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Brake fluid levels

Many dealers and aftermarket service shops advertise and provide multipoint fluid "topups" with oil changes or regular maintenance packages. These offers often include adding brake fluid to the master cylinder reservoir. This is an undesirable practice. There are only two reasons why the brake fluid level falls in the reservoir. The first is that brake fluid level goes down an acceptable level during normal brake lining wear. When the linings are replaced, the fluid will return to its origi-nal level. The second possible reason for low fluid level is that fluid is leaking out of the brake system. If fluid is leaking, the brake system requires repair. Adding additional fluid will not correct the leak. If the system was properly filled dur-ing delivery of the vehicle, no additional fluid should be required under most cir-cumstances between brake pad or shoe replacements. This information can be reinforced with customers by referring them to the brake fluid section of the owner’s manual. GM vehicles over the year have used many brake fluid reservoir styles. The following guidelines apply to plastic-bodied fluid reservoirs. They do not change the original service recommen-dations for the older, metal-bodied units. Both black and translucent plastic reservoirs are used. Reservoirs may have a "MAX" fill mark only, a "MIN" fill mark only, or both "MAX" and "MIN" marks. The cover does not have to be removed from a translucent reservoir to see the fluid level. It is a good practice to keep the reservoir cover in place unless necessary to reduce the risk of contaminating the system. Use the following guidelines to assist in determining the proper fluid level.

When adding brake fluid, use brands bearing the DOT3 rating only.

At no time should the fluid level be allowed to remain overfilled. Overfilling the brake reservoir may put unnecessary stress on the seals and the cover of the reservoir. If the reservoir is overfilled, siphon out excess fluid to comply with the guidelines below.

If, under any circumstances, brake fluid level is extremely low in the reser-voir or the "Brake" warning indicator is illuminated, the brake system should be checked for leaks, and the system re-paired, in addition to bringing the fluid level up to the recommended level. A leaking brake system will have reduced braking performance and will eventu-ally not work at all.

Some vehicles have reservoirs that are sensitive to brake fluid levels, and that may cause the "Brake" indicator to flicker on turns as the fluid approaches the minimum required level. On ve-hicles with this concern, increase the fluid level slightly within the recom-mended guidelines.

If the reservoir has a MAX level mark, the reservoir should be returned to the MAX level only when new brake pads or shoes are installed. If the reservoir fluid level is at the halfway point or above do not attempt to add additional brake fluid during routine fluid checks.

If the reservoir has both MAX and MIN indicators, the fluid level should be maintained above the MIN indica-tor during routine fluid checks. It should be returned to the MAX indi-cation only after new brake pads or shoes are installed.

For reservoirs with only a MIN indi-cation, the fluid level should be main-tained above the MIN indicator during routine fluid checks. Return the reser-voir fluid level to full only after install-ing new brake pads or shoes. A full reservoir is indicated on translucent, snap cover reservoirs by a fluid level even with the top level of the view win-dow imprinted into the side of the reser-voir. On screw-top reservoirs in black or translucent plastic, the full level is just below the bottom of the filler neck.

John Fobian

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