Rearend Relief
Q: I have a '63 Chevy Fleetside truck in original condition, and I need to know some things. What rearends out of newer trucks are interchangeable without a lot of hassle? I'm putting a 700-R4 in it, bolted to a 355. I am looking for something with a good gear for highway use. I'm currently using a 10-bolt rearend. If I just change the third member, what gears should I go with? Any answers would help.
Shane Fishel
Mooresville, IN
A: You've really hit a soft spot in my heart. When I was 16 years old we used a '63 Chevy 1/2-ton Fleetside to tow my dad's race car to the track. This was a $600 truck with a 292ci six-cylinder and three on the tree. After breaking my first two cars I moved on to the truck because Pops figured I couldn't break a truck. Well, the three-speed Saginaw wasn't long for this world! I got really good at dropping out the trans and swapping in a new First gear. I went completely through this truck, restoring it, and finally swapping in a 327ci and a Muncie four-speed in the later years.
The '63 model came with either leaf-spring rear suspension or the famous truck-arm suspension that to this day NASCAR uses in its rear suspension. For many years it actually used the factory truck arms in the race cars. None of the later-model 10-bolt 8.5- and 8.625-ring-gear 1/2-ton truck rearends will bolt right in. The leaf-spring mounting pads are in different locations. It would be very easy to cut off the factory pads and weld some new ones in the proper location for your springs. If your '63 is truck-arm suspended, you'd need to cut the factory pads off the original rearend housing and weld them to the late-model housing. It may prove quite tricky getting the original pads off the housing without damaging them too much. Also, the truck-arm design uses a Panhard bar to locate the rear axle from left to right. You'd need to fabricate a bracket to attach it to the new housing.
You stated that you have a 10-bolt rearend and a drop-out pumpkin. This is the earlier-design rearend and quite possibly a 3/4-ton design. Finding gearsets for this early design will be tough. Check with Randy's Ring and Pinion for direction on a gearset.
Swapping in a 10-bolt 8.5 from a mid-'90s-or-later truck is a piece of cake. As for gearing, we'd look for a 3.42:1 rearend to drop in. This is a great ratio that will balance performance and freeway manners. Trucks have larger-diameter rear tires than passenger cars. This, in combination with the 0.70 overdrive of the TH700-R4, will really bring the engine speed down on the freeway cruises. Check out Speedway Motors for components to make your rearend swap a snap: weld-on spring perches that will match right up to your housing and U-bolts to hold it in place. Make sure before you strike an arc with the welder that the axlehousing is centered between the framerails and that the pinion angle is pointed down around 2 degrees more than the driveshaft angle at a loaded ride height. This will keep your U-joints happy and allow for the full range of suspension travel.Sources: ringpinion.com, speedwaymotors.com