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Discussion Starter #1
I just bought a used 97 RAV4 - 4 door yesterday. We noticed that a few times on the drive home the brakes felt squishy.

Most of the time, the brakes work well. The pedal only presses in a small/normal amount. Occasionally (seems completely random), the pedal presses in a lot (not quite to the floor, but quite far). When this happens, the brakes still work, but much less well. The stopping distance is quite a bit longer. While this is happening, if we release the brakes and brake again, they work like normal again. What could this be?

I was hoping to replicate the problem this morning while parked with the engine on. I pumped the brake many times and it never happened. I did notice that every time I pressed the brake pedal, I heard air blowing around my feet. Not sure if that is normal or not.

Here is the car's brake related servicing history:
- 12,500 miles ago: front brakes, rotor and front brake hoses replaced. Rear brake service adjust
- 18,600 miles ago: brake fluid changed
- 52,000 miles ago: rear brakes changed

With this servicing done, should I assume it's not a brake hose leak or air in the brake lines?


I've been trying to mostly do my own car repairs lately, so would like to try this myself, but because of the seriousness of brakes, if it's anything too complicated, I will bring it in somewhere.

Thanks.
 

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Maybe either air in the lines, and/or a brake hose is bulging. Dangerous problem -- fix immediately.

If not done already, replace all four hoses and then flush/bleed the lines. I recently bought a pressure-bleeder, and once I got used to it, it works really well (and did this very job on my RAV4).
 

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Since the problem is intermittent, I suspect that you may have a caliper piston that sticks occasionally or caliper or a brake pad that is not sliding properly.

Whatever the actual cause is, it causing your brakes to drag and overheat. This can result in brake fading, which has the effect of loosing friction between the pads and the rotor. This problem shows up as a normally hard pedal, but the feeling that the brakes are not slowing down the car.

If the dragging is severe enough it can cause the brake fluid to boil within the calipers. This problem shows up as a soft brake pedal and the loss of braking power.

If brake drag is the cause of your problem, you may notice the odor of overheated brakes (when you are experiencing the problem) or the vehicle may tend to pull to one side or another. If you have a non-contact thermometer (i.e. Infra Red thermometer) you may measure excess temperatures on one or more rotors.

I suggest you get a brake service done.
 

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Seems to me that the problem might be with the master cylinder and its role in the safety-related dual braking system. Since the master cylinder has a dual-part piston one of the piston seals may be failing and may seal intermittently, meaning that occasionally there would be braking on only two wheels.
 

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if we release the brakes and brake again, they work like normal again.
I think that statement in itself narrows down the problem. If the cause was overheated brakes as I suggested they would not start working normally a split second later.

I'm pretty sure Blogson has diagnosed the problem correctly. Get this fixed ASAP.

Seems to me that the problem might be with the master cylinder and its role in the safety-related dual braking system. Since the master cylinder has a dual-part piston one of the piston seals may be failing and may seal intermittently, meaning that occasionally there would be braking on only two wheels.
 

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Discussion Starter #8
I replaced the brake master cylinder last wednesday then flushed the brake fluid and the problem is fixed. I wanted to drive for several days before I posted to make sure and it hasn't repeated the problem since.

Thanks for the help.
 

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Good to hear that you fixed the problem so that your brakes are working fine. Thanks for the update!
 
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