SM318 to Saginaw 4 speed

[Sleipnir]

Shouldve posted here.

I was wanting to swap out my 4 bolt cover sm318 to a floor shift Saginaw 4 speed. Would I be able to bolt it right up without swapping the clutch or messing with the drive shaft? Will it bolt up to the bell housing thats on there? It's going behind a 250.

[crazy longhorn]

You wont need to swap the clutch, & the trans should bolt right up to your 67 bell. You will need to nut & bolt the bottom 2 on the trans to bell, as the truck trans takes the bolts on the bottom into the trans case. The spilne will be wrong on the slip yolk(no biggie). Next on the driveline....it depends on which 318 ,that you have, the long tail, will keep the drive shaft @ proper lenght. If you have a short tail 318, you will need to cut the front shaft, to fit the Saginaw trans. Longhorn

[Sleipnir]

Originally Posted by crazy longhorn

You wont need to swap the clutch, & the trans should bolt right up to your 67 bell. You will need to nut & bolt the bottom 2 on the trans to bell, as the truck trans takes the bolts on the bottom into the trans case. The spilne will be wrong on the slip yolk(no biggie). Next on the driveline....it depends on which 318 ,that you have, the long tail, will keep the drive shaft @ proper lenght. If you have a short tail 318, you will need to cut the front shaft, to fit the Saginaw trans. Longhorn

How big of an issue will there be if I don't have the spline on the slip yoke match? Also how do I tell between the long tail and short tail? Last question the 4 speed is coming out of a car transmission will that be OK?

[crazy longhorn]

The slip yolk, from any 350 turbo will fit (just match the U joint caps). Most likely 1310 U joints on the 1/2 ton truck. Measure the lenght of the 2 trans....if its off, it will be by a bunch Last ?, YES, that car trans will fit the 67 truck bell....but as I mentioned, the truck trans will run the bottom 2 bolts through the bell & into the trans ears. You need to nut & bolt the bottom 2 , to run the car trans. This is no issue, I have done it several times Longhorn

[geezer#99]

Are you sure about the tranny bolting up Mr. Shorthorn. I thought the 67-68 had a bigger input bearing retainer. 5 1/8 IIRC compared to 4 7/8 for the Saginaw. 69 and newer were the same.
There are sleeves available if needed.
Other thing to watch for on a sag is the first gear ratio. The weakest ones had a 3.43 1st gear.

[crazy longhorn]

Originally Posted by geezer#99

Are you sure about the tranny bolting up Mr. Shorthorn. I thought the 67-68 had a bigger input bearing retainer. 5 1/8 IIRC compared to 4 7/8 for the Saginaw. 69 and newer were the same.
There are sleeves available if needed.
Other thing to watch for on a sag is the first gear ratio. The weakest ones had a 3.43 1st gear.

68 was the 1st yr on the 5.125 bell hole/retainer...67 on back was the same 4.687 as the car bell shorthorn

[geezer#99]

Upon further research you are correct!
I was close!
Thank you Mr. Shorthorn!

[crazy longhorn]

Just another couple thoughts.....from one gezzer to another, I do agree that the lower 1st geared trans will be the weaker of the mix. Behind the inline 250,IMHO none should be a problem. I ran a low geared 1 , for 25,000 miles & ran it hard behind a "warm" 331. It finally took a dump, behind a 355 in my longhorn....(6500 rpm shift into 3rd gear)! The thing that I will say & stress, every time that trans was out for a clutch, the input bearing was replaced in the trans, as well as the pilot bushing. Longhorn

[Sleipnir]

Originally Posted by crazy longhorn

Just another couple thoughts.....from one gezzer to another, I do agree that the lower 1st geared trans will be the weaker of the mix. Behind the inline 250,IMHO none should be a problem. I ran a low geared 1 , for 25,000 miles & ran it hard behind a "warm" 331. It finally took a dump, behind a 355 in my longhorn....(6500 rpm shift into 3rd gear)! The thing that I will say & stress, every time that trans was out for a clutch, the input bearing was replaced in the trans, as well as the pilot bushing. Longhorn

Thank you longhorn for all the help! Luckily the trans doesn't have any grooves on the input shaft so it should be a 2.84 first gear! I measured the trans in the truck and it's about 16-17 inches so I think I'm in the clear. I'll need a low hump right? I also need to find a shifter since the trans doesn't have one on there. If I was going to spend $400 on a Hurst shifter I'd rather pay to get the trans rebuilt

[crazy longhorn]

Originally Posted by Sleipnir

Thank you longhorn for all the help! Luckily the trans doesn't have any grooves on the input shaft so it should be a 2.84 first gear! I measured the trans in the truck and it's about 16-17 inches so I think I'm in the clear. I'll need a low hump right? I also need to find a shifter since the trans doesn't have one on there. If I was going to spend $400 on a Hurst shifter I'd rather pay to get the trans rebuilt

That should be a good 1st gear, as the inlines usually ran a 3.73 gear in the rear On the hump, the low hump will work on that trans. Another thought, if you have a bench seat....you might opt for a tri 5 (55-57 chev shifter). You might source it used(swap meet,Craigs, or evil bay). That inline sets 3 1/2 " closer to the firewall vs the smallblock. I will have to get back with you on the trans lenght....but 16-17" sounds shorter than a Sag or muncie 4spd. Best of fun longhorn

[Sleipnir]

Originally Posted by crazy longhorn

That should be a good 1st gear, as the inlines usually ran a 3.73 gear in the rear On the hump, the low hump will work on that trans. Another thought, if you have a bench seat....you might opt for a tri 5 (55-57 chev shifter). You might source it used(swap meet,Craigs, or evil bay). That inline sets 3 1/2 " closer to the firewall vs the smallblock. I will have to get back with you on the trans lenght....but 16-17" sounds shorter than a Sag or muncie 4spd. Best of fun longhorn

Well I picked up the new saginaw last night and it's about 21 inches so it's longer than the sm318. So does this mean I'll need to shorten the drive shaft or is there a way to swap the drive shaft from another truck?

[crazy longhorn]

If you can find a complete shaft, from a 71-72 truck, with an inline (same wheelbase as yours), it will have the longer saginaw trans. The saginaw is the same lenght (3 or 4 spd)& the shaft should bolt right in Best of fun, Longhorn

[Sleipnir]

Originally Posted by crazy longhorn

If you can find a complete shaft, from a 71-72 truck, with an inline (same wheelbase as yours), it will have the longer saginaw trans. The saginaw is the same lenght (3 or 4 spd)& the shaft should bolt right in Best of fun, Longhorn

Another question for you longhorn. Would switching to a single driveshaft be better? The carrier bearing has never been replaced so I'm wondering if switching to a single driveshaft would be better. My only issue is I need a 69 inch shaft from what I can tell. At least that the measurements from the tail shaft on the transmission to the end of the diff.

[crazy longhorn]

You will be right on the borderline of a no no, with a 1 pc shaft that long. Some guys have done it, but you need a large diameter tube to support the lenght. On a 4-4 1/2" diameter tube, a steel shaft will be very heavy, & may be hard to balance. Some vans use a large diameter aluminum shaft....but you may also have issues clearing the hole in the crossmember for the carrier bearing. IMHO, you would do better to shorten & rebalance your shaft....but you may talk with some driveline guys on the pros/cons. I beleive there are some guys on the board that do driveline work for a living....I would leave that to them, for their expertice Longhorn

[Sleipnir]

Originally Posted by crazy longhorn

You will be right on the borderline of a no no, with a 1 pc shaft that long. Some guys have done it, but you need a large diameter tube to support the lenght. On a 4-4 1/2" diameter tube, a steel shaft will be very heavy, & may be hard to balance. Some vans use a large diameter aluminum shaft....but you may also have issues clearing the hole in the crossmember for the carrier bearing. IMHO, you would do better to shorten & rebalance your shaft....but you may talk with some driveline guys on the pros/cons. I beleive there are some guys on the board that do driveline work for a living....I would leave that to them, for their expertice Longhorn

Thank you sir! I didn't want to shorten mine because they look pretty beat up and I called a drive line shop and they quoted me $600

[Captainfab]

IMO if you use the HD carrier bearing, there is absolutely no reason to not use a 2pc driveshaft on a longbed.

[Sleipnir]

Originally Posted by Captainfab

IMO if you use the HD carrier bearing, there is absolutely no reason to not use a 2pc driveshaft on a longbed.

Do you think that because the driveshaft is 50 years old I should replace it? Looks pretty rusty but I don't think I have any vibrations. Also, I may need one of your brake booster brackets soon

[Captainfab]

Unless the rust is so severe that it has compromised the integrity of the tube, there is no need to replace it. Just clean it up, paint it, replace the u-joints and carrier bearing and you should be good to go. And of course shorten the front shaft if needed.

I will be leaving on vacation tomorrow and will be back in the 14th. I can build and ship a booster bracket to you then.

Originally Posted by Sleipnir

Do you think that because the driveshaft is 50 years old I should replace it? Looks pretty rusty but I don't think I have any vibrations. Also, I may need one of your brake booster brackets soon

[Sleipnir]

Originally Posted by Captainfab

Unless the rust is so severe that it has compromised the integrity of the tube, there is no need to replace it. Just clean it up, paint it, replace the u-joints and carrier bearing and you should be good to go.

I will be leaving on vacation tomorrow and will be back in the 14th. I can build and ship a booster bracket to you then.

Thanks for the advice! Much appreciated and I'll let you know after the 14th if I need one

[Sleipnir]

Ok so I have sourced my shifter and my driveshaft! Would I be able to just bolt everything in or do I need a new slip yoke for the car trans? I got a 2 piece from a 71 3 speed truck.

Also, what should I do with the column? How do I make sure that the old three on the tree wont cause me any stress down the road?

[crazy longhorn]

The shaft should slide in, yolk & all .....as far as the column, you can knock the pin out, & just remove the lever, & drop the old 3 spd linkage rods off The only thing you will loose is the back up lites As you get into the swap, feel free to ask more ? , if needed....Longhorn

[Sleipnir]

Originally Posted by crazy longhorn

The shaft should slide in, yolk & all .....as far as the column, you can knock the pin out, & just remove the lever, & drop the old 3 spd linkage rods off The only thing you will loose is the back up lites As you get into the swap, feel free to ask more ? , if needed....Longhorn

Thanks Longhorn! I dont have backup lights on it now so that shouldnt be an issue Once I source a pair I'll worry about moving the switch to the new shifter

Hopefully, I'll get started on this project this weekend and knock it out quick!