My faithful 245 has just developed an interesting problem. The brake failure light has come on and the brake pedal has gone soft. This has been accompanied by an extremely rough idle. If I pump the brake pedal quickly the pedal firms up a (little) bit AND the idle smooths out and rises. As soon as I stop pumping the pedal the idle drops and becomes rough again. I'm thinking that the brake booster has failed but does anyone else have any thoughts? (BTW, my car is carbureted so the brake booster is driven by manifold vacuum).

Last summer my car had the exact same symptoms. Put in a new master cylinder and the symptoms went away.

The original Volvo check valve on the booster is poorly designed. One day, I ran over a bump and the cap on the front of the check valve came off. It took me a longer distance to stop my car and luckily I did not hit any car. It was very dangerous.

If you still have the original check valve, you’d better to get it replaced for the safety reason.

Well, my 245 seems to possess the ability to self heal. The brake failure light has gone out, the brake pedal feels normal, and the rough idle has somewhat smoothed out. When the weather warms up (say, mid July) I'll have a closer look at the master cylinder. In the meantime, thanks for everybody's input.

If you pull out the check valve on the booster, also pull out the grommet that holds the check valve and use a small flashlight to look inside the booster. If you see what appears to be moisture, one of the seals in the master cylinder may be starting to fail, allowing brake fluid to leak into the booster.

If the master cylinder is failing you will notice lower amount of brake fluid in the reservoir. Check for damp oily ares of brake fluid leakage on the bottom of the booster. It may not be immediately apparent there is leakage.

I'm currently in the process of replacing the booster and master cylinder because I did a brake job wrong and bleed the breaks like an older american car (pedal pump method), thus damaging the seal in the master cylinder. I found loads of brake fluid in the booster. thankfully I have learned the correct way to bleed now. Also of note, the problems with braking stiffness and loss of fluid appeared more than a year later.

It was tough to get the break booster out of the PNP car I found, the instrument cluster was already gone and I removed several of the heating ducts to locate all the nuts for removal. Once I got home and had more tools at my disposal, it was not too bad. If you have a bunch of 3/8 extensions (1' to 2' of extensions), a knuckle joint for your socket and 13mm deep socket you don't need to pull out any other parts inside the vehicle to remove the 4 locknuts holding the booster to the firewall. However, removing the instrument cluster does make things easier to locate.
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'82 245 B21F-MPG-LH 1.0, '83 244 B21FT-K-Jet, '86 244 B23F-LH 2.0

"Alfsen" had a brake booster failure due to a cracked check valve (its plastic, what a great material to make car parts from!).

I found a suitable and cheap check valve at the local O'Reilly Auto Parts store in the Dorman "Help!"(TM) display.

Prior to finding the part, I made a temporary repair by sealing the cracked valve with tape.

Regards,

Tatra Mike
Seattle, WA

1985 244 "Alfsen" (wife's car - the good one)
1984 245 "Buster" (the kid's car, now sold)
1985 245 "Cosmo" (parts car, sold off for move to WA)
1985 245 "Daisy" (back seat down, full of tools, the work truck)
1985 245 "Earl (CA vehicle 'retirement' program)

Thanks Mike, I found the exact Dorman check valve you describe at the Canadian mecca of auto parts ... Partsource.

Your problem is a failed master cylinder. That's what turns on the brake failure light, a difference in the pressure between the two systems.
The check valve has nothing to do with it. It only prevents air at a higher pressure from entering the booster unit.
The rough idle is a rich mixture in the carb. When you pump the pedal you lean out the mixture in the intake manifold because you are adding air to the manifold through the apply valve in the booster.
If the booster failed you'd know it when driving. The pedal would be very hard to push in comparison to the amount of stopping force. That's the downside to four wheel disc brakes. You'd pull the steering wheel off and break the seat back.

Well that's my take on it anyhow.
And all 200's use manifold pressure to run the booster, fuel injected included.

Thank you for your response. Just to clarify, would the failure of the master cylinder cause the rough idle? (the idle was fine before the brake failure light came on)

My Haynes manual (yeah I know, the book of lies) indicates that "some" fuel injected 200 series cars utilize a vacuum pump to provide vacuum to the brake booster. There is even a section that describes it's removal, overhaul, and installation.

The vacuum pump was an assist to the manifold pressure. On some emission engines the vacuum produced was lower than needed it was thought. Haynes is right on that one. I removed a lot of those pumps back in the day and they seem to have made no difference. Volvo did weird things like that.
I can't figure how the bad master could affect idle, unless something really strange like the piston isn't returning and the booster is in the apply position all the time. If the pedal comes back to its normal height then its a coincidence I think.

Before trying to find a new vacuum booster (and the headaches removing it from a pnp and swapping your car's), consider the small, plastic check valve in the line from your manifold to the booster (I don't know 1977 cars, but it may be the plug that leads the vacuum hose into the booster as it is in later cars). Or the hose itself.

It really sounds like your brake problem is related to the intake. This check valve, when working properly, lets the manifold draw air out of the booster (generating the vacuum) but not back in -- a one-way valve. Replacing that (I hope you can buy a new one at your Volvo dealer because, being plastic, any 1977 version is way past its "sell by" date unless it's been in a box all these decades.

The only thing that bothers me is that you said that the brake pedal gets soft -- actually, without the help of the booster, the pedal should actually get very hard (although it should drop farther) -- maybe that's what you meant?

Good luck.

Thanks Ken, I will take a look at the check valve and its related hose. The soft pedal AND the rough idle has me thinking I may be dealing with a couple of separate issues at once. Like you point out, a failed booster SHOULD result in a stiff pedal. I'll get "Ghosty" up on some jack stands this weekend and see what is going on.

This probably doesn't apply to you, but I had a bad caliper one time ('90 245) that in turn caused the brakes to go instantly mussy and completely unusable - with the obligatory brake light suddenly going on as well. All of this out of the complete. And on top of a half mile high steep hill to boot. I was able to get the vehicle home via side streets and Drive-2. After a 20 mile ride home, the brakes suddenly started to behave normally. Took it to my mechanic the next day and he traced the situation to a bad caliper that had been installed a month or two earlier. If I understood correctly, there is a mini-piston inside caliper, and that piston was defective.