GM Astro/Safari 1985-1996 Repair Guide

Master Cylinder


See Figures 1, 2, 3, 4 and 5

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Fig. Fig. 1: Many of the earlier models covered by this guide utilize 2 completely separate reservoirs ...

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Fig. Fig. 2: ... remove the cover ONLY from the side that requires fluid

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Fig. Fig. 3: If there are no markings on the reservoir, keep the fluid approximately 1/4 in. (6mm) from the top

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Fig. Fig. 4: Late-model vehicle, such as this 1996 Astro, use a 1-piece reservoir assembly ...

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Fig. Fig. 5: ... but fluid is added in the same manner, clean the cover, remove and pour


BRAKE FLUID EATS PAINT. Do not allow it to spill, splash or otherwise contact painted surfaces of your vehicle (or at least ones that you care about). If an accident should occur, don't panic, just immediately flush the area with plenty of clean water.

Use only heavy-duty DOT-3 brake fluid. BUT JUST AS IMPORTANTLY, use ONLY fresh fluid from a sealed container. Brake fluid attracts and absorbs moisture from the atmosphere, which can significantly lower its boiling point. Should fluid boil during heavy use (towing a trailer or hauling passengers and luggage) the fluid will turn to a gas and all/most braking ability could be lost almost instantly. Although the most manufacturers do not require a periodic fluid change for their brake systems, it is a good idea to fill the system with fresh fluid, bleeding out all of the old brake fluid through the wheel bleeders, at least every few years. Keep in mind that over time moisture will even enter a sealed system lowering the brake fluid's boiling point and causing internal corrosion to brake components.

If you decide to change the brake fluid, you will save a LOT of time by removing MOST of the old fluid from the master cylinder reservoirs, before you begin. Replacing the old fluid with fresh before you begin the bleeding procedure will simply require you to bleed a smaller amount of fluid completely through the system before the fresh fluid reaches all bleeding points. For more details on brake bleeding procedures, please refer to Brakes of this information.


The brake fluid level should be checked EVERY TIME YOU OPEN THE HOOD. At the very minimum, a thorough inspection of all fluid level and all components should be conducted every 6 months.

Before opening the master cylinder reservoir ALWAYS use a clean rag thoroughly clean the reservoir cover and immediate surrounding area. Failure to do this could allow contaminants to fall into the fluid when the cover is removed. These contaminants, if forced through the system by the master cylinder, could destroy seals, leaking to leaks, repairs and possibly even brake failures.

  1. Most vehicles covered by this guide use translucent plastic reservoirs, so the cover does NOT need to be removed in order to check the level. Also, most reservoirs will have fill marks or lines on the plastic. The fluid should be about 1 / 4 in. (6mm) from top of the reservoir.
  3. If the level is low, thoroughly clean the reservoir and cap(s), then remove the caps to add fluid. Some early-models may have a separate rubber diaphragm seal under the cap. If it is not removed with the cap, it should be carefully removed before fluid is added.

Remember to ONLY use fresh fluid from a sealed container.

  1. When you are finished, be sure the cap (and separate rubber seal on some early-models) is properly seated.