Where to find what my stock transmission is in 1990 GMC Sierra?

[sniperlif3]

Well i have a 1990 GMC Sierra (C1500) that has the stock 2wd transmission but i cant seem to find what the exact transmission is that is in my truck... I know that it is a 700R4 or a 4L60(E) but im not sure which one came stock and how they were built origanlly...
Does anyone know either where to find this information, or maybe know the exact information?

I am wanting to get a replacement transmission, or rebuild the current one so that i can boost it up from stock... One of the most key things that i want to see that is available is if i am able to get another gear somehow so that i can increase efficiency and performance...

 

[Molson02536]

This right side (Passenger) of an '89 and later 700R4, the transmission RPO code MD8 will be stamped to the front of the bell housing. the 4L60 is essentially the same trans as a similar-vintage 700-R4. All GM transmissions use the new identification system: the first digit is the number of forward gears (4), the letter indicates whether the trans is intended for front-wheel-drive (T for transverse) or rear-wheel-drive (L for longitudinal) applications, and the last two numbers provide a guide to the unit's relative torque capacity (60, in this case) compared with other GM transmissions. If both nonelectronically controlled and electronically controlled versions of an otherwise similar transmission design are offered, an E suffix (for electronic) is appended to the designator.

Use the serial number located just above the pan on the passenger side of the transmission and there you'll find a letter M(700), believe it's 4th digit. This first digit is the most important. This will indicate what year the transmission was built. Note: GM used "9" for years 1982 AND 1989. The easiest way to identify between the two years is to look at the passenger side of the case. Any 700R-4 built before 1989 will have the pressure taps, while all units built after 1990 will not. With the pan off, all 1987 or later units had an auxiliary valve body. 4L60E (electronically shifted 700s) produced 1992 and up. Can be identified by the large electrical connector just behind the 2-4 servo on the passenger side.

If your looking for a 700R-4 that will hold up in a performance application, the clear choice is to build the 1989 or later models (without the pressure taps). These units have the larger input shaft, larger input sprag, 10 vane pump, and the updated gear train.

One big update for 700s and 4l60s are the use of the newer 4l65 5 pinion planetaries and updated and reinforced sungear shells. Give California Performance Transmissions a call you can talk to the trans man him self Art Carr. Oh he answers the phone too.

http://www.cpttransmission.com/