DIY: Disc jockey
Replacing your tow vehicle’s brake pads.
Replacing your tow vehicle’s brake pads
Disc brake pad replacement is one of the easier jobs to do on your tow vehicle (or caravan, if it’s equipped) and could save you money and the hassle of paying someone else to do it for you.
The key thing before you take on a job like this, though, is to decide whether or not you have the skills to do it. If you’ve never worked on your vehicle or van before, it would be better to get a good mechanic to do the job. Brakes are an important safety item, so you don’t want to get it wrong when working on them. If you do, you’ll also be liable if things go pearshaped on the road because of your work.
This is a job that would ideally occur with a brake fluid bleed and disc rotor thickness check (or rotor surface machining/replacement) and, perhaps, greasing the slider pins (with brake grease).
You can tell if your disc pads are on their way out in a few ways. First, there’s the easy but not always accurate way – some cars have a low pad sensor that will illuminate a light on your dash to tell you the pads are ready to be replaced. Others will squeal when the brakes are applied, which tells you the friction material is low. But the best way to tell is to have a look at them. You need to see on top (or underneath) of the caliper to see how much friction material is left. Some wheel designs have thin enough spokes that you can have a peek through but, for most, you’re going to have to take the wheel off to have a proper look. It depends on the vehicle, but when the friction material gets to around 2-5mm, it’s time to fit new pads.
GETTING TO WORK
To be sure about minimum pad thickness and any remove/replace variations for your vehicle, you’ll need to get a workshop manual for your vehicle. You’ll need a wheel brace, a jack, axle stand, a screw driver, a torque wrench and a brake caliper piston tool. Aside from new pads (you replace them as a set for both rear wheels or both fronts to help avoid uneven braking performance), you’ll also need brake fluid (again, check the specs for your vehicle but, for most vehicles, DOT 4 is okay), some wire (such as coat-hanger wire) and a syringe. Optional items include brake cleaner and, if you’re bleeding brakes, a brake bleeder kit.
First, get the syringe and (assuming the brake fluid is up to the ‘max’ mark) remove about half the fluid in the brake reservoir. This is so that later, when the caliper piston is pushed back in (pushing brake fluid back up the line to the master cylinder and reservoir), the fluid doesn’t overflow out of the reservoir. Dispose of the old brake fluid in a container that you can later take for oil recycling (available at refuse collection centres).
Then it’s time to release tension on the wheel nuts (or bolts, if so
equipped); half a turn is usually enough. Then chock a wheel on the axle you’re not working on and get your jack ready to go. Find the correct jacking point (again, the workshop or owner’s manual will have this information) and jack up the corner of the car you’re working on. Once the wheel has lifted off the ground, get an axle stand and place it under the vehicle under a secure point (again, refer to the workshop/owner’s manual) and release the jack so that the axle stand is taking the weight. I prefer to keep the jack in place, taking some of the weight as a back-up.
With the wheel removed, you can unbolt the caliper from the caliper carrier. Then remove the caliper from the carrier and secure it with wire in a position so that you can work on it. Be careful not to let the caliper hang on the brake hose, or twist or bend the hose excessively.
Remove the old brake pads from the caliper (in some cases, though, the pads are contained by the caliper carrier) and put aside. The pads shown here should have been replaced long before they were – you can see where the friction material was completely worn away on one corner of a pad, leaving the backing plate exposed.
This pad, being down to metal, would have scored the rotor and it will require machining or replacement (again, this should be done in pairs, not
just a single rotor). In fact, you should consider measuring the width of the rotors (at the mating surfaces of the pad and rotor, not at the edge) to ensure the rotors have not worn past their specified range.
The piston(s) within the caliper are designed to stay hard up against the backing plate of the pad as the pads wear. So the piston has to be retracted into the caliper body when new pads are fitted. Some will retract with very little pressure (pushing a brake pad against the piston with your hands will be enough) while others will need a brake caliper piston tool or similar to push the piston back. Some vehicles’ caliper pistons retract by screwing them in.
FITTING THE NEW PADS
Now the new pads can be fitted to the caliper, making sure you have them in the correct orientation (it can be easy enough with some pads to install them upside down) and that your hands are clean when you fit them (so you’re not transferring grease on to the pad surfaces) and now is the time to spray brake cleaner on the pads if you did accidently mark the pad surfaces with grease. It is also a good idea to spray the rotor on both sides and the caliper and caliper carrier with brake cleaner while they’re apart. Brake cleaner removes deposits and evaporates quickly (and doesn’t need washing or wiping off).
The caliper carrier can now be released from its securing wire and mounted back on to the caliper carrier and, once you have checked carefully that it is mounted in the correct position, it can be bolted back on to the caliper carrier to the specified torque.
Now it’s time to refit the wheel and wheel nuts. Then lift the vehicle on the jack enough to remove the axle stand and then wind down or release the pressure within the jack. Remove the jack and tighten the wheel nuts to the specified torque (usually around 110Nm for cars and 120-130Nm for caravans, but you must check with the manufacturer).
Check around the work area to ensure everything has been refitted correctly and that all tools are removed from in and around the work area. Also check you don’t have any ‘spare’ parts lying around except for the used brake pads.
Now you can top up the brake fluid reservoir, as required. Start the vehicle and move forwards and backwards at no more than walking pace, and check brake pedal feel and listen out for any unusual sounds from the brake area. Finally, take the vehicle or van for a test run and check the brakes work as they should – but do make sure you don’t have a vehicle behind you before doing a brake stopping test!
4 3 Jack the vehicle up and support it with a support stand. First, remove some fluid from the brake fluid reservior.
1 2 Some of the basic needs for a brake pad change include brake fluid, new pads and a syringe. First, remove some fluid from the brake fluid reservior.
5 Remove the wheel nuts and then remove the wheel.
6 7 Remove the caliper retaining bolts. With the caliper supported, unclip and remove the old brake pads.
9 8 Push the piston back into the caliper to allow clearance for the new pads. Here, you can see, on the top left, that the old pad was down to the backing plate metal. Pads should not get to this point before replacement.
10 Fit the new brake pads.
11 Optional, but always a good idea – spray the caliper and disc liberally with brake cleaner. 12 Refit the caliper to the bracket and tighten the retaining bolts to the specified torque. 13 After you refit the wheel and nuts, remove the stand and jack and check wheel nut tension, then top up the brake fluid once again.