78 sm465

[76shuvlinoff]

78 2wd with an SM465 transmission I just changed the oil in the differential using 80-90 and I need to do the transmission. Could I get away with using something lighter than 80-90? Should I? Looking for possibly easier shifting but I am not going to sacrifice a transmission for it. With advances in lubricants these days just wondering if there's option.

And how do you fill it? Can you actually get a bottle of gear oil up in there?

[95 S_Trucker]

I can’t help with viscosity, I always run gear oil.

To fill it, I pop the shifter out and fill it through the shifter hole until fluid comes out the hole on the side of the case.

[WorkinLonghorn]

My Chevy Chassis Service Manual for 1969 (same transmission) says 80 for cold climate, 80/90 for warmer and 140 for consistently over 100.

Near the gear lube in the parts stores you will find a little hand pump that has a tube that you insert into the fill hole. add oil until it just starts to leak back out. It screws onto the top of the oil jug.

[76shuvlinoff]

Originally Posted by 95 S_Trucker

I can’t help with viscosity, I always run gear oil.

To fill it, I pop the shifter out and fill it through the shifter hole until fluid comes out the hole on the side of the case.

Popping the shifter out... once I slide the boot up is that pretty straight forward? Anything to be wary of?

[76shuvlinoff]

Originally Posted by WorkinLonghorn

My Chevy Chassis Service Manual for 1969 (same transmission) says 80 for cold climate, 80/90 for warmer and 140 for consistently over 100.

Near the gear lube in the parts stores you will find a little hand pump that has a tube that you insert into the fill hole. add oil until it just starts to leak back out. It screws onto the top of the oil jug.

I may take a little road trip to Autozone tomorrow. Thanks!

[tucsonjwt]

I have a SM465 in my 83 C20. I have a leak in the front of the transmission so I use whatever cheap 80-90 oil I can find. I filled my transmission through the fill hole using a cheap fluid pump attached to the gallon jug of oil. It takes about one gallon, maybe a bit more. You are supposed to fill it until it starts to drip out of the fill hole. The plastic hand pump is about $10 and a gallon of GL5 oil is about $15 -$20 at the parts stores or Walmart. I have read about some guys removing the shifter and filling it through the top but that sounds too extreme for me.

In would not mess around with any weight oil lighter than the general recommended. You will never be speed shifting a SM465, and they are far from precise pieces of equipment. If your transmission is difficult to shift you probably have something wrong with your clutch or transmission.

There is a lot of discussion on using GL4 only on these old manual transmissions because GL5 might eat the synchros. The labels on the GL5 jugs usually say it is OK for GL4 transmissions. This youtube video discusses that issue. Bottom line, don't worry about GL5. Of course, when you take your truck to the dragstrip you will want to change out the oil the $400 per gallon racing oil.

https://www.youtube.com/watch?v=Z7NpsMZ9pBQ&t=725s

[kipps]

I've had granny four speeds out of two trucks now. A sm465 in a chevy, and something very similar in a ford. In both cases, the stick was out already, so it was piece of cake to fill the tranny through that top hole before replacing the stick.

It will take you much longer to remove and replace the shift boot than it will to get the stick out and back in. Don't remove the shift boot all the way, since that would require removing the shift knob. Just pull it to the top of the stick, and hold it there with your head while disconnecting the stick. Use a channel-locks, press the pivot ball down about a 3/8 inch, and simultaneously twist the pivot ball to the left(I think that's the direction). Lift the stick out. Takes a few seconds.

[tucsonjwt]

Maybe I'm supposed to be using 140 here in the HotZona desert. I think I would need both hands to shift it.

[95 S_Trucker]

Originally Posted by kipps

I've had granny four speeds out of two trucks now. A sm465 in a chevy, and something very similar in a ford. In both cases, the stick was out already, so it was piece of cake to fill the tranny through that top hole before replacing the stick.

It will take you much longer to remove and replace the shift boot than it will to get the stick out and back in. Don't remove the shift boot all the way, since that would require removing the shift knob. Just pull it to the top of the stick, and hold it there with your head while disconnecting the stick. Use a channel-locks, press the pivot ball down about a 3/8 inch, and simultaneously twist the pivot ball to the left(I think that's the direction). Lift the stick out. Takes a few seconds.

That’s the way to do it, make sure it’s in nuetral first.

[76shuvlinoff]

Did it through the top this morning. Worked great!
Thanks

[1976gmc20]

Learn to double clutch (up and down), and don't rush the shift. If you do it right then you can shift with thumb and index finger, and it will practically pull itself into gear.

These are truck transmissions. I've actually had more experience with the SM420 in a two ton, plus whatever 5 speed IH used to put in their medium duty trucks. But I've had at least three SM465's including the one in my namesake.