66 gmc c10 transmission swap to sm465

[danieljpeter]

Hey all,

I'm not too happy with the transmission that came in my 66 GMC. It was the factory 3 speed, I think an sm-318. It was 3 on the three, and someone converted it to a floor shifter. The shifting action isn't really great, kind of sloppy and inconsistent. Plus the shifter is all the way over to the left of the tunnel and my leg hits it pretty hard. In addition, I have some clutch chattering. I also could use a lower first gear. So I decided to pull the tranny and do the clutch and reinstall a different tranny.

The SM465 is a great truck tranny. Really plentiful, cheap, and durable. It is also top-loading so the shifter will be in the middle of the tunnel away from my leg. So I picked one up and I'm having it rebuilt so I can be confident it is good before I go through all the work to install it.

The truck has a good running 327 in it. It has the bell housing with the motor mounts attached and a crossmemeber right underneath. There is no crossmemeber attached to the back of the trans.

Here's what I think I will have to do for the swap:

Pull tranny, bellhousing, bellhousing cross member, clutch assembly, flywheel.

Resurface / replace flywheel, rear main seal. If flywheel is not 168 tooth, replace with 168 tooth version.

Install mechanical actuated aluminum bellhousing that will fit small block chevy and the SM465. The bellhousing I have won't work with the sm465.

Modify transmission tunnel sheetmetal to fit around the larger transmission. I can cut my tunnel along the stamped lines in the floor and get a replacement screw in tunnel from a junkyard, or just cut and weld the one I have.

Install transmission to bellhousing.

Make crossemember that mounts to rear of transmission using a new stock mount.

Probably have custom driveline made. I have a 1 piece driveline now, but I'm assuming the length will be wrong or the ujoints won't match.

Hopefully the mechanical clutch linkage will hook right up.

Hopefully my current starter will work. I may have to get a mini starter or some other replacement.

Please correct my understanding of this process if you see anything wrong. I haven't done this particular swap before, and would love to hear from someone who has.


Thanks!

Dan

[kizer]

Here is some info I found on the same Transmission.
http://www.novak-adapt.com/knowledge/sm465.htm

[60-66 Nut]

Dan, welcome to the board. There are alot of nice folks here. The site that kizer gave you has alot of good info on the SM465 and several other transmissions.
Sounds as though your truck has the original bell housing and cross member. If so, then it should be the 168 tooth flywheel with the 3 bolt starter mounting directly to the bell housing. You can put an aluminum bell housing if you wish, but you will have to have the block mounted starter to go with it. The only reason your bell housing won't work with the SM465 is because the input flange pilot hole is too small. You can also find you a cast iron bell housing from a 68-72 GM truck with the six or V8 that will bolt right in place of yours and use the same starter. The Novak site also tells you how you can have your housing fitted to the SM465 input flange. The two bottom bolt holes on the newer SM465's will not have any threads like the older transmissions, but you can just use longer bolts with nuts and lock washers, no biggie.
As I'm sure you already know, the 327 has a 2 piece internal rear seal, so you will have to drop the pan to change it.
Your drive shaft will not work on the SM465. The 465 has a bigger rear u-joint and does not have a slip yoke, so you will need to incorporate a slip-yoke into the drive shaft. The easiest way is usually with a 2 piece drive shaft and a hanger bearing, but a good machine shop can weld a stub shaft onto your drive shaft to match a slip yoke that will fit the transmission.
And as you said, the floor pan will of course have to be modified.

Best of luck with your swap.

60-66 Nut

[slorio]

Here's a good write up on 3 to 4 speed conversions. It is for an SM 420, but should be similar for the SM 465. It is from Jolly's GMC website:

http://www.6066gmcguy.org/3-to-4-speed.htm

I hope this is helpful.
Regards,
Steve
New Orleans

[60-66 Nut]

Yes, Jolly has some real good tips and pictures there. I like the driveshaft he used, nice piece. The only thing I read that wasn't quite correct was on the SM465 input shaft. He said the SM465 has a larger input shaft; this is true only for the SM465's that were used in the 2 ton and larger trucks that used the 1 1/2" input shaft. The 1/2, 3/4 and 1 ton SM 465 still used the 1 1/8" 10 spline input shaft.

But all in all, a very good and informative read.


60-66 Nut

[danieljpeter]

Great information so far. Looks like I have a couple of options on the bellhousing.

If I switch to a newer aluminum bellhousing, can I be sure that my engine block is set up to bolt the starter to?

Did some blocks not have the holes drilled and tapped?

Thanks,

Dan

[padresag]

Originally Posted by 60-66 Nut

Dan, welcome to the board. There are alot of nice folks here. The site that kizer gave you has alot of good info on the SM465 and several other transmissions.
Sounds as though your truck has the original bell housing and cross member. If so, then it should be the 168 tooth flywheel with the 3 bolt starter mounting directly to the bell housing. You can put an aluminum bell housing if you wish, but you will have to have the block mounted starter to go with it. The only reason your bell housing won't work with the SM465 is because the input flange pilot hole is too small. You can also find you a cast iron bell housing from a 68-72 GM truck with the six or V8 that will bolt right in place of yours and use the same starter. The Novak site also tells you how you can have your housing fitted to the SM465 input flange. The two bottom bolt holes on the newer SM465's will not have any threads like the older transmissions, but you can just use longer bolts with nuts and lock washers, no biggie.
As I'm sure you already know, the 327 has a 2 piece internal rear seal, so you will have to drop the pan to change it.
Your drive shaft will not work on the SM465. The 465 has a bigger rear u-joint and does not have a slip yoke, so you will need to incorporate a slip-yoke into the drive shaft. The easiest way is usually with a 2 piece drive shaft and a hanger bearing, but a good machine shop can weld a stub shaft onto your drive shaft to match a slip yoke that will fit the transmission.
And as you said, the floor pan will of course have to be modified.

Best of luck with your swap.

60-66 Nut

it would not have been the original b/housing as it was a GMC with a sbc installed in it
ron

[C10 - C90 Bill]

I would go with an original Cast Iron Bell. One with the larger 4-Speed hole in it. I'm not too familiar with the newer parts but does your Aluminum Bell have a bottom pan for easy access?

Bill

[danieljpeter]

No, the aluminum one goes all the way around the flywheel and doesn't have the motor mount provisions.

I will see if I can find a cast iron version from a 68-72. If I can, hopefully my stock throwout arm will work with the sm465 throwout bearing. I think it will since those bellhousings came with sm465's.

I guess I should still make another crossmember the support the rear of the tranny. I will have three sets of mounting points for the drivetrain!

Any tips on where to find a high hump for a 66? Are they very common in wrecking yards?

Thanks,

Dan

[C10 - C90 Bill]

I believe the clutch fork will work, but if they are different you can always get one from a truck vendor at a reasonable price. There's really no need for an extra crossmember, but putting one in will make it stronger, if you prefer.

Bill

[60-66 Nut]

Dan, I agree with Bill. I think it would make things much simpler to stay with the cast iron bell, but that's up to you. The SM465 can use the same throwout bearing as your 3 speed, just make sure you have the right one for your pressure plate(diaphram or lever type). The old style fork should work in the aluminum bell, but you will have to make sure and use the correct fork pivot ball. They are different for the old cast fork and the stamped fork. As for clutch linkage, it would be much easier to stay with what you have. The later model linkage is completley different, as the engine is positioned different in the truck. You will need to use the pivot ball on your engine, not the one on the aluminum bell.

Like Bill said, if you stay with a cast iron bell there is really no reason to build another crossmember, but again, that's up to you.

You may even be able to have your old housing machined out to the correct size without cutting the transmission input retainer. I think the reason the Novak site talks about cutting them both is because they are using the aluminum bell, and don't want to remove too much material. The old cast iron bell should have plenty of meat there, so it should not be a problem. Maybe someone has done this before and can tell you for sure.

60-66 Nut

[craigs-toys]

i have the cast bell ive heard you cant post forsale items on threads so pm me and we will talk abought how to get it to you if your interested

[danieljpeter]

Originally Posted by craigs-toys

i have the cast bell ive heard you cant post forsale items on threads so pm me and we will talk abought how to get it to you if your interested

I ended up finding the cast bell housing at a local flea market! score!

I got the swap done awhile ago, came out great.

I cut the floor hump out, and built a new bolt in floor hump by sectioning up some humps from the junkyard. I didn't want a hump as high as a high hump. The high humps don't leave a lot of footroom. So this one is just a little higher than a low hump model. The shift tower on the top of that sm465 actually comes up through the hole in the hump, but the boot covers it all up.

Built a long handled shifter, with a custom knob.

Got a new clutch fork boot. Reused the old clutch rod. New 12" flywheel, clutch, pressure plate, throwout bearing.

Got a new custom driveline made with a slip joint in it.


Thanks again for everyone's help.

[chevy283]

do you have any pics of the trans hump you built. im doing the same trans swap as you and dont want the big hump. thanks

[Ham-er]

Congratulations!

I did a similar thing except that I went from an SM420 to the SM465.

Went thru the same troubles except kept the high hump.