lewiswynn2

I've been reading the posts and have learned a lot but I still have a little confusion.

I have a 71 Cutlass Supreme Conv with a 350 engine and a 350 trans. I'm planning to swap the transmission and here are a few questions...

Can I swap the 350 for a TH700R??? I've read that I will need to shorten the drive-shaft 6". Some have said that I can only swap in a TH200R. Is that correct???

What is the best choice (if there is one)???
I'm only cruising, not racing, but I need some get-up and go when I hit the gas.
I'm may need to change the rear-end gears to complete this project.
Any recommendations on where to buy the trans??? I see them for sale in every mag/website/etc.
Any help is appreciated.
Thanks,
-Lewis

joe_padavano

Olds engines use what is called a BOP bellhousing (Buick-Olds-Pontiac). It is different from the Chevy bolt pattern. Most GM transmissions were available with either of these patterns (and some with both on one case), but the 700R4 was never made with the BOP pattern. That means that to put one in an Olds, you need an aftermarket adapter plate kit. The other problem with the 700R4 is that it has a crossmember mount location and overall length that are unique to that trans, so you need to relocate your trans crossmember to a custom location and you need a custom driveshaft.

The 200-4R is preferred for several reasons. First, the gear ratios are slightly better than those on the 700R4 (the drop from first to second is not as severe and the O.D. ratio is slightly higher, for lower highway RPMs). Second, the 200-4R is available with a BOP pattern, so it bolts right up. Third, it is the same overall length as the TH350, so your original driveshaft can be used. Finally, the trans mount is in the TH400 location, so while you need to move the crossmember, your frame is already drilled at the right place since the TH400 was optionally available on your car.

The two issues with EITHER trans are 1) neither is strong enough in stock form - you will need an aftermarket version built to take the higher torque, and 2) moving the crossmember requires different e-brake cables. The good news is that with the 200-4R, you simply need to get the cables for your car with the TH400 option. Only the front and intermediate cables change. The rear cables that go to the wheels remain the same.

matt69olds

Use the 2004r trans. Find one in good condition and install a Trans-Go shift kit, or order one from CK Performance with his servo and govenor. A stock 2004R in good condition will easily handle a mild 350 with the correct valve body calibration. The 2004R in Grandma Caddilac is the same as one in a Turbo Buick with the excepton of the valve body and servo. The TV cable has to be adjusted correctly also, not "close enough". Spend whatever time and money is needed to get it right.

Allan R

IIRC the front and rear cables are the same, it's only the intermediate cable that's different.

joe_padavano

Sorry, no. The front AND intermediate cables are different part numbers and lengths for TH400 applications vs. other transmissions in the A-body cars.

droldsmorland

Adding to this post... IMO... I would not put a stock THM2004R behind a 350 (unless you luck upon a GN or GNX 2004R, good luck). There are subtle differences between the GN and a grocery geter 2004R. And since the GN even more improvements have come around to address the 2004Rs short comings, as its a popular swap now. So the aftermarket support is there whereas it was not 10 years ago. I realize your not building a 1/4 mile brawler with steam rollers but it certainly couldn't hurt to purchase a properly beefed up 2004R. A stock 2004R will work fine for a while as long as you aren't hard on it. You will get significantly more life out of a professionally modified unit verses simply modifying a run of the mill unit. I've had these things apart, internally they are puny compared to a 350 or 400. They are really not designed to be put behind anything with any torque unless modified with a little more than just valve body and governor mods. These items will not add strength to a 200s weak spots. In fact it will make them show up sooner.
My advice is to purchase a warrantied professionally assembled/dynoed unit from TCI, B&M, Art Carr or COAN. They already have the necessary mods, are dyno tested and come with a warranty. Give any or all of the above a call and discuss your needs with their tech line. They will guide you. Good luck let us know how the mod works for you.

hookem horns

Lots of advantages on the 200, but what's wrong with the TH350 in it now? They can be rebuilt fairly inexpensively, with the valve body set up from factory mild to full manual depending on your preferences. A 3.23 or 3.42 rear end will help off the line and still be OK for highway use. Decent low cost option for a cruiser.

That said, I'm having some issues with my TH350 and the 200 is very enticing if the budget allows.

Allan R

Advantages for a 200? What would that be? The TH200 is a much weaker transmission than a TH350 and is not the same as a 200 4R. Are you abbreviating the 200 4R to mean 200? Because the 2 transmissions are different.

hookem horns

Yes, 200-4R properly built like Joe describes above.

matt69olds

There were a few uprades done over the years, but the changes were made across the entire transmission line, not just the GN trans. In 1984 there was a change made to the heat treat on the low/reverse sun shell, I believe there was also some changes made to the overdrive carrier. The biggest changes between a Buick GN trans and a regular 2004R is the valve body, servo, and govenor. The hard parts are the same. I have taken many stock 2004R transmissions and put them behind 455 and they live, AFTER the above upgrades. CK Performance has a package that includes the needed parts. The new Trans-Go kit includes the parts to upgrade the servo, and springs for the govenor, but I havent installed one yet. The 2004R isnt a bad trans, it just hasnt outgrown its early reputation.

lewiswynn2

I've been going back and forth on this one. Everyone has made some really good points that have been right on the money.
I think I'm leaning to staying with the TH350 trans for several reasons.
- stays original on the drive train
- no need to do additional mods
- still has good performance
- lower cost to rebuild

I visited a local trans shop this week and he estimated about $1300 or so (we know what that means), plus he wanted to keep the car 3-4 days. I thought it was a little high considering I can buy a dyno tested trans for the same money...but the store bought would not be the original trans. I'm going to check with another shop for pricing but the important thing is to get a good job from a shop that will stand behind the product.

Any comments???...and thank you for the excellent insight. Without the forums I'd never find so many solid opinions to consider!
-Lewis

droldsmorland

Ya put the #s trans on the floor and purchase a beefed semi-auto valve bodied TCI 350 from Jegs or Summit. Dyno tested, 1 year warranty. Rebuild the #s 350 at your leisure maybe even attempt it your self. They are not hard to do but you do need a few specialized tools and a good video. Use the TCI Synthetic clear fluid in either case. Change the fluid and filter after 1000 miles.
Have you looked into a Gearvendors OD unit? Could put one of those behind either trans for whats essentially a 6 speed trans.(you split the 3 forward gears so 1...1.5, 2...2.5 etc).

TexasT

Also the stator support is heat treated on later model units. The pump got hard pump rings. The overdrive carrier on early units has a phenolic (plastic) bushing and the latter units, including the brf units, got a bearing.

Nothing that can't be upgraded during an overhaul. You just have to trust the builder to do it.
I didn't do anything special to mine. I did put upgraded clutches in the direct and a better band and aftermarket servo for 2nd. I made some mods to the vb and plate that were mentioned on the interwebz. Larger boost valves, different springs, hard pump rings and upgraded slide spring. Some careful assembly. It has been in the car since Dec and I've been driving it back n forth to work.

arcee1951

It is up to the individual, and I agree with everything said. (I may run for Senate) I did some wild stuff with my 66, and wanted to keep the 4:56 posi rear end in. That with the Jetaway 2 speed, wasn't working, though great from light to light.

I ended up having a 200 4R built. It came out of a 4 4 2, though the guy beefed it up. When I asked him if it would take the power of a 330 with 310 hp, he took me out back and showed me his 70 Chevelle with a 454 in it, and said he built his 200 4R for that, and didn't baby it. Good enough for me.

I screwed up by taking the 4:56's out and putting in a stock rear end. They are either 2:73's or 2.78's. What I found out, was that the speedometer was spot on. I should have gone with 3.23's or 3.45's. At any rate, we did the math on it. It should do 150 mph. It won't, and I wouldn't have the guts, as I had it at 120, and it felt like I was achieving flight. If the wind isn't blowing, and I'm not on hills, it will get 24 mpg. The bad thing is, that, if there is any wind, or hills, the tranny will downshift often. Live and learn.

RocketKid70

What about a Gear Vendors overdrive unit? You can probably get one for the price of a professionally built trans which would still need other pieces, such as a quality converter. I think they run around $2600?