Auto transmission swap

Scott,
If you want drama-free interstate cruising without the hassle of a computer, your only two options are a 700-R4 or a 200-4R. There is much ongoing debate as to which is better, but both are extremely capable. While the 700-R4 is generally accepted as the stronger unit in stock trim, thanks to the advances forged by the Turbo Buick scene, the 200-4R can survive in 8-second drag machines without a hitch. To help you decide, Farah points out some key differences between the two. "The 700-R4 has a deeper First gear ratio of 3.06:1, but that results in a bigger drop in rpm between First and Second, and it also has a taller overdrive," he says. It is slightly larger in size than the 200-4R, and Gearstar's Level 4 big-block unit is rated to handle the torque of a stout 502. "The 200-4R has a taller 2.74:1 First gear ratio, so it doesn't have that big drop between First and Second. It is slightly smaller in size than the 700-R4, can handle up to 800 lb-ft of torque, and uses less power to turn."

Hope this helps,
Dan

Here's some 200R4 info:

DIMENSIONS:


TAG DECODE:

TH-200-4R transmission tag:
___________________________________________
| 117 1T86OG0346 |
___________________________________________

117 = Julian date of day of year
1T86OG0346
1 = shift built 1, 2 or 3
T = Three Rivers
86 = Model year
OG = Model
0346 = Serial number

But if you just looking for a fast way to identify the trans on the spot. You might want to just print this pic and take it with you.

Dan
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Automatic Transmission Identification & Description
Automatic transmission types are generally identified by their pan shape.


The THM200 and the THM250 have pans shaped like a THM350, HOWEVER, the THM200 will have the words HYDRAMATIC DIV. and METRIC stamped into the pan.

Automatic Transmission Description & Usage
-THM200 - Light duty, "metric" 3 speed transmission.
-THM250 - Used in small 4 cylinder cars (Vega, Sunbird, Monza) from 1973 to 1981 and some Nova/Camaro/Chevelle 6 cylinders in 1974 & 75. The 4 cylinder models have 4 large cooling holes near the torque converter, while on the "bigger cars" there are no cooling holes.
-THM200-R4 - Used in GM rear wheel drive cars with the 3.8 V6, 305 & 350 Olds and 301 pontiac from 1981 to 1989. This is a 4 speed, overdrive unit.
-THM350 - Medium duty 3 speed trans used from 1969 to 1989, Used in Buick, Olds, Pontiac and Chevrolet cars and Chevy & GMC light trucks until 1987. Generally used in straight and V6 and small block engines. Generally able to handle up to 400 foot pounds of torque.
-THM375B - This trans is identical to the THM350, but is considered a heavier duty transmission.
-THM375 - This transmission is a derivative of the THM400 sharing the external appearance of the 400. It'll be marked 375-THM on the bottom of the tailshaft housing. It's a light duty version of the THM400, has ABSOLUTELY NO RELATION to the THM375B, and was found in 1972 to 1976 full-size cars. The Turbo 375 was modified to accept the Turbo 350 driveshaft yoke.
-THM400 - The THM400 was GM's Heavy-duty 3 speed transmission used from 1964 to 1990. Used on large displacement, high torque engines and engines with towing packages. Generally found in Chevy & GM trucks, cadilacs and large displacement engined, full size GM rear wheel drive cars.
-THM700-R4 - 4 Speed transmission used in GM cars and light trucks with the 2.8, 3.1, 4.3, V6, Chevrolet built 305, 350 and 454 engines from 1982 to 1992.
-4L60 - Early 1990's saw the 700R4 renamed to the 4L60, and "electronic" models were named 4L60E. 4L60 means 4 forward speeds, L = longitudily mounted (rear wheel drive). 60 is the strength rating (less than the 4L80).
-3L80 - The 3L80 is a renamed THM400, used in the early 1990's. The 3L80HD would be the THM475 (heavy duty unit).
-4L80 - An overdrive model of the THM400. The 4L80E would be the "electronic" model.
Transmissions with a suffix of "C" on the end of the type (THM200C) indicate the transmission has a lock up torque converter.

a buddy and I just completed a conversion project on his
67 90wb. we removed the three on the tree for a 700r4,
shortened the driveshaft three inches and had ballanced,
removed the carb and replaced it with a tbi sys from a 92
astro van. I got a kit for the lock-up converter off of ebay
for about 25.00 one wire with no switches to mess with,
worked great, and was very easy to install. His van has
a 336 in the rear end and it now turns about 1900rpm
at about 70 mph. We made a hanging bracket for the
trans. The hardest part of this project was re routing the wiring
for the computer and other components that we left inside of the
van insteat of inside of the dog house. I will includ a few pics.

Here is a shot of the gas tank, 88 chevy van, and the shifter cable set up
it is from an s-10 blazer with a floor shifter, auto cable is about 9 feet long.

Scott,
Can't remember. One of those off eBay somewhere....

Dan

Hey to all- Im doing this swap now - using a 3rd gen xmember- as I have a parts van for my 2nd gen- on the subject of rear gears swapping for better fuel mileage ? Ive done that year back on my 67 vette- went from 3;70 to 3;08 - worst thing i ever did!!. If u have a low ratio set already in the van - IE:3.50- 373-4:11=up just do the 700r4 swap - cheaper & will deliever the fuel mileage and the extra benefit is the fact u still have the pulling capacity of the low ratio rear set gears!! the high gear ratios will use more fuel to get things rolling and during pulling -ive learned !! Thanx to all

The guys in the know are "WWW. Bowtieoverdrives.com theyve got it all & are good at this trans stuff.

panelmanrd wrote:a buddy and I just completed a conversion project on his
67 90wb. we removed the three on the tree for a 700r4,
shortened the driveshaft three inches and had ballanced,
removed the carb and replaced it with a tbi sys from a 92
astro van. I got a kit for the lock-up converter off of ebay
for about 25.00 one wire with no switches to mess with,
worked great, and was very easy to install. His van has
a 336 in the rear end and it now turns about 1900rpm
at about 70 mph.We made a hanging bracket for the
trans. The hardest part of this project was re routing the wiring
for the computer and other components that we left inside of the
van insteat of inside of the dog house. I will includ a few pics.

Nice TBI setup would you like to share how you did it?

I agree with Twinpilot. My van came with the 3.73 rear end and I thought for sure I'd need to switch it to a higher ratio. But I put in the 700R4 first. That way I could give these gears a try. And it is really nice! Best of both worlds. I want to get a tach so I can give you guys some actual numbers. But based on the feel of it, I'm not planning on switching. I put in a rebuilt 250 engine and it takes off pretty good from a stop. And on the freeway the RPMs are very reasonable. (I can drop it down into Drive to see how it would be with any non-overdrive tranny - quite a difference.)

But the important part is, even a new 250 isn't a powerhouse. On the freeway, when I start going up an incline, even a slight one, I can feel it starting to bog down. I can end up with the pedal to the metal and there ain't no more. So then I can downshift into D to get more power. So if I had 3.08 or 3.36 gears, I'd hit that bogging point sooner, right? And dropping it into D would help but it wouldn't be as low as mine.

Someone once wrote a long post on how lower RPMs is not always better. It doesn't always mean more MPG. There's a sweet spot where you're getting the most torque(?) and it is usually at the higher RPMs.

The true test will be when I start driving it enough to go through a few tanks of gas so I can determine my MPG...