Lousy brake pedal feel

chrisn81 · Post by **chrisn81** » 22 Aug 2016, 19:02

So the pedal in my 855 has felt like crap for a little while now and it's finally time to do something about it. Pedal gets rock hard when it's off and holds pressure fine. When it's running it's spongy and takes more pressure than it should to stop. If I pump them it firms up on the second pump and the pedal feels great (until I let go, then it's back to sponge-cake). I put a couple of junkyard check valves on the booster just to rule that out and it's exactly the same on all of them. Before I go buy a booster, am I missing anything else?

Post by **tryingbe** » 22 Aug 2016, 19:29

Bleed the brakes lately?

chrisn81 · Post by **chrisn81** » 22 Aug 2016, 20:02

That's on the agenda too, but since the pedal pressure is fine when pumping I'm not expecting night-and-day results.

Post by **abscate** » 22 Aug 2016, 23:33

Brakes that pump up are a classic symptom of air in the lines

m96ag · Post by **m96ag** » 23 Aug 2016, 10:50

Do you use ceramic or OEM pads?

Post by **scot850** » 23 Aug 2016, 11:52

Also check the vacuum check valve in the booster. Usually it is fitted at the end of the vacuum line where it goes into the booster. It is a plastic part and fails with age and you get little or no help. Having said that, normally that give a hard peddle.

Also check the master cylinder is not leaking into the booster. The seal fails and it leaks are hidden. I smelled it before I figured out what it was.

Neil.

chrisn81 · Post by **chrisn81** » 23 Aug 2016, 16:57

scot850 wrote:Also check the vacuum check valve in the booster. Usually it is fitted at the end of the vacuum line where it goes into the booster. It is a plastic part and fails with age and you get little or no help. Having said that, normally that give a hard peddle.

Also check the master cylinder is not leaking into the booster. The seal fails and it leaks are hidden. I smelled it before I figured out what it was.

Neil.

Yeah, I already ruled out the check valve (as I said at the top, last time I was at the junkyard, I pulled a couple off other cars - same symptom with all of them). As for the master, the fluid level hasn't changed at all since I bought the car, and it still holds pressure when the car is off so I don't suspect a fluid leak anywhere.

Consensus seems to be that I should see what a full bleed/flush does before I do anything else. Sounds like a plan. Thanks, all.

94 850 wagon · Post by **94 850 wagon** » 01 Apr 2017, 18:25

I've recently had similar braking , 850 N/A wagon that's been sitting for about a year at my pops. I found a busted fuse that was ringing the door open chime ALWAYS. As I was checking each fuse one of them didn't light up, it wasn't broken, but not green lighting, so after that I decided to changed every single fuse. That second fuse turned out to be the ABS pump motor...

I had also pulled the ground strip in between the left headlight and battery and cleaned off all kinds of rat poop and leaves and such. Later on, the brakes seemed better than before , yet not one hundred percent. I'm using the mityvac and following the Volvo manual, started on the back left and after about an hour or more, I had only about a half inch of fluid in the pump.... I ended up using the wooden closet dowel that used to hold the hatch to pump the brakes with the motor running, and the hand vac pumped and holding pressure. I reached back to crack the valve while holding the brake pedal as hard as possible and it worked! Fluid came rushing into the pump tank and I closed the valve.

I was so over it I put the dust cap and wheel back on then decided to take a break, now I'm writing this. Well, it seems like it could be a few things, so I'm gonna start with the simple, cheap inspections and hope I can figure this thing done!

Post by **hausmeister** » 04 Apr 2017, 04:52

Interesting, I also have a similar issue. On my s70 the breaks are very good. on my 850 they brake fine, but feel extremely spongy and I lose booster pressure as soon as I turn the engine off. Check valve is ok, already replaced. Also replaced the fluid + bled each wheel...
I thought it must be the brake booster... but I am reluctant to change it.

Post by **oragex** » 04 Apr 2017, 05:22

The braking system on P2 with ABS seems to keep air inside the ABS valves unit sometimes. Not easy to get rid of this trapped air, other than with a bleeding pump connected at the master reservoir cover.