Jim Grant's Tech Tips
'91 Geo Tracker, Brake Booster Failure
Q: I own a 91 Geo tracker with 177K. After the truck gets hot it will ping, hesitate and blow off-white smoke out of the exhaust. I have replaced the EGR and had the top of the engine flushed, it still happens. There is a hose that goes from the brake power booster to the intake manifold. I was told this could possibly be the problem. I didn't believe it, but I crimped it off and the smoke stopped. I removed the crimp and the smoke returned. Although that solved the problem, I can't drive it that way because the power brakes dont work. Any ideas ? Power brake booster? Master cylinder? Check valve? I just spent $700 on repairs and I don't want to spend another $1000 for a master and booster.
- Charles L.
A: If the information you provided is correct then your brake master cylinder must be losing brake fluid. If the rear seal of the brake master cylinder fails it can allow brake fluid to leak out the rear of the master cylinder. The rear of the cylinder just happens to be bolted to the power brake booster. The brake booster, as you have proven, uses engine vacuum to create power assist for stopping the vehicle. In some vehicles, a leaking brake master can leak into the power brake booster. The fluid in the booster will be drawn into the engine and burned. If pinching the vacuum hose to the power brake booster did, in-deed, correct your smoking problem then you likely have a defective brake master cylinder. The brake master cylinder can be replaced separately of the power brake booster. However, there is a concern with the brake fluid in the power brake booster causing damage to the diaphragm. The boosters diaphragm can be damaged by extended exposure to brake fluid. If it fails, you will lose brake assist and the engine may go into fits of stalling. Power brake boosters are pricey units, but you can check on a used one from an auto recycler; it could save you a good amount of money.