TECHNICAL GUIDE JAGUAR XJS BRAKES Are they to be feared or easy DIY?
The Jaguar XJS utilises discs and calipers at the front and rear for its dual-circuit, servo-assisted braking system. Fourpiston calipers with ventilated discs are fitted at the front, and at the rear, there are either inboard solid discs mounted next to the differential, or more accessible outboard solid discs (ventilated from 1995). In the case of outboard discs, the handbrake system consists of shoes inside a drum section of the disc. The handbrake mechanism on an inboard set-up features a separate set of calipers. Routine servicing of the brakes is essential to avoid corroded and sticking slider bolts, pistons and brake pads. When working on any aspect of a car’s brakes, safety is a top priority.
Always keep food and drinks away from where you are working to avoid contamination. Wear disposable gloves, especially if you have skin problems. And if you have respiratory problems, wear a breathing mask to reduce the risk of inhaling brake dust and dirt. Make sure the car is securely supported on axle stands or with a ramp before removing the road wheels and working on the brakes. If grease contaminates the braking surface of the pads or disc, clean it off with brake cleaner.
Brake discs and pads should be renewed in sets across an axle. So, if one front brake pad is unevenly worn or worn to the limit for instance, all of the front brake pads must be renewed. The same applies to brake discs – if one rear disc is worn or damaged for example, all of the rear discs and pads must be renewed. After servicing the brakes, it’s always important to pump the brake pedal before driving the car to ensure the brakes are operative. This ensures the pads are set in position, ready for use.
FLUID AND FLEXIHOSES
A good starting point for servicing the brakes is to inspect several parts, such as the brake line that’s routed underneath the XJS, any connections and flexi-hoses. Look for corrosion in the pipework, leaks from connections and flexi-hoses and deterioration of the rubber. If the corrosion is only light and it can be cleaned off, do so and protect the exposed metal with a smear of grease.
It’s worthwhile testing the moisture content in the brake fluid. The brake fluid should be renewed every couple of years, but it can also be tested with equipment that costs around £10 from most motor factors.
When you’re ready to start servicing the brakes, some useful tools to have with you include a hammer, drift, pliers, side cutters, flatblade screwdriver, torque wrench and water pump pliers. A 15mm socket and 7mm Allen key are also needed for rear outboard brakes. Consumables, such as brake cleaner and a suitable brake grease are worth using.
The front brakes on the XJS consist of a traditional design of four-pot caliper. The pads are retained with two pins, which are in turn secured with tiny R-clips. So the first components to remove are those small R-clips, which can be quite fiddly to extract. Small pliers or side cutters can help here. Make sure these R-clips are refitted because they help to keep the pins secure.
The two longer and larger brake pad retaining pins need to be drifted out of the caliper. If correctly fitted, they are extracted from the back of the caliper. Once they are so far out, use a pair of pliers to pull them free. Make sure they are clean (use a wire brush or abrasive paper to clean them) and straight – they can be renewed. When extracting the brake pad retaining pins, there are a couple of spring clips that help to keep the brake pads secure and prevent them rattling. The ends of the spring clips are looped around the pins, so upon removing the last pin, the spring clip is in danger of flying out (unhook them before this happens).
Before extracting the brake pads, it may help to force the pistons in a little. Use a pair of water pump pliers to squeeze the outer edge of each brake pad against the side of the caliper. Don’t squeeze against the braking surface of the pad because it may crumble. Before applying pressure, check the fluid level in the reservoir to make sure it doesn’t spill over when pushing the retaining pins, there are a couple of spring clips that help to keep the brake pads secure and prevent them rattling. The ends of the spring clips are looped around the pins, so upon removing the last pin, the spring clip is in danger of flying out (unhook them before this happens). Before extracting the brake pads, it may help to force the pistons in a little. Use a pair of water pump pliers to squeeze the outer edge of each brake pad against the side of the caliper. Don’t squeeze against the braking surface of the pad because it may crumble.
Before applying pressure, check the fluid level in the reservoir to make sure it doesn’t spill over when pushing the friction material of the brake pads, clean inside them with a flatblade screwdriver. Brake dust collects inside here when the brakes are applied to prevent it being trapped between the pad and the disc, so it’s worthwhile cleaning it out.
Use a flatbladed screwdriver to clean inside the brake caliper, where the top and bottom edges of the brake pads sit. Avoid touching and potentially damaging the rubber dust boots around the pistons of the caliper when using the screwdriver to clean. A quick check of the pistons inside the caliper can be conducted with a pry bar. Lever against each piston to make sure it retracts. This also helps with refitting the brake pads or fitting new pads. However, as mentioned, check the brake fluid level inside the reservoir before doing this to make sure it doesn’t rise too much and spill out. If the level is too high, you may have to syringe some out or mop it out with clean paper towel, but remember that brake fluid is corrosive if it gets onto paintwork. When you’re ready to refit the brake pads, or fit new ones, apply a smear of brake grease along the top and bottom edges of each brake pad and the backs where the pistons make contact. Do not apply any brake grease to the friction material of the brake pads. Reassembling the brakes should run smoothly, providing there’s enough space to slide the brake pads into position. Make sure the retaining pins are fully seated (fit them from the back of the caliper) by tapping them into position with a drift and hammer. And make sure they are correctly positioned to refit the R-clips through the tiny holes in them. This can be quite awkward, especially when the two spring clips need to be kept in position at the same time.
REAR INBOARD AND OUTBOARD
The rear inboard brakes on the XJS are accessible from underneath. They’re similar to the fronts, with retaining pins, R-clips and spring clips to remove, but only a couple of pistons to retract. A ramp or inspection pit helps with working on them. The handbrake is operated via a separate set of calipers, which have their own brake pads. These are also accessed from underneath the vehicle.
Outboard discs are also more difficult to service than the front brakes, with handbrake shoes acting on the inner section of the disc, which acts like the drum. It’s worthwhile removing the brake disc to be able to clean and inspect the handbrake shoes. First, the brake pads for the footbrake need to be extracted. A large spring clip should be fitted on the outside of the caliper, which must be fitted to comply with the MOT test. It’s worth making a note of how it is fitted to help with refitting it later.
Each single piston rear brake caliper uses two 7mm Allen key slider bolts. These can be extracted from the back of the caliper and cleaned to remove any corrosion or dirt that prevents them moving freely. With the slider bolts removed, the caliper can be levered off and the brake pads extracted. The inner brake pad has a spring clip on the back of it, which sits inside the piston of the brake caliper, so it may need a little leverage with a screwdriver to help remove it. The brake disc cannot be removed without removing the caliper carrier.
This is secured to the upright with two 15mm bolts, which will be tight, so a breaker bar or long-handled ratchet may help here. With this component removed, the handbrake shoes may need to be backed-off to remove the brake disc, but first make sure the handbrake is off. Backing-off the handbrake shoes involves finding the adjuster. Rotate the brake disc until the inspection hole on the face of the brake disc is at 12 o’clock. Shine a light inside to look for an adjuster, then use a long thin flatblade screwdriver to turn it and back-off the brake shoes. You’ll soon know whether the adjuster is being turned in the right direction or not when the brake disc either locks up or starts to rotate more freely. If the adjuster proves difficult to turn, spray a little penetrating fluid over it via the inspection hole.
When you’re confident the brake disc can be removed, lightly hit the face of the drum part of the brake disc with a hammer to help release the brake shoes and remove it. Once removed, the brake shoes can be sprayed over with brake cleaner and inspected. If they can be reused, clean around the backplate with a wire brush, apply a light grease to the adjuster at the top and the handbrake mechanism near the bottom.
Try to move the shoes using a screwdriver to ensure they are free, then apply a tiny smear of brake grease to the inside edge of the ends of the brake shoes. This will help to reduce the risk of them dragging against the backplate when the handbrake is applied and released.
Check the thickness of the brake disc is sufficient – its minimum thickness may be displayed on the outer edge. Inspect inside the brake disc where the brake shoes make contact. If the braking surface is in good condition, it can be reused. Light corrosion or a lip on the inner edge can usually be cleaned off with abrasive paper or a flat file. After refitting the brake disc/drum, adjust the handbrake shoes until they lock the brake disc, then back them off by a quarter of a turn. After adjusting both sets of handbrake shoes, check the adjustment on the handbrake cable to see if any slack needs taking-up. When reassembling the rear brakes, the 15mm bolts that secure the caliper carrier in position should be fitted with thread lock and tightened to the recommended torque setting. Just like the fronts, refit the brake pads with a smear of brake grease on the backs and top and bottom edges. And don’t forget to refit the outer spring clip and to pump the brake pedal before driving the car.
The front-to-rear brake line for the XJS’s rear brakes is routed underneath the offside floors. Testing the brake fluid helps to check its moisture content. It should be renewed every couple of years.
Inspect all flexi-hoses for perishing, damage and leaks.
Use a hammer and drift to extract the retaining pins for the front brake pads. Squeezing the edge of the brake pad against the outer edge of caliper helps to retract the piston and make space for extracting the front brake pads. Clean inside any grooves in the brake pads, which is where brake dust collects.
Levering the pistons in on the front calipers helps to check they are free-moving. Single piston rear brake calipers use 7mm Allen key slider bolts.
Inspection hole on each outboard rear disc needs positioning at 12 o’clock to back-off the adjuster for the handbrake shoes.
The rear brake pads on the inboard brake discs are accessible from underneath the XJS.
Apply a tiny smear of brake grease to the inside edges of the handbrake shoes (top and bottom) to prevent them dragging on the backplate.
Spray a light grease over the handbrake shoes adjuster once the rear brake disc has been removed.
Acacia Farm, Bristol Road,
Rooksbridge, Bristol BS26 2TA
Tel: 01934 750 319
North Wales Jag Centre
71 Builder Street
Llandudno LL30 1DR
Tel: 01492 870150
Disclaimer Readers wishing to carry out any of the tasks outlined in this technical feature should ensure they have the necessary skills and equipment to do so safely. If you are at all unsure about any of the information we have outlined, consult a specialist and if necessary, ask them to carry out the work for you. Kelsey Media and featured specialists cannot accept any responsibility or liability for attempting any of the work outlined in this feature.