Hey guys maybe you can help me figure out this issue I just got. I have a '94 S10 Blazer 4x4 with a 4.3L V6. I've had it for years with no problems. It hasn't been driven too much lately, only a couple times a month for the last 3-4 months.
Anyway, I took it out today on a very short trip (less than 2 miles). On the way home, the brakes BARELY worked, pretty sure I lost my vaccum assist. On top of that, the engine started racing on its own and wouldn't idle. I was very close to home, so I fought on and made it back safely. As soon as I pulled in and shut the engine down, coolant started pouring out of the overflow container, so I assume it was overheating as well. Unfortunately, my temp gauge doesn't work, so I was unaware of this problem.

So.... what could cause overheating, no vacuum assist to brakes, and the engine racing on its own? I'm assuming there is some vacuum problem that could cause the revving and failed brakes, but would a vacuum issue cause overheating as well? I've never had any of these problems at all, so I'm certain that one thing must have cause all these anomalies. ANY help is appreciated. Thanks.

 

If your booster failed, it could cause the engine racing & hard brake issue. Overheating should have no connection to the other two things though unless it was a intake manifold gasket failure which caused coolant to be sucked into the engine.

 

Thanks for the advice. I believe I can attribute the overheating to having the engine attempting to race as I was holding the brakes, I'm sure that heated everything up. I have had times when the brakes felt much harder to push before, but it was very infrequent. What's the proper way to test and confirm a dead booster? Is there any thing specific I should know about attempting a brake booster install? Any help is always appreciated. Thanks, Chuck.

 

The booster is fairly easy to replace.

The booster should hold vacuum after the engine is shut off. I would start by installing a new check valve on the front of the booster to eliminate that as a potential vacuum leak path back to the engine. Start the engine and let it idle for a bit. Then shut the engine off and pull the check valve from the front of the booster. If you hear a rush of air into the booster, it is holding vacuum appropriately. If not, then the booster has a leak in the diaphragm.

 

its not hard at all. i know on my 86 with basic tools i changed my brake booster in about an hour. i do have one question concerning this. i heard somebody say that when i replaced it i should replace the inline cylinder (possibly the check valve). what would happen if i didnt?

 

The check valve is only a few dollars. If it were bad, it would result in a loss of vacuum pressure in the booster whenever the truck is off. This would require the booster to be pumped down each time the engine is started and may cause it to run poorly, not to mention the brakes would be stiff until it reached the proper vacuum level.