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1947 to 1959 Chevy GMC Front Disc Brake Caliper Conversion
The Hollister Road Company Disc Brake Conversion was designed to be used on 3600 and 3800 Chevrolet Truck from 1947 to 1959 with single rear wheels. There is a difference between front wheel hubs on single rear wheel and dual rear wheel trucks and both can be 8 lug. The dual rear wheel truck has what's called a hub extensions that moves the front wheels out about 6 inches from the brake drum. This was used on dual rear wheel and some single rear wheel trucks that were heavy duty such as Civil Defense 1 Ton, Forest Service 1 Ton and Fire Trucks 1 Ton. There has been the rare occasion that a 3600 had dual rear wheels and a regular front hub was used. The pictures in this write up show a single rear wheel front hub that was used on 3600 and 3800 trucks
There has been a change in the original kit, we now weld on all the spacers needed. The only loose spacers in the box are the stud grinding spacers. Some backing plates will need extra modification to fit the new style brackets, do not modify the bracket to fit the backing plates.
All the pieces that are supplied in the kit have been pre-assembled to an axle and spindle of the year and weight class that you specified.
We assembled the kit with a new Bendix brand rotor, caliper, brake pads and new mounting hardware to insure they fit properly when you receive it. When you assemble them it may however be necessary to true up the disc rotor once the rotor is mounted to the hub. This is an easy task for any automotive machine shop.
What’s in the kit?
2) Spindle to caliper brackets 3/8” thick. 1020 steel
4) Upper spindle spacers . These are fixed to the brackets
2) Lower spindle to bracket spacers .
4) Grade 8 flange bolts ½” x 2-1/2” with lock nuts – no washers used.
4) Grade 8 bolts 7-1/16” x 2” with lock nuts and washers.
2) Aluminum Wheel spacers machined to fit the GM rotor with studs and 16 rotor alignment collars attached.
2) Utility 1" diameter spacers for shortening stud.
The bracket is made from 3/8"1020 Steel. It has high fatigue strength, abrasion and impact resistance, toughness, and torsional strength; it’s the same material as the spindles. The spacers are made from 1020 DOM steel.
The first step is to strip off the old brakes, as you do inspect the existing parts for rust and corrosion, if they are damaged replace them, if the kingpins are sloppy replace them as well.
These pictures show the bolts reversed; they should point outward with the nuts showing not the head when we are done.
You can slide in the lower bolts to keep the backing plate on but they will be reversed later. This is where you decide if you want to use the backing plate and a dust shield. If so cut the backing plate as pictured and trim to fit.
Adding the brackets:
The spacer always goes to the spindle side. The notch in the bracket is for the caliper bracket so we don’t put it on the wrong side caliper mount bracket and keeps the caliper bleeder at the top. The flat bracket will be stamped R or L.
The new grade 8 fine thread bolts are 3/8” to ½” longer than the original bolts you took off and are needed to compensate for the spacers on the brackets and used on the lower arm.
With the parts off and kingpins refitted we can start the assembly. You need one caliper to spindle plate, and two yellow 7/16” bolts, two yellow 7/16” washers. Slide the bolts with one washer on it through the plate and into the spindle add backing plate if used and add a washer and nut. If the backing plate is used you may not get a washer to fit there.
Now take one 3/8” x 1/2" ID spacer and the one new ½” black flange bolt. Pass the black flange bolt through the steering arm, through the silver spacer and in to the spindle add one nut no washer.
There is no spacer on the lower front just the bracket. Point the bolt outward on the front side as well. We need this for turning clearance because we moved the arms inward by 3/8” of an inch. insert the bolt through the arm, bracket and spindle, add a nut. Torque all the bolts to specifications. Use the prevailing torque nuts on the new bolts. Prevailing torque nuts are one use only so don’t tighten them till you’re ready to final torque them. If you want to snug it all up get some regular fine threads 7/16” and ½” nuts to test with.
Wheel Spacer and stud spacers:
Replace the original wheel studs and lugs with new ones. They are 60 something years old and should be tired by now; it’s a cheap and simple insurance policy and we are adding more stress on them with this upgrade. Press them out not hammer them out. Hammering will add lateral run out to the package as a whole.
In the kit there are 16 threaded collars, one on each stud of the aluminum wheel spacer. They are 14mm x 1.5 thread . These will help keep the rotor from slapping on the new studs when stopping and helps with vertical run out. They need to be at the bottom of the stud but not tightened. Screw them all the way down and back them off about a 1/16 or 1/8 turn. They need to be somewhat loose. Do not Loctite them.
The new studs you put in the old hubs need to be shortened so they clear the back side of the rotor when it’s on the aluminum wheel spacer. Use the included slide on stud spacers as a guide, there are 2 included, the cone goes up. Use your lug nuts to hold them in place hand tight and grind them just to the top of the nut. These spacers can also be used to pull the rotor onto your wheel spacer once the studs are ground to the proper height. Now make sure you have no burrs or raised spots on the hub flange, remove all the old gasket material. NAPA has a hub cleaner that goes on a drill to clean up the surface without removing material. You can take a flat file and just touch up the edges so the aluminum spacer sits very flat and has no lateral run-out when put on to the hub. Replace the old wheel studs and lug nuts. Now put the aluminum wheel spacer on and tighten the nuts evenly to torque specs. The lug nuts will be what center the new wheel spacer and rotor so take care in cleaning and tightening the lugs I advise using a torque wrench. You will have to re-torque them in 100 miles or so. At this point you want to put the hub and wheel spacer assembly on the spindle and make sure its running true with .000 - .002 run out. You Tube has many videos on how to check lateral run out, record the run out for later comparison. If it’s more than .002, take it back apart and check the hub run out. Run out should be no more than a standard disc brake run out. Run out should only be a few thousand’s in the .000 - .002 range for the entire package. With that said NAPA make thin spacers to correct excessive run out and you may have to rotate the wheel spacer on the hub and or rotor to get within tolerance. 2500 HD 13” disc is .000 to .002 so we need to be very close on the hub and aluminum spacer and not compound the lateral run out when done.
This is a you tube video on checking and correcting lateral run out
Now we pull the rotor onto the aluminum spacer. Push the hub into the rotor and take the 4 spacers marked “W” and the lug nuts and screw them on the 14mm stud in a 9, 12, 3 and 6 o’clock positions. Start slowly drawing up the hub assembly on to the stud spacers. The tolerance is close here so you may have to turn some to get it all the way on. Don’t hammer it. If you need to you can remove the rotor with the putting two bolts in the screw holes and pushing the hub out. Remember to clean up any burrs left by the studs. If it still doesn't’t go unscrew the spacers and put a small chamfer on the top edge so it guides into the rotor stud hole easier. Once the rotor is on; check the run out and compare the first run out so you know that it is actually flat on the wheel spacer. Correct any run out.
Leave the nuts and spacers on the hub and load the bearings and seals. Reuse the existing metal dirt shield and mount the hub rotor assembly and adjust wheel bearing to specs.
Because we hang the caliper off the front of the axle you will put the left caliper assembly on the right side with the bleeder facing up, it will not fit the left side bracket.
You should now have in hand two 16mm caliper bracket bolts. Place the bolt through the spindle bracket and the cast caliper bracket and screw in the bolt, do the same for the bottom hole. The bolt is a tight clearance here and may need to have the hole slightly sanded don’t run a drill or reamer in it we need to as tight as possible but not binding. Torque the bolt to specs. The bolt torques to 220 ft/lbs. I know mine only goes to 150 also so borrow one you don’t want this falling off.
With the bracket installed load the rattle clips and pads and spin the rotor and check for run-out, make sure they sit correctly on the rotor and in the caliper bracket.
It should look like this. Add the hoses and lines. You should have the 2 stud spacers left nothing else.
Needed parts list.
1, Wagner CRB134347Caliper with mounting bracket
1, Wagner CRB134348 Caliper with mounting bracket
2, BENDIX PRT5261 Rotor
1, BENDIX RD784 Brake Pad
2, wheel seals NATIONAL 40973S for original hub, check for your year
Left and right hoses. There are two brackets on the new hoses and one can be cut off, the other used as a hose mount.
4, Carlson® H805caliper mounting bracket bolt or GM 18026702
these mount the caliper bracket to our spindle bracket
2, DORMAN HW1457 Hydraulic Hose Clip, these clip the hose to the stock hose bracket. You do need to notch the old bracket a bit for the tang on the hoses.
2, Banjo Bolts DORMAN 484205 (484-205.1)
4 copper hose washers, they may come with the hoses
2 Inverted flares for the hoses. They use a 7/16 nut with a 3 /16 line. They can be purchased at http://www.fedhillusa.com or other brake parts retailers
A12-3 - 7/16" x 24 tpi male fully threaded steel nut, .550” long overall, it’s red in color. If you’re using ¼ lines then a standard nut will do.
If you have access to a recycler then you may be able to score these parts for as little as $100 - $150. Just make sure you get all the bolts, clips and flare nuts along with the hard parts
Express van use the same parts just look for 8 lug 8600 lb brakes.
Dorman Replacement studs and nuts for the stock Chevy GMC hub
Studs - 610-183 1/2"-20
Lug nut - 611-016 1/2"-20
Master Cylinder Considerations.
Using the stock master cylinder is not recommended on a disc brake system. Do not mix front modern disc brake with original rear drum brakes. We recommend using a disc brake master cylinder with an 7" dual diaphragm booster and a 1.25" cylinder bore. 2500 HD Disc brakes require more fluid movement than a 1/2 ton 7/8 or 1" cylinder can deliver. You can purchase the matching booster kit from us as well. This master booster should product approximately 1200 psi of line pressure and works with the stock brake and clutch pedal.