mbeeman350

I really need to do the conversion from a TH400 to a 200R4 (or 5 speed Tremec). Wondered if those who made the change to an AOD are still happy with their choice and had any comments or suggestions. As always thanks

MakoShark72

Road trip of 1012 miles, 75 mph, 25 mpg. I am thrilled!!!!

scottw

If you do a search, you will find MANY happy people that swapped to a 200 or 700. Overdrive is a great thing. Not that I know, I'm with you and still have a 400.

spikebot 81

I made the swap in april 2012. I wanted a 2004r to handle 400hp+. After researching all the big venders I desided to have a local independent trans shop do the build. This new trans has a full preasure valve body. The shifts are a bit harsh but the good thing is the TV cable only controls shift points therfore eliminating the posibility of burning up the trans due to improper tv adjustment. I have the lock up feature set up to only apply in 4th gear. This transmission has a much lower 1st gear than the th350c so still have the factory 2:87 to 1 rear gear. I did all the mods for install myself and did purchase a new crossmember from BTO. Resent trip to WA coast 145 miles one way netted 20mpg. This 81 with the new engine and trans is now truely a hotrod. Very pleased with the mod.

7T1vette

I swapped out a perfectly functioning THM-400 for a 700R4 two years ago, primarily to help the engine survive longer. I like to drive it to car shows anywhere in Tennessee, but driving longer distances on the highway was out of the question without an overdrive transmission. Nearly 3000 rpm for 2-3 hours at 70mph was uncomfortable for the engine and ME...too hot, too noisy, too much wear on an original engine with 200+K miles on it.

Now, the engine lopes along at just over 2000 rpm and gets over 20 mpg at 70mph. It is comfortable for me, the engine will last that much longer, and more Tennessee folks get to see a '71 Corvette on the weekends.

Except for the few headaches of working out the installation 'bugs' and some additional cost, it's a "no-brainer" modification for those needing/wanting to do more highway driving. I will say that an O.D. transmission is NOT for everyone. If you don't do much highway driving and/or you have a differential with less than a 3.36 ratio, you might want to think about it a little more. With a 3.08 rear gear, you will need to place the shifter in 3rd range for in-city and suburban driving, or it will want to 'hunt around' shifting from 3rd to O.D. Of course, on the highway, a 3.08 car with O.D. will be running at 1750 rpm at 70 mph. Just realize what the results of an O.D. tranny in your car would be, before you take the plunge.

Douglas Mariani

redwingvette

Still very happy with the mod/upgrade.
Install page

77vetteluva

I don't know what I could add that hasn't already been said. It is a no regret decision.
Things to plan for:

~Cross member mounting - I got a custom cm from BTO. Some original cm's will work
~You will have to install a TV cable. Adjustment is critical. - Not the same as a kick down cable
~Be prepared to have a circuit plan to control torque converter lock up - Lots of options here
~You will need to modify your shifter for an OD detent - Kits are available
~TH350 yoke and drive shaft length match 2004R but I don't know about TH400 or 7004R

Even with all this it is well worth it!

mbeeman350

Wow, thanks to everyone for the great response and for all your comments and suggestions. A tremendous amount of good and useful ideas. I have been researching this for a while here on the forum. I am leaning toward changing my 3:08 rear gear to a 3:55 for a little more fun. Also thinking about and researching the MSD TBI Fuel injection.

Anyone wish thsy had gone to a Tremec or any other 5 speed manual setup?
thanks again!! Mark

Vette5.5

Couple more things to throw into the mix. TH350's have a 2.50 1st and 1.00 3rd, with 700R4's having 3.05 1st and 0.70 od 4th, so maybe not such a hurry in switching out the 3.08 axle. Friend of mine did a Keisler TKO 5 speed conversion in his 79' with 3.70 axle Muncie 4 speed, and with the TKO's lower 1st gear, could easily get by with less rear axle. I did a 700R4 conversion on another BB car with 3.70 axle, and 1st gear is a real burn out king.

mbeeman350

Looking at the Tremecs TKO 400/500 these are a wide ratio box with a 3.27 first gear. The TKO 600 is a close ratio box and has a 2.87 first gear. The 700R4 has a 3.05 first gear, while the 2004R has a 2.78 fist gear. I have the original TH400 with a 2.48 gear.
There's a thread here on the forum and on Bowtie Overdrives website that discussse the torque multplication and effect of using 10 as your target for first gear selection. For example, take the TH400's 2.48 gear x the rear gear of 3.08 and this equals 7.63. Now if go to 2004R with a 2.78 gear with the 3.08 rear gear and this moves closer to "10" at 8.56.
Now switch out the rear gear to a 3.55 and this number moves up to 9.86, with a 3.70 rear gear =10.2.
With a 700R4 wit the 3.05 gear and 3.08 rear gear this gets close to 10 with a 9.39, with a 3.55 rear gear =10.82
Only issue I see the the 3.05 of the 700R4 is the spread between fist and second. Not as bad with the 5 speed Tremecs with the extra gear.

7T1vette

I installed a 700R4 in my '71 SB car, because I had access to that transmission at a very good price. But, if all things were equal, the best choice for me would have been the 200-4R trans. The gear ratios are a bit better (although neither trans needs to start in 1st gear for normal driving), but the installation would have been much easier as the driveshaft and crossmember would not need modification/replacement.

Street Rat

Great information all. I have the 350C which I despise. A 2:87 rear axle ratio and want it to be able to get respectable mileage and cruise the highways. The 200 R4 sounds like the ticket.

stingraymyway

briankeery

Fantastic thread guys, very informative. Question.....as far as the 200 goes; is there any specific year/application that we should be looking to pull these trannys from? Or will any 200 do?

Thanks for the advice.

Brian

iokepakai

Researched this subject to no end until I decided to go with a Richmond 6spd.My 76 had a TH350 with a 3.08 rear gear,pretty boring to drive around.Didn't want the added expense to change rear gears so I needed at least a trans with a 3.XX first gear.The Richmond 6spd was the best choice.The gear spreads are just about perfect with not much rpm drop between shifts.The .76 6th gear OD works well with the 3.08 rear gear,I can use 6th as low as 45 mph without lugging the motor.Rowing thru all 6 gears is a blast and the engine just humms along at hiway speeds returning an average 20mpg....The trans is close to same length as the TH350 and I was able to use the same driveshaft with a TH400 yoke.Here's my write up: http://forums.corvetteforum.com/c3-t...am-change.html

73ss

My Trans builder said next to the 442/GN/SS trans, which are getting hard to find, The full size Caddy's with 307 olds power are the best. Late 80's~early 90's.....If you are junk yard hunting, Grab the cable bracket as well. Fits nicely on a chevy Q-jet.

7T1vette

Or mid-80's Buick Gran Sport with 200-4R auto. But, any of them can be re-built with stronger components so they will hold up well to V8 power. Find one and have a local trans shop (NOT one of the chain stores) rebuild it for the HP you have. Or call and see if they have one they will exchange for your old tranny.

Street Rat

Going to look at one out of a Caddy tonight! 307 Olds motor and TH 200R4 transmission.

c6silver

I'll be doing this swap into my recently acquired '73 LS4 with A/C. My trans came out of an 87 Buick GN, but like an idiot I didn't get the converter (which I think is the highest stall stock at 1900 rpm)...so I guess I'll have to buy aftermarket or look for a used GN converter.