Tom’s Bronco Parts Power Brake Booster
Tech article by admin and filed under BrakesProduct Review by Jon Hanna (Admin)
Recently I installed the “No Modify” Power Brake Kit from Tom’s Bronco Parts and have been very happy with the results. In addition to being a nice kit, what really sold me was the fact that the booster design fits with no fender modification.
The kit was very complete and the install went smoothly. It probably would have taken less than a day if I hadn’t detoured to clean up my engine bay. The new pedal feel admittedly took me a while to get used to. I’ve been driving my 72 Bronco with non-power brakes for more than 10 years. But now that I’m used to it I really enjoy driving the truck more. The braking feels more secure and requires very little pedal effort.Tom’s Power Brake Kit
Above are photos of the kit as shipped. Included is the booster, bracket, master cylinder, master cylinder brake lines, adjustable pushrod with rubber seal and vacuum hose with clamps.
Prepare the booster bracket:
Install the new rubber seal/bellows that the pedal rod goes through, then the pedal rod. Thread the adjuster nut and connection fork onto the new pedal rod. At this point don’t worry about how far to thread the fork. This will be adjusted later. Connect the fork to the bell crank (pivot bar) on the bracket using the supplied pivot pin, but don’t put the cotter pin in just yet.
Installation
Removal of old master cylinder:
Start by removing the brake lines that go from the master cylinder down to the distribution block (also called an “H block” or “pressure differential switch”) If you have a 76-77 Bronco you should have a proportioning valve instead of the distribution block found on earlier models. After removing the brake lines plug them to avoid air and moisture getting into your brake system.
Take a measurement of the brake pedal height from the floor board. You’ll need this later when adjusting the new connecting rod. Now, from under the dash disconnect the rod at the brake pedal. Save the clip and any bushings. Now unbolt the master cylinder from the firewall. The new booster bracket uses one of the master cylinder bolt holes as well as 3 others. You’ll need to remove those three bolts. See the arrows on the photo above. Now is a good time to clean and repaint your firewall if it needs it.
Place the booster against the firewall and secure with the 4 bolts. Now adjust the length of the pedal-to-booster connecting rod so that your brake pedal is at the same height it was previously. Tighten the lock nut to secure the rod fork. Then reconnect the rod fork to the booster bracket arm with the supplied pivot pin. Be sure to secure with a cotter pin.
You should always bleed the master cylinder to get rid of any air. Air in the master cylinder will go straight into the brake lines and make it that much harder to bleed the system afterwards. This is called “bench bleeding” although you can do it on your bench or attached to the vehicle. Pick up a simple kit from your local parts store, which will include various size fittings and 2 rubber lines. Thread the fittings into the master cylinder, attach the tubes and loop them back into each reservoir. (You can avoid buying this kit if you don’t mine destroying your old master cylinder hard lines. Just cut them and bend them back into the reservoirs like this.)
Now it’s time to attach the brake lines from the master cylinder to the H-block (or distribution block). The H-block shown is the most common configuration on drum brake Broncos and is always confused with a proportioning valve. This IS NOT a proportioning valve. It’s only a junction for the brake lines, which also serves as a brake warning light switch. It wasn’t until 1976-77 that Broncos came stock with proportioning valves. Here’s a photo.I highly recommend getting new brake lines. The set I got from Tom’s fit perfectly and made the install simple. If you need to adjust them be very careful not to crimp or make any sharp bends. Always use flare wrenches when working with brake line fittings. Normal open end wrenches can round off the corners. Don’t use teflon tape on brake line threads. Brake lines seal using the flared seat at the end of the lines, not the threads. If you have a leak it’s because the seat isn’t sealing properly, not because fluid is getting past your threads.
Attach the supplied vacuum hose to the check valve at the booster. Attach the other end of the hose to a vacuum source, either on the intake manifold (shown) or at the base of the carburetor. Be sure to route the vacuum hose away from exhaust/headers and steering components.
Now climb under the dash and reattach the brake pedal and switch to the push rod. Use your old clip (check that it’s in good shape) and any bushings you took off originally. Be sure to check that your brake lights go on when you step on the pedal. Note the cheesy wiring fix done by a previous owner who was too lazy to find the correct factory plug. Of course I’ve now owned the truck longer than he did and I still haven’t fixed it!
Check and double check all brake line fittings to be sure none are leaking. Check that you filled the master cylinder after bleeding and the cap is secure. Check your brake pedal is securely attached to the rod. Check that the pedal operates smoothly with no binding or loose feel. Did I mention to check everything again? Remember, these are your brakes you’re dealing with. It doesn’t get much more important than that.
My first few test drives resulted in some strange behavior. The stopping power was there, but seemed to come on all at once. The first 2″ of pedal travel was very easy and didn’t brake very hard. Then the next 1/2″ brought the truck to a halt. A quick call to Tom’s Bronco Parts suggested it was probably my rear brake shoes needing adjustment. Apparently this is pretty common. If the rear shoes aren’t adjusted properly they take too long to kick in resulting in a lurching stop.
For tech questions or install problems please contact:
Tom’s Bronco Parts
2294 Sage Rd.
Medford, OR 97501
(541) 779-1339
info@tomsbroncoparts.com
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