Hi Klaus,
Is this your R or the 850? It sounds to me as if your e-brake cables need to be replaced, which seems to be fairly common and more common on the AWD due to the way the cable is routed around the rear axle. The common problem is that teh cable sheathe cracks from age and the suspension motion over time. Then moisture gets into the actual cable and corrodes so that it is hard to pull up, and then won't release because the springs are not strong enough to overcome the corrosion resistance. On a FWD, the cable is run pretty straight from a bracket just in front of rear wheel opening into the brake backing plate. One side of my '95 855 had a split just to the rear of this fixed bracket. On the AWD (at least assuming it is run the same as the XC) the cable runs from this same bracket in a very tight loop so that it enters the brake backing plate at a right angle. There is also a locating clip in the middle of this loop, on teh suspension arm. These cables have lots more breaks, and on our XC, both cables failed, and both sides had several breaks including at the junction with teh backing plate, and at the locating clip on suspension. The XC is my wife's, and she never uses teh e-brake either, so it is not a question of use but rather the motion of the suspension. On the XC, I also had to replace the brake shoes, as the cable was not fully releasing for a while before I noticed it.

The cables are at FCP for either car, although they don't list them for the XC. I think they were in the range of $40 each. Problem is that you have to remove a lot of stuff to do the swap (console, rear seats, etc). On the XC, I had a particular problem removing a large bracket that is added to the AWD car on the left rear, just ahead of the wheel well, that traps the e-brake cable above it. I don't remember the size nut, but I had to send one of my sons to the store for a new socket to fit - it was the only one I didn't own, something in the range between 18 and 22mm I think - just check in advance (this bracket has three nuts, but they are two different sizes also).
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Mike Sullivan ('95 855T (88k), '98 V70XC (92k), '95 855 NA (135k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k), '91 745 (196k), '93 965 (147k) .