Weird braking in 2005 Jetta

I have a 2005 Jetta 2.5 with 45k on the odometer. I bought this vehicle used last November with 36k on it. I drive A LOT.



Shortly after acquiring it, I noticed that sometimes when driving in heavy, heavy rain or in extreme cold (I live in Vermont) that the brake pedal will be very stiff and it feels like there are virtually no brakes. If I take my foot off and reapply, it generally resolves and the brakes seem fine.



Two weeks ago, while approaching a bend in the road at around 60mph, I pressed on the brakes and had this same experience (It was raining and cold that day). I can honestly say that I almost died of fright because it was like having NO brakes. I pressed harder on the pedal and it seemed to pop a bit, and then I could feel the vacuum assist and the wheels actually locked up and I slid in the sand on the road (the car is equipped with ABS, so this seemed extra odd to me). Luckily there was a smaller side road that I just slid onto and came to a stop; if that road had not been there I would not have made that curve and would have gone off the road.



I typically take my car to a great VW mechanic in Williston, VT, but I reluctantly brought my car to a VW dealership this morning because I figured I have ~5k left on the warranty, and this seemed like a potential warranty item.



The dealer, of course, “can’t recreate the problem” and also told me “there are no stored codes” for them to diagnose the problem. They did tell me that the rear brakes are way down and the rear rotors also need replacement, which is VERY typical of these VWs (google “2005 Jetta brakes” and you can see this). I’m fine with replacing them, but I remain highly skeptical that this is related to the problem I have been experiencing.



I’m no idiot, I’m a lifelong gearhead, and I know a stiff brake pedal when I feel it – this is not worn down brakes, this is what feels like an intermittent loss of vacuum assist. The problem happens very intermittently, and 99% of the time the brakes feel strong and fine. Not to be the gripey guy, but I’m suspicous that as soon as the mileage hits 50,000.1 and the car is out of warranty the dealership will suddenly be able to diagnose this problem.



I’m nervous to drive the car now. The service advisor could offer no explanation to this problem, and even said that it was unlikely that the worn down rear brakes would cause the symptoms I’ve been experiencing. Anyone have any thoughts or suggestions?

I would start by flushing the brake hydraulic system, and seeing if the symptoms go away.