1990 240 DL. Here is the problem. If the car is shut off, the brake pedal gets hard after about 4-5 pumps as it should. Start the car, and the pedal goes pretty much to the floor, and no amount of pumping it will firm it up. No brake warning light at all. Backstory... brakes worked iffy at best as the car had been sitting for two years or so. That said, all four rotors and calipers were replaced, new pads, new brake hoses and new Master Cylinder (bench bled before installed). Entire system was power bled starting with the wheel farthest from the master. Fluid level is fine and does not drop, it is just a very soft pedal with the engine running, or if it sits over night. Oh yeah, the car is non-ABS and the vacuum check valve at the booster was replaced as well. Aside from re-bleeding it (again), any ideas?

Help!!

 

Check your rear brake calipers. Is the bleeder on the bottom or the top. If the bleeder is on the bottom you need to swap the calipers left/right.

 

Nope, checked all 4 calipers, and the bleeder screws are on top where they are supposed to be. I've jacked the car up with the rear higher than the front, and I guess I will try pressure bleeding it again tomorrow after work.

 

The only thing left to check is the integrity of the vacuum booster.
Are you able to swap it for a known good one?

 

No, do not have a known good one. The one on the car is original, so it may very well be bad. Gonna mess with it this weekend.

 

you could try the brake pedal test;
Turn off engine, press brake until all vacuum has been bled off, press and hold pedal while starting car. Pedal should depress slightly as vacuum builds.
You could also use a vacuum gauge to check for bleed off (diaphragm leakage) and also to test for adequate vacuum build from the manifold

 

Sounds like an internal leak in the master cylinder.

 

Well, I pressure bled it twice with the *** end about 6 inches higher than the front and it seems to have a lot firmer pedal. Pedal is firm with the vacuum bled off and sinks slightly when the car is started. So....it seems that it took 4 times bleeding it, twice with the nose down to get all the air out.......sheesh!

 

Ok, looks like I spoke too soon. To recap, here is what is going on, and what has been changed.

The issue: Brake pedal gets firm with 4 or 5 pumps and the engine off (so far so good right) Start the car and the brake pedal sinks, not a little bit, but a lot.....like 1 or 2 inches off the floorboard lot. Try to drive the car and the brakes work well, you just damn near have to push the pedal to the floor to get them to grab. Shut the car off, pump the pedal 4 or 5 times, and the pedal is high and firm. Start it and it sinks almost to the floor. An interesting note, if you pump the brake pedal with the car running, the engine stumbles a bit until you stop pumping the pedal. and if the car sits for a couple days, the pedal is soft unless you pump it before starting.

What has been changed. All 4 rotors, all 4 Calipers (yes the bleed screw is on top on all 4) All brake pads and hardware, all rubber brake hoses, new master cylinder (bench bled twice), new vacuum valve on the brake booster, new brake fluid and pressure bled 4 times. No fluid leaks. Basically everything has been changed except the booster, and the hard lines. What the hell is causing the issue? The brake booster, or?

HELP please!

Thank you

 

did you vacuum test the booster? That's all that's left

 

No, haven't tested it yet, but like you said, that's all that's left, unless I got a bad Master cylinder. Guess the next step is seeing if the booster holds vacuum or not

 

It's not your booster -

Pump the pedal after you turn the car off so the pedal is hard. The next morning is the brake pedal just as hard as it was the night before? (don't start the car) If so - there's no air in the system, the master cylinder is doing it's job (it's new right?) and the caliper pistons all are moving freely.

" if you pump the brake pedal with the car running, the engine stumbles a bit " - that is normal because when you pump the pedal the booster is sucking in air making the engine lean (the air the booster is using does not go through the air mass meter)

Have you considered (since the car seems to stop normally) that this is just the way your Volvo feels?

 

[QUOTE=hoonk;533140]It's not your booster -

Pump the pedal after you turn the car off so the pedal is hard. The next morning is the brake pedal just as hard as it was the night before? (don't start the car) If so - there's no air in the system, the master cylinder is doing it's job (it's new right?) and the caliper pistons all are moving freely.

" if you pump the brake pedal with the car running, the engine stumbles a bit " - that is normal because when you pump the pedal the booster is sucking in air making the engine lean (the air the booster is using does not go through the air mass meter)

Have you considered (since the car seems to stop normally) that this is just the way your Volvo feels?[/QUOTE

That is a possibility I didn't consider. I'm going to do the hard brake pedal overnight test again tonight just to be sure. One thing I remembered I did not check when I replaced the master cylinder was the booster pushrod to master cylinder plunger length. Thanks for a way forward Hoonk!

 

Ok, after sitting overnight once the pedal is firmed up, the pedal is not as firm, but still pretty firm ....I'd say about 80% of what it was 12 hours prior. Start the car and it still sinks to about 2 inches off the floor when you press the pedal. Gonna try checking the booster rod to master cylinder length next. Outside of that.....?

 

P - did you say you also replaced the lines to the booster? I recall on my S40 that we had a brake vacuum line replaced due to a failed check valve. Not sure if there's a similar design in play here. In the Gen1 S40s, there's a vacuum assist pump that kicks on when the car first starts to help build the vacuum in the booster but the symptom there was just a hard pedal until the engine ran long enough to build vacuum, never a change in pedal position. I'd probably be thinking along the lines of air in the system/ failing seal somewhere (master? proportioning valve? ABS valve body? etc? There's also the possibility that one of the parts you've installed was bad out of the box...

 

I only replaced the vacuum check valve going to the booster. The vacuum line looked fine. I'm going to mess with it a bit this weekend, and check the lines as well as the pushrod to master cylinder length since it is a new master cylinder. I'll figure it out one of these days (&#128513. I'll post when I do......trust me

 

Didn't get to look at the car today 😞, but did some thinking. Could it be possible a failing vacuum pump is causing the problem? If I pull off the vacuum hose from the booster and hook up a vacuum gauge, what reading should I look for with the car running? I'm assuming the vacuum pump is run off the camshaft.

 

There is no vacuum pump. Vacuum is created normally by the engine on the intake stroke.

 

Weird, because I found a couple for sale online, and my Haynes manual even mentions it. Must be for a diesel model that used to be available. Anyway, you are correct, I traced the line from the booster back to the intake manifold.

That said, here is a synopsis. I checked all the vacuum lines and they are new and tight. Booster check valve works properly. Pump the pedal 3-4 times before starting and the pedal is rock hard. Start the car and the pedal drops.....quite a bit and no amount of pumping gets it to engage higher. Took it for a test drive and the brakes work, but the pedal is really low before they engage, and they do not grab hard unless you really press down hard.

So, in a nutshell, they seem to be functioning properly, it is just the pedal is soft and engages really low and the brakes do not grab very hard unless you pretty much stand on them. No leaks were found and they have been pressure bled 4 times. Soooo. how can I get the pedal to engage the brakes sooner and firmer?? .

 

BY THE POWER OF ALL THAT IS GOOD AND HOLY....IT'S FIXED!! Long story short, the brake booster pushrod adjustment was WAAAY out spec. After several adjustments, the pedal grabs where it should and the brakes grab hard and smooth with no dragging. Don't know what the PO did at one time, but it now works like it should. Thanks to everyone who stuck with me through this ordeal. I've been a shadetree mechanic for more years than I care to think about and I have never had a brake system kick my butt like this one did, and it turned out to be the booster rod was severely out of adjustment......go figure!