SM465 Transmission
 

I just rebuilt my 350 SBC and it should be putting out about 350-400HP and I'm ready to install it with the tranny (4 spd, which was cleaned and inspected). But I just got a sinking feeling.

Is the standard gearing in this tranny able run well with the low end performance I did with the engine? I assumed I could change the rear end gearing to get the streetable performance I'm after. This is a truck I will use mostly around town and wanted nice performance.

BTW, I bought an upgraded clutch to handle the added power and resurfaced the flywheel.

Thanks
Rich

Re: SM465 Transmission
 

These trans are geared for low speed acceleration hauling loads and are not really reliant on increasing low end power or torque. They're reliant on being low geared, which they are.
More favorable ratios of car trans like Muncie m21 close ratio can really benefit from an extra 50 ft/lbs torque because they are taller geared.

I don't think I'm smart enough to teach you what I'm trying to say, but the point is a truck trans like the 465--part of it's designed purpose was to MAKE UP for low power engines using lower ratio'd gears--so you could get work done no matter what engine ya got.


This diminishes the value of increased power/torque.(mainly because you have to change gear before gathering an ideal amount of speed).
Yes, you can help stave of this "issue" by changing your rear end gear. But The most ideal thing you could do is also changing your gear ratios--and you do that by swapping to a different trans.
You sound like you have a simple need for this truck, I think you'll be perfectly happy with your current drivetrain, as long as your rear ratio is numerically lower than 3.55:1.

Re: SM465 Transmission
 

I would consider a newer Silverado Manual Transmission like the nv4500 for a replacement. You will get an better gear ratios and overdrive and loose about 100 pounds in the conversion.

Re: SM465 Transmission
 

My other truck is an '81 K20 with a 350 that I blue printed and built to have 350 hp and 350 ft-lbs. I also had an SM465. I put over 100,000 miles on that combination hauling out of state many times. The engine was done in by a dime size piece of Keith Black piston that broke off when I moved off the shifter in 3rd gear to change the radio station. It slipped out of 3rd and over revved the engine. That transmission is bullet proof when it comes to torque, at least from a small block it is. You don't have anything to worry about.

I would try to address the slipping out of gear issue because that's something that I heard others experienced also. I went with a friction disk and pressure plate that could hold more torque. I did burn the friction disk a couple of times, but they were rare situations.

I swapped it for a NV4500 to get the overdrive because my truck had 4.11 gear ratio. There was very little difference in the 2 gears between 1 and 4. The 1st gear ratios are nearly identical, and 4th is the 1:1 ratio.

Re: SM465 Transmission
 

As Accelo mentioned.... Do This.

http://67-72chevytrucks.com/vboard/s...d.php?t=673588

Best of both worlds, still have low gear but you also have overdrive. Also easy to do.

LockDoc

Re: SM465 Transmission
 

Dashman, was the NV4500 pretty much a bolt-in?

Re: SM465 Transmission
 

Gear ratios displayed below for the two transmissions.

M465 transmission- 6.54, 3.57, 1.57, 1.00
M4500-transmission 5.61, 3.04, 1.67, 1.00, 0.73

Turbo 350 transmission 2.52, 1.52, 1:00

Easy to see that the truck transmission are a lot lower ratios than the 350 automatic.
Both the truck manuals are designed to start in 2ond gear. First is really low for pulling.
The real advantage to the NV4500 is the O.D which drops the rpm by one third.
You will not believe how much it lowers the noise in the cab when in overdrive.
Gas mileage can increase by as much as 30%.
Good look what ever you choice/budget dictates.

Re: SM465 Transmission
 

Dasman, I should mention I have a 1967 C-10

Re: SM465 Transmission
 

Thanks Accelo. I'll probably put in the 465 and enjoy the truck. Like I mentioned I had it gone through and its solid. Hopefully it performs well. If not I got myself another project! It never ends.

Re: SM465 Transmission
 

You would need to change the clutch from mechanical to hydraulic. The driveshaft would also need to be shortened.

If you are mostly using the truck around town then I don't see how the nv4500 would be worth the effort because the biggest upside to the swap is having a 5th gear for highway speeds. The SM465 and the NV4500 are both slow shifting truck transmissions, both are great for doing truck stuff and shifting like its a truck. If you want to go fast from stop light to stop light then a M21 would be the better option.

Re: SM465 Transmission
 

My Jimmy has 350,000 miles on it. 250,000 on the original motor and now 100,000 on the built 327. When it first went in it had a 228 degrees @ .050 duration cam and liked to pull HARD to 6500 rpm. That was a terrible combination for the SM465. The cam was replaced with one that had 210 @ .050. The power band of the smaller cam works really well with the SM465. My little motor only 331”, 9.8:1 running a Weiand 8004 and a JET Stage II Q-jet.

So, if you have a motor in the more than 350” range and a cam with 220 degrees or less duration @ .050 I think you will be quite happy. My truck has 4.10 gears but 35” tires so effective gear ratio about 3.25 or so. 5% more than the 3.07 and 28” tires.

Re: SM465 Transmission
 

When I swamped to the NV4500, I got the bellhousing from Advance Adapters to retain the mechanical clutch. I also had to do a custom cross member because the tail housing has the mounting pad, and is essentially it's own adapter.

Got it, C10, a 2wd. The NV4500s are running about $2,300. You might want to do some research on the Tremec transmissions for a street truck. The close ratios could be better, and shorter throws.

Get your truck running, and enjoy it a bit before you plan the next upgrades. Sounds like you're going to have a fun engine. I used to love the way mine would "grunt" after about 4,000 rpm. ...so smooth too.

*EDIT: I've seen your post before Leon. That was a great idea and process.
The '92-'94 NV4500 relevant ratios are 1st 6.34:1 gear; 2nd 3.44:1; 3rd 1.71:1, this is the one I found, and it nearly matches the SM465.

Re: SM465 Transmission
 

You do not have to change to a hydraulic clutch with the NV4500. You can use all of the stock clutch components and bell housing. Check the link in my post above.

Re: SM465 Transmission
 

I do not think you'll have any issues with the SM465. Yes, the NV4500 is nicer with the OD, but the SM465 is a robust transmission. As long as you're not dropping the clutch and beating it like a race car you'll be fine. Many other threads are highly supportive of the 465 for just about anything you can throw at it.

https://67-72chevytrucks.com/vboard/...e%20extra%20tq.

Re: SM465 Transmission
 

I would like to use the truck to go to swap meets which will involve highway mileage. I know it revved like crazy so I can see the NV in my future.

I believe I heard on Roadkill that a company make an add on overdrive unit. I'm not sure if that was manufacturer specific or a generic add on. Anyone know about that?

Re: SM465 Transmission
 

https://www.gearvendors.com/hrgm4sm.html

Maybe you can find a used one that would be cheaper

Re: SM465 Transmission
 

Dang, I wish I knew this before I sold the NV4500 I had.