The Stovebolt Site Forums The Shop Area Engine Shop 1955 2nd 3/4 ton 4speed third member exchange

I have read the post on changing out the third member in order to at least go 60 down the road. I located a salvage yard in Iowa that claims to have some 50 and many 60 through 70 trucks to choose from. once I have been to the yard I will let you all know if it is a good parts source. My question is this.
Has any one done this yet?
IF so can I tell the ratio of the donor with out dismantling the pumpkin?
The older gentleman that owns the gold mine is short on patients and not willing to spend the time, he just wants me to find a truck and he will cut it out.
Would any automatic 3/4 ton from the 60's or 70's be a improvement on what I currently have?

Thanks

Hy dgallagher, yes a differential from a 60s-70s automatic could be an improvement, be careful there were differentials of different manufacturers in those years. As for identifying without removal, on the end of the pinion there may be some numbers stamped, some will be the part number, some might be the ratio expressed as 35-7, divide the larger number by the smaller number and you get the ratio in this example 5.0 to 1, hope that helps.

If you are after a 4.10 ratio, the most consistent tale is that they existed in the years 67 to 72 on 3/4 Ton trucks with automatics. Now, I have also been told that the truck should have coil springs. Apparently for some of the years there were trucks with leaf springs and I believe Dana rearends. It is always possible that an optional ratio might have been installed at the factory, or there after. The 4.10 crown gear has 41 teeth.

What 3B and truckernix said... I have heard also.

I got a 4.10 from a 1971 3/4 ton with V8 and auto trans. It is an easy replacement, easier to replace than the gears in a non full float rear end. Lots of people have done this.

Beware, you can get a 4.57 gear that was also in the 3/4 tons and that won't improve your highway speed that much. They also have 5.14 gears in the 1 tons that you DON'T want unless you want to go slower. I've heard 3.90's exist, but never seen one.

Some of these differentials had the "no slip" option. This is essentially a detroit locker inside the carrier. It's a bit more rare, and might be just what you want. Mine (with locker) has a metal tag on the front top of the pinon support.

Only way to know for sure the gearing is to take it apart and count the teeth. Other than that, lift one side and rotate the wheel untill the pinion makes one full turn. Multiply the turns of the wheel by 2 and that's your ratio. If you can't get the wheel to rotate freely, then it's either a locked differential or a busted one.

Good luck!