Difference between revisions of "NG 900/9-3 Front Pads and Rotors"

Revision as of 16:58, 1 December 2009

Overview

Front brakes have vented discs with a single-piston floating caliper. This means the caliper consists of two parts, a bracket which is attached to the wheel backing plate and does not move, and a "floating" brake pad housing. The floating part mounts on two guide pins which are attached to the fixed bracket, and slides back and forth a fraction of an inch as brakes are applied and released.

The floating part of the caliper has to be removed to get access to the pads, but it can be left attached to the rubber brake line. If the rotor is worn, it can take extra effort to remove, because the pads may catch on a ridge which forms on the edge of the rotor. On reassembly, the retaining springs usually have to be forced back in place. While inspecting the brakes, note the shape of the head of the rotor set screw for future use. On early models it takes a fairly small metric hex bit.

Removal

Retaining Spring

The spring is fairly stiff, to keep the outside brake pad firmly in place. It comes off easily when one end is first pried out of the retaining hole using a screwdriver or a pair of pliers. Note its position on the caliper for later, removal is much easier than reassembly.

Guide Bolt Sleeve and Caps

The guide bolts are behind the wheel backing plate, as seen from the top of the wheel at left. When brakes are applied, the caliper piston pushes on the inside brake pad, and the floating portion of the caliper slides along the guide bolt to apply pressure to the rotor equally from both sides. The bolts are inside a rubber sleeve, protected by a dust cap which has to be removed for access.

Guide Bolts

The bolts (also called "slide pins") have a 7-mm hex head. They can be unscrewed using a long allen wrench, or a ratchet with a bit holder as shown on the left. The bolt fits snugly into the sleeve. After it has released from the threads in the fixed portion of the caliper, it has to be removed carefully to avoid damage to the sleeve.

Pad Housing

The housing must be loosened by rocking it back and forth before it can be removed. This pushes the caliper piston and the inside brake pad back, so it will clear the raised lip on the edge of the rotor and lifted off . The housing can be left attached to the brake line, and supported by something like the box shown on the left.

Pads

The outside brake pad is flat and can be pried off easily.. The inside pad has an attached spring which slides into the caliper piston. Check the rotors for scoring and uneven wear, and the pads for 5 mm minimum thickness. Measure the friction material, NOT the entiere pad. Clean the housing and the pads with a wire brush, and apply some brake grease to the back of the pads before reinstalling in the housing.

Rotors

To remove the rotors, the caliper bracket and main caliper bolts have to come off. The bolts are tightened to a fairly high torque (78ft-lbs), and may require some extra leverage to break loose. After removing the caliper bracket, the rotor is only held by a small set screw. It is tightened only lightly, but may need penetrating oil if rusted, to avoid stripping the head.

Installation

Pads

Insert the inside brake pad into the housing. Push the inside pad and piston in far enough to make sure it will go over the rotor easily. If the pad and piston do not move easily, use a C-lamp or a tool available in any part store to compress the piston. Insert the outside pad, and replace the housing on the fixed part of the caliper.

Bolts

Clean the guide bolts with a rag, and if necessary with solvent, and lubricate the cylindrical portion of the bolt with a rubber-friendly lubricant or brake grease. Insert the guide bolts into the sleeves, and tighten to the specified torque, about 20 lb-ft. Fit the caps back in place.

Spring

Install the spring back on the caliper. One end of the spring is inserted into its retaining hole first, then the spring is pushed into position against the brake pad. The second end can be pulled into place using needle-nose pliers. Make sure the ends are pushed all the way into the retaining holes.

Wheels

Stock front brakes shed a lot of abrasive black dust. Normally it can be cleaned fairly easily using any product like WheelBrite, or household detergent and a soft brush. If the metallic powder remains on the wheels too long, it may become permanently embedded in the finish. For best results, tighten wheel bolts in a star pattern, on alloy wheels to 86 ft-lbs.

Information

Tools

• Needle-nose pliers
• 3/8 drive ratchet
• 5-mm hex bit (set screw)
• 7-mm hex bit (guide bolts)
• 10-mm hex bit (caliper bracket, if removing rotor)
• Torque wrench (optional)
• Wire brush
• Brake grease
• Anti-Seize

Pad Thickness

Torque Wrench Settings

• Guide bolts, 19 lb-ft
  • (20.5 lb-ft for 1997-'98)
• Caliper bolts, 78 lb-ft
  • (81 lb-ft for 1997-98)
• Rotor set screw, 3 lb-ft
• Wheel bolts, 86 lb-ft
  • (74 lb-ft on steel wh.)

References

Saab EPC 5-0120

Haynes Ch 9, section 4

Notes

If new pads were installed, bleeding the brakes is recommended.

Brakes on later models are larger and pads have different part numbers for 1997-98 models.