During a moderate to hard stop my brake pedal loses pressure and drops about 1/2", then firms up before coming to a stop, sometimes accompanied by a noise and vibration at the pedal. Any body else have this?

 

Had that happen to me stopping while backing up! Has never occured before and haven't noticed it since, though it has only been about a week since it happened.

Mark

 

I've read in my shop manual that the brake booster might be going out if it acts like that. But what do I know....I'm just a shade tree mech. I hope that's not the problem, seeing how it's still new.

 

I think it's called "anti-lock brakes". The symtoms you mention are in your owners manual.

 

I don't remember reading about "don't worry if your brake pedal loses pressure, drops about 1/2", then firms up. It's the anti-lock brakes." If it is, let me know what page it's on. I'd like to read it for myself.

The noise and vibration at the pedal is most likely the anti-lock, but the 1st symptom isn't (IMHO).

Spike

 

It sounds like the ABS might be trying to operate with air in the brake lines or calipers. You might take it to the dealer, or try bleeding the brakes yourself.

 

depending on the mileage and driving style, it might be wise to go ahead and flush the fluid and replace with new.

 

My breaks do this too..

It seems to me that it happens only on the very first moderate breaking after starting the vehicle up and driving it. It's almost like the anit-lock break computer is engaging and pulsating the breaks, when you ARE NOT skidding or pushing hard enough to cause a situation where you would actually NEED the antilock mechanism..

I've almost had a few accidents a few times because I went to hit the breaks and all they did was pulsate instead of actually stop the truck.. then as soon as I stop, and try the breaks, they work prefectly..

Guess I should pull some mods off and take it in

-Dale

 

I have this problem also. It feels like the ABS is engaging, but it happens in situations where only hard braking is needed, no sliding to require ABS.

When I took my car in the first time, the tech mentioned an ABS code. Now that I think about it, he didn't investigate it to my knowledge (lawsuit!?). I need to find out what code that was.

 

Mine does the same as Dales????

 

Mine too.

 

Sounds like many of us have it. I'm reluctant to bring it in with the mods, hoping to know what it is first. If it is ABS it would be premature, its too low a frequency to be ABS, and the pressure loss requires modulation (increase then decrease) to stop normally. Mine is usually accompinied with a rubber slipping/jumping sound felt at the pedal. Poss. vacuum / booster abnormality? Note no symtom during hard (or lite) stopping, only a moderate pedal triggers it, and it occurs just before comming to a stop (5 - 10 feet).

As I recall, a loss of vacuum boost firms the pedal up higher, whereas a loss in hydrolic pressure drops the pedal, therefore this should be a hydrolic issue? jim, its predictable under these conditions. Wouldn't air show itself more regularly? Is there any system to suppliment hydrolic pressure if it drops?

 

If anybody has found out what the prob is please let me know.

Thanks

 

I've had my pedal go awful low a few times. But when I hammer the brakes at a moderate to high speed they feel fine So my answer to your question, is I don't know, but I am in the same boat. I think, hope it's air in the lines

 

and agree with speeding bob: need to have fluid totally flushed out of the system,fluid is losing it,s viscosity due to high heat. good shop will do it for around 65 bucks