GM Full Size Vans 1967-1986 Repair Guide

Master Cylinder

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FLUID RECOMMENDATIONS



Only high quality brake fluids, such as General Motors Supreme No. 11 Hydraulic Brake Fluid, Delco Supreme No. 11 Hydraulic Brake Fluid or fluids meeting DOT-3 specifications should be used.

LEVEL CHECK



See Figures 1, 2 and 3



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Fig. Fig. 1: Remove the brake master cylinder cap



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Fig. Fig. 2: Add the proper amount and type of fresh clean brake fluid



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Fig. Fig. 3: Proper master cylinder fluid level

Beginning in 1967, Chevrolet and GMC vans were equipped with a dual braking system, allowing a vehicle to be brought to a safe stop in the event of failure in either front or rear brakes. The dual master cylinder has 2 entirely separate reservoirs, one connected to the front brakes and the other connected to the rear brakes. In the event of failure in either portion, the remaining part is not affected.

On 1967-69, the master cylinder is located beneath an access in front of the driver's seat. On 1971 and later models, it is mounted to the left side of the firewall. On 1973-75 G-30 and G-3500 models with the Hydro-Boost power brake system, it is mounted transversely near the center of the firewall.

  1. Clean all of the dirt from around the cover of the master cylinder.
  2.  
  3. Be sure that the vehicle is resting on a level surface. If necessary, remove the floor mat and access cover.
  4.  
  5. Carefully pry the clip from the top of the master cylinder to release the cover.
  6.  
  7. The fluid level should be approximately 1 / 4 in. (6mm) from the top of the master cylinder. If not, add fluid until the level is correct. Replacement fluid should be Delco Supreme No. 11, DOT 3, or its equivalent.
  8.  

It is normal for the fluid level to fall as the disc brake ads wear.


WARNING
Brake fluid dissolves paint. It also absorbs moisture from the air. Never leave a container or the master cylinder uncovered any longer than necessary.

  1. Install the cover of the master cylinder. On most models there is a rubber gasket under the cover, which fits into 2 slots on the cover. Be sure that this is seated properly.
  2.  
  3. Push the clip back into place and be sure that it seats in the groove on the top of the cover.
  4.  
  5. As necessary, replace the access cover and floor mat.
  6.  

 
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