Hello db.

You MAY have one of my pet hates, and a commonly ignored brake condition that is simply rusted in brake pads.
Every car that I have 'taken over' in the last god knows how many years has needed the inside of the calipers descaling with a hammer-thru screw driver and hammer untill the pads were quite free to slide under the action of the piston(s)and the wobble deflection of the disk.

repair shops seldom do this, and I have seen them hammering in new pads beliving it to be the right thing to do.

I had a 940 that was very bad. The rear brakes only worked if I pressed very hard and then only after a quick pump.

Because the pads are not responsive they do not have a close fit to the disk and hardly ever do their proper job hence the rusty disk.

I prefer my pads to be 'a rattling good fit' in the caliper, and properly lubricated with the right high-temp stuff, and nice new clips etc.

On the 940 I had to remove the caliper, and smash out the old pads,they were only about 20% worn but horrible.

Hope this helps.

Very best regards.
Howard. Isle of Skye.

Make sure the caliper retainers are not broken or rotted. They tend to crap out usually after salty winter weather.

The master cylinder does not make a calculation of pressure for the rear brakes. That is left up to the ABS module, if I remember correctly.
Most calipers that die tend to lock up in the death squeeze, not open. How old is your brake fluid? There could be moisture or air in the rear lines.

To verify your rear calipers not functioning, try this: Using your left foot for the brake, and an empty stretch of road, at about 30mph with your foot on the throttle and the other on the brake, try to stop. Push real hard on the brake and light on the throttle. Too much throttle is not good for the tranny!

The idea is to get the rear rotor shiney. If it still does not work right, and you have flushed the fluid, then you need to fffind out the real cause. Remember, the rear brakes only supply about 35% of the pressure that the front brakes use.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)