3 speed manual trans service info please

[skinnan]

I have a 72 C-10 I'm re-doing. I bought a chevy crate 350 for it. Originally had a 6cyl and 3OTT. I converted it to a floor shift and added a sweet hurst indy shifter. I want to keep because I like it and the wife learned to drive in one of these trucks.

My question is, what is the best way to service (fluid wise) this transmission? What type of fluid, where is it filled at, how is it drained, etc...? I've search all over and apparently most people don't like this transmission because they are either swapping to a 4 speed muncie or going automatic. I really can't find any information for proper service.

Also, will this transmission handle a mild street built 350? I assume it will based on some of the info I've seen but I know there are people here that know first hand.

Thanks for any response in advance.

Scott

[AussieinNC]

Passenger side of the trans you will find a pipe plug...about half way up the side...

Undo this upper one first, and leave it out.

Now undo the center and lowest bolt that connects the tail housing to the main case.

This bolt should have a copper washer on it, dont lose the washer.

Remove the bottom bolt and drain the old oil out into a container..

Wear latex gloves and have at least a one gallon container to drain into.

It will take a while to drain.

When finished draining, replace the bottom bolt and copper washer.

Refill with approx 3 pints of 80-90 gear oil. I use a hand pump and hose to refill these...fill until the new oil just starts to run out of the center fill hole. Replace the fill pipe plug.

Note...on some transmissions there is no drain capability...you have to use a suction pump to suck out the old oil...

[weim55]

Do not use a synthetic oil. I tried this once and the oil is too slick for the syncros to work properly, it turned my saginaw 3 speed into a crash box. Switched back to non synth 80 90 and all was good again........

Steve weim55 Colorado

[Alex V.]

The scientific explanation for weim55's problem is probably GL4 vs. GL5. It would be more critical with synthetic lubes, but a GL4 is preferred over a GL5 in brass-syncro transmissions regardless.

[skinnan]

you guys are awesome, as usual. Thank you so much. I get myself around these old trucks pretty good but I don't know much about transmissions in general.

Any clue what this trans is called? I've seen sm265 I believe. Not sure though.

[68panelman]

My 67 3 spd has the lower drain and side fill

[Tx Firefighter]

Originally Posted by 68panelman

My 67 3 spd has the lower drain and side fill

You have a Muncie SM318 which is the earlier three speed trans. The description given by Aussie is for the later Saginaw 3 speed like the OP should (emphasis added) have. The Saginaw doesn't have the drain plug unfortunately.

[skinnan]

any idea where I might get a good syphon for this?

[Tx Firefighter]

Aussie led you right on the drain being the lower bolt. As far as refilling, I have always used the tall skinny bottles of lube with the pointy top from the local parts store or even Walmart. No siphon needed. Just stick the point into the fill hole and squeeze. You sometimes need to use a little piece of hose pushed down onto the point to allow the bottle to fit up next to the trans. It will be self explanatory when you get under there and look at it.

[skinnan]

thanks everyone, you guys rock!!!

[phlegm]

resuscitating an old thread, I am getting ready to change the fluid in my 3spd manual transmission and my rear diff. in this Aussie (who gave a great explanation) said 80-90 gear oil. I bought about 4 quarts of the Castrol 80-90 limited rear slip diff oil to do my differential... same stuff? The words "limited slip Differential" are making me wonder.

[AussieinNC]

You dont mention if your rear gear is limited slip or not.

All differentials use gears, bearings and shims. Limited-slip differentials have additional clutch packs. Since there is nothing in any differential that is not in a limited-slip differential, there should be no harm in using a limited slip friction modifier oil in a non-limited-slip differential, although there is no need for it.

Manual transmission gear oil is a different composition....if you use limited slip differential oil in a manual transmission you may have issues with the thick oil affecting the synchro functions....just grab some standard 80-90 gear oil and fill er up.

[phlegm]

Thanks Aussie that's what I figured, I will just go find some std gear oil for the transmission. I do have positrac rear end on that truck.