89 renix


when i step on the brake i hear pump like air sound

is this the symptom of a bad brake booster? been this way since i bought the XJ about 4 years ago so i dont know if there any loss in braking power


thanks

 

I don't know abour your Jeep, but my 1986 Commanche actually has a vacuum hose attached to the brake pedal. When I press the brake, I too hear the sound of air hissing. I'm thinking it's supposed to create a small, intentional vacuum leak to increase idle speed a bit while you're stopped and in "Drive", but I'm not sure.

My Comanche has several systems on it to increase idle when you turn the wheel, when the A/C is on, etc. Back then, they were desperately trying to meet emissions requirements and one way to do that was to make the idle speed very low. Thus, any load on the engine required increasing idle speed.

I've thought about disconnecting that thing many times, but just never got around to it.

 

A whoosh sound is normal. The booster normally has negative air pressure (vacuum), and then when you step on the pedal you open a seal that allows outside air to rush in and displace the vacuum (this causes the diaphragm to expand, which is what helps to push the brake rod--power brake assist). The whoosh sound is the outside air rushing in.

 

Might be to dump vacuum in the cruise control.

 

This?

 

Good possibility it's bad.

Before just replacing it, consider the WJ booster and master upgrade.

 

Probably. My 85 Cadillac has a vacuum relief for the CC on the brake pedal.

 

It's a redundant system for safety reasons.

Electronically, it kills power to the cruise and simultaneously dumps the system's vacuum to be sure it shuts off when the brake is applied.

 

That's right. The CC uses a diaphragm to hold the throttle, so dumping the vacuum pressure forces it to disengage mechanically

 

OK. Looks like I was referring to the TCC. My Comanche does in fact have cruise control. The TCC has a vacuum line connected, right? If it's hissing, does that mean it's bad? Or, is it supposed to do that?

 

No hissing!!