!Firm brake pedal!

[Bluebird]

Brake booster or vacuum pump??? My brake is very firm, truck will stop with a lot of foot effort . I've replaced the check valve at the brake booster, master cylinder is full, put a new vacuum/electric plug box that is inside the left fender. No fix. How can I test the booster or the vacuum pump? Thanks in advance for any help, or step by step resources to fix ether or component. I've check previous forum entries, I have not found and specific answers.

Happy Holidays Patrick.

 

[DMcLeod]

Pumps are quite reliable, but worth a check. Disconnect pump hose at check valve, put a gage on it, start truck, read vacuum (mine was 21inches - I can't say for sure what spec is, but right near there).

It's more likely a hose leak or booster diaphram leak. To check, I took the hose off the sensor you referred to on the drivers fender, and put the gage there. Start truck, read vacuum. If you now have a very low reading, this should tell you that you have a major leak somewhere.....could be hose, booster diaphram, or something? If I remember correctly, I tested vacuum with only the booster hooked to the system (all other ports plugged). That way I was testing only the booster for a leak, and sure enough, I had zero vacuum, so I replaced the booster.

Hope that helps, and hope you find it! Don't rule out the hydraulics side completely, but I think you're on the right track to check the vacuum system out first.

 

[DVolk]

call Mysteryman !!!

 

[DMcLeod]

Pump output spec is 8.5 min, 25 max inches vacuum.

If booster vacuum falls below 8.5 inches for 8-10 seconds or more, the switch sensor that you replaced will complete the circuit and illuminate the brake warning light on the dashboard.