The Stovebolt Site Forums The Shop Area Engine Shop 3 speed w/ Granny Advice

Has anyone overhauled a 3 speed granny out of a 1950 3600 before? Mine sounds great in first, second, and granny, but when I put it in road gear it has a pretty loud whine in it. I am assuming it is a bearing or something wrong with a gear in there. 80w90 gear oil is what I have in it. How hard is it to tear down and rebuild? I have a press, micrometers, dial indicators,etc. I have never done one this old before. I have just come from the "1965 Ford Mustang" school, and I am getting an all new education from the "1950 Chevrolet School"

1950 THREE QUARTER TON,

If you have all those tools, it sounds like you would be all set. This transmission is probably the SM420 and is actually referred to as a true 4 speed..not to be confused with a three speed.

There is a outfit called Novak Transmission that has tons of info on this popular transmission, and has complete rebuild kits for it. If yours is a 'howler', maybe bearings would fix it up.

Goggle Novak Transmissions and check out their site.

Stuart

What Stuart said. The description you give isn't really wrong, it's just not terminology in general use today. One bit of advice I will give tou, get a shop manual, or visit the Online Manual Project/ Old Online Chevy Manuals. Both are exellent places to get factory information if you don't have access to a print manual.

Man, is there no end to the knowledge on this site?
Thanks for the link to Novak Stuart. My 420 was whining pretty bad the one time I drove it, and I just contributed it to straight cut gears, shows how little I know about the tranny. I was going to put off tearing into it till the frame off next summer but after seeing that I can get a brg/syncro/gasket kit from Novak for $200 I think I just might pop it out this winter while I'm doing the rest of the mechanicals on it. Sure wish the pumpkin was that cheap to rebuild, I'd do it now also.
Denny Graham
Sandwich, IL

I was also looking at the Novak component page and when you look at the eight pictures of transmissions there, the NP435, SM465, SM420, and T18/T19 look amazingly similar. I’d like to look into the availability, applications, dimensions and ratios of these boxes just to see if any would be adaptable to the 216 AD. Mostly interested in the useless first gear in the 420. I haven’t had a chance to read through their data base but it is very thorough and well done. Has anyone already been there??
Denny Graham
Sandwich, IL

Denny,

First gear is NOT useless! How do expect to get 10,000 lbs moving with a 235 if not through a nice low gear.

Useless? I pull a small boat around sometimes. The granny gear is essential for taking the boat out of the water on the steep ramps around here. We also have a lot of very steep hills in this neighborhood. Some that you have to stop on at certain intersections. My posi helps also. It is also useful for inching forward in backed up traffic or drive-thru lines. I just let the clutch out a little, I don't need to give it gas or ride my brake.
If you live in a flat area and your truck is no longer used as a truck, but a trailer queen or a weekend cruiser, I can see not needing it.

Agreed, if my 3600 didn't have 4.58 gears I'd never pull our 3000 lb. boat out of the water and up the ramp. What's difficult for me (with the 235) is maintaining any speed on long hills. It's frustrating always seeing such a long line of cars piling up when I'm going 20 mph on a 50 mph stretch. Getting it moving isn't quite the same as moving it along.

Get a good book & add snap ring pliers to your tools & you should be able to do it. They are pretty basic. It,s probably your mainshaft rear brg. thats bad. Look at the front one real close or buy a complete rebuild kit.

not for my 'bolt, but i've ordered parts from them for my jeep-conversion. added an NP435 4-spd, and needed a new output shaft and transfer case adapter. that project was the first time i'd ever attempted to work on a transmission, and it went flawlessly. replacing the output shaft was simple.

fwiw, the ratios are 6.68:1 (1st), 3.34:1 (2nd), 1.74:1 (3rd), 1.00:1 (4th), and 8.26:1 (rev).

also, the only reason i installed the transmission was to obtain that "useless" granny gear.

most of the np435's are drof versions, but there are also dodge and chevy versions, too, although for most of those, the 1st gear ratio is around 4.0:1, instead of 6.68:1.

Your "noise" sounds like what happened to one of my old trucks. I was driving along in 4th gear and it just started making a terrible noise from the trans. When I got the trans out and the top cover off, I saw that it had a tooth broken off one of the gears. It was quiet in all gears, except 4th.

Thanks for the advice. I have been driving it for two weeks now and it is really loud. So loud in fact that my wife can hear it in her car when she is following me! I have a 1948 chevrolet 1 ton that has the emergency brake lever attached to it. I think I will stick in to see how it works. I kind of like the emergency brake lever on look too. Hopefully everything fits. I cant imagine that it would be different. It looks the same. I am praying it doesn't howl like this one.