race Director
Joined: Nov 2006
Posts: 13,177
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
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Cruise-In VIII Veteran
Convert to a manual 5 or 6 speed.
lose the fun sucker automatic all together!
you did ask for suggestions!
lose the fun sucker automatic all together!
you did ask for suggestions!
Melting Slicks
Joined: Apr 2021
Posts: 2,659
Likes: 2,117
From: Minnesota
Turbo 350’s are the same length as a 200-4R. Since you have a TH-400 you’re looking at driveshaft modifications regardless of which one you go with.
You say you have an L-48 in your other posts, so the maximum torque capacity of a stock 200-4R should be just fine. The 200’s have a much smaller difference in gear ratios between 1st and 2nd, so I would be leaning more towards that rather than a 700. Only other thing to consider would be your rear end ratio.
Don’t let other people tell you how to enjoy your car.
You say you have an L-48 in your other posts, so the maximum torque capacity of a stock 200-4R should be just fine. The 200’s have a much smaller difference in gear ratios between 1st and 2nd, so I would be leaning more towards that rather than a 700. Only other thing to consider would be your rear end ratio.
Don’t let other people tell you how to enjoy your car.
Thread Starter
Heel & Toe
Joined: Jul 2024
Posts: 16
Likes: 1
Thanks Piersonpie and LeMans Master. I guess with age comes the desire for convenience so I’m sticking with the auto. I never thought I’d “elect” to go with an auto but here I am. At this point, with the low HP L48, I just want the modification to involve as little fabrication changes as possible.
Melting Slicks
Joined: May 2021
Posts: 2,263
Likes: 1,308
From: Fleming Island, FL
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Newcury
Get a 200-4R. NO, you don't have to modify the driveshaft.
You can get a conversion U-joint to adapt to the Turbo 400 driveshaft.
You can also use your gear selector with a minor mod to the lower bracket that bolts to the tranny pan, you can also use a dremel on the Detent Plate up top if you want to be able to select 1st gear.
I replaced a Richmond 6-speed with a 200-4R. I've been rowing gears for decades. If I want to put the Manual back in it's relatively easy. I left the clutch pedal assembly in place if I ever wanna do that.
I recommend you get a tranny crossmember that lets the exhaust pass-under.... makes exhaust R&R and Tranny R&R lots easier.
I have done all those things. I'll find a couple of useful links for you....in a sec.
Get a 200-4R. NO, you don't have to modify the driveshaft.
You can get a conversion U-joint to adapt to the Turbo 400 driveshaft.
You can also use your gear selector with a minor mod to the lower bracket that bolts to the tranny pan, you can also use a dremel on the Detent Plate up top if you want to be able to select 1st gear.
I replaced a Richmond 6-speed with a 200-4R. I've been rowing gears for decades. If I want to put the Manual back in it's relatively easy. I left the clutch pedal assembly in place if I ever wanna do that.
I recommend you get a tranny crossmember that lets the exhaust pass-under.... makes exhaust R&R and Tranny R&R lots easier.
I have done all those things. I'll find a couple of useful links for you....in a sec.
Last edited by carriljc; Jul 15, 2024 at 12:20 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Newcury
Here are A couple of threads....well worth the read before you head off to do it.
Also...there is a Tranny Guru named David Husek located in New York. He actually spent like 20-30 minutes talking to me about transmissions, the Governor, specifically..... very helpful. If you're going to throw money at something ....
https://www.corvetteforum.com/forums...t-details.html
https://www.corvetteforum.com/forums...-pictures.html
Also - if you need the conversion U-joint part number just say so....
Here are A couple of threads....well worth the read before you head off to do it.
Also...there is a Tranny Guru named David Husek located in New York. He actually spent like 20-30 minutes talking to me about transmissions, the Governor, specifically..... very helpful. If you're going to throw money at something ....
https://www.corvetteforum.com/forums...t-details.html
https://www.corvetteforum.com/forums...-pictures.html
Also - if you need the conversion U-joint part number just say so....
Last edited by carriljc; Jul 15, 2024 at 12:21 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Here is conversion U-joint part number for you. Double check me but pretty sure this will work:
Check ebay--- new ones are lot cheaper there than anywhere else I found....
Conversion/Adapter U-joint Spicer 5-134x or TRW 20056 (Part number on receipt is PRJ-20056)
I had to go the other "way" since the Richmond uses a Turbo-400 yoke....
https://www.corvetteforum.com/forums...post1601594797
Check ebay--- new ones are lot cheaper there than anywhere else I found....
Conversion/Adapter U-joint Spicer 5-134x or TRW 20056 (Part number on receipt is PRJ-20056)
I had to go the other "way" since the Richmond uses a Turbo-400 yoke....
https://www.corvetteforum.com/forums...post1601594797
Last edited by carriljc; Jul 15, 2024 at 12:37 PM.
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Safety Car
Joined: Aug 2001
Posts: 3,683
Likes: 201
From: Waterford Mi
I installed the Bowtieoverdrives 200-4R in my 73 many years ago. My TH400 had a bad casting at the pan seal that I could not keep from leaking. With the 3.55 rear gear it was a great upgrade.
Thread Starter
Heel & Toe
Joined: Jul 2024
Posts: 16
Likes: 1
Thanks Redwingvette. After hearing from quite a few folks I’m going with the 200R4 as well. I’m little concerned about the wider pan, maybe a different cross member, and the shifting into first gear issues. But having the OD seems it’s well worth it.
Drifting
Joined: Aug 2016
Posts: 1,773
Likes: 923
From: Arizona
there are a number of options for the crossmember, I used the bowtie overdrives crossmember for less than $200 and it fit perfect, no pan issues at all with the exhaust
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Newcury
Both of those issues are non-problems. Especially since you have an automatic and can just follow Golfobsessed 's lead on the bowtie pass under crossmember. Or you can modify your removable auto tranny crossmember to let the exhaust pass under.... just a little cutting and welding.....
As far as being able to select first gear.... it's in one of the links added in post # 7...but here is a direct connection to that being addressed: https://www.corvetteforum.com/forums...post1604916531
Both of those issues are non-problems. Especially since you have an automatic and can just follow Golfobsessed 's lead on the bowtie pass under crossmember. Or you can modify your removable auto tranny crossmember to let the exhaust pass under.... just a little cutting and welding.....
As far as being able to select first gear.... it's in one of the links added in post # 7...but here is a direct connection to that being addressed: https://www.corvetteforum.com/forums...post1604916531
Last edited by carriljc; Jul 16, 2024 at 07:22 PM.
Instructor
Joined: Apr 2005
Posts: 136
Likes: 41
From: Arvada CO
I did the TH350 to 200 4R about five years ago and it has been great. I have a 10-15 min highway commute every morning and she does great. I went with a non lockup for simplicity and I don’t regret it. It is a great upgrade. Good luck.
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Just crossed my mind that the 82s (and maybe 80 & 81?) have that goofy tranny crossmember that is neither straight, nor even, nor the flat surface on top to mount the 200-4R, and does NOT have pass through holes...... in luck since he can just replace it with the Bowtie Overdrives crossmember where the exhaust passes under.....
Once you get the crossmember that lets the exhaust pass under you can route your pipes similar to this beautiful job by MattoonVette
https://www.corvetteforum.com/forums...post1604898317
Once you get the crossmember that lets the exhaust pass under you can route your pipes similar to this beautiful job by MattoonVette
https://www.corvetteforum.com/forums...post1604898317
Last edited by carriljc; Jul 17, 2024 at 12:33 PM.
Race Director
Joined: Mar 2017
Posts: 11,923
Likes: 4,495
From: Virginia
Just crossed my mind that the 82s (and maybe 80 & 81?) have that goofy tranny crossmember that is neither straight, nor even, nor the flat surface on top to mount the 200-4R, and does NOT have pass through holes...... in luck since he can just replace it with the Bowtie Overdrives crossmember where the exhaust passes under.....
Once you get the crossmember that lets the exhaust pass under you can route your pipes similar to this beautiful job by MattoonVette
https://www.corvetteforum.com/forums...post1604898317
Once you get the crossmember that lets the exhaust pass under you can route your pipes similar to this beautiful job by MattoonVette
https://www.corvetteforum.com/forums...post1604898317
Fortunately, all 80-82 cars have removable crossmembers, even the 4-speeds.
Safety Car
Joined: Aug 2001
Posts: 3,683
Likes: 201
From: Waterford Mi
I used the stock crossmember with no modification. The front universal and u-joint I bought with the trans. I had to make my own TV cable attachment for my Holly 4175 carb because at the time nobody made a kit to fit.
I also bought the shifter detect plate for the stock shifter so I didn’t have to screw around trying to make the stock detent plate work.
I also bought the shifter detect plate for the stock shifter so I didn’t have to screw around trying to make the stock detent plate work.
Drifting
Joined: Aug 2016
Posts: 1,773
Likes: 923
From: Arizona
The 80-82 crossmember has a welded trans mount and needs to be replaced for the 2004r install, 79 and under have a bolt on trans mount that can be removed to accommodate the 2004r without modification (maybe a small amount of hole reaming)
if you need to move exhaust out of the crossmember holes there are a few crossmember options or modify stock, I used the bowtie overdrives crossmember which will accommodate both single sided exhaust and both sided exhaust.
G- Force was my first option but wasn't available in stock at the time and frankly was happy with the bowtie crossmember, I am not sure the G-force would have accommodated my CC single sided dual exhaust
if you need to move exhaust out of the crossmember holes there are a few crossmember options or modify stock, I used the bowtie overdrives crossmember which will accommodate both single sided exhaust and both sided exhaust.
G- Force was my first option but wasn't available in stock at the time and frankly was happy with the bowtie crossmember, I am not sure the G-force would have accommodated my CC single sided dual exhaust
Drifting
Joined: Aug 2019
Posts: 1,508
Likes: 495
there's about a 3/4 of a inch difference between T350 mount and 700 of a 1982 , I thought about elongating the hole for the 700 swap on my 1980 T350C but went G Force because ultimately I want to have 1974 dual exhaust
Le Mans Master
Joined: Jan 2001
Posts: 6,711
Likes: 1,371
Newcury
There is no need to re-invent the wheel. Get a tranny crossmember that allows exhaust to pass under and follow the lead of MattoonVette on exhaust routing..... it's dang beautacious.
(I also have a post on fabricating your own crossmember but you have a removable crossmember so buying a pass-under is just easier. If you want to see the fabrication just say so.)
https://www.corvetteforum.com/forums...post1605761394
There is no need to re-invent the wheel. Get a tranny crossmember that allows exhaust to pass under and follow the lead of MattoonVette on exhaust routing..... it's dang beautacious.
(I also have a post on fabricating your own crossmember but you have a removable crossmember so buying a pass-under is just easier. If you want to see the fabrication just say so.)
https://www.corvetteforum.com/forums...post1605761394