When I have to stop quick, I have to push very very hard on the brake pedal. With normal stopping I don't seem to notice it much. My understanding is that the ABS system can't cause this problem. How do I figure out what is wrong?
The booster is a likely cause. Check vacuum to the booster and the integrity of the check valve at the booster. If there are vaccum leaks associated with the booster (some can be internal to its valving), it will lack capacity for a good stab at the brakes. Run your engine, then shut it off, and see if the booster has enough vacuum charge in it for one or two brake applications. Run the engine and shut it off and see if it has vacuum charge after sitting for a few minutes.
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')
You describe my own experience with a '97 Grand Voyager. Brakes are fine on the move and capable of stopping the vehicle (when rear drums are adjusted properly) just fine. However, at slow speeds (5 - 10 mph) when you need to stop abruptly, even very high pedal pressures will not bring the car to a sudden stop,and this is not the ABS cutting in. Usually it is not an issue, but when you are in slow nose to tail traffic which suddenly stops, it can get interesting! Maybe the later models with discs at the rear don't have this "feature"
I agree! I was surprised to see this the 3rd or 4th post down the thread instead of the very first.
It may not be the booster itself, it could be the check valve where the vacuum line feeds into the booster. I've seen cases where the check valve is bad and you don't notice it in normal driving because the engine can restore vacuum to the booster in the half-second or so between taking your foot off the gas and putting it on the brake, but in a PANIC stop you lift off the accelerator and hit the brake before vacuum can recover.
It has nothing to do with drums or disks on the rear. The front disks ALONE should be able to stop the car quickly if everything is working right. Rear brakes typically contribute 20% or less to the total stopping power of the car, and besides that drums CAN produce as much stopping power as disks- they just can't do it repeatedly from high speeds.
Yes, but if the rear drums are not adjusted properly due to worn shoes etc., then you will experience greater than normal pedal travel before the front brakes start to bite. But as an example my previous vehicle, a 2.2ltr turbo-diesel Toyota Estima MPV (Japanese version of the Previa albeit slightly narrower) had drums at the back and didn't behave in the same way.
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