1989 Audi brake problem

I've looked through as many old messages as I could but my problem hasn't quite been addressed. I have a 1989 Audi 200 turbo, non quattro. It has 160,000 kms and was stored for 6 years.
I bought it this past February and it was great as long as the weather was cold. Now that it's hot out the front driver's brake locks on when the car gets hot. Only that one brake. Basically, as long as the temperature stays at 90 celsius it's okay but if it gets up to 100 celsius the brake will engage. It will even engage while the car is sitting idling, if it gets warm enough. The rotor hasn't warped -yet. The brake fluid has been flushed twice, the hydraulic oil has been replaced once, the calipers have been cleaned twice, and the accumulator has been replaced. Nothing has helped. While the brake is engaged the brake pedal will either be stiff or go almost to the floor. And if I'm on the highway it will suddenly release and then slowly lock on again. Suggestions by several mechanics at this point is the ABS control unit. The idea is that it sits close behind the rad and is getting too hot. I should mention that the fan doesn't come on until the car is at 100 celsius and only stays on for about 15 seconds, not enough to cool the car down. Any ideas? Is it a brake problem or a cooling problem? Or both? And what would you suggest for a repair? The ABS unit is $2800 brand new but I've found a used one for $250. I'm hesitating to buy it, though, after spending over $600 for the accumulator and just wasting my money. This has been going on for the last few months and I even had to buy a beater car to have something to drive until someone figures out what's wrong with my Audi. Any help would be very much appreciated!
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ABC controller failure on the T44s is very rare.
I would check two things:
- The mechanic's comment about the controller (and Master Cylinder) getting hot because they are located right behind the radiator fan is a good place to start.
A trick to see if your Master Cylinder is bad is to carry a bottle of cold water with you and when the brakes lock, get out and pour the water over the master cylinder. If the brakes free up you have a bad mc and it needs to be replaced.
- Your observation that the fan only comes on at 100C and runs for only 15 seconds suggests that you have a problem with the system that operates the radiator fan. This involves a resistor pack under the radiator, relays and a thermoswitch on the radiator. I would bet on the thermoswitch on the radiator being bad and you are only getting the fan to run when the engine is very hot.
The fan is actually a three speed governed by the resistor pack. Fan speed one operates when AC is on. Speed two should cycle when you are idling in traffic and should usually handle the cooling itself. Rarely will you hear fan speed three. It is very loud and sounds like a jet taking off.
The thermoswitch is only about $30. Changes easily and is located just under the lower radiator hose on the back of the radiator.
I would use the water bottle and change the thermoswitch.
TonyJ Formerly four T44s '84 - '91
Amigo wrote:

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Amigo wrote:

> ...

I'm admittedly putting forward a theory here, but when have the flexible brake lines on the front been changed the last time? Flexible lines get affected by the brake fluid over time. They get spongy and grow inwardly.
The theory is, that the open internal cross section of the brake line is only minimal by now due to the age of the line. Now when it gets hot, it expands further, applying pressure to the caliper and pressing it against the disk. Possibly even closing off the cross section completely, which might explain that you could have everything between stiff and to the floor on the pedal.
Changing the flexible braking lines might be a good idea anyway on such an old car if not already done. And it's not overly expensive, right?
Regards
Wolfgang
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Amigo wrote:

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Thanks for the quick replies TonyJ and Wolfgang! The car is booked in to go to another shop in 2 days but I'm hoping my husband can figure out what's wrong first. We're going to try what you've suggested. Please, if anybody else has any ideas, keep the suggestions coming. I'm selling my beater car and have to get this one on the road. And this time I'm taking it to the Audi dealership instead of a German car shop so it's going to be more expensive.
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Just a thought on the dealer vs independent mechanic choice.
The dealers have competent mechanics but they are trained on the later models. The ones that were trained on the T44 series have changed jobs by now. The point is that the independents often are more experienced with the T44s now. You would need to get references for independents to know which ones are good.
Amigo wrote:

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Right on!

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wrote:

As another poster amened, Tony is right. If you are in the western New York area, go see CDI Cars in Victor: they have several mechanics who know these older cars. They rightened up my 1985 4000S when she needed it (I do miss Helga, I must say, but I also do love my 98.5 A4 2.8Q) at not a lot of money, and the repairs always held up.
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Thanks you guys. Unfortunately, we live in Canada and there are few German car shops in our city. We went to a wreckers where you get your own parts today but there were only Audis older than ours, as usual. The cost for the parts for these cars is ridiculous. This is so frustrating. Tonight my beater car died and wouldn't start. I've got to get my 200 on the road.
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Well, it looks like it's the master cylinder. I drove it today until the brake was so tight it would stop the car without me touching the pedal. I poured 2 big pop bottles of cool water over it and when I got back in the brake was off and the car drove home without a problem. I even think I know where I can get one. I'm keeping my fingers crossed that this is it and I can finally drive my car without worrying the whole time. My only concern is that the water also cooled off the ABS control and that it still might be that. Thanks guys! I really, really appreciate you taking the time to respond to my question.
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