As long as opinions are being tossed on the table:

Re: Leaking Brake Distribution Block - Post Mortem[200/85] posted by Steve Seekins on
Thursday, 23 December 1999, at 9:43 a.m.

The 200 series through 1985 seem to be prone to this failure. I published a safety warning on these distribution blocks several years ago in Rolling. It is not necessary to have a 240 pound pedal pusher to suffer the failure. Normally, the blocking valve in these blocks does not move - and in those systems that have not been flushed every two years (I suspect that this includes most Volvos from the 80s), the corrosion builds up in the cylinder bore. Then the first time that the piston moves a little, the corrosion cuts the seals and the leak starts - could be very small or relativeloy significant. You may not even notice it, and the piston may not move enough to trip the brake warning light. However, the result is that fluid can leak from BOTH circuits of the dual triangular system with no warning light, and you can suffer a total brake failure!! In the year that I published this article (sorry, I don't remember which issue it was) we had at least three members with this failure, and two of them were driving when they had a total brake failure. Since that time, Volvo has recommended regular brake system flushes, and they have changed the brake distribution blocks - they are no longer made of iron, but are alloy and the corrosion problem should be much less.

The way to check them is simply to unplug the sensor wire and unscrew the plastic switch from the block. ANY evidence of fluid in the sensor cavity means replacement of the block. It simply is not worth risking brake failure!

As noted, this is also a very good reason to flush the brakes on a regular schedule and use a pressure bleeder like the Eezibleed or the Power Bleed --
Steve Seekins
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Re: 240 brake pedal pressure[740-760/1986] posted by Steve Seekins on
Saturday, 11 April 1998, at 7:15 p.m.

The brake warning light is actuated by a small switch on the brake distribution block - located on inner side of left frame rail below master cylinder. You man have to remove (unscrew) the switch after disconnecting the wire from the terminal on top. If there is any evidence of brake fluid inside the switch cavity, the distribution block is toast and needs to be replaced. There is a piston inside the block with some seals on it. If there is any corrosion in the block, and the piston moves, the seals are often damaged and leakage occurs. It is possible to lose fluid from both sides of the brake system through this block. Anyway, of there is no evidence of fluid there, step on the brake pedal hard a couple of times while the switch is removed. Then reinstall the switch. Hopefully the piston will have centered itself and the brake light should be out. If not, then disto block likely needs replacing as the piston is stuck to one side or the other. I have had a couple of people tell me that they have had success disassembling the block, cleaning the bore, and replacing the seals.
Volvo Club of America