|STOP what you are doing and fix those brakes!
Your new P15 project just rolled up on the flatbed tow truck. The previous owner had been pretty honest about the condition and as the tow driver unloads you remember his comment "Oh and the brakes are a little soft". You hop in, and as your friends help push the car up the driveway you tap the brake pedal. It goes to the floorboard and stays. As the garage door loom closer in the rear view mirror, you pull the emergency brake and nothing happens. Suddenly you stop, saved by a rock quickly thrown behind the rear wheel. Definitely a little soft.
Brake overhauls should be one of the first projects on your restoration list. Working brakes permit you to safely control the car in the shop area. The brake design used in this era of flathead mopars are notorious for wheel cylinder leaks and difficult to adjust brake shoes because of the non-servo design. With a single chamber master cylinder a brake line failure takes out the entire brake system. Since our project P15 needs a full brake system overhaul we will do it right ones and have years of safe service. First you will need to source needed brake components. They are still available from a variety of sources in NAPA if you have the correct part numbers. You will also need a factory service manual. Plan your time realizing a full overhaul will probably stretch over two weekends.
History and Terminology
Chrysler acquired a new hydraulic brake technology from Lockheed in the mid-thirties. This design used a double anchor, non-servo design. In servo design brakes one shoe "helps" the other by forcing the secondary shoe against the brake drum. Non-servo brakes have a shoe attached at one end, called the heel, to an eccentric anchor bolt (the "major" adjuster).(Red "A"). It allows the shoe heel to be adjusted toward the brake drum. A second eccentric cam ("minor" adjuster) is used to move the other end of the brake shoe ("toe") outward to compensate for brake shoe wear. As seen in the first drawing it is impossible for each shoe to "help" the other because both are anchored. The forward shoe (Red "F") is self-energizing, that is, the free end of the brake shoe ("toe") is forced into contact with the revolving brake drum (Blue arrows moving outward into the brake drum). As it moves toward the anchored end of the brake shoe friction tends to force the shoe even tighter against the brake drum. The reverse shoe (Red "R") is not self-energizing (Blue arrows moving into the shoe).While a major advance over previous generations of automotive brake technology, the difficulty in adjusting the shoes lead other manufacturers to move to a servo design with a self centering shoes. Chrysler stayed committed to the non-servo technology until the mid fifties.
This is true for single wheel cylinder setups usually found on the rear drums. (Second Drawing)
Both P15s and D24s use a front dual cylinder setup with a single end wheel cylinder for each shoe.
The advantage of this configuration is both brake shoes are now self-energizing, providing additional braking ability.
Get the car up on jack stands. I usually place two under the rear axle and two under the frame near the front door hinge and just behind the frame bend. Also pull the floor mat and transmission access panel on the front floor. This provides easy access to the master cylinder. First check the wheel backing plates for brake fluid leaks. If a leak is present a oily stain will collect at the bottom of the backing plates.Inspect the rubber boot on the master cylinder. Brake fluid presence indicates the master cylinder is leaking. Also inspect the rubber flex lines behind the front wheels and rear axle for crack and leaks. Remember any failure of a line leaves you with no brakes. Visually inspect all of the steel brake lines. The original stock steel ones will be rusted on the outside. Pay close attention to the lines coming out of the master cylinder. The springs on the lines protect them from damage but also provide a great spot for rust to grow.
Starting up front pull the tires. Using a ¾? wrench, back off the two minor shoe adjusters at 9:00 and 3:00 o?clock. Turn the wrench up and towards the wheel spindle/axle to release the adjuster. When the wheel freely spins remove the wheel bearing dust cover pull the cotter pin, nut and washer. Pull the drum straight off the front spindle. Be careful not to drop the outside wheel bearing as the hub clears the spindle. Don?t be surprised if what you see behind the drum is not a pretty sight. Usually the wheel cylinders will have leaked on the brake shoes and return springs may be missing or broken. Next check the inside surface of the brake drum. Any deep gouges from a worn out brake shoe?
Rear Brake Drum Removal
Unlike most "modern" cars, rear brake drum removal requires a special brake drum puller. These are available at most automotive tool rental shops. Drum pullers that attaches to the rim of the brake drum should never be used as they will permanently damage your rear brake drum. Finding replace drums is both difficult and expensive. Many tool rental shops have the correct puller for $30 to $40 a day or you can purchase one for about $125 dollars. Once you have the correct puller start by backing off the "minor" brake adjusters using a 3/4 inch wrench on the back of the backing plate. The wheel must turn freely. Next, remove the axle cotter pin and locking nut. An air gun is very useful for breaking the nut loose. For safety you may loosely re-attach the axle locking nut. This insures the drum won't fly off the axle when it breaks free. Attach the puller to three of the lug nuts and snug the puller against the axle.Using a large hammer strike the puller arms until the brake drum breaks loose. An air gun can be used instead of a hammer on the puller adjustment nut. Once free off the drum and be sure to remove and save the square steel key. I have seen posts recommending heating the drum to help break it loose. I have never needed to heat a drum and do not recommend it. It is very difficult to control the heating and you may cause serious damage to the underlying components such as axle seals or wheel cylinders.
If the drum is stuck usually the brake adjusters are not fully retracted. If the car is drivable loosen the axle locking nut 1/8-1/4 inch (keep the cotter pin) and slowly drive it around a couple corners. This will usually break the rust bond. If the shoes are rusted to the drums and they wont turn you will need to remove major adjuster. Remove the nuts on the anchor bolts that hold the major adjuster on the backside of the backing plate. Drive the anchor bolts toward the drum. When the anchor bolt shoulder clears the brake shoe bracket the shoe will pull back from the drum breaking it free and allowing removal. Our project P15 has all the standard problems: cracked flex lines, rusted steel lines, leaking master and wheel cylinders, broken and missing return springs, no pads left on the shoes and one brake drum badly scoured from a shoe bracket. It?s time to do a complete overhaul. I generally strip down all wheels at once, but if you feel uncomfortable you won?t remember how thing go together start with a single wheel. I also take the approach all the mentioned parts will be replaced with new or remanufactured parts. I feel this is the correct methodology for a new project where you don?t know the history or quality of previous repairs.
Remember brake fluid damages paint! Have some denatured alcohol on hand to clean up any accidents and a container to capture and store old fluid. Starting with the rear, detach the brake line coming from the rear axle. Capture any residual brake fluid in the line. Using either a brake spring tool or large flat screwdriver, pop off the brake shoe return springs. Wear eye protection and don?t put your face down close as the can fly outward as the release. Remove the two large anchor bolts at the bottom holding the shoes on the backing plate. These anchor bolts are the "major" adjusters. After removing the backing nut, slide the bolt out the front. Two steel spacers will fall from behind the shoes. The anchors have a large smooth shoulder, followed by a cup shaped retainer with a felt pad inside. The felt is a lubrication wick. Once the anchor bolts are out, the shoes can easily be removed. Two small bolts hold the single wheel cylinder to the backing plate. With the parts all removed check the seal where the axle passes through the backing plate. Now is the time to replace is and it will guarantee a leak won?t ruin your new brake job. Unbolt the five nuts and slide off the backing plate. Usually an axle shim(s) will be behind the plate. This is also a good time to inspect the rear wheel bearing lubrication. Check the Tech Tips on Rear Axle Lubrication and your shop manual for more information.
By the way, don?t throw anything away yet. Set them aside so you can check the fit with the replacement parts.
Front brakes tear down in a similar way with a couple extra steps. Cut the rubber flex line between the frame and backing plate. Be ready to capture the brake fluid in the line. Unscrew the hose from the wheel cylinder on the backside of the backing plate. Using two wrenches separate the flex line stub from the chassis steel line and pull the "C" ring holding the end. Remove the small feeder line between the wheel cylinders. Next remove the two return springs. Identify the two anchor bolts and note how they are bolted to the front suspension. Remove the cotter pins securing the anchor nuts. Hold the anchor bolts with a wrench on the outside while removing the nuts inside the wheel well. They can be quite stubborn and may require a penetrating oil and impact gun to break loose. With the anchors out the shoes can be removed.
Master Cylinder Removal
Remove the floor pan.
Detach the two brake lines as the rear of the master cylinder. Very gently depress the brake pedal to force out any remaining brake fluid. Pull the cotter pin from the clevis which connects to the brake push rod. Depress the clutch pedal, than slide out the clevis pin. The brake pedal is now free from the master cylinder. Unscrew the bolts holding the master cylinder to the frame being careful not to spill any remaining brake fluid.
Brake Line Removal.
Our P15 has the original steel lines. They are very rusty and need replacement. From under the car, using two flare nut wrenches, remove the steel line where it meets the rubber flex line directly in front of the rear axle. A flare nut wrench supports the fitting better is less likely to damage it. On the rear axle remove the two steel lines from the T fitting. They also have clips holding them to the rear axle. Working forward, pop off the clips holding the brake line to the frame. In some cases they may be riveted to the frame and can be pried open with a screwdriver. As your remove the old lines make a note of the clip locations. I use chalk mark so I don?t miss any during re-assembly. If any clips are broken now is the time to replace them.
Moving forward, remove the first section from the master cylinder to the stoplight switch junction block. Leave the junction mounted to the frame while you unscrew the front two lines. Then steel line can be removed. Working forward, two small bolted clips hold the passenger side line. The clips are on the radiator cross member and accessed from below. If your car has steel dust shields they may need to be removed. Set the lines aside so you will have patterns for the new lines.
Parts list For Full Brake Overhaul
Putting It Back Together
Reassembly is straight forward and fun, but you have some choices to make. Do you want your replacement lines to look 100 percent factory original or just be functional and safe? If you want 100% original than purchase a brake line set from a reproduction supplier such as Inline Tube or Classic Tube. These come ready to install, with all the factory bends and tubing material of either steel or stainless steel. They have all the stock details, such as the springs wrapped around the lines where they connect to the master cylinder. Stainless lines will last for the life of the car but cost more. Steel lines can easily be bent with hand tools so "final adjustments" are easy to accomplish. Stainless is more rigid and harder to work but more durable.
Another option is to use stock lengths of steel brake line from your local parts store. Lengths usually run 12, 18, 26, 40 and 60 inches. Use the old lines to match the size and shape.Make sure you purchase steel brake lines. With these different lengths you can piece together your replacement lines. Don?t forget to purchase couplings to join the different sections. A tube bender is also needed.
If you did not purchased a kit you will need to measure and shape the lines using the old ones as a pattern. Use a tube bender so you don?t kink or collapse a line. I highly recommend lever action benders. They allow up to 180 degree bend and won?t damage the steel line.
You will need a 45 degree double flare kit for the brake ends. All brake lines MUST use a SAE 45 Degree double flare. Like tubing benders there are many types available and most are junk. I recommend using a lever action die kit like K Tool International KTI70081.
They are available from Eastwood and some sites rent them if you purchase brake line supplies from them. They produce excellent quality flares quickly and you don?t waste material which often happens with cheaper flare tools. If you do make a mistake, replace the line with a new one. Don?t use kinked lines. The majority of lines are 3/16? diameter and can be shaped easily with hand tools.
Considering the effort, tools and material costs associated with replacing your brake lines it is usually cheaper to have the lines duplicated by a professional service company like Inline Tube or Classic Tube. They also offer the option of stainless steel tubing which is more reliable long term and difficult for the amateur home mechanic to work.
Take your brake drums to a machine shop to have them turned. This is essential to successfully adjust the brake shoes. To my surprise on my four vehicles the brake drums previously had never been turned so the machinist had plenty of metal to work with.
Check The Anchor
The anchor bolt head has a stamped arrow pointing to the high side of the cam. To adjust the brake shoes with the brake drum installed, you must turn it from the backing plate side. Some anchor bolts have wrench flats on the bolt ends for adjustment. If yours don?t, file off two flats for a crescent wrench or cut a screwdriver slot in the threaded end. I have had better luck using the wrench flats as you can clip on a vise grip for easy adjustment. Also put an identifying mark indicating the cam high point (The arrowhead on the face of the anchor bolt).
Order new wheel cylinders, springs, flex hoses, master cylinder and brake shoes. This is also the best time to repack the front wheel bearing and rear axle bearings including replacing all the seals. Check your service manual for the correct procedure for repacking and adjustment. Nothing is worse than ruining a brake job because you didn?t replace a $5.00 seal!
Starting with the rear axle replace the seal in the backing plate. On the bench you can safely knock out the old one. The edges of the seal should point toward the center of the car. Using a seal driver seat the new seal squarely into the backing plate. Stake it at three spots to lock it in position. Reinstall the axle shim and backing plate. When bolting the backing plate don?t over torque and strip the bolts. Take apart the wheel cylinders and lubricate with brake fluid. Some manufacturers provide a pre-lube in the wheel cylinder package. Bolt the new wheel cylinder in place. Crack the bleeder just to be sure it is not jammed then close it.
Assemble the anchor bolts with the cup shaped retainer holding the felt washer. They keep the shoes and anchor bolts from rusting against the backing plate and often dry out. The felt should be impregnated with a small amount of brake grease. If the felt is hard I use a few drops of oil to soften it, then squeeze dry. If you squeeze the felt and oil comes out you have too much. Only high temperature brake grease should be used. Make sure your hands are grease free before handling the brake shoes. Insert the anchor bolts through the heel of the shoe and the spacers on the backside of the shoe. Don?t forget the lock washer under the nut. The anchor bolts and nuts should be tight enough to hold all parts in position, but still be rotated with a crescent wrench to adjust the shoes.
At the brake shoe toe, line up the slots in the wheel cylinder pins. Reinstall the two return springs. You can use brake spring pliers to help guide them in. I have had better luck using a long thin Phillips screwdriver to position them in the shoe hole. If the spring hangs on the edge of the shoe use a rubber hammer to seat it. Make sure the arrows on the anchor bolts are pointing toward each other (fully retracted) and the minor adjusters are all the way in. Coat the tapered axle shaft with a very thin coat of anti-seize or brake grease. This will make drum removal easier next time. Slide the brake drum on the axle. When fully seated align the keyway and tap in the steel key. You can hold off on final tightening of the lock washer and hub nut until after adjusting the brake shoes. However the brake drum must be installed before you bleed the brakes. For reference the axle nut is tighten to 150 foot pounds and don?t forget the cotter pin when you finish the job.
Front brake assembly is similar with a few extra steps. Install on the upper wheel cylinder the rubber flex line. The other end will be attached to the chassis later. Prep the anchor felts same as the rear. Install both wheel cylinders brake shoes and anchor bolts. Leave the anchor bolts loose so you can align the parts. The arrows should point at the other wheel cylinder. Install the short feeder line from the top cylinder to the lower using new brake line. Again make sure the minor adjusters are backed off. Reinstall the brake return springs. When finished install the front drum and tighten the wheel bearing nut per the service manual. The wheel should spin easily. After bleeding the brakes you will remove the drum for brake shoe adjustment.
You need to make a choice as to what type of brake fluid to use, Dot 3 or Dot 5 also known as silicone fluid. Dot 3 was originally used is readily available at any parts store and is cheap. Downside is the Dot 3 fluid will attract moisture from the air, leading to corrosion and leaking of wheel cylinders. This is especially problematic in cars that sit for periods of time. It will also damage paint. Dot 5 does not attract moisture nor damage paint like Dot 3. However it is more expensive. I have been using Dot 5 for over 20 years and recommend it.
On the master cylinder make sure the pressure relief vent is clean and open. It is a small hole in the bottom of the reservoir and must be clean and free of any dirt. It can be seen when you take the filler plug out and is directly below the opening. If you don?t see the hole you will need to dissemble as the pressure relief vent is clogged. This small hole allows the pressure to be relieved when the brake pedal is released and unless fluid can flow easily through it one or more of your wheel cylinders will lock up until that pressure is released. On the bench fill the master cylinder with brake fluid and pre-bleed it before installation. Follow the instructions with the master cylinder, or if missing fill the reservoir and gently push in the cylinder with a screwdriver. Discard the fluid expelled from the master. Then plug the outlets. I use two small corks. Re-bolt it to the frame. Carefully reattach the rod and clevis pin. You will probably have to hold the clutch pedal down to get it in place.
|The last step is installing the new brake lines. This
step goes quickly if you have purchased a reproduction kit. Word of
warning: be very careful not to cross thread fitting, especially
where lines join brass "T" blocks. Use a flare nut wrench so you
don?t damage the flare nut. You should be able to run the nut almost
all the way down in the fitting without any tools. Also be sure to
hold the fitting with a wrench as you tighten the brake line into
it. They will crack or strip it you use too much force. The flex
lines are held on to the chassis bracket with a small "C" clip. You
must use two wrenches when attaching the steel line to the rubber
flex line. The flex line must not spin as you tighten the steel
line. Check the clearance on the rear axle flex line and make sure
it does not contact any chassis parts. Check your chalk marks to
make sure you have the lines securely reattached at all the hold
You will replace the following lines:
|The Home Stretch
The last two steps are to bleed and adjust the brakes. Bleeding purges the air trapped in the new lines. If the air is not purged the pedal will be spongy because air compresses under pressure. When all the air is flushed out hydraulic fluid won?t compress resulting in a firm brake pedal. First crack open then close all six bleeder valves on the back of wheel cylinders. Pump the brake pedal a couple times and don?t be surprised if it goes all the way to the floor. Now add additional fluid to the master cylinder reservoir. What you are doing is filling the new brake lines with fluid. Always start with the longest brake line and finish with the shortest line.
Use this order for bleeding:
Bleeding is usually a two person job one at the wheel cylinder the other at the master cylinder. NEVER depress the brake pedal with a brake drum removed. The wheel cylinder will pop out spilling fluid all over your brake shoes !
The standard procedure for 2 person bleeding starts with attaching a piece of tubing to the wheel cylinder bleeder valve. Lead the other end into a bottle filled with a couple inches of brake fluid. The end of the tube MUST stay below the fluid in the bottle otherwise you will such air back into the system. Have your helper pump the brake pedal a few times and hold the pedal down. Crack open the bleeder valve and air will squirt out of the line. With the bleeder open the pedal will travel down. After a second or two, close the bleeder valve. Pump up the brake pedal, hold and open the bleeder again. When only fluid comes out, no bubbles, the line is clear and you are ready to move to the next wheel cylinder. Keep a close eye on the amount of fluid in the master cylinder reservoir. Keep it full of fluid or you will be pumping air down the lines with the master cylinder.
A word about bleeders. Bleeding the brake systems can be a frustrating time consuming and sometimes expensive process. I personally have had poor luck using the standard procedure mentioned above. Many times the bleeder line pops off the bleeder spilling fluid all over and allowing air back into lines. Often the helper pumps the master cylinder dry forcing you to start all over again. And sometimes I just couldn't get all the air out of the brake lines. I have also tried using a vacuum pump with a reservoir for the expelled fluid. This too was not very successful as maintaining air tight contact between the vacuum hose and bleeder valve proved problematic. After opening and closing the valve a couple times the hose would start to lose it's tightness around the bleeder valve. I now use a pressure bleeder from KD tools, Model 2910. Basically it is a pump up lawn sprayer with a pressure relief gauge and valve. A rubber fitting with a quick release air hose coupler is clamped to the master cylinder filler hole providing an air tight fit. You manually pump the bleeder up to 5 pounds of pressure and open the line to the master cylinder. Brake fluid flows from the pressure bleeder tank filling the master under pressure. Now the entire brake system is under 5 pounds of pressure. You simple go to each bleeder on the wheel cylinders, crack them open until no air bubbles are seen, then move to the next wheel cylinder. I can do two passes on all wheel cylinders and finish in less that ten minutes. It's also a single person job and the large reservoir of brake fluid in the bleeder tank keeps the master cylinder from running dry. Lastly the pressurizing of the brake lines makes finding leaks easy.
Be aware the pedal will not firm up until ALL the air is expelled so don?t get discouraged if things don?t seem to be getting better after two or three wheel cylinders. It is my experience you will have to make a least two passes through all the wheel cylinders before they are fully bled. When the pedal holds firm the system is full bled. Don?t be concerned about pedal height, as it will go up as the brake shoes are adjusted.
Brake Shoe Adjustments
These cars have a "reputation" for poor brake performance. However the reputation is unearned and can be attributed to improper brake shoe adjustments. Because special equipment is required to do the job correctly many mechanics without the correct tools just "finish the job" by a quick adjustment of the minor adjusters. As mention earlier the anchor bolt moves the heel of the shoe toward the brake drum while the toe is adjusted by the minor adjuster. Two adjustments are needed. A "minor" adjustment compensates for normal wear and a "major" adjustment is done after installing new brake shoes. To correctly adjust the shoes they first must be "centered" to the axle on the backing plate so the drum will slide over the shoes. Lockheed provided a tool which mounted of the axle spindle while swinging an arc around the shoes. While the factory service manual provides considerable detail regarding this adjustment you must have a Brake Gauge Tool MT-19H tool. Unfortunately these tools are impossible to find. So what are options?
One option is an Ammco Model 1750 Brake Gage. Ammco 1750 tools are the aftermarket replacement for the MT-19H adjuster. Similar to the Lockheed tool they show up on Ebay on a regular basis. Don't be surprised if the bidding reaches the $150.00 - $200.00 range. They are quite popular with the Ford and Mercury owners which also used Lockheed brakes in the 1930s. One advantage of the 1750 is you can use it to "mic" the drum diameter and preset the gage to compensate for the amount of metal removed by the machinist when the drums are turned down. Check with other forum members in your area as they may have one to borrow. Also this site will soon have one available for rental.
The Plymouth Bulletin #229 (March-April 1998) has an article on how to build a low cost replacement MT-19H. You can order reprints from the Plymouth Owners Club store. Similar to the Plymouth Bulletin approach is using a bearing, flangette and For the front spindle use a Fafnir RA103-2 bearing and 62MS Flangette (bearing holder). Attach your dial indicator to the flangette. For the rear brakes use a clamp or magnetic holder to attach the dial indicator to the rear axle. Then rotate the axle to center the shoes. Both of these methods will allow you to quickly center the shoes relative to the axle. The factory shop manual provides the required shoe to drum clearances for your car. Using these clearance numbers will prevent the shoe from dragging against the drum. The Ammco tool has a build in aid for this adjustment. If you use the flangette you will have to do a bit of math using the dial gauge. I usually install the drum, move the major adjuster out until the shoe just contacts the drum. Then remove the drum and set the dial gauge to indicate that diameter is the maximum. Center the shoes all the way around to that diameter, them adjust the toe and heel diameter with the anchors to the amount specified in the factory manual. Your dial indicator will allow a very accurate adjustment. When finished adjusting the shoes reinstall the drums as mentioned above. Check the adjustment and torque on the front bearings and rear axle nuts. Be sure all cotter pins are installed including those used on the front anchor bolts. As you complete the adjustment procedure you will notice the pedal height has gone up. (NEVER check the pedal height with a brake drum removed!) This is because the distance the wheel cylinder pistons have to travel before the shoes contact the drum is less. Lastly check the master cylinder push rod adjustment. The correct adjustment results in 1/8 to 1/4 pedal free play.This is the distance the pedal will travel before the push rod touched the master cylinder piston.
A last option (and least desirable) is to use the following adjustment procedure found in an old Clymer service manual. It should only be used if no other option is available. The Downloads page has a guide to assist you if you choose this method. It is highly recommended you have a proper major adjustment done with the correct tools by a professions shop if you use this adjustment for a short term solution.
|Onto a road test.
First, from 25 mph make 8 or 10 mild stops. Follow this with 8-10 more at 45 mph at 1 mile intervals. Try to avoid severe use during the first hundred miles or so. This will allow the shoes to seat without overheating them. After the first 1000 miles check the minor brake adjustment. With a properly adjusted and functioning brake system I think you will be surprised at your braking performance. And congratulations, you are now on the road for years of safe and reliable brake service.
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