When I was installing my struts I bled the brakes. I decided to bleed the system also but I lapsed and forgot to check the fluid in the master cylinder. I bled the system 3 times and there's no air comming from any of the bleeder screws. The Brake failure light still stays on now everytime the car is running. Is there still air trapped in the brake system and if so how do I expel it?

Andy

84 242ti

Replaced the master cylinder and proportioning valve on my `83 245 this week. Took 3 evenings and ~1 gallon of DOT 4. Used a (homemade) pressure bleeder; I recommend it. Volvo brakes are too complex to bleed effectively any other way. Bentley says bleed at least a pint from each caliper.
The brake failure light never came on for me. And while I sem to have more pedal than I expected, I don't have any softness or fade.

Yes, the piston in the distribution block has not reset. Plus, you may have air in one circuit but not the other. BTDT got four front pads worn to a wedge shape and metal to metal real quick.

The solution depends on how much air got in. Into the lines down from the MC or beyond the Distribution block.

Try this: Perform a partial pad replacement on all four wheels, start with the RR wheel. That means do everything except actually replacing the pads. One step is to move the pads tight to the calipers which pushes the pistons all the way in. Do both pads. This will push quite a bit of fluid (and air?) back up into the MC. Do the LR wheel next, then the RF and the LF wheel last.

After all that, with the car still off the ground, gently pump the brake pedal and build up pressure. See how it feels. Start the car and try it again, gently.

If the Brake Failure light is still on here's another idea: The idea is to weaken one circuit at a time, attempting to move the failure alert piston to move one direction and then the other. Open a rear wheel bleeder and step on the brakes hard and briefly. Add fluid and do the same on the opposite wheel.

If that doesn't re-set it, you may have to do another bleeding to clear it.

Good Luck,

Bob

:>)

It may be that warning switch is not resetting or you may still have air somewhere in the system. If air gets in at the master cylindar, it has a long way to go to get out. I replaced my MC and had to bleed twice. Are you following the rather complicated bleeding sequence for the front calipers? I got an EZBleed tool which uses air pressure from a tire and it has worked much better than pumping the brakes. It hasn't happened to me but other have said that pumping the bkakes to bleed sometimes ruins the seals on the MC piston.

Andy,

Had the same prob when I changed a stuck caliper on an '83 242, also had the prob on the 140s in the old days.

Bet your bleeding is fine.

Familiar w/ "pressure differential warning valve"? Is up front, left somewhere. Is supposed to trigger warning light once the master cylinder goes low in one of the two circuits. A pressure controlled switch/plunger thingy.

On the 140s the "business" part of the valve that sets off the light would unscrew; once you had this out, upon replacement the valve would "reset" and the light would go off.

I remember calling the dealer years ago when I had the 242 and he said to follow the same procedure on the 240. But when I was under there, it seemed to me the switching part was not intended to be removed, there wasn't even a hex on it.

Memory's foggy, that car was a rustbucket and maybe I just didn't pay enough attention. In my case, I put black tape over the warning light as the car was headed for the crusher soon anyway.

Check into this further: I'm sure others have been down the same road and might have better memories.