Converting a 1967–1972 C10 to front disc brakes

The factory front drums on an Action Line C10 were adequate for 1969 traffic. They are not adequate for a modern interstate on-ramp, and they are considerably less adequate after they have faded once. This is the most worthwhile modification you can make to one of these trucks if you actually drive it. It is also completely wrong for a judged restoration, and I would rather say that at the top than at the bottom.

01Before you commit

This is not correct. A 1967–1972 C10 left the factory on drums and a judge will mark you down for this. If the truck is going to be shown, buy the drum parts and stop reading. It is 2WD only. The 4WD front end is a different assembly entirely and this kit does not fit it. You need a dual-circuit master cylinder. More on that below, because it is where most people get this wrong.

02Tools

A 3/8 and 1/2 drive set, a torque wrench that reads to 150 lb-ft, a ball joint separator, a large hammer, a bearing packer or clean hands, and a flare nut wrench set. Do not use an open-ended spanner on brake lines — you will round the fittings and then you are making new lines. Jack stands. Four of them. Not a jack.

03Stripping the front end

Break the wheel nuts, lift at the frame rail, get stands under it. Pull the wheel and the drum. If the drum will not come off, back the adjuster right off through the slot in the backing plate — do not lever at the drum edge, you will bend it. Remove the caliper-side brake line at the flexible hose. Have a pan under it. Cap the hard line or you will drain the entire master cylinder onto the floor. Take the cotter pin, castle nut and outer bearing out, pull the hub, then unbolt the backing plate. Separate the tie rod end and the upper and lower ball joints, and the spindle comes off.

04The first thing that bites you

The ball joint tapers will not let go. They are a fifty-year-old interference fit and a pickle fork will destroy the boots — which is fine if you are replacing the joints and expensive if you are not. The method that works without damage: leave the castle nut on, threaded down flush with the end of the stud, and hit the *side* of the knuckle boss squarely with a heavy hammer. The shock distorts the boss and the taper releases. It usually takes three or four hits. Hitting the stud itself just mushrooms the threads.

05Fitting the new spindles

The new spindles bolt straight to the original upper and lower ball joints. Torque the ball joint nuts to spec and fit new cotter pins — always new, never reused. Pack the bearings properly. By hand, working grease through the rollers from the back until it comes out the front, not just smeared around the outside. A bearing that has been "greased" by wiping some on the cage will fail within a season. Set the bearing preload the old way: torque the spindle nut to about 12 lb-ft while rotating the hub to seat everything, then back it off completely, then finger-tighten and back off to the nearest cotter pin hole. The hub should turn freely with no perceptible in-and-out play.

06The master cylinder question

Here is where people go wrong. The original single-circuit drum master cylinder has a residual pressure valve in the outlet that holds about 10 psi in the system permanently. Drum brakes need that — it keeps the wheel cylinder cups expanded against their bores so they do not weep. Disc brakes must not have it. Ten psi of residual pressure holds the pads lightly against the rotors all the time, and they will drag, get hot, and eventually cook. So you need a dual-circuit master cylinder with the correct residual valving: none on the front circuit, 10 psi on the rear. Every proper conversion master cylinder is built that way. Do not reuse the original. While you are there, the dual circuit is a genuine safety improvement in its own right. A single-circuit system loses all four brakes from one leak, with no warning.

07The proportioning valve nobody fits

Discs bite harder and faster than drums. Front discs with rear drums and no proportioning gives you a truck that locks its rear wheels under hard braking, which on an unladen pickup is how you end up facing the wrong way. Fit the adjustable proportioning valve in the rear circuit. Set it to about mid-travel to start, then find an empty piece of road, brake hard from 40, and see which end locks first. You want the fronts to lock marginally before the rears, always.

08Bleeding

Bench-bleed the master cylinder before it goes on the truck. Not optional — a master cylinder with air trapped in the bore will not bleed out on the vehicle no matter how long you pump. Then bleed at the wheels furthest from the master cylinder first: right rear, left rear, right front, left front. Use fresh DOT 3 from a sealed container. Fluid from a bottle that has been open in the garage since last year has absorbed water and its boiling point is on the floor.

09Torque specifications

• Caliper bracket to spindle — 85 lb-ft
• Caliper slide bolts — 35 lb-ft
• Upper ball joint nut — 65 lb-ft plus to the next cotter pin hole
• Lower ball joint nut — 90 lb-ft plus to the next cotter pin hole
• Tie rod end nut — 45 lb-ft plus to the next cotter pin hole
• Wheel nuts — 90 lb-ft in a star pattern

10Bedding in

Pump the pedal until it is firm before you move. It will go to the floor on the first stroke and that is normal. Then ten stops from 35 mph down to about 5, moderately firm, without coming to a complete stop. Drive for ten minutes without touching the brakes to let it all cool evenly. Do not park with your foot on the pedal while the rotors are hot — you will print a pad shape onto the face and feel it as a judder forever afterwards.

11Then get the alignment checked

You have changed the spindles. The geometry has moved. Get it on a rack.