|Workshop :- Front Brake Discs and Front Pads|
Changing the front discs and pads is a pretty routine task for anyone who maintains their own car, but if you have never done it, then this guide will hopefully show you what's involved. My car is an Automatic and as they are "heavier" on the brakes as you don't get any engine braking from the gearbox, like a manual, you will find you will most likely change your pads more often.
After a recent weekend trip to North Wales, my car began to suffer brake fade during a long decent, so it was most likely worn discs and pads would have contributed to this. I had noticed the pads were low at a recent tyre change, My discs also had quite a lip on the edge as well, so I chose to renew them at the same time. The Lip on my discs was quite significant, and just by my experience from working on cars, I could see they needed changing. The minimum thickness for the front discs should be as below :-
I measured my discs once they were off, and mine were down to 20.2 mm, so as you can see from the above table, they definitely needed doing!!!
Obviously you can measure the disc when still on the car to see if they need doing or not.
There are many suppliers of Discs and pads for the Discovery 2. Obviously you could go to Local Dealer and buy them there, they will be about the most expensive you could buy, but you know they will do the job. There are also "performance" discs around including drilled and slotted discs from manufacturers like EBC.
For road use these discs can improve braking performance no end on the Discovery as its a heavy old truck to bring to a halt, how ever, "if" you take your truck off road in the mud on regular occasions, slotted and drilled discs "can" fill up with mud and muck and you could damage the disc face when braking. For this reason I chose to use standard vented discs from Mintex. They are probably a improvement over "genuine" discs, but not at the premium cost.
First of all, loosen the wheel nuts, then jack up one side of the car and support it on an axle stand. Its ok to leave the jack with the weight on, but put an axle stand in place just in case the jack fails. I would STRONGLY advise you use a trolley jack to support the car, its far more stable than the factory bottle jack supplied
Once the car is up, remove the wheel. The brake disc is held in place with a countersunk screw. These screws EASILY get chewed up and therefore are a pain to remove, for this reason I had bought new ones in preparation for doing the Job. The screw part numbers are SF108201L and are only £0.45 p each. If yours come out, then great carry on. It was a good job I had new ones because I started on the drivers side and the screw was pooped!!. So then you have to drill them out.
There is 2 ways to do this, 1. You just drill the head off the screw and wait till the disc is off and remove the rest then, or 2. If your used to using them, drill down the centre of the screw and use a screw extractor to remove it. I chose this time to drill the head off, after almost getting through, the drill actually "bit" into the screw, and as I reversed the drill to free it off, the screw came undone!!
Next you have to remove the caliper retaining bolts. These are also the "sliders" that the caliper moves in and out on. There is 2 of them, 1 at the top and 1 at the bottom. Both are 12mm.
Once those bolts are out, you can remove the caliper out the way, Be careful not to "stress" the brake pipe, so don't let the caliper "hang" on the pipe, it will quite happily sit on the track rod out the way.
This now reveals the pads. They can now be simply removed and thrown away.
"If" your just changing the pads, clean the caliper and pad retainer of brake dust using a brake cleaner spray, or even car washing stuff with an "old" stiff brush will do as well. AVOID breathing in any brake dust as it is very hazardous to your health !!!. REFER further down this article in the refit section for torque settings of the caliper bolts etc
If you changing the discs as well, you now need to remove the rest of the caliper. This again has 2 bolts, 1 at the top and 1 at the bottom. They are both 19mm and amazingly 12 point bolts. You will find it easier on the top bolt to carefully unclip the ABS wire from its retainer, this will give you more room for a socket and ratchet to get on the top bolt.
Give the carrier assy a good clean of brake dust etc. Make sure all the water is gone from the holes before re-fitting it. Check the rubber boots on the sliders are in good condition and the sliders move in and out freely.
Give the machined areas, and the ends of the sliders a small smear of copper grease ready for re-fitting. NOTE the "flats" on the sliders, these hold the sliders from spinning when you re-fit the bolts back in
Now that the carrier is off, you can "if you lucky" just wiggle the disc from the hub. My drivers side disc came off easily, the passenger side which experiences heavier braking due to a right hand drive vehicle, needed some "gentle" persuasion with a large block of wood and a club hammer. To aid getting of the passenger side, I needed to rotate the disc to hit it all the way around as it's only exposed a little because of the mud shield. NOTE!!! to rotate it, you need to put the vehicle in neutral, ensure its chocked and the handbrake is on !!!
Once the disc is off, clean the mating surface where it sits on the hub of any dirt and rusty / flaky metal. Once its clean give it a small smear with copper grease where the disc meets the hub.
While the disc etc was off, I also took the opportunity to clean the mud shield, hub etc and the whole general area of mud and brake dust etc which was there from my last off road experience. I also made sure the ABS wheel speed sensor was secure and the wires looked good and intact.
Also give the hub a good clean where the alloy wheels fit on, then re apply a small smear of cooper grease all the way around.
Now your ready to refit the new discs and pads. Fit the new disc into position and secure it with one of the new screws. Tighten the screw to 10 Lbs ft. If you don't have a torque wrench, just "nip" it up. Use some brake cleaner or solvent to clean the "factory" oil off the disc that is used to coat it against corrosion
Once the disc is on, you can refit the carrier assy back to the hub. Tighten the 2 19mm bolts to 175 NM or 129 Lbs Ft. Ref-fit the ABS sensor wire back into its retainer if you removed it earlier for more access to the top bolt.
Grease the edges of the new pads where they slide on the caliper with some more copper grease. Also add some grease to the backs of the pads where its pushed by the caliper and piston, and to where the pad sits / slides on the caliper.
Below is the carrier assy, pads and disc re-installed. You can see the areas to apply the copper grease. NOTE !! avoid at all costs getting ANY grease on the disc or friction surface of the pad !
Now to refit the caliper back on you will have to "push" the pistons back into the caliper to allow it to go over the new thicker pads and disc. Some cars need a special tool to wind the piston back as it rotates on a very coarse thread. The land rover pistons simply go in and out.
Before you push the pistons back, remove the cap off the brake reservoir to allow the fluid to be returned back to the reservoir.
NOTE !! If you have topped up your brake fluid to the max mark recently and you have had worn pads, you will overflow the reservoir, so keep and eye on the fluid level as you push the pistons back into the caliper. If the fluid gets to high, you will need to remove some, use something like a syringe or similar tool, but be careful not to get any dirt into the reservoir AND don't let any fluid come into contact with your vehicle paintwork. You may find the reservoir will not get to full until you do the second side.
To push the pistons back, you can use a large pair of "swan" neck pliers, a g-clamp or anything that gives a constant push. I used my oil filter pliers as they open very wide and grip well.
AVOID at all costs any damage to the piston seals!! A constant pressure on the push is better than a quick squeeze. Because it has 2 pistons, you will find one may start to come out again as they both get nearly fully closed, but just work each one a little at a time. They are fully in when the rubber seal shows no more ribs.
Once the pistons are fully retracted, refit the caliper over the new pads, you may have to squeeze the sliders in a little to get it into position. Once its in position, make sure the "flats" on the sliders are sitting correctly against the caliper, refit the bolts and tighten to 30 NM or 22 LBS ft
Once the caliper is back on, give the brake pedal a few pushes to "seat" the pistons back up against the pads. I took the opportunity to clean the insides of the alloy wheels and then applied a small smear of copper grease to where the alloy wheel meets the brake disc surface.
Refit the road wheel and tighten the wheel nuts by hand. Remove your axle stand and lower the vehicle off the jack, then torque the wheel nuts to 140 NM or 103 LBS ft and your done!!
Now repeat the task on the other side!!! remembering the brake fluid level goes up when retracting the pistons, once you have done both sides, check the fluid level is at the max mark.
When all is complete, take the car for a small test drive and try to avoid "heavy" braking for approx 100 miles to allow the brakes to "bed in"