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Front brake pads and discs - Part 1


Difficulty - Medium

Time - about 40 minutes per side.

Tools required - After lifting and securing the vehicle you need a 14mm and 17mm spanner, large screwdriver, g clamp, Coppaslip or similar copper based grease. The very best standard road going pads (and more than a match for most web available "performance" pads) are genuine Toyota which are available at a discounted price from Lindop Bros. Pm Parts_King for details.

Introduction

The front caliper is of the reaction type and is very simple to work on. When the brake is pressed, the piston pushes the inner pad into contact with the disc. When the inner pad has contacted the disc an equal and opposite force pushes the caliper (which is free to slide on guide pins) backwards and this in turn is connected to the outer pad via the caliper bridge. The outer pad is then brought into contact with the disc under equal pressure and the brake is applied. There are no return springs to release the brake. Only deformation of the piston seals and the action of the disc clearing the pads allows the brake to release. In a similar way there is no adjustment of the brake as the wear is compensated for by the piston travel and the caliper sliding on the guide pins. As the pads wear, fluid is displaced from the master cylinder reservoir and there is enough capacity of fluid to cater for fully worn front and rear pads. When new pads are fitted, the fluid is pushed back into the reservoir and for this reason the fluid should not be topped up between brake pad changes unless the fluid drops below the "MIN" mark or the warning light indicates that a leak has occurred and this case the fault should be investigated immediately. The only time the fluid should be topped up is at the two year service interval when it should be changed.

Specifications

Minimum pad thickness - 1.0mm

Minimum disc thickness - 23mm Note; There will almost always be a lip of rust around the outer diameter of the disc and the greatest wear will always be on the wear path around 15mm from the outer edge of the disc. This is because there is a higher rotational speed at the outside diameter and also there is some "off brake" contact as the hub bearing allows some swaying movement of the disc when cornering.

Brake Fluid - SAE J1703 DOT3 Note; TGB are currently supplying DOT 5.1 which can be mixed.

Procedure

You are responsible for making sure the car is safe. For best results use a trolley jack and axle stands. If you do use the supplied jack, remember that it is only a very temporary device for changing a wheel and under no circumstances should you risk putting any part of your body under the vehicle.

You can make things a little easier by turning the lock as I have done in these photos. The steering should only be turned when the vehicle is on an axle stand and turning the wheel while using the supplied jack will possibly result in the vehicle falling to the ground - don't risk it!

To change only the pads, undo the bottom retaining bolt with a 14mm spanner. If the back nut turns just use a 17mm spanner to hold it;

IMG_1750.jpg

Use a screwdriver to prize the caliper outwards;

IMG_1751.jpg

.......and swivel it upwards;

IMG_1752.jpg

If you are only changing the pads use the g clamp at this stage to carefully push the piston back into the caliper;

IMG_1763.jpg

If somebody has topped up the brake fluid it will be pushed out of the top of the reservoir. Either syphon some fluid out, collect as much as you can with rags or undo the bleed nipple on the caliper and allow the fluid to be displaced. If you do the latter, follow the instructions for bleeding the brake. Easiest way for future reference is do not top up between fluid changes as indicated above!

Note the position of the pads and shims. They are a slightly different shape to each other and the kit comes with 2 pairs of different shaped pads. If you get them mixed up, look at the back of the old pads and you will see the shape of the piston on the inner pad - they can't really go in wrong. Use the screwdriver to ease them out of the carrier. Clean the shims and place them onto the new pads with the arrows pointing in the direction of rotation. You can apply a thin film of coppaslip between each of the contact areas as this will act as a squeal dampener. Just to clarify, the owner supplied these pads and I would always recommend the genuine Toyota ones. There is no need to apply anything to the genuine Toyota pads as they will be silent in operation;

IMG_1762.jpg

Clean the stainless steel locating carriers. These easily come out but to avoid being confused about where they go, keep them to their relative locations, if necessary doing them one at a time. This is a first class idea which allows the pads to slide on a low friction stainless steel abutment rather than directly in the cast iron carrier which often corrodes and can cause the pads to stick and wear unevenly. Clean them as best you can - a bit of wire wool works grand;

IMG_1760.jpg

If you are only doing the pads, place them into the caliper. One has a bent piece of metal which acts as a wear indicator by squealing when wear allows the pad to contact the disc;

brakewear.jpg

This goes at the inside and at the top;

wearind.jpg

Here is an exploded view of the whole assembly;

brakeparts.jpg

Drop the caliper back down, pushing the guide pins back to allow alignment and fit the bottom bolt - 26Nm (20ft/lbs).

Important; press the brake pedal until it goes hard as this pushes the piston/pads out to the disc. Don't wait until you move the car as when the pedal goes to the floor you will panic and make a mess of the seat! If you do forget - don't forget you have a hand brake!!!

Refit the wheel and lower the car - wheel nut torque - 103 Nm (76 ft/lbs)

See part 2 to change the discs.

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