The Stovebolt Site Forums The Shop Area Driveline Help selecting a new rear end for a '51

I am new at this, but went ahead and bought a "frankenstein" '51 3100. It has a 350 ci engine, but don't know the year. Don't know the tranny (could be orginal), or the rear end, but told the rear end has been replaced.

I tried to replace the brakes, but could not find parts since I did not know what I was looking for. Easier to start from scratch.

So, my question is, do any of you all have recommendations for what I should put on as a replacement? Looking for gas mileage/highway speeds over burning rubber, so I am thinking 3.73 or 3.55 ratios.

If you can see the driveshaft turn as the truck moves, the rear axle has definitely been replaced. Try posting some links to pictures at somewhere like Photobucket, Hunt 101, etc., and somebody can probably make an educated guess at what's in there now. Posting pictures directly to the site creates problems for some of our members with limited bandwidth or very expensive internet access, so no direct-posted pics, please. Does the rear end still have the 6-lug wheels on it?
Jerry

Welcome to the 'bolt Mater. If you can post any casting or stamped numbers on the rear end someone on here will probably be able to identify it for you. Also, do you know what the ratio is now? If you're not sure do this:

Jack up the rear of the truck and put the tranny in neutral. Mark the tire and the driveshaft with chalk or masking tape, or whatever. Rotate the tire 20 times while counting the driveshaft revolutions. Divide the number of driveshaft revolutions by 10 and you've got the ratio (i.e. 41 revolutions would be a 4:10 ratio)

Note, if the rear end is a posi (both rear wheels turn in the same direction as you turn them) just rotate the tire 10 times and divide by 10.

Is this the same for a 57?

No, all trucks since 1955 have been open driveline.

An S10 rear is a good choice. You can find them in a variety ratios from 3.08 to 4.56 posi or not.... disc or drum

GU4=3.08
GU5=3.23
GU6=3.42
GT4=3.73
GT5=4.10
H04=4.11
HC4=4.56

Just something to throw out there, I had a Toyota Land Cruiser in the shop a few days ago, a '95 model year. The rear axle measured 65" WMS to WMS. it not only had factory disk brakes and a 6 lug bolt pattern, but is also a full floating axle. Stock gearing is a bit deep, somewhere around a 4.30, but there are 4.10 and 3.70 gearsets available for them.
BTW, I have never seen an S10 with anything deeper than a 4.11 ratio, factory literature, owners manual, and shop manual supports this.

Thanks guys. I just got back for business travel and starting to work on this again. I will take your suggestions to Pick a Part and the local Cash for Clunkers and see what I can find.

Some mid 60's Ford passenger cars had 9 inch fords of withs about 61.5 and centerd pinion gears. I would do that... infinite choices for gears. Also, on my 59, I used a posi disc break rear from a cop car caprice. it had 3.23 gears in it. After a few hours with the plasma cuter and grinder, I was ready to weld on my new purches.

P.S. It was 61.5 inches wide mounting surface to mounting surface. The pinion was not centered. It was off by a tiny amount, but not enough to cause an issue.

Now that the 9" Ford has been mentioned I guess it's safe to point out another FoMoCo differential that is both readily available, is 60" wide from mounting surface to mounting surface, has 31 spline axles, most are 3.73, are available in both big drum and also disc brakes, are positraction and can be had for around $100.00.

These are found in the 94 Explorers (drum) and the 95+ (disc). They also have a slight offset which does NOT effect balance and the emergency brake setup controls both sides with one cable. In addition, the axle codes (D5, D7) are on the sticker on the drivers door. The vast majority of V6 Explorers use a .63 OD transmission and the 3.73 posi diff is the standard fair.

Personally, I think the 8.8", with the 31 spline axles is nearly as tough as the 9" and aside from having a 5 on 4-1/2" bolt pattern would be a good option. I've been running one behind a built 5 speed 355 SBC in my Retro Hot Rod and think it's a great diff for the money. Have pics of the diff and install in my Webshots Hot Rod album.

If you go this direction be sure to get the U-bolts and the bottom plate as the axle tubes are 3-1/4" diameter.

Dave

I agree. 8.8s are strong and in some ways maybe even better. If you go the 8.8 route, remember when you torque down the u bolts they have very thin tubes...

Also.....in addition to being pretty thin walled the axle tubes are just pressed into the center housing. This can work both ways; you can narrow it 2-1/2" (approx) by popping out the left side longer axle tube, cutting out enough so you can use a right side axle or you can use it as-is and do some spot welds between the axle tubes and the center housing.

The TracLok (posi)feature, can be easily checked for excessive wear with the diff still in the vehicle......simply select one that has a minimum of play when you push-pull on the hub. Even with 100K on the vehicle there is very little obvious wear on the internals and with the volume of 3.73 Posi diffs available for a whole lot less than buying a gear set and installation kit, it makes for a viable option.

Dave