Well, my pedal felt a bit mushy when I got home I saw that the back half of my reservoir was empty. I filled it up and pumped the brakes a few times, then checked all around the car for leaks. The leak was between the reservoir and the cylinder, the reservoir felt loose and the rubber seal looked bad.

It is possible to just replace the seals and keep the reservoir, or should I just replace the whole cylinder? I don't plan on keeping this car much longer, so I really want to limit the money I spend on it. Thanks in advance.

Yes, you can buy new seals from your Volvo dealer (use OEM, don't be cheap with such cheap parts as these seals) -- if these two "doughnuts" cost you more than $5, I'd be amazed (I can't remember the price I paid).

The big trick is getting them installed, however. It's easy to remove the reservoir (just bend it over -- after you've emptied it as much as you can, and have lots of rags to absorb the fluid you couldn't suck out -- and it will pop out).

But after you put the seals in place on the master cylinder, putting on the reservoir properly is tough! If you don't push it on far enough for the nipples to "snap" into place in the new seals, they will continue to leak.

I made a template (of marine "wood", really a synthetic, but you can use anything else) of the reservoir with a cutout for the opening, and then placed that over the reservoir -- it would distribute the clamping force over the whole reservoir so it wouldn't be crushed. Then I used a big C-clamp to squeeze the reservior onto the cylinder and into the seals, having it press on the template instead of directly on the plastic reservoir. A little rocking motion, and they inserted all the way.

Good luck.

Damn,
Put the new seals in($20 by the way, ugh) and everything seemed fine. Went for a test ride, no leaks at the seals, but the pedal went way down and the brake failure light came on. The pedal seems good now, but the light is still on. Any thoughts, did the cylinder just go? No obvious leaks anywhere.

It could also be purely coincidence, and the switch (in the "octopus") has just gone bad at this same inconvenient time.

Again in my '84, a little less than a year ago, the light started to glow, and then light up fully, staying lit. Yes, this pattern is a little different than the sudden onset of your light, but I'll share anyway.

Well, I knew I had no leaks or M/C problems, so I assumed it was a bad switch. The octopus's switch is replaceable ....

Braking Warning Switch (in block) rebuild kit: 272702-2 ($36.23)

...so I bought the kit. When I removed the old switch, it was clearly bad. Put the new switch in, and everything works like it should now.

So if you think you need a new switch, it's easy.

Sorry to hear that the saga continues. Here are my thoughts....

I reread your original post and you said it felt mushy (to be expected from an empty circuit, but) and as a result, you probably had occasion to push the pedal (and the M/C's piston inward) farther than usual. And that's probably the reason for the current problem.

As you'll recall from countless (literally) posts on this forum when someone does their brakes fluid flush for the first time using the pedal method, when they've pushed the pedal down unusually far, it moves the piston into "virgin" territory of the cylinder, where crud and rust has accumulated -- this invariably destroys the integrity of the piston's seals. Now you have a M/C with an internal leak (the fluid just circulates from the pressure side of the seals back to the unpressurized side), with the moving fluid allowing the pedal to sink. Early signs of this are sometimes intermittant -- don't trust that "...the pedal seems good now...." Be sure.

As for the other part, the warning light, that could have been building since you lost fluid in one circuit. That "octopus" under the fender compares pressures in the two circuits -- an inequality pushes its piston to one side where it closes a circuit to light the dash light.
And if the M/C is still leaking internally, it could create the pressure inequality that would trigger the octopus's switch.
It usually "latches" when it's triggered (a feature of the switch), so the light will stay on subsequently.
When you're sure there are no leaks (including the M/C), or air bubbles in the lines (have you done a thorough flushing?), you could try to give the pedal a hard, fast jab! Sometimes that bounces the piston back in place.
Otherwise, you may have to crawl underneath and screw out the switch (at the center of the octopus) to let the piston self-center itself; then reinstall it.

I made another post, I suppose I should have left it here. I took out the sensor, cleaned it up a bit, and replaced it which turned the light off and apparently reset the piston.

And regarding the other post, the reservoir only leaked on one side, being the side without the fill hole. I took it out for a drive and it seems everything is working okay. Thanks for the assistance.

The latching and the screwing out of the switch pin is a myth left over from the 140 cars, that indeed worked that way. The 240 warning sensor is self resetting by springs in either end, but crud and rust will make it sluggish after 20 years. If you are able to center it by removing the contact pin, it is not by design but sheer coincidence. The round end of that pin offers nil resistance to the travel of the differential piston.

When one side of the reservoir emptied, it is most assuredly because of a leak at a caliper, and now air is in one half of the system, so the calipers must be closely examined for signs of a leak (wheels off) and then the system must be bled of remaining air.

OK, I assume you filled the resevoir before you went for your first spin, although you did not say so.

If the pedal is OK now (firm and not too much travel), you need only to get the light turned off.

The light is on because the shuttle valve in the brake junction block has been moved by differential pressure from its central position and cannot get back to center, even after the differential pressure has been relieved.

The junction block is the 7-ported thing, mounted on the driver's-side chassis rail below the master cylinder, to which all your brake lines are attached.

Here's a link to a thread that includes a picture of the shuttle valve parts. Take a look before following the instructions below:

http://www.brickboard.com/RWD/index.htm?id=875432

You probably can get the light to go out by:

1. Unscrewing and removing the sensor from the junction block. (The sensor is the thing with the wire attached--remove the wire first). Removing it will free up the shuttle valve.

2. Pressing the brake pedal with not a lot of force. Tthat should center the shuttle valve.

3. Screwing the sensor back in, and reaattaching the wire.

Good luck.
--
jds

Yes, you can replace the rubber seals between the reservoir and the master cylinder. I do not see them listed on the FCP Groton site but I am sure that is where I got several sets in the last few years. You might need to call them.

I have found the easiest way to remove the reservoir is to simply push it to one side while adding a little lift to it. Be sure to remove as much brake fluid as you can before doing that and put a lot of rags down under the master cylinder as you do not want brake fluid on painted surfaces.

Pull the seals loose from the master cylinder and lube the new ones with brake fluid before inserting them. Then simply reinstall the reservoir.

Since you have not introduced any air into the system you simply need to add fluid to the correct level.

I guess there is always the possibility of having an old reservoir break when removing it but I have not had that happen to me.

Randy

Sorry about the brake problem.
I also have '86 245 and it too was leaking from the master cylinder reservoir.
After replacing the whole master cylinder I was still having brake problems. It turned out to be the brake failure detection valve which is under the driver side wheel arch on the 86. This has 6 brake lines connected to it and it is common for the brake failure sensor to leak. This would explain your brake failure warning light coming on.
The other possibility, which is a bigger problem, is that sometimes master cylinders leak into the servo-assist brake booster. Left unchecked this will damage the brake booster which is an expensive item.

Good news,
I had added a tiny bit of fluid over the last year or so, it must have just been a slow leak that got worse over time. Thanks a lot.