Checking the stoppers

Jan. 1, 2020
A friend of mine was driving his high mileage Toyota Camry and experienced normal stops right up to the point where one brake pad finally wore thin enough that it left its perch and shot out.

These, along with the tires they’re connected to, are responsible for bringing a 3,000-plus pound vehicle from road speed to a stop over and over for thousands of miles.  The middle photo is a rotor with its cooling fins packed full of mud.  The right hand picture is what happens when the pads grind the rotors thin enough that the piston comes out of its bore.  Scary stuff.

A friend of mine was driving his high mileage Toyota Camry a few years back and experienced normal stops right up to the point where one brake pad finally wore thin enough that it left its perch in the caliper and shot out of there without warning. His pedal went to the floor and he had to swerve off of the yield lane over onto the grass to avoid driving under the side of a passing semi trailer.  It happened because the Camry’s rotors had been repeatedly machined but not measured too many times (I did not do this work, by the way). The moral of that story is to always measure the thickness of the rotors and the diameter of the drums when doing the brakes, even if they look good. And it’s a no-brainer that we should replace the rotors rather than machining them if they’re too thin.

Every driver desperately needs to be able to trust that left pedal. The old adage that “a miss is as good as a mile” might make some brake failure stories humorous, but brake failure is no laughing matter, and there are many other stories involving failed brakes that are life-changing in a very bad way.

Iron, Steel and Linings
Drum brakes are still very common and require more inspection effort than discs, particularly when the shoes have dished the inside of the drum and/or the drum is rusted solidly to the hub. Most foreign nameplates have 8-mm threaded holes near the center of the drum where bolts can be screwed in against the hub flange for drum removal. A smart tech working an unfamiliar platform will leave the drum brakes on one side assembled for comparison while doing the opposite one. When machining drums, measure them first for service limit and don’t let the drum pass the bit too fast or you can thread the drum while machining it and cause noise concerns.

It is always amazing how much punishment and neglect brakes can put up with and still stop the vehicle in a fairly normal fashion. It’s also amazing how some folks are at doing those grass-and-dirt patch jobs (see right).

Those drum-style parking brakes that are in the rotor hat on newer Chevy pick-ups usually are worn out and are easy to replace while doing the rear disc pads. On the ball-and-ramp park brakes used on some rear disc systems, you need the tools to screw that rear caliper piston back in rather than simply shoving it, so don’t get blind-sided on that deal. If the park brake cables are rusty and cause the brakes not to release, those cables might need to be replaced. This happens sometimes on older pick-ups.

If we’re doing any service at all on a vehicle and we’ve got it on the lift, we’re remiss if we don’t at least bust out a flashlight and have a look at the disc brakes, both front and rear. Disc brakes usually feel just fine, but we’ve all heard them make noise when the lining gets thin enough that the sensor reed begins to sing against the rotor. A few platforms have pads with an imbedded wire that illuminates a dash panel warning light when the lining is worn to replacement thickness. And be sure to check both pads on each rotor; a caliper that won’t float sometimes will wear the pad completely out on the piston side while leaving the outboard pad looking really good. When pad lining exhibits wedge-shaped wear, that means one end of the caliper is hung and won’t float. Replacing the bolts and boots on calipers that have that hardware is a must if those parts are compromised, and make sure the caliper abutments are clean, rust-free and lubed on the older ones that ride in slides.

The drum brake isn’t dead – some 2012 Chevy pickups have drum brakes. These are kind of hidden and often get ignored until something obvious happens. Leaking wheel cylinders tend to stain the tires with wet streaks, and shoes that are as worn as the ones in the middle picture will herald their need for replacement with a jolly grinding noise

When machining disc rotors that are thick enough, on-car is the smoothest way, but doing it right on a bench lathe works, too. According to Ammco® your cutting bits run cooler when you’re making a 0.010-inch cut than when you’re making a 0.002-inch grind, as counter-intuitive as that might sound. Make sure there are no rust or bumps in the hub area when mounting the rotor. I like to brace a wrench and hold it gently against the spinning hub to be sure the hub is running true before beginning the cut. 

When you’re done with the machining, use a drill and a refinishing pad to non-directionalize the finished surface on both sides of the rotor, and Bendix® says to wash the surfaces of the rotor with soap and water before installation to remove all the embedded filings. With new linings installed, drive the car and burnish the new pads to the rotors using the Bendix 30-30-30 method, which is defined by 30 normal stops from 30 mph with a 30-second cool down in between.

The fluid is every bit as important as any other part of the job. It tends to transfer to the calipers as the pads get thinner, and so the level needs checking regularly. But so does the condition. These dip strips are a dynamite way to determine whether or not a flush is needed. The darker

The Fluid
A few simple pointers where fluid are concerned. Fluid level is a no-brainer, but checking brake fluid level should be supplemented using the Phoenix Systems® dip strips to check for copper alpha reactions in the fluid. This dip strip test is a dynamite way to sell a necessary flush. The strips cost $70 for 100, and you dip the strip in the master cylinder reservoir, shake off excess fluid (not on the fender) and then watch it for a minute to see how purple it becomes. There is a color code card you use to determine how purple is too purple. The coolest thing about this is that it’s a good show-and-tell when dealing with a skeptical customer. That being said, flushing is good if you do it right and bad if you do it wrong.

I’ve said this before, but don’t ever use a copper tubing union (right) to repair a brake line. The only right way is with a double flare and a union like the one on the left.

Decades ago, Delco marketed a purple colored alcohol based flushing product called DeClean – it’s so old now that you can’t even find it online (or at least I couldn’t). But I bought cans of it from my Delco parts supplier in the 1970s and used it for flushing brakes and even on HVAC systems when the compressor had failed. I don’t know when they stopped making it, but I might have been using old stock from that ancient parts store. I’d pump a bunch of it through the system and then push the stuff out with new brake fluid. Well, I used some denatured alcohol to do a high-mileage 2000 Chevy pickup that way and had the HCU fail. After he drove it for a day or two, the HCU started trapping pressure on the business side of the system, the brakes wouldn’t fully release.  The rest of the rubber parts were pristine, but the alcohol had broken stuff loose and moved it around in there, which fouled up the Hydraulic Control Unit. The best way (my opinion) is to use clean fluid, and we have done that on many a vehicle with no ill effects.

These fairly comprehensive and affordable disc brake kits are sold at most parts stores and cover a multitude of different disc brake types.

Pistons, Cylinders and Air
If a brake caliper is stuck, it can be rebuilt (which isn’t hard to do right), though it’s a lot quicker to simply replace it. But don’t condemn a brake caliper without first making sure it’s the caliper that’s at fault. If one comes in with a locked and smoking wheel and you open the bleeder screw to find that the caliper lets go of the rotor, you have problems between the caliper and the reservoir. If somebody has let the caliper hang on its rubber hose a few times (don’t do that), the hose can come apart internally. But that usually causes a brake pull in the opposite direction from the bad hose. Pressure trapped at the caliper is typically master cylinder or combination valve related. ABS system parts can cause that problem, too. I once saw a 2002 Chrysler Sebring with rear rotors that were downright rusty. The rear brakes were getting no fluid pressure at all, and that turned out to be a bad proportioning valve.

Drum brake wheel cylinders are easy to check – just pull the boot back on the wheel cylinder and if you see fluid there, the cylinder needs to be rebuilt or replaced. In the 1970s, we always rebuilt the wheel cylinders as a part of a routine brake job, but these days almost nobody does that any more. But when replacing wheel cylinders, be prepared to replace or properly repair the line on old rusty, mud-slinging or salty road vehicles.

Ever have a pull you couldn’t figure out?  This Waekon® tool has sensors that fit between rotor and pad for the purpose of measuring pressure. The two wildly different readings you see on the right came from a single brake activation on an Acura we were checking for a brake pull, and we were able to track that problem to the ABS HCU.

When bleeding the brakes, make sure you delve into the shop manual instructions to make sure you’re doing it right, lest you work long and hard and come to ruin. My guys worked their fannies off on a 2008 Nissan Frontier a few days ago before I directed them to follow the wheel bleed sequence in the shop manual. They had started with the farthest wheel from the master cylinder and worked their way around to the nearest one but the pedal still felt spongy. On that truck, you absolutely won’t have good pedal unless you follow the published sequence. You can’t go RR, LR, RF, LF on that one. If you do it in the right order, you’ll get the air out quickly. If you bleed the wheels in the wrong order, you’ll work on it for hours. Some vehicles require a scan tool and the operation of the HCU pump.  Others have release buttons that have to be held during the bleed procedure. 

Tools for brake bleeding abound, and some are better than others, but I teach my students to use a clear hose attached to the bleeder screw and a clear plastic bottle. Learning the old-fashioned way first is best, as not every shop has a brake bleeder. It’s also good to start the engine and feel the pedal even after it feels OK without vacuum applied to the booster, or else you might think you’re done when you’re not. Be aware that a leaking master cylinder can dump its fluid into the booster, so watch for that.

On a Wing and a Prayer
What about those vehicles we service that belong to drivers who are either so adaptable or so obtuse to either continually ignore or don’t notice that their brakes either don’t sound or don’t feel right? These drivers are some of the same folks who don’t think they need to change the oil as long as the car still seems to be running OK. 

Then there are the brakes that have been patched or modified by a do-it-yourselfer. You know, the ones with missing hardware that are held together with the wrong bolts or bent coat hangers? The ability of a car’s brake system to work as well as it does even when sloppily patched is pretty amazing.

We had an SUV of that stripe come into the shop one day a couple years ago. The owner had called earlier to say she wanted her front brakes done and asked how much it would cost. I called my parts guy and he didn’t ask me anything about how the vehicle was equipped, he just gave me prices and I passed the information along. After all, what was she likely to need besides pads and rotors? The customer had her daughter bring in the SUV. When we got the wheels off, we saw all manner of missing hardware, misassembly, etc. We set about to do the brake job with the parts my supplier sent and found that this one needed more expensive rotors because it had ABS. That doubled the price of the job, and in the melee of having her shout at me on the phone, I forgot to mention that we also needed a hardware kit, which was an additional $25, which led to more shouting later.

If the master cylinder is going dry and you don’t know why, don’t forget that it can discharge its fluid into the brake booster.That’s what happened here, and this fluid in front of the diaphragm was causing the front brakes to drag and heat up.

Now for an extremely important question: What if she had said no to the repairs in the beginning and told us to put it back together the way it was? The simple answer is that if we were a regular shop, we couldn’t comply – not without serious liability. We fixed her brakes and did it right. But if we had been red-lighted on the repair, we would have been wise to render the vehicle undriveable so she would be forced to have it towed away rather than letting her drive it away with brakes we reassembled the wrong way we found them.

If a vehicle leaves your shop on the hook and somebody else patches the brakes to get it back on the road, you’re pretty much in the clear.  But even if the customer signs a waiver when the vehicle is picked up and drives it away under its own power, you can still get sued and lose if the patched brakes are the cause of a crash. And if the crash causes a serious injury or takes a life, well, it’s unpleasant to finish the thought.

Brakes are some of the most regular and most profitable repairs we get and they’re probably the easiest jobs to do right.

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