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98 Jetta TDI hydraulic system

We just received this vehicle from my mother in law, who is not driving any more. It’s a cream puff–79,000 miles, beautiful condition. Problem is the clutch engages lower and lower to the floor, and eventually the shifter gets stuck in gear. The brake pedal slowly sinks to the floor when at stops on hills. Our mechanic tells us these two are connected because both the clutch and brake run off the same hydraulic system. 1st time he said the fluid was filthy, and he emptied the system and put in clean fluid. Worked for a little while and then we were back where we started. Second time he replaced a couple parts on the clutch, replaced this fluid, and this time it ran like a dream for a little over a month. Then the problem just returned. Again he says the fluid is filthy, and now we are looking at replacing the master cylinder and again changing the fluid. The theory behind why this is happening is that my mother in law let the car sit for half a year before passing it on to us. She didn’t do much driving the 6 months before that either. I’ve done research, and this doesn’t appear to be a common problem by any means on these cars. But I wonder if anyone has encountered a problem like this. We’ve spent over $600 so far, and this master cylinder is looking to be mighty pricy. Many thanks.

The clutch and brake systems share the same fluid reservoir. VW recommends flushing the brake system every two years, because the fluid is hygroscopic meaning it tends to absorb water, and water is not good in a hydraulic system. I typically go three years between fluid flushes, but your mother-in-law probably never flushed the hydraulic system from 1998 until the car was transferred to you. So yes, the stuff he flushed out was probably very nasty and could have contained particles of rust.

VWs use a special fluid, so one of the things you need to ask is whether your mechanic uses the right fluid. As for replacing the master cylinder, yes, that might be necessary. Does the clutch seem to be working okay now?

Does your mechanic specialize in Volkswagens, or German cars, or does he also work on American and Japanese cars? I recommend finding someone who is a VW expert, and preferably one who really understands TDI engines. Eventually you’ll need a timing belt change – this should be done every 60k miles for your year’s engine.

he emptied the system and put in clean fluid

Did he flush out all the old fluid in the brake and clutch lines?
Or did he just drain and refill the reservoir?
I would have replaced the clutch and brake master cylinders from the start,
given the old fluid.