Overdrive Transmission Swap Info for GM units

by 77mali Thu May 16, 2013 6:04 pm

Page say's copyrighted material so providing link only.

Kudo's to this dude Mike for sharing & creating such a detailed webpage. It's really something else & is full of info & answers just about any question one might have about swapping to an OD GM Trans...pretty cool.

http://www.rowand.net/Shop/Tech/AutomaticOverdriveTransmissionSwap.htm

by pila Fri May 17, 2013 12:36 am

The folks on El Camino Central forum do a lot of switching to OD transmissions on the G body Elcos. The 2004R is a bolt-in in place of some 3-speeds, like a TH350 etc, with only 3/8" difference in drive shaft length etc
Some favor the 700R4 instead. Some '87 and '86 Elcos came with the 2004R transmissions, with the 305 engine.

by thatfnthing Fri May 17, 2013 9:33 am

The 200-4R came behind a lot of V-8's (including the Monte SS) and was the trans of choice for the G-bodies in general. The 700-R4 was used in Camaros. However, the stock 200-4R unit is not strong enough to withstand even mildly-serious power -- it must be rebuilt with better components, then it's a great trans.

by driveit Wed Apr 16, 2014 1:31 pm

Will I need a different shift linkage if I swap from a 350 to a 700r4?

by pila Wed Apr 16, 2014 8:28 pm

The quadrant in your steering column will not have all the notches for all the selections, even though the transmission does. Some folks have used the 3 speed column and didn't have the 1st gear manually selectable, but had the rest. I don't know if any later column with OD could be swapped in there...

by Joe73 Wed Apr 16, 2014 9:27 pm

Plenty of mods on the net to make your existing column or floor shift work with all 4 gears of an od unit. I've even seen a pick of a mod that you can do to your factory detent plate to allow it to work with an od unit. Here's some info if you want to do the swap.

http://www.shiftworks.com/chevelle-64-67.htm They have everything you need and do sell the detent plate separately.

700R4 Shift Detent Plate Conversion Kit is what your looking for.

But I have seen some mods with pics and drawings on the net that you can do yourself if your handy with a grinder.

by pila Thu Apr 17, 2014 4:50 am

The early years of the 700R4 were not as durable as the late 80s years. Good info on the column shifters Joe !

by driveit Thu Apr 17, 2014 12:18 pm

Found a transmission last night and thought it was what I needed until I got there. I believe it is a TH200.
Overdrive Transmission Swap Info for GM units TH200_pan

Overdrive Transmission Swap Info for GM units TH200_pan

Overdrive Transmission Swap Info for GM units Th200

Anyone know anything about these. I think they are a pretty weak transmission from what I have read. I am not even sure that it is an OD.

by driveit Thu Apr 17, 2014 12:21 pm

Nvm. I just read that it is basically a light duty version of a TH350. Totally bummed! My chances to make to the Hot Rod show are not looking good.

by thatfnthing Thu Apr 17, 2014 12:44 pm

driveit wrote:Found a transmission last night and thought it was what I needed until I got there. I believe it is a TH200.

Anyone know anything about these. I think they are a pretty weak transmission from what I have read. I am not even sure that it is an OD.

The 200 and the 200-4R are not the same animal. The 200 is only a (very) weak 3 speed. The 4R is longer, has a 16-bolt pan shaped like the state of Nevada (not just a square with the corner lopped off), and had 'METRIC' stamped on the pan in big letters. And, obviously, 4 speeds. The 4R came behind V8's and V6's in the G-bodies (Monte, Cutlass, GP, Regal). In its stock form, it won't take a lot of abuse (unless you can find one from the turbo Regals), so it will need to have some upgrades to handle serious power. If you don't plan to abuse it, though, it should be fine with daily driver duty.

by driveit Thu Apr 17, 2014 4:04 pm

I need an OD for mostly daily driven use. I lead foot daily driven use!

by thatfnthing Thu Apr 17, 2014 4:30 pm

Lead foot can be fine if you're still at stock horsepower levels, because the G- and F-bodies were at similar levels when those transmissions were used. But as you start pouring money into the motor, you can't expect to go from 200hp to 400hp without also having to upgrade the trans, too.

However, don't forget the OD trans is a matched set with the rear gears -- if you go from 1:1 at the trans to .67:1 overdrive, the tall stock rear gears will cause your RPMs to be too low, and your driveability and mileage will be worse, not better. With an OD trans, you will also need to go to a higher numerical gear in the rear -- figure 3.42 as a minimum.

by Joe73 Thu Apr 17, 2014 4:38 pm

And also. With a 200r4 you get a 2.74 first gear ratio as opposed the 2.52 a turbo 350 has. So you will get a better launch as well as nice highway cruising.

Although, a 200r4 supposedly uses more hp to run it.

http://www.oldengine.org/unfaq/leadfoot/trans.htm

by thatfnthing Thu Apr 17, 2014 4:51 pm

Joe73 wrote:Although, a 200r4 supposedly uses more hp to run it.

Maybe, but I'm not sure it's enough to notice. I certainly never noticed any difference with mine. It's definitely a bit heavier, though, especially with a lockup converter factored in.

by driveit Thu Apr 17, 2014 5:03 pm

Here will be the setup.

350 - 30 over
Stock 882 heads
weiand single plane intake.
Edelbrock 600 card
No Name headers
Accel HEI Supercoil
Flomaster mufflers.

That is it. Mild cam you can barely hear any lope to it at all. I don't remember the specs on it.

Doubt I would even hit 300 hp. What do you guys think?

by Joe73 Thu Apr 17, 2014 5:54 pm

What rear gears? I'd have the 882 heads milled .010. That will up the compression slightly. And I'd pass on the single plane. They're for upper rpm power. Dual plane will give you more low end torque.

by chevellelaguna Thu Apr 17, 2014 7:29 pm

Agree single plane will kill your bottom end torque. I agree about milling the heads, however don't spend much on iron heads there are lots of cheap aluminum versions out there that you can swap on at a later date.

by driveit Thu Apr 17, 2014 8:00 pm

Right now I have to put up with the single plane until I can find a dual. My dual plane was stolen out of my mom's garage. I hope to find one this summer at a show cheap. Gears I think are a 2:76. I thought it was a 2:80 something, but it is probably a 2:76. Stock gear for a malibu with 6 cylinder and Th350.

by dynchel Thu Apr 17, 2014 8:13 pm

driveit wrote:Right now I have to put up with the single plane until I can find a dual. My dual plane was stolen out of my mom's garage. I hope to find one this summer at a show cheap. Gears I think are a 2:76. I thought it was a 2:80 something, but it is probably a 2:76. Stock gear for a malibu with 6 cylinder and Th350.

yeah, I think my originals were 2:72's......so I went from one extreme to another. ( I now have 3:73's)

by driveit Thu Apr 17, 2014 8:33 pm

If I get the 700R4 would a 2:76 be an ok gear? I was thinking of going with a 3:42 later on with it, but would that defeat the purpose of getting the extra gear?

by chevellelaguna Thu Apr 17, 2014 8:52 pm

That's the purpose of an overdrive trans, you can go with a lower (numerically higher) rear gear ratio, and in overdrive, your final drive RPM's will be lower.

by thatfnthing Fri Apr 18, 2014 9:12 am

driveit wrote:If I get the 700R4 would a 2:76 be an ok gear? I was thinking of going with a 3:42 later on with it, but would that defeat the purpose of getting the extra gear?

In an OD trans the third gear is 1:1 (i.e. 1 revolution of the driveshaft for each revolution of the crank), which is what your old TH350 was. The problem is the 4th (OD) gear, which will not play well (whether it's the .70:1 in the TH700-R4 or the .67:1 in the TH200-4R) with any rear gear below 3.42. Your engine will lug and suck down more gas because the engine RPMs are now way too low.

So if you want to keep the OD trans in third gear all the time, it will be like it always was. But then you wasted your time, money, and effort getting the OD trans in the first place.

Your rear gear is probably 2.73:1, which was the option back then for mileage. For performance, you got a 3.08:1.

by driveit Fri Apr 18, 2014 12:01 pm

I have a 3:08 set. Would that be best to use?

by thatfnthing Fri Apr 18, 2014 3:57 pm

In OD it will suck slightly less than a 2.73.

by Joe73 Fri Apr 18, 2014 4:20 pm

I say 3.42 at the least. You will be very happy with some 3.73 gears. Because 3.73 x 2.74 (first gear) = 10.44 That would be a real nice launch.
But 2.73 x 2.74 = 7.4 Not so much fun there. You would like to be in the 9-10 range when you calculate.

Now for the .67 or .70 4th gear ratio, you will be fine with a 3.73 and the car will be real fun to drive.

Just remember, if your drag racing the car, you dont want to go through the traps at the end in 4th gear. You want to be topped out (rpm wise) in third and maybe just click it into 4th right before the traps and let off.

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Overdrive Transmission Swap Info for GM units

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