The Stovebolt Site Forums The Shop Area Engine Shop 1965 3/4 Ton Top Speed & Transmission Question

What was the top speed of a 1965 3/4 ton truck with the stock motor and transmission?

My uncle recently purchased a 1965 ¾ ton truck, and it reportedly has a school bus transmission in it – and a top speed of roughly 50 mph. You don’t use first gear at all on the road with the bus transmission – you start in second. It’s a three-speed transmission, but first is like a “granny low” gear.

What transmissions would go in a 3/4 ton truck and would a strock transmission give better speed?

The stock 4-Speed trans for that truck would be a SM420, which is either very similar or exactly like a school bus trans. Unless very specifically verified, it could very well be the original trans in there. Many don't use the Granny Gear on the road, like I do. Changing the trans won't give it any extra speed as 4th gear will still be 1 to 1, unless you go with an overdrive. With what you have, what would make it go faster at a lower RPM, would be to change the gears in the rear-end.

Bill

Ok, cool! Thanks for the information. I believe the guy he bought it from told him the truck had a school bus transmission, but of course he could very well have been mistaken. Although, I believe that it is a three speed transmission (counting the "granny low" first)? I'll have to confirm that.

Thanks for the quick info!

If it is a 3 speed it would have a column shifter. You may think first gear is granny low because the rear gears are 4.57's. The standard 3 speed 1st gear is 2.94 and the 4 speed is 7.06 - that's a granny. There was a warner HD trans offered in earlier trucks that had a 3.17 first gear. I'm not sure if it was available in 65. It has the overall size of a 4 speed.
Fred

I had a 1964 3/4 ton with the "truck" 4-speed. SM420 I guess. With a V8 in it it would run freeway speeds just fine, despite the low rear end ratio. Of course the motor was wound out pretty good. But it would go _well_ over 70. How much I don't really know; not sure how good the speedo was, but I passed people easily.

Now, with a 6 in it you might not get the high RPMs. Dunno what you can win a 250 or 292 to.

Get us some details! What engine? What rear end?

George

Thanks for the replies and information!!

Ok, it is a 4-speed. I don't know why I was thinking it was a three speed. I should probably go hang my head in shame, huh? Haha!

The floor plate over the transmission inside the truck is actually from a bus, apparently - it doesn't fit quite right. It's school bus yellow, too. The owner that had it before said that he blew an engine trying to push it too hard at highway speeds.

As for what rear end is in the truck... I don't know.

The engine is apparently a 250. I actually haven't had a chance to take a real close look at it myself, but that's what people have told him. I do know that the plate inside the truck says "230". Of course that doesn't mean anything since the engine has been swapped at least once that I know of.

What kind of gears would work in the '65 3/4-ton rear end? Anything from a 1/2-ton? I only know a little about '63 and up trucks and absolutely nothing about 3/4-ton trucks!

You'll need to find a 4.10 3rd member from a '68-'72 Chevy 350 automatic 3/4 ton. 1/2 ton parts do not interchange.

Ok, thanks for the information. I did not think that they did, but thought I would ask just in case!

Hey Robbie, also the 250 wasn't avaliable until '66. That doesn't mean it didn't get a 250 put into it later, but it originally didn't come with one. Might want to verify it's a 250 before you order parts for it

Robbie,

The 3/4 and 1-Ton's have a "Full Floating Rear" and as mentioned above is different from a 1/2 Ton rear.

Bill

Yeah, this is something I have thought about. Most people who have seen it have said it's a 250, although there was one person who called it a 256 or something like that - which I imagine is wrong. Like I said before I haven't actually had time to go over it very closely myself. How do I tell what it is? Are there any dead giveaways as to the difference between a 230 and 250? Also, it has an electronic ignition and the newer style oil filter. I wonder if the engine came this away or was just updated by the previous owner. I know it's not the original engine, because, as I said before, the previous owner destroyed the engine that was in it when he got it trying to push it too fast.

Robbie,

Next to the distributor, there is a pad on the engine block with some letters and numbers. Also look on the passenger side of the block, towards the back, between the oil pan and side covers and you should see a date code there. Let us know both of those and we can try to determine just what engine you have and year it is.

Also I just sent you a PM.

Bill

Unless the PO went crazy, its not a 256 because that is a Jeep engine. I've always had 250's in my truck from as long as I can remember, so someone else will have to help determine the difference between the 230 and 250, other than reading off the cast #'s off the engine. Sounds like you have a good sized project going though.

I still haven’t been able to get a chance to write down those engines numbers, but in the meantime I have another question… (I figured since I already had this post started I would ask it here, and since it is sorta similar…)

On a ‘65 3/4-ton truck, do you have to pull the axles when you change the rear brakes or wheel cylinders?

As usual with the common misinformation on these trucks, I have gotten several answers,

“Yes.”
“No.”
And details on dropping in an old sawmill motor, and something about “Catfish?”

I’m still not sure what that last one was all about…

I think the answer is yes. My 49 has Huck-style brakes, so the drums just slip off the hub, after removing a couple of flat head screws. My manual is for a 54, with Bendix-style brakes. I would guess it is similar to yours. On that model, the drum and hub come off the bearings together, and to do that the axles must come out. Look for flat-head screws between 2 pairs of lug nuts, and look for space around the lugs and hub. Your drum may just come off.

If not, with the appropriate tool, not a hard job, actually. Undo the bolts on the end of the hub and screw 2 of them into the 2 threaded holes that were empty when you started. Tightten them evenly, and out comes the axle (it's a built-in puller). A hint. Do this with the truck on the ground and the wheel chocked so you can apply more torque to the bolts. Don't need to jack up the truck until the next step.

Now, find the correct hub socket (NAPA, etc.) and undo the first inner hub nut(?). The socket is about 2 inches dia with the same number of teeth as notches in the outer edge of the nut. I had to fab up a hold-down that I held in place with the lug nuts and went over the socket edge to hold it in place while I applied torque, otherwise the teeth popped out and I hit the floor.

Don't put the socket away yet. A spacer comes out, and then another hub nut (same as the first). The hub should now come off and the drum with it. Do the brakes right the first time, so you don't have to do it again for a while!

When going back together, remember to properly toque the outer hub nut. Alot of guys forget to do that, thinking that snugged up us all that's needed. It isn't. That outer nut torques to 150-175 ft/lbs. Failure to torque it properly can result in wheel loss. I've seen that happen on a late '70s 3/4 ton that was serviced in the shop I work at (not by me). Same goes for the hubs on the front of a 4x4.