I'm unclear of the order of events, and I'm not sure if what you're seeing with the adjuster is related to this problem. First of all, if the adjuster lever is hanging down too far, look at where the cable guide is sitting on the rear shoe. If you have the more common shoe setup, that guide has a stretched area under the hole where the hold down spring goes through, That part has to sit in the hole in the brake shoe, then the hook on the spring holds it in place. It's common for that guide to pop out as you're tugging on the spring to install it. That will let the guide sit too close to the axle shaft and will in effect, make the adjuster cable too long. The adjuster lever will hang down too far and never come up high enough to turn the adjuster star wheel. The additional clue, if you look closely, is the spring appears to be bent or not seated properly where it hooks through that guide and into the shoe.
That cable guide will not cause the other symptoms you described. At its worst, it will simply cause that brake to gradually get out-of-adjustment over months or years resulting in a lower than normal brake pedal.
There's a number of things to look for that can cause a shudder. The first one is a parking brake cable that is rusted in the partially-applied position or is adjusted too tightly. Ford has had a real lot of parking brake cable problems since the mid 1970s. They commonly rust and get sluggish within a year or two, especially if you live where we throw a pound of road salt on an ounce of snow, and / or if the right cable goes way around by the rear bumper, then comes into the backing plate from the rear, on trucks, or you have the infamous 90 degree cable under the passenger rear seat, for cars.
Since you replaced the cables, ... Actually, you said "CABLE", not "cables". Did you replace the front one or both rear cables? It's the two rear ones that cause most of the trouble. This might not be possible yet, but when you have old cables, apply the parking brake at least about half way, then let it release slowly with your foot when you pull the release handle. You don't want it to snap back. Now look underneath, just ahead of the two rear wheels, where those cables come out of their casings. The cables are going to have dirt and dust on them. You're looking if the first 1/2" or so of the cable is clean and shiny right where it comes out of the casing. If it is, it hasn't fully released. Grab that casing and flex it with both hands. If brake shoe return spring pressure pulls the cable to the fully-released position, that cable is sticking and must be replaced. Never try to lubricate a sticking cable. When mechanics do that on trade-in cars during the safety inspection, it is sure to come back on a tow truck, particularly on Ford products. Someone is going to test for proper parking brake operation, the cables won't release, and you'll be walking!
If the cable doesn't release further when flexing the casing, it is either rusted really tight or it is adjusted too tight. The next step is to remove the drum and watch the shoes. If the cable is rusted tight, the shoes won't move when you flex it unless it's only rusted at the front. If the shoes DO move, readjust the main cable to loosen it a little. When it's too tight, the parking brake pedal will only go down freely about a quarter of the way or less. You should be able to push it about half way down.
The sticking cable keeps the shoes out too far where it's easy for them to grab and release the drum. That's one of the things that can cause the shudder, including when you're not applying the brakes. The next thing to look at is the tops of both shoe frames must be making contact with the fat anchor pin on the top of the backing plate where the return springs are hooked to. If they're being held away, the parking brake cable is adjusted too tight, or one of the rear ones is sticking. Next, look at the strut bar between the two shoes. Besides the two shoes resting firmly on the anchor pin, there must be a little more slack in the cables so you can push that bar against the anti-rattle spring pressure with your thumb. Typically you should be able to move that bar 1/8". If there's no free play, it's holding pressure outward on the shoes and any little vibration can make the front shoe grab the drum and chatter.
Check that the shoes are installed properly. The ones with the shorter linings go toward the front of the truck. Their only job is to grab the rotating drum and try to rotate with it. Doing so pushes on the star wheel adjuster which pushes the bottom of the rear shoe into the drum to engage it. (The wheel cylinder pushes the top of the rear shoe out, also to engage it). The longer lining always goes to the rear on the 90 percent of vehicles that use the "duo-servo" drum brake. Those are the ones that have the movable lower anchor;... The star wheel adjuster in most cases. The rear shoe is the one that does the stopping. It's the one that wears the most, that's why it's longer. On some smaller cars the rear shoes are all the same so you can't mix them up. Those will have a fixed lower anchor that can't move.
Another common cause of a shudder is grease contamination from a leaking axle seal. Brake dust and gear lube combine to form a gooey mess that makes the linings stick to the drums too much and they don't slide smoothly. The fix for this is new shoes AND a new drum. Brake drums and rotors are made from cast iron which is porous. Once the drum and lining friction surfaces get hot after they've become contaminated, the grease soaks in and will never come out or evaporate. No matter how much you clean those parts, you'll never have smooth brake operation. The same applies when handling those parts with greasy hands. Experienced brake system specialists will even wash their hands with soap and water to avoid contaminating the linings with fingerprint grease. That's why you'll always see them carrying drums and rotors by their edges, never by the friction surfaces.
If you get any kind of grease contamination on the linings or metal friction surfaces, it is generally acceptable to wash it off with brake parts cleaner as long as the parts have not gotten hot yet from normal braking. A lot of shop owners don't accept that. To prevent damaging their reputation, many of them insist the mechanic must discard shoes that have had grease on them.
Another cause of abnormal drum brake operation is grooves on the backing plate. You'll see each shoe has three spots along each side of the frame where they ride on raised spots on the backing plate called "lands". Rust and brake dust must be cleaned from those six lands, then a coating of high-temperature brake grease is applied to prevent a minor, but annoying squeak when the brakes are released, and to reduce the wear that takes places from the shoes sliding back and forth there. If you look at Chrysler shoes, the frames have three bent-over tabs that create a large surface area, so it's very rare to find grooves in the backing plates. GM shoes don't have those tabs. The edges of the shoes grind into the lands and create grooves. Those grooves can cause a shoe to not apply fully under light braking, and not release after hard braking. Either condition can cause a shudder. The front lands usually wear the most because that shoe is expected to rotate a little each time the brakes are applied. When that shoe gets caught on a groove, it doesn't apply outward pressure to the bottom of the rear shoe. Only the piston in the wheel cylinder applies pressure to the top of the rear shoe. The rotation of the drum tries to push the top of the rear shoe back to the released position. That can set up a shudder if the shoe constantly applies on top then gets pushed back.
Ford shoes have small tabs kind of half way between the Chrysler and GM designs so grooves in the backing plates aren't a real big problem, but it's still something you want to check for.
The last thing to look at is when you remove and reinstall an old drum, there are going to be one or three round spots of rust on the mounting surface corresponding to the holes in the flange on the end of the axle shaft. Those rust spots must be cleaned off before machining a drum, (or rotor). Failure to do that will make them sit crooked on the brake lathe and a warp will be machined in. Even if you don't have them machined, if you reinstall one in a different orientation, those spots of rust will prevent the drum from sitting squarely on the flange. You'll have a wobble in the drum and the wheel. Tho low spot of the wobble will hit, then release, from the drum's friction surface once per wheel revolution. You'll feel that as a brake pedal pulsation.
Related to the machining, anti-vibration devices must be used on drums and rotors. If you ever hear them "sing" or vibrate on the brake lathe, you'll see the mechanic running over there to stop that from occurring. That vibration will machine in what looks like the teeth of a file. Manufacturers actually specify the proper "surface finish" they want so vibrations and shudders don't develop. That always involves taking a very slow, light final cut, and usually using a scuff pad or sandpaper by hand as the last step. If the final cut is too deep or too coarse, meaning the cutting bit was moving out too rapidly, the shoes' linings will dig into those grooves and on one side they will walk away from the backing plate, then snap back after a few wheel revolutions. That chattering usually goes away, but it could take a couple of hundred miles that include some fairly hard stops. Most customers aren't willing to put up with that. This can cause one type of brake fade too. Only a small percentage of the lining actually makes contact with the drum, so you have to push harder than normal on the brake pedal. Higher than normal heat builds up, then the binders in the friction material can melt leading to glazing, and they can give off a gas that gets between the mating surfaces and prevents friction from being developed. This is a bigger problem with front rotors that have been machined too coarsely. The symptom on the rear can be a chatter or shudder, but more commonly the brake pedal feels fine but the vehicle just won't slow down like it should. Typically the cure for that is to park it and let the brakes cool down for an hour or two, then just drive off like normal. To avoid this, the mechanic is supposed to go on a test-drive that includes a half dozen fairly hard stops with sufficient time in between each one for things to cool down. The worst thing you can do is take the truck with no test drive, and immediately put it through a lot of city stop-and-go driving. That's where the brakes usually get the hottest.
Most of the mass merchandisers that do brake work put a tag on your mirror explaining to take it slow and easy on the brakes for the first hundred miles. That is to give sufficient time for the grooves in the friction surfaces, from the machining process, to wear down. Then the linings will make closer to 100 percent contact and become most effective. The people at dealerships and smaller independent shops are supposed to verbally tell you this, but too often you only talk with the cashier when you come to pick up the vehicle.
Wednesday, March 10th, 2021 AT 11:43 AM
