The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Rear Diff

Just got a good look under my bed(I took it off). My rear diff has an "MA6 30" stamped on it. It's a ten bolt in a circular pattern.
Can anyone tell me what all of this means? Can you pinpoint what type of gears I have inside?

Thanks for your help!

How many lugs? The only sure way to determine the gear set is to remove the rear cover and count the ring gears & pinion gears and divide the large number by the small number. This will give you the actual gear ratio, regardless of what the tag or casting numbers indicate.

I have 6 lugs.

MA, 3.90 ratio, 6 30, built on June 30th.

Thanks Longbox!
So if I wanted to change gears to pick up a couple of MPH's, do I go higher towards 4 or lower towards 3?
BTW...it's a 3-speed.

Thanks again!

You would go towards 3. However, there really aren't any option with the original Eaton rearend. The only factory ratios were 3.90 (standard), with 4.11 and 3.38 as options. At this time, only 3.38 is available as replacement gears. Most of the vendors carry this gearset, plus Patrick's carries them as well. Another option that may save you some money over changing the gearset would be to swap to an overdrive transmission. The original style overdrive, which is the same trans as the 3 speed but with a 2 speed auxilliary trans in the tailshaft, will bolt right in with little alterations other than some wiring and adding a control cable for the lockout. These transmission are fairly easy to find, and can usually be had for under $200. I did this swap on my '55, which has the same gears as yours, I can cruise the highway at 75 mph and only turn 2400 rpm. I do admit to having bigger than stock tires, which cuts the rpm down as well. It's a very enjoyable transmission to drive, very flexible, as it essentially gives you 6 forward gears and can be used as a gear splitter just like the big trucks.

Thanks again!
Do you have a supplier name for the overdrive transmission? I know absolutely nothing about this part of the truck. Any help would be appreciated. I'm looking to get up to 65 - 70 MPH. I'd be happy with that.
Learning to do all of this stuff is why I bought the truck. I've learned tons in a year's time. However, transmissions/clutches/rear diffs are not my forte.

I found mine at a swapmeet, but they pop up regularly on Ebay and I think I saw one recenty in the Swap Meet section of the forum here.
I see you're from Indiana. Are you close to the Indianapolis area? There's several good swaps in Indy, I beleive there's a Super Sunday meet comming up next month sometime after Thanksgiving. They have those at the State Fairgrounds on 38th street. I've seen those overdrives there quite often.

Thanks Longbox!
Does anyone have a picture of an overdrive transmission that I can use in my 62 C10? Does anyone know where I can get one?
Any help would be appreciated.

Here's what the overdrive looks like. Here's the right side. The main trans is the same as the standard 3 speed, and functions essentially the same.

I was wondering if you know of a part number for the overdrive or a why that would make it easier for me to search for it? Also would this work with a 61 Apache 4x4 with a 3 speed + granny transmission? Would you also need to shorten the drive shaft due to adding the OD?

I need one so if someone has one please let me know!
Thanks