Should the Brake Booster Be Doing This?

[markinms]

87 BII 4X4.

Brake pedal goes to the floor when applied and must be "pumped" for the brakes to stop the vehicle. Each time the brake pedal is applied I can hear the sound of vacuum being released from a location under the dash.

With the vehicle stopped and turned off, each press of the brake pedal releases more vacuum until it's gone. Usually 4-5 presses.

When the engine is running the brake booster seems to be drawing a great deal of vacuum when the brake pedal is pressed. For example, with engine running the vacuum guage reads steady at 18". Each time the brake pedal is pressed, the reading drops about 5" and with continuous pressing the vacuum guage drops to nearly 0"

I don't know if this has always been this way or just recently started. I'm troubleshooting an engine miss/surge issue and was checking for vacuum leaks when I noticed this.

Any thoughts or suggestions? I'd sure appreciate your help!

Thanks!
Mark

 

[Dirtman]

Certainly sounds like you need a new booster.... if the internal check valve in the booster leaks you not only have a vacuum leak but will cause a spongy pedal that needs to be pumped up like you describe.

 

[markinms]

Is the brake booster hard to replace? Any tips or tricks for making it as easy as possible?

 

[tinman_72]

A failing brake booster will cause the pedal to become very stiff. It sounds like the master cylinder to me.

 

[markinms]

Problem has been resolved. I replaced the brake booster and master cylinder and bled the system. Brakes are back to working like they used to.

Now the Rear Antilock Brake Light stays on. Trying troubleshoot this now.

Any ideas?

 

[RonD]

It was the master cylinder, just FYI

Did you plug back in the fluid level sensor on the master?

 

[markinms]

I agree, based on feedback, that it most likely was the master cylinder. I replaced the brake booster because I already had a new that I had purchase a few years back.

I did plug the electrical fitting back in. Tomorrow I'll check to make sure all wire are making contact correctly and that it's not loose.

 

[duffy]

As for the ABS light, I chased one of those for quite awhile until I read some where about a wire off the battery ground that could easily come unplugged (several inches from the battery itself).....it had and once plugged back in it worked fine. It only effects the ABS apparently.

 

[markinms]

Thanks, I was unaware of that. I take a look later today. It would be great if that's all it is!