700R4 transmission in my 1990 gmc sierra 4x4?

[Ethan]

i got a 1990 gmc obviously. it has a 305 in it. the transmission is only a 3 speed auto. im just trying to figure out if its the 700R4 or not. some people told me it was but others said it was a 4L60. i honestly have no idea.
20+ year mechanic, it truely is a 3 speed. it say on the cluster- P R N D 2 1. and at 50 mph its running at 2000 rpm, with over-drive it would be about 1200 to 1300 rpm. i just gota say thanks for the help man. i really appreciate it. now, the next question is, would it be hard to put the 700R4 in it. or should i just leave it alone???
also, thanks to you Charlie. thank you to both of you for the help in narrowning my search! much appreciated.

 

[Molson02536]

i got a 1990 gmc obviously. it has a 305 in it. the transmission is only a 3 speed auto. im just trying to figure out if its the 700R4 or not. some people told me it was but others said it was a 4L60. i honestly have no idea.
20+ year mechanic, it truely is a 3 speed. it say on the cluster- P R N D 2 1. and at 50 mph its running at 2000 rpm, with over-drive it would be about 1200 to 1300 rpm. i just gota say thanks for the help man. i really appreciate it. now, the next question is, would it be hard to put the 700R4 in it. or should i just leave it alone???
also, thanks to you Charlie. thank you to both of you for the help in narrowning my search! much appreciated.

The 1990 GMC Sierra 1500 came with a 4L60 transmission which is a updated 700R4, here are some differences.

The V8 style 4L60 and 700 are the same. the converters are the same , the flex plates bolt pattern for converter are the same. All bolts are still metric. 700 trannys have always been fully metric. There are minor differences in 700r4 & 4L60's, but they all interchange parts. Later design parts are better. Some valve bodies & separator plates do not inter change from late to early design.

Early 700 pumps and stator parts must be watched for mis-match. You will have little or no pressure with mismatched parts of early pump / stator designs. Also a 4L60/700R4 transmission from 4.3 V6 engine will have different boost valve to control the shift firmness. And make sure you have the correct flexplate for the engine. The bolt pattern for the converter will bolt to any 700 / 4L60 converter for V8's. 3 piece 4L60/65E trannys use different converter bolt pattern( bell housing unbolts) if you decide to upgrade the 4L60 to a 4L65 which the planetary had 5 gears in the sun-shell rather then 4.

As for you say you have a 3 speed, you may have a TH350-C. The TH350-C version had an electronic lock-up converter to increase fuel-efficiency at cruising speeds. The TH350-C lockup version can be indentified by an electrical plug on the left side of the transmission. When paired with an aftermarket TCC control unit, these can be desirable transmissions with more efficient at cruising speeds. The conventional TH350 had part codes of M33, M38 & M39. The TH350C had codes of MV4, MX2, MX3 & MX5.

If you do have a 4L60 (700R4) Pull off the side cover on the trans (very easy to do) and pull the Governor out and check the gear. Its plastic and tends to break or strip off. If its ok, make sure the valve inside the Governor moves freely too.

Good luck and hope this helps.