My plan for the truck's drivetrain was to keep things close to stock, but update to modernize and give it more performance. I plan to keep a carburetor. I plan to change out the 3 speed automatic transmission with a 4 speed automatic. I plan to keep the original 12 bolt rear axle and put in a limited slip differential. A fleetside longbed C-10 weighs somewhere between 3750 and 3850 pounds, so it needs a strong drivetrain.
The truck came with the original 350 V8. The odometer shows a little over 60,000 miles, but it could easily be 160,000 miles. The stock spark plugs are AC Delco R45 with a .035" gap. The original 1970 350 engine has a 9.0:1 compression ratio and is rated at 170 to 200 hp net at 3600 RPM and 310 net lb-ft of torque at 2400 RPM.
This truck originally had a distributor with points. This was already been changed over by a previous owner to a GM HEI distributor. I will continue to use an HEI ignition. The new engine will likely have a billet hydraulic roller cam, and the distributor will need a drive gear with a melonized coating.
I'm using the original ram horn cast iron exhaust manifolds with a 2" collector, coated with paint with ceramic in it. The exhaust is mandrel bent 2 1/4" diameter dual exhaust pipes. These manifolds use 3/8"-16 x 2.25" long bolts on the outside positions, and 2.75" long bolts in the middle.
The new engine will likely not have a location for a mechanical fuel pump, so I will use an electric one.
Because the current engine does not have hardened valve seats for unleaded gas and has ring problems with the #3 cylinder, I plan to change it. I want a 1st generation Chevy V8 with a hydraulic roller cam, for lower wear on the cam.
My choice for a replacement engine is an HT383 engine from Chevy Performance. This has Vortec iron heads with a 1 piece rear oil seal, a roller cam and a 9.1:1 compression ratio that runs on 87 octane gas. This has a forged 4340 steel crankshaft, powdered metal connecting rods and hypereutectic aluminum pistons. The valves are 1.94" and 1.5" diameter, and the valves have .431" intake and .451" exhaust lift. The roller cam has a 196 degree intake and 207 degree exhaust duration at 0.050". This puts out 314 hp and 427 lb-ft, through a Ramhorn exhaust manifold with good torque available at low RPMs. This has pressed-in rocker studs and stamped steel rockers. This comes with an oil dipstick and tube.
I'm using a serpentine belt system so that I can fit a late-model high output alternator. The serpentine belt with a tensioner keeps even pressure on the pulleys and keeps the belt from slipping, or wearing out the bearings on the accessories if it is too tight. I'm choosing a later stock setup. I'm using a Saginaw canister power steering pump, a Sanden A/C compressor and a CS-144 alternator. I'm using the brackets, pulleys, thermostat housing and power steering pump from a 1989-1995 Chevy 1500 truck.
I'm using an aluminum radiator from DeWitts, an aluminum fan shroud I got on eBay, and two 13" Spal electric fans to keep the engine cool. I'm controlling the fans with a PWM controller from AutoCool.
I have a stage 2 long reverse rotation water pump from Stewart (P/N 23123), and a Stewart-modified Robert Shaw 195 degree thermostat that has holes to allow Vortec heads to have a water jacket bypass.
The lower radiator hose is a Dayco E70664 with a 1 3/4" inside diameter at both ends. This lower hose needs to have about 6" trimmed off the radiator end when using a long water pump. And when putting this hose on the radiator, make sure it goes on all the way - don't let the radiator shroud get in the way.
With the serpentine drive, the original upper radiator hose comes too close to the serpentine belt near the alternator. I'm using a thermostat housing from an 88-95 Chevy truck which is GM P/N 10147884 or Dorman P/N 902-694. This sends the hose more up from the engine than the original setup. The new upper radiator hose is AC Delco P/N 26025X, which has a 1 1/2" inside diameter at each end. This upper hose needs to have about 6" trimmed off of the thermostat housing end.
The stock transmission is a TH350 3 speed automatic transmission. I plan to switch to a 700R4 4 speed automatic transmission when I change the engine. The 700R4 needs to be updated with heavy duty parts. I plan to use a BowtieOverdrives level 3 700R4 transmission.
I will get a cross-member and lock-up wiring kit from BowTieOverdrives. I will use a Lokar TV kick down cable. With a 4 speed transmission, I will keep the old steering column designed for a 3 speed, but will use a Lokar transmission shift arm to make the original 3 speed column work with a 4 speed transmission.
Chevrolet Performance recommends a 2400 to 2800 RPM stall speed torque convertor for the SP350/357 engine. I plan to use a 2400 RPM stall speed converter from BowtieOverdrives. But for the ramjet/HT383 cam, 1700-1900 is more appropriate.
The 1970 C10 long bed pickup trucks with a 350 V8, TH350 transmission & a 12 bolt truck rear end have a driveshaft that is a 2-piece design with a center support bearing. The TH350 transmission used here has the longer 9" tailshaft, which is 1/8" shorter than a 700R4.
The 2 piece driveshafts used on longbed 1/2 ton C10 trucks with an automatic transmission do not have the best reputation. On these trucks the only slip joint is in the front half of the driveshaft where it goes into the transmission. The problem is that the front half of the driveshaft is pressed into a carrier bearing that is suspended in a rubber mount, and the carrier bearing is bolted to the frame of the truck. The back half of the driveshaft has no slip joint. So when the driveshaft needs to move on the slip joint, it stresses the rubber mount for the carrier bearing, eventually tearing it apart.
There are 2 ways to fix this:
The crossmember has holes for both the light duty and heavy duty bearing brackets. The brackets are riveted in at the factory, but the old one can be cut off and a new one bolted in place. The carrier bearings cannot just be swapped from a light duty to a heavy duty one, since the bearings ride on a different part of the driveshaft, so the driveshafts & bearings need to be changed as a set. A driveshaft from a C20 or C30 from 1967 to 1972 fits, but make sure it is from the same length truck (shortbed, longbed or longhorn), and has the same engine & transmission. Even if the donor truck matches, the measurements should be checked.
I am going to use Captain Fab's HD carrier bearing bracket and a driveshaft from a 1984 C20 Suburban with a 350 V8 & a 700R4 transmission. The Suburban has a wheelbase of 129.5", while the 1970 C10 has a 127" wheelbase. So the driveshaft will need to be shortened. The HD driveshaft is stronger than the U-Joints, so using solid body (not cross-drilled to make them greasable while assembled) 1310 U-Joints from Dana/Spicer (Spicer Life series) will allow 700 lb-ft of torque for short durations.
From 1963-1970, the rear axle had a width of 62" from wheel mounting surface to wheel mounting surface (WMS-WMS). During the 1970 model year until 1972, they changed to 63.5" WMS-WMS. My truck has a 63.5" wide axle.
The axle shafts of the rear Chevy 12 bolt truck axle were replaced with Moser axle shafts during the rear brake upgrade to change to the new wheel bolt pattern. The truck came with a 3.08 rear axle gear, and was switched to a 3.42 ratio from Yukon Gear. The stock open differential was replaced with an Auburn Gear limited slip differential. The Chevy truck 12 bolt axle with 30 spline Moser street axles should be able to handle 600 hp & 600 lb-ft of torque.
The original factory wheels were 15" x 5.5" with 6 lugs on a 5.5" bolt circle, with G78-15-B tires. The wheels were 15" x 7" with the same bolt pattern when I bought the truck. The wheels I am using are American Racing Torq Thrust II - 1 piece with a polished finish in a 17" x 8" size. The 17" diameter is needed to clear the front brakes. I am using Michelin Latitude Tour P255/60-17 tires (29.1" diameter).
During the brake upgrade, the bolt pattern was changed to 5 lugs on a 5" diameter. Not all 17" wheels will clear the Kore3 front brakes, but the wheels and brakes were common enough that there were pictures of this combo on other vehicles on the Internet. Even then, a 1/2" spacer is needed between the hub and the front wheels to get room to pass the hub center through the wheel and to get clearance between the caliper and the inside of the wheel. With the 1/2" spacer, the caliper will be about 1/8"" from the inside of the wheel surface.
These Torq Thrust II wheels in this size and bolt pattern come in 4", 4.25", 4.75", 5", 5.25" and 5.75" backspacing. I'm using the 4" backspacing (-12 mm offset) to push the tire/wheel out to help fill the wheel wells. This offset gives about 1 1/2" clearance between the inside of the tire to the frame in the rear, and helps keep the wheels/tires from rubbing the PB Fab A-arm anti-sway bar mount on the front. Note that the rear axle on 1970 1/2-72 C10 trucks (63.75" wheel mounting surface to wheel mounting surface) are about 1 3/8" wider (11/16" on each side) than 1967-70 1/2 C10s (62.375" wheel mounting surface to wheel mounting surface).
I found center caps for the wheels that have a Chevy bowtie logo on them to replace the American Racing logo. I'm using Gorilla Guard wheel locks on the wheels.
I am keeping the gas tank behind the seat so that I can have a spare tire stored in the original location under the bed. I've got a dual exhaust, but the pipes exit on the sides just behind the rear tires, so they do not get in the way of the spare.
The issue is that the original wheel/tire combo is 8.4" wide and 28" in diameter and I am running a wheel/tire combo that is 11" wide and 29.1" in diameter. After cutting off the original spare tire mounting hardware because of rust, I got some replacement hardware. I got a cross strap for a 1975-1987 Chevy truck, but the original part will work fine if it can be cleaned up. The issue is that both of the bolts holding the cross strap need to be longer because of the wider tire. The bolt for the removable side (rear passenger's side) from a 1975-1987 is long enough. The other fixed bolt (front driver's side) needs to be about 12" long, and have 1/2"-13 or 1/2"-20 threads. I used 2 nuts on the fixed bolt side with JB Weld to make it theft resistant, and used the factory hand nut (it has a plastic threaded insert) on the other side to be able to function with some rust.
The removable nut side can be locked in place with a padlock that has an adjustable shackle that comes off - the U-shaped shackle is put through the eye loop on the nut and put through the hole in the cross brace, then locked in place with a Master Lock model 510D. It is a good idea to put grease on the key lock area and put tape over the key area to keep rust from freezing the lock up over time.
To hold the wheel in place on the cross brace, I removed the original brackets because they looked like they would scrape up the inside of the wheel. I used a couple of bolts facing up as pins to go through the wheel mounting bolts holes, and then used lug nuts to hold the wheel tight. I am using a powder coated 17"x 8" steel wheel instead of an aluminum wheel for my spare to keep corrosion away a little.