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Discussion Starter #1
This just started tonight: I'm stopped and after a minute I notice the car is drifting forward. I brake harder, it stops, but the pedal sinks and it starts again. I checked my brake fluid and it looked pretty low so I bought some DOT 3 and added to the max line. That didn't do anything, apparently. I can come to a full stop just fine, I just can't stay full stop unless I use the parking brake to assist.
 

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Definitely a brake problem! Probably serious! What year & mileage.
 

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This just started tonight: I'm stopped and after a minute I notice the car is drifting forward. I brake harder, it stops, but the pedal sinks and it starts again. I checked my brake fluid and it looked pretty low so I bought some DOT 3 and added to the max line. That didn't do anything, apparently. I can come to a full stop just fine, I just can't stay full stop unless I use the parking brake to assist.
This happened to my 95 Acura Integra few years ago and it was the master cylinder, replaced with a new one for about $55 and all is good.
 

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Hopefully you checked for any leaks at the wheel caliper cylinders, and elsewhere under your RAV.
 

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Discussion Starter #6
This happened to my 95 Acura Integra few years ago and it was the master cylinder, replaced with a new one for about $55 and all is good.
Yeah, I just watched a bunch of videos on it and that seems to be the likely cause, but brakes being the most important part of the car, imo, I don't think I'm ready to add this one to my projects list. As it is I barely managed to do the transmission fluid the right way (I over-filled by about 4 ounces) and that turned out okay, but Monday I have to do the oil, coolant, differential, and transfer case changes. Brakes and the spark plugs I think I'll go to the shop for. Spark plugs are totally unrelated to this and on the 4 cylinder look easy, but there's too much that could go wrong with me taking things off the 6.
 

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Discussion Starter #7
Hopefully you checked for any leaks at the wheel caliper cylinders, and elsewhere under your RAV.
Nope, but I periodically look under the car for leaks in general and haven't seen any. I'll look under it tomorrow before I go out. I don't have an impact wrench at the moment so I'm not very inclined to take the wheels off, but maybe when I do the oil Monday since I'll have it on the jack stands anyway.
 

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Nope, but I periodically look under the car for leaks in general and haven't seen any. I'll look under it tomorrow before I go out. I don't have an impact wrench at the moment so I'm not very inclined to take the wheels off, but maybe when I do the oil Monday since I'll have it on the jack stands anyway.

If there is a leak from a wheel caliper cylinder it should be visible without having to remove the wheels, since the fluid should run down onto the inside of the wheel and accumulate on the inside of the rim. Good luck in finding out what the problem is!
 
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yep . . .master cylinder, you can check for leaks but chances are its leaking back to the bowl. Not a terrible project.
many videos to assist
 

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Discussion Starter #10
yep . . .master cylinder, you can check for leaks but chances are its leaking back to the bowl. Not a terrible project.
many videos to assist
Changing the master cylinder looks as easy as changing a light bulb, and while bleeding the lines seems like it's easy enough that's the part that seems daunting to me. I mean what if I change it and do that last part wrong, will the brakes seize or something?
 

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I agree it's probably an internal leak in the master cylinder. The only concerning issue for me is having to add fluid. Normally when the fluid level goes down it's due to the fluid remaining in calipers as the brake pads wear. So if it goes low again there is an external leak somewhere, probably at a caliper as mentioned.
I just replaced all four rotors and all pads on our '06 RAV4 with 125K. Only the sliders needed freeing up. When I was done the fluid level at the master cylinder came right up to the full line w/o adding any.
 

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Discussion Starter #13
I started driving this morning and noticed the brake light was on. So I stopped at a gas station on I-95 and checked the brake fluid. Empty. So I added the rest of what I had and drove home to get my 2012 Focus. I'm in that right now, and it's not stick, not the ST, so it kind of sucks but the brakes work in the Focus.

Tomorrow I'm going to take it to a local brake place that does free inspections. I'll see what they say the issue is. If it's just the master cylinder I'll do it myself. If it's more I might let them do it. I don't have a lot of extra cash right now so I hope it's just the master cylinder.
 

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Discussion Starter #14
The brakes themselves are most likely too complicated for me to do without help. I watched someone do it once years ago, but I wasn't really paying attention...
 

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The brakes themselves are most likely too complicated for me to do without help. I watched someone do it once years ago, but I wasn't really paying attention...
Good idea but it'll probably be expensive since once they get started with brakes most shops want to go all the way - for your safety and their liability. Brakes are nothing to DIY w/o 100% confidence.
Losing fluid certainly means a leak somewhere - probably a caliper but possibly a brake line altho that's not likely on a 2009 vehicle. I'd really be surprised if the master cylinder is bad.
 

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Hopefully it's nothing super expensive. I have a car payment to make and I'm behind two weeks on that.
 

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Good idea but it'll probably be expensive since once they get started with brakes most shops want to go all the way - for your safety and their liability. Brakes are nothing to DIY w/o 100% confidence.
Losing fluid certainly means a leak somewhere - probably a caliper but possibly a brake line altho that's not likely on a 2009 vehicle. I'd really be surprised if the master cylinder is bad.
I just came home and when I looked in the garage there's a huge puddle f what I'm assuming is brake fluid at the right rear wheel.....
 

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Classic symptoms of master cylinder failure.
I'd agree if there was no loss of fluid, but thinking about it that's what used to happen years ago, a seal in the MC would fail and the fluid would get sucked into the intake manifold buy the vacuum. Haven't heard of that in a long time - or at least a few months ago when it happened to my 1968 Volvo 1800S.
Also have never heard of a "hole in the piston." Probably just a simple explanation for a failed seal between the piston and caliper bore. Like saying a 4WD RAV4 has a viscous coupling instead of a variable electro-magnetic coupling attached to the rear differential.
 
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