snike3

Well, I'm thinking about swapping out the transmission in my '75 for something with overdrive. My wife doesn't like how the car sounds like it's taking off when you're on the interstate (and how she can't talk to me without yelling) and I don't like how quickly the fuel tank needle falls...

Anyway, I've been doing a lot of reading on 700-R4 vs 200-4R and have come to the conclusion that the 200-4R is less of a pain for similar gains. I was wondering if anyone that's changed to the 200-4R had to alter their u-joints or driveshaft length?

I read in a bunch of forums that the driveshaft only would have to be modified for the 700-4R but when I talked with a rep from Bowtie Overdrive, he thought it might have to be.

Also wondering if it's worth swapping out my crossmember for Bowtie's custom bolt-on one since I'm changing from the TH400 where the mounts are very close?

'75

I put a 200-4r in my 75 where the TH400 was. The drive shaft does not need to be modified. You will need a slip yoke from a th350 vette and probably a 1310 to 1330 conversion u-joint(commonly found at all parts stores) No need to change cross members, the stock one will work, just have to slightly file out or elongate the bolt holes for the trans mount.

snike3

Bowtie is asking $110 for a new yoke and it looks like the Corvette catalogs want something like $130-160... Seems like getting the yoke from them is decent deal.

Thanks for the info!

682XLR8

I have the 200R4 also....no need to modify the driveshaft or change out the crossmember....as mentioned earlier you will need a conversion u-joint(can dig the number up for you later), BTO will get you set up with whatever you need
It's a good idea to have the driveshaft balanced also while you have it out

redwingvette

I also changed my TH400 to the 200-4R. I got everything from BTO. Well worth it.
The only part I could not find was the bracket that the steering lock cable attaches to the trans with. I had to make one. If you need one I can get you the drawings. I made several at the time but I do not have the time to make them any more.
Good luck.

hammadown

http://forums.corvetteforum.com/c3-t...e-a-200r4.html

http://forums.corvetteforum.com/c3-t...too-short.html

drop down to post 46
http://forums.corvetteforum.com/c3-g...rogress-3.html


Hammadown

scottyp99

What is your diff gear? If it's pretty steep, like a 3.70 or higher (numerically) the 200 would definitely be the way to go. If you have a highway gear, you might want to take another look at the 700 with it's low first gear. You said the better half doesn't like how it winds out on the highway, so you may have a pretty steep gear in there, '75 'vettes could be ordered with a diff gear anywhere from 2.73 to 4.11 (The last year 4.11 gears were offered on the Corvette)

http://corvettec3.ca/axle.htm


Keep the shiny side up!
Scott

myko

Arggg! I am in the same boat but I have an '80 with the TH350c. Everytime I think I am ready to order a 200r4 I see something like this. I don't mind the launch through 1st and 2nd with the TH350+ 3.07 diff the way it is now.
With relevance to the OP - how much difference will be noticed between the 700 and the 200?
For my situation - how much more pain will the 700 be to install vs the 200? I have read threads on each; anyone done both?

77vetteluva

This might be something to consider...I swapped from a th350 to the 200. If the 400 cross-member is like the 350 where the exhaust goes through tubes you may have clearance issues where the shape of the 200 pan partially blocks them. I got a BTO cross-member and it fit perfectly making room for the exhaust. Well worth it.

scottyp99

With a 3.07 diff, the th350 gives a first gear final drive ratio of 7.74, the 200 gives 8.41, and the 700 gives 9.39. The rule of thumb says 10:1 in first gear, but it's just a guideline. All it really means is that the more gear you have in first gear, the better the car will go from a stoplight, up until about 10:1, where you start to get into a situation where 1st gear is too low of a gear, and the thing starts to drive more and more like a tractor! A better way of saying the rule of thumb might be "Don't go much more than 10:1 for 1st gear final drive." If you have a th350 now, I think the only real difference between installing a 200 and a 700 is that the driveshaft needs to be shortened with the 700, which really isn't that big of a deal. Although, some people say that they don't like the big jump between 1st and 2nd gear, but that may just be from people who don't have a wide enough powerband to cover it. Plenty of hot cars have come out of the factory with 700s or 4l60s, and it's not an issue with the broad torque curve that factory cars have. For what it's worth, my Roadrunner back in the day had an 8.7 first gear final drive, and that thing would boil the tires until I let off the gas in first gear. It was a pretty stout 440, though, so that might be applea and oranges. The 200 swap is attractive for people who presently have a th400, (especially if they already have a steep diff gear, like a 3.70 or more)because the tranny crossmember can be used as is, and the driveshaft doesn't need to be cut, making the swap quite a bit easier than a 700, which would require both. I have a '80 'vette with the 3.07 diff also, and I have decided to go with the 700, because of my high diff gear, the fact that I am building my engine with a nice, wide flat torque curve, and because I already have a good core, but if I were the OP, I would probably lean toward the 200 also, because of the ease of the swap, and we don't know his diff ratio, but it sounds like it may be pretty low. It's probably the smart way to go for him, but I think the 700 is the smart way to go for me.

For the OP: I believe you can use your existing crosssmember, but an aftermarket crossmember will be lighter, if that is something that matters to you. I don't know anything about the exhaust issue posted above, one way or the other, but it sounds legit, so that may be another reason to use an aftermarket crossmember.


Keep the shiny side up!
Scott

snike3

Hey thanks for all the great responses!

So my rear differential ratio is 3.08 (confirmed using the numbers and I'm fairly certain it has never been rebuilt). I originally had chosen to go with the 700-R4 because it's basically "the go-to" for hot rods. After reading how much easier the swap for a 200-4R was from a TH400 and the "smoother transitions", I was sold on it. Not to mention the local transmission shop thought it would be the better bet for me. The transmission guy said what I really should get is the TH400 with an overdrive (can't remember the model number) which unfortunately requires the tunnel to be modified for the transmission to fit. Not up for that, so 200-4R it is...

Anyway, I found a guy in town that's going to rebuild my differential with a 3.55 ratio. My mechanic agreed that 3.55 would be appropriate for my new engine so I can get good starts and still have a good experience on the highway.

As far as my questions go, I'm definitely going with the Bowtie Overdrive 200-4R and I'm going to use my stock crossmember. The rep at Bowtie thought their crossmember would reduce the weight by only about 10 lbs. That is fairly significant, but I'm not drag racing so 10 lbs is not a big deal to me. I'll just save the $190 for my differential rebuild. As for the exhaust. I don't have to worry about it. I have side pipes with hooker headers. Those exhaust hole sit empty (the Bowtie crossmember would make it look cleaner... hmm...).

snike3

Those are really good posts to read! The car looks awesome by the way! My project started with a simple radiator and water pump swap and has turned into a monster... It just keeps making sense to do one thing after another.

vanice

I had 2 1/2 true duals on my 77 and had no issues with the exhaust using a stock crossmember

CA-Legal-Vette

That does happen

You won't regret the change. Makes a surprising difference in the drivability of the car.

nate99

Did anyone set up the TV system themselves, or did you have a shop do it?

MakoShark72

Had local trans shop "build" my 200-4R. Did the install and set up the TV cable myself with BTO's cable and instructions. Had the shop check it out. All good.

redwingvette

I set mine up myself as well. Just follow the instructions on the BTO website and watch the pressures.

rosslato

You can get the Yoke at most auto parts stores. can't remember which one i went to but it cost around $35 5 yrs ago.