i am pretty sure that the master cylinder is on the fritz.
i went to maine for 4 days (we took my friend's car) and left the volvo to sit.
when i first drove it i noticed that the pedal seemed a little soft, but the brakes still worked fine. (side note: the brake failure light has been flickering on and off over bumps, and whenever else it felt like it). this morning on my way to work they were almost useless. the pedal goes all the way to the floor, and then they work only as though i was coming to a very gradual stop. i pretty much used my transmission as a braking system.
fun!

i am pretty sure that the master cylinder is on the fritz.



i think you answered your own question.

fwiw mine is about halfway there...
--
'92 240 208k totalled 4/14 - '91 240 182k miles

Sometimes it helps to know what makes the brake failure light come on, and, also, what can allow the brake pedal to move with little braking occurring.

The 240's without ABS have a dual circuit system. One circuit connects one part of the MC to one piston/cylinder on each front wheel, and one of the rear wheels. The other circuit is similar, a cylinder/piston in each front wheel and the other rear wheel.

If you look at the MC, you will see two "output" lines going down to a connecting block mounted on a frame piece. Two lines into it, six lines out of it, and an electrical connection.

That octopus block contains a sliding piston that moves only if the pressure in one circuit is not balanced by the pressure in the other circuit. If it moves, the movement closes the ground side of the brake failure lamp lights.

The piston moves if there is a leak in one circuit, and there can be other reasons, too. Note that the grounding is what makes the light come on, so a ground occurring elsewhere could make your flickering light.

The MC has two separate pistons, and the fluid reservoir is divided, too. If one part is low and the other not, there's a leak. Be sure that your MC is full on both tanks.

If a piston seal is worn, light pressure on the pedal can let the fluid flow past the piston - pedal moves and no braking. Heavier pressure seems to cause the seal to flare out and make a tighter seal, and braking can then occur.

I have tested the MC while waiting for a green traffic light on level roadway. Car in Drive, let off the brake to let the car roll slowly, then lightly apply the brakes, does the pedal "sink"? If yes, step harder on the pedal, brakes hold OK? MC needs replacement or repair (same labor, similar cost). Get a Volvo part.

Good luck with your diagnosis and repair.

Bob

:>)

thank you. in your test, if the pedal continues to sink, will that also indicate failed MC? you state that if you step harder and they work better that the MC is to blame. i am wondering if the same is true if they continue to be far too soft.

through all my troubles today, the light continues its erratic behavior of the past 8 months of successful braking. if there was a grounding issue, would this prevent the light from staying on, or will it cause a permanent "boy who cried wolf" light?

The test is two parts: Both the slow downward pedal movement under light pressure and the firmer pedal when pressing hard on it.

The slow pedal-to-the-floor happens because the piston seals are worn and fluid can slip past. With hard pressure the seals get pushed out onto the cylinder walls so they seal better.

Actually test #1 can be considered proof of a bad MC. The hard pressure part tells you that although the MC is failing, the car is somewhat driveable.

A few tips I've picked up on changing non-ABS 240 MC's.

It can be done without having to bleed the system. The idea is to have the two pressure lines disconnected for a very short time. That way any air that gets in will stay in the vertical lines, where it can float up into the reservoir and out.

Use a helper. Loosen up the mounting bolts to finger-tight. Loosen the two line fittings, but keep fluid from leaking. (Have a wipe-off rag at the ready, brake fluid eats paint.) Take off the mounting bolts. Take off the line fittings and pull out the MC. Hand old MC to helper and quickly put the new MC into place. Helper holds it there while you hook up the pressure lines. Tighten to finger-tight to be certain to not cross-thread the soft brass threads. As you can see, many variations are possible as to who does what.

Lastly - put in the mounting bolts and tighten, tighten the pressure fittings, and top up the reservoir to the full line. DOT-4, of course.

Take a slow test drive. Ideally the repair is done late in the day so the car can sit overnight and any air bubbles can float up and out before and serious driving is necessary.

Good Luck,

Bob

:>)

Would you agree that driving a car with useless brakes is a very poor idea, regardless of the reasons for driving that car?

yes. would you agree that never did i condone the fact that i executed a poor idea?

Ok,


What is the brake fluid level?

Are there any leaks?

The brake failure lamp is there for a REASON. Stop and check the system before ‘‘Driving to Maine’’.


Goatman

you either didn't read what i wrote and think that i drove my car to maine, or your criticism of me going somewhere while my poor ole' car sits at home alone is only because you think my life should start and stop with my car even when i planned the trip months advanced. either way, shut up about it, because it doesn't help, is insulting, and is utterly irrelevant. the only reason i even mentioned the trip was for anecdotal reasons, and it was important to mention that the car had been sitting for 4 days. this forum does not serve as a venue for you to criticize those who you do not think know how to maintain a car as well as you do-it is a venue to help people maintain their cars. there is an opinion forum on this site if you wish to express yours-car maintenance threads are no place to say such things and as you can see, detracts from the purpose of the thread (well, i guess i could've ignored you). if you are going to continue passing judgment i ask you respectfully to not reply to my threads anymore-and if not for that reason, then for the simple fact that i have not received one helpful reply from you since i began posting on this site.



there are no leaks that i could find, and the brake fluid level is where it should be, as it has since i got the car.
through this website i was able to discern that a brake failure light flickering could just be a grounding issue, and since the brakes worked flawlessly through 8 months of ownership, including a pad and rotor change in the first month, i felt safe in assuming that it was an electrical issue, as these cars are known for such things-especially one that is 28 years old with over 240K on its ticker. today i feel safe in assuming that my master cylinder crapped the bed. perhaps it was a many month long crapping of the bed, but it showed no signs of crapping before this week other than a light that would sometimes flicker, and sometimes wouldn't come on for an entire commute.

I agee with your assesment of some of the posters on this site, I think they forget these are older cars with lots of problems and sometimes you got to hillbilly fixes etc, and I think they feel better than thou since they have a basic understanding of a basic auto.

In regards to your issue check mc and fluid level ,if you have a helper have them pump brakes and check each wheel for leaks, I have had good luck with power bleeders,

Good luck dont let the 'elite 'keep you from asking questions.
I have had some wonderfull help from this site and I also have had some rather poor attitudes on some limited times.

I am texting eight now and a stop sign is approching


ooch missed it

Fix it before you crash...it will only get worse...could be MC could be you have almost no brake fluid left.
--
Patrick ('68 220, '92 Eurovan, '53 GMC PD4104)

i will not drive it before it gets fixed or before i get my other car on the road, whichever comes first. i was in a bind this morning, because it began shortly into my commute to work, and i kinda had to get home this afternoon.