After 5 weeks summer rest rotors trouble

[sibir]

Our family went abroad this summer for 5 weeks. Both the 850 wagon and the '98 V70 stood outside without being moved for that time. Now both of them exhibit the same problem when braking: There is a very pronounced sort of brake shudder, but not the "steady" vibration kind. It feels like there is a single bump on the rotor, so when braking once per wheel rotation the pads grab something.
I thought it might be some rust and wear off after a while, but after driving for a week it is still there. Also, I was expecting the wheels to get out of sync and that the wheels would individually produce this sound/feeling, at least two wheels. But it remained the same as if there is only one wheel doing it, however it's the same on both cars.

I took the wheels of the V70 but, of course, that gives me access only to the outer side of the rotor. I found a rough spot on a rear rotor, but I was suspecting the front rotors, although I cannot tell where the tremble comes from.

What now? Garages around here do not grind rotors anymore, as far as I know. But I do not feel like buying a complete set of rotors either. Maybe I can isolate the rotor by temporarily clamping brake lines?

Any ideas or similar experiences out there?

[MadeInJapan]

I would say that your rotors developed some rust on them. Drive them hard and brake hard...get rid of the rust and you should be back to normal (of course I could be wrong). Could also be the rear e-brake that has become seared (also from rust) and is catching as you go down the road.

[vegasjetskier]

The same thing happens to my cars. Since I live in an area with corrosive air, when my cars sit for while the rotors rust everywhere except where the pads are touching. Then when I drive I get the pulsation. I just live with it because as soon as I fix it, it just happens again. I guess the solution would be to keep the cars in a garage, but that's not an option for me. Good luck.

[madorion]

Hi All,
It takes about fifteen minutes per rotor but it works. Take an 4 inch angle
grinder with a 60 or 80 grit flat 4 inch flap wheel grinding disk and chamfer the 1/4 of the edge of both sides of the rotor, at a 45* angle. Calipers can be removed but not necessary. I usually do it during a brake pad change.
Long sweeping motions without taking off too much in any one area. The back side of the rotors is a bit of a challenge, but it can be done at the cost of one flap grinding disk and one and half hours of your time. Excluding positioning, jacking the car and wheel removal.

[sibir]

It turns out that on both cars it was the REAR driver side disk which had big corroded areas inside and outside. I suspect part of the problem may have been cheap metal-based pads. Next time I will buy the more expensive ceramic ones...
I just put new rear rotors on my wife's V70 and used her good passenger side rotor to replace my bad driver side rotor.

Still I am puzzled, why both cars on the same rotor? The pad should not be touching the rotor, so why localized corrosion?

[wheelsup]

I think the pads very slightly touch the rotors even when at rest if I'm not mistaken.