Easy question

[Brandonc20]

Hey All,

I need to change my gear oil in my granny transmission. how hard is that? and what kind our gear oil do I use?

[markeb01]

Here is a link with more information about your transmission than you'll probably find anywhere else. For oil recommendations, take a look at the small box in the lower right corner. As noted in the text, I'm running straight 50 wt engine oil in my Richmond 4 speed and it works great. I didn't have my SM420 long enough to ever change oil in it so I can't comment on the effectiveness in this transmission.

http://www.novak-adapt.com/knowledge/sm420.htm

[blackedoutharley]

Replacing the gear oil is very simple. What I do is to drive the truck a good distance to get the trans up to temp.
When I switched to Redline synthetic oil I did the following.
Set up all my tools, jack and stands.... drove the truck to run the errands I need to get done and came home the long way. This got the trans good and hot. Promptly jacked it up and pulled the drain plug and let it drain overnight.
Next morning I reinstalled the plug and pulled the shifter to refill.

By driving it you get it hot and the thick gear oil drains better. You can use either a 90 wt gear oil or I used Redline MTL synthetic.

[fryer1979]

Thanks for that link Mark, you just helped answer a question I have been searching quite a while for an answer to.

[Brandonc20]

After reading the link, I should probably use 50w engine oil. I am in southern california and its about 105 degrees. Does anybody disagree?

[Brandonc20]

Originally Posted by blackedoutharley

Replacing the gear oil is very simple. What I do is to drive the truck a good distance to get the trans up to temp.
When I switched to Redline synthetic oil I did the following.
Set up all my tools, jack and stands.... drove the truck to run the errands I need to get done and came home the long way. This got the trans good and hot. Promptly jacked it up and pulled the drain plug and let it drain overnight.
Next morning I reinstalled the plug and pulled the shifter to refill.

By driving it you get it hot and the thick gear oil drains better. You can use either a 90 wt gear oil or I used Redline MTL synthetic.

So you actually pull hte shifter out of the cab to refill? or is that just easier to do when refilling?

thaNKS everyone for thier input!!

[markeb01]

Here’s a link that explains viscosity equivalents. There is a link to the comparison table in the 3rd section titled “Where does a 20w-50 crankcase oil Cross with a 75w-90 gear oil.

http://www.bgprod.com/blendr/viscosity.html

The manual transmission expert that put me on to using 50w recommended Valvoline straight 50 weight. I buy it at Napa Auto and have to ask for it at the counter. They don’t stock it on the shelves out front, but they do carry it in the back.

From what I’ve read the 90w gear lube has higher sulfur levels to manage the higher pressures experienced in axle gears, which aren’t needed in manual transmissions. Minimizing the sulfur is supposed to help the synchros and any thrust washers last longer.

A Google search will provide numerous links on this topic if you don’t receive additional input here on the forum.

[Brandonc20]

thanks everyone for their feedback.

[blackedoutharley]

Originally Posted by Brandonc20

So you actually pull hte shifter out of the cab to refill? or is that just easier to do when refilling?

thaNKS everyone for thier input!!

Yes, as you may imagine it is much easier to sit in the truck and pour oil through a 3" hole in the floor than to lay on my back and try to pump it through a 1/2" hole on the side of the transmission.

An empty sm420 holds about 5 qts. I used the Redline MTL and it helped smooth the shifting and eliminated some of the noise. I would not run engine oil but to each his own.

Originally Posted by Brandonc20

After reading the link, I should probably use 50w engine oil. I am in southern california and its about 105 degrees. Does anybody disagree?

In the Richmond transmission I might, but a Richmond is an entirely different beast than a SM420. BTW, it will be 104 here on Sunday & Monday.