Transmission Swap Question

[Jon87V20]

Hello. I have an '87 Chevy Suburban Silverado V20 with a 350/TH350 and I'm not sure which transfer case is in there. I'm wondering if it's possible to swap the TH350 for a 700R4? The reason being, is, I would just like to have the extra gear on the highway. I'm trying to pinch every last mpg I can out of the truck as it's going to be my daily driver for the foreseeable future and I'd like to have it not spinning up so much all the time. Is there a chart somewhere that shows what transmissions bolt up to what engines and transfer cases etc.? I'm a transmission noob in general. I don't even know if the 700R4 is the best swap for the situation. Is there another tranny that would be a better candidate? I hope this isn't a severe re-post. Thanks so much in advance!

[zieg85]

TH350 was gone by 87 so if your truck has one it was transplanted in it.  TH400 and 700R4 was the automatic choices in 87

[LTZ C20]

As Zieg said, if you have a 350, it was swapped in. Either 700 or 400 were your options then. Do you have a build sheet or RPO sheet for it? That will tell you which of the 2 it had originally, making a swap easier. If you want OD, there are lots of options, but if you want it cheap and easy, the fastest and easiest is the 700 it probably had new anyway. Swapping in newer 4 speeds will be more expensive, require other parts the 700 won't, including stand alone computers and possibly drive shaft and/or tcase modifications. I swapped in a 700 for my old 350 and I didn't even have to get a new drive shaft.

[Irish_Alley]

trans length
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32506.0

th400 and 4l80e are a 32 spline

700r4, 4l60 and th350 are 27 splines

sm465 from 68-78 is 10 splines (35 for 2wd)
79+ is 32 splines (35 for 2wd).

[LTZ C20]

trans length
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32506.0

th400 and 4l80e are a 32 spline

700r4, 4l60 and th350 are 27 splines

sm465 from 68-78 is 10 splines (35 for 2wd)
79+ is 32 splines (35 for 2wd).

No true, early model 700s and 200 R4 are 27 spline. Late model 700s (87-up) and 4L60's/4L60E's are 30 spline. My 89 4L60 is 30 spline.

[Irish_Alley]

talking about the input or output shaft?

[LTZ C20]

talking about the input or output shaft?

Input, but just realizing again that his truck is 4wd. I'm a special kind of stupid tonight lol.

[Irish_Alley]

The 700 did get its input shaft upgraded to 30 splines if going behind a sbc. This started in 84

[LTZ C20]

The 700 did get its input shaft upgraded to 30 splines if going behind a sbc. This started in 84

The 30 spline inputs didn't start being used until 87 when the 700s were re-engineered and renamed as 4L60's, in 84 they were still the first generation 700s using 27 spline inputs. If I remember correctly, the 700s came out in 82-83 so 84 is only the 2nd or 3rd year of production use, 3 years before the re-engineered models.

[1967KaiserM715]

I can check my 85 700, pretty sure it was a 27 spline input.

And I think 81 was the first year, saw a suburban ad, and they were touting it as the first year for an overdrive automatic, course it very well could have stated new for the next model year as well...

Sent from my LGL34C using Tapatalk

[Irish_Alley]

https://youtu.be/41k8IZxMFuw
http://www.monstertransmission.com/700R44L60-Forward-Input-Shaft-Drum-30-Spline-1985-1993_p_6444.html#.V9roUZgrKM8

[LTZ C20]

I wouldn't trust that guy as far as I can throw em.

[Irish_Alley]

not even the second link for just the input shaft and drum

[Jon87V20]

Thanks for all the info! Maybe it doesn't have a 350 in it then. I'm probably wrong on that and it's a 400 most likely. So it sounds like a 700 should more or less bolt right in between the motor and the t-case? I'm assuming I would have to make sure to get one with the same spline count as my current tranny?

[Irish_Alley]

a th350 will have 27 splines on the output like the 700r4 but a th400 will have 32. if its a 87 no it shouldnt have a th350 but my 86 did but it wasnt from the factory.