Saginaw 3 speed to SM465 swap

[zermoa4]

I have a 250/saginaw 3 speed right now in my 76 GMC. I have a 454 i want to drop in, but i doubt the 3 speed would last very long (especially how i drive it). An SM465 is a much stronger transmission, and since i'm on a pretty much shoestring budget right now, it fits the bill. I can get one for 50 bucks, but first I need to know what i would need to swap it in place of my 3 speed. Thanks.

[xbanone]

I just finished the exact same swap last week. My truck started life as a 76 GMC 4x4, 250 I6 and 3 speed trans. A few years ago we swapped in a 305 and kept the 3 speed.

In July I pulled the saginaw out and sent my $50 Sm465 to the local trans shop. I put in a new Luk clutch and it just bolted in right in place of the 3 speed. Of course, I had to cut a small hole in the floor for the shifter. I used the 3 speed clutch linkage and new polyurethane trans mounts on the original crossmember.

My truck is a 4x4 so I had to get the correct trasnfercase adapter to use with my Np205.

It is a very straight forward swap and easy to do. I wish I had done it years agao when we did the 305. Next to come is an aluminum head 355 or 383.

Oh yeah, don't forget to get the SM465 bell housing, the sag. bell has a smaller inner diameter on the input shaft.

[zermoa4]

did you need to mess with the driveshaft at all? I've talked to a couple people who said I would definitely need to change the length, and probably the yoke as well. Thanks for the awesome response too.

[xbanone]

Originally Posted by zermoa4

did you need to mess with the driveshaft at all? I've talked to a couple people who said I would definitely need to change the length, and probably the yoke as well. Thanks for the awesome response too.

Are you a 4x4 or 2wd? I can only speak of the 4x4.

In 4x4 trucks, GM made up the difference in drivetrain length with the transfercase adapter. The Sm465 is much longer than a Saginaw, therefore has a shorter adapter. The transfer case and crossmember are in the exact same place. GM did this so they could use the same drive shafts on 3 speed and 4 speed trucks.

In a 2wd, I would have to assume the tailshaft would be the difference. If the total legnth of the transmission is the same, and the yoke is also the same type you should be OK. I would put money on the Sm465 being longer overall, in which case you would have to shorten your drive shaft. Shortening of a drive shaft is usually pretty inexpensive at a shop and can be done at home if you have a chopsaw and a welder.

[zermoa4]

Yeah, its a 2wd. I figured i would probably have to. Thanks.

[Keith Seymore]

I'm not familiar with the SM465 terminology: what trans is that (in layman's terms)?

Thanks,

K

[Pyrotechnic]

That's the 4 speed with a granny gear. Iron case, top loading shifter.

Ratio's

6.55
3.58
1.57
1.00

[xbanone]

The SM465 is made by Muncie and also known as the CH-465. it was used from 1969-1991 in GM and Dodge. The SM stands for Syncromesh.

[Keith Seymore]

Ah - thanks.

I'm quite familiar with the trans, now that you mention it, but hadn't heard it called that.

In fact, when I was a line supervisor, one of my guys ("Banana" was his name) installed that big ole shift lever. I've done a few myself....

K

[wwporkchop]

I have a 1966 c10 that was 3 on the tree with the saginaw 4 speed i want to put in a sm465 4 spped in it but i noticed my drive shaft has a yoke to slide in 3 spped! Anyone know what i need to do to driveshaft to make sm465 to work its also shorter than my 3 speed transmission! thanks

[tucsonjwt]

While we are on the subject, my SM465 shifter has slop in it side to side. My drivetrain guy says this is normal for a granny tranny, and the only way to stop it is to weld the shifter to the mount, but that would cause vibration in the shifter. Is this true or false?

[MalibuSSwagon]

http://www.pirate4x4.com/tech/billav...465/index.html

Give that a look for the shifter issue.

As for the driveshaft issue, find yourself a 2 pc. driveshaft out of a 2WD 73-87, and modify the rear driveshaft to fit your truck

[tucsonjwt]

Looks like the pirate guy did not get the intended fix either, unless you count hose clamps

[Keith Seymore]

Originally Posted by tucsonjwt

While we are on the subject, my SM465 shifter has slop in it side to side. My drivetrain guy says this is normal for a granny tranny, and the only way to stop it is to weld the shifter to the mount, but that would cause vibration in the shifter. Is this true or false?

True. But you might decide you are able to live with it (it won't vibrate bad all the time, only as you pass through various driveline resonances).

You might also see if you can improve the rubber isolation of your shifter, either by replacing the O rings (if it is that style) or maybe by wedging/pouring additional rubber into the square base (if it is that style).

K