28 replies to this topic

[AdventureSubaru]

Thought the pads were getting low because the brakes were getting less responsive. Back ones were about shot so i replaced them with a slight improvement. Fronts are still in good shape.

Got a rotor that's a little warped up front but it's been that way for a while. Shudders as you slow at higher speeds.

But good meat to the pads and rotors all around but the brakes feel weak. Am I looking for a new master cylinder?

[Durania]

If you pump the pedal with the car off, does the pedal eventually firm up?

[ocei77]

Check to make sure the calipers are closing. May be just sticking sliding pins.

O.

[Fairtax4me]

Were the pads worn evenly on each side? (outer vs inner pad, and left side of the car vs right side)
How old is the brake fluid?
What condition are the rubber brake hoses in? Any evidence of cracking, blistering, or swelling?

[porcupine73]

How are the front rotors and pads? Rusty at all or anything? The rears make only a small contribution; the bang for the buck is in replacing the front rotors, pads, and even calipers. If you suspect the booster you can to that three step test to make sure it is good.

I've been using the Advance Auto silver brake pads with good results. They don't last nearly as long as ceramics, but --- they will chop right through rotor rust pretty fast, and that is important to me. The ceramics they I don't know, they will not polish off rotor rust, at least not very quickly, and will have diminished breaking for a looonggg time if the rotors are rusty.

[AdventureSubaru]

Haven't been driving this car as much lately so I pretty much forgot I posted here.

Seems a bit worse and the brakes are weak unless you pump the pedal. Then they firm right up. Not losing fluid anywhere that i can tell. Reservoir is full.

Do a brake bleed anyway? I worry about those bleeder screws in a rusty part of the country.

[grossgary]

i saw that one time...it was as if it was such a small leak there was no visible loss but enough for the fluid pressure not to work right. after some serious work out it finally blew and leaked above the gas tank...so the prior small leaks just hadn't made it to the ground yet but were enough to blow off pressure.

not saying that's common or likely. something else is probably more likely.

[porcupine73]

Having to pump the pedal to build up pressure sounds most likely like a small leak or a bad booster.

Yes my 90's soobs both of them sprung brake line leaks above the gas tank. Not a terribly hard fix, basically spliced in under the rear seat and ran new line to both rear wheels.

[1 Lucky Texan]

it's been decades since I had a car with that symptom - needed master cylinder rebuild.

[AdventureSubaru]

Any good way to test the booster?

I'll look for any leakage above the tank and see if that's the issue.

[Fairtax4me]

Booster and master cylinder test:
Start engine. With engine at idle measure vacuum at booster if you have a gauge and adapters to do so, if not move to next step.
Press brake pedal down hard and release. Wait a few seconds, then stop engine.
With engine off press brake pedal hard several times. The pedal stopping point should move up with each press. Also a slight whoosh sound should be heard as the pedal moves down.
When brake pedal stops moving down press pedal hard and hold. The pedal should stay firm. (If it starts to sink the master cylinder is bad or there is a leak)
Still holding pedal down hard, start the engine. The pedal should immediately drop approx. 1-2 inches as vacuum builds in the booster. The distance the pedal drops can vary depending on the vehicle, but should go more than 1" but not more than 2-2.5". If the pedal does not drop right away when started, the booster may be leaking or the supply vacuum to the booster may be inadequate or the line or check valve is clogged.
Continue holding the pedal down hard, if the pedal sinks the master cylinder may be bad. Pump and hold the pedal several times then inspect under the car for any evidence of leaks.

[AdventureSubaru]

Press brake pedal down hard and release. Wait a few seconds, then stop engine.
With engine off press brake pedal hard several times. The pedal stopping point should move up with each press. Also a slight whoosh sound should be heard as the pedal moves down.
When brake pedal stops moving down press pedal hard and hold. The pedal should stay firm. (If it starts to sink the master cylinder is bad or there is a leak)

This part checked out okay. With the engine off, the pressure seems to build and stay there. All seems as it should.

Still holding pedal down hard, start the engine. The pedal should immediately drop approx. 1-2 inches as vacuum builds in the booster. The distance the pedal drops can vary depending on the vehicle, but should go more than 1" but not more than 2-2.5". If the pedal does not drop right away when started, the booster may be leaking or the supply vacuum to the booster may be inadequate or the line or check valve is clogged.
Continue holding the pedal down hard, if the pedal sinks the master cylinder may be bad. Pump and hold the pedal several times then inspect under the car for any evidence of leaks.

Here's where it's showing issues. Start the car, the pedal drops a few inches catches a bit of pressure but then slowly sinks almost all the way to the floor. You can pump pressure up again, but it sinks slowly.

Basically, it's acting like it has a fluid leak, but hasn't lost a drop of fluid.

Time for a new master cylinder?

[porcupine73]

I think so, I think that means the fluid is leaking past the 'cups' on the master cylinder piston. Sometimes this will occur if you were bleeding the brakes and pushed the pedal down much further than it normally goes or all the way to the floor. The piston bore can have rust in it since the cups don't normally go down that far, then they get cut up when pushed into that area.

[AdventureSubaru]

Just seems odd to me. Any master cylinder failure I've encountered before had some sort of leak attached to it.

But the reservoir is still full and pressure is escaping somewhere.

[AdventureSubaru]

Also - Assuming its the MC, I've started shopping for one. Is this something that should come from Subaru.

Can I get away with something like this?

http://www.ebay.com/...e2eee99&vxp=mtr

I saw the Exedy logo and have had good experience with their clutches but is Daikin the same company? and is an MC from them going to be decent quality? Not looking for top of the line (the thing has 300k plus) but something that won't fail on the road as my wife uses this car as a commuter during the week.

[Fairtax4me]

I don't know that Exedy makes brake master cylinders. And no the part in that listing will not work. That listing is for a CLUTCH master cylinder. Same principle different part, not interchangeable.

I have never had trouble with parts store rebuilt MCs but I can't say how long they'll last. I think I've bought maybe two ever and I didn't keep the cars long after. I've had good luck with used MCs though.

[AdventureSubaru]

HA! I didn't even catch that it was for the clutch. Good to know. Looks like I'll be placing an order. Can't think of it being anything but the MC so I'll put a new one in there and see if that solves it.

Bench bleed these things the same as most MCs?

[soobiefreak85]

Sounds silly, but pull the cap off and check the plastic soft sleeve on the inside the cap. If that is pushed out, push it in to its natural position. It should be flat. I have seen brakes get spongy or weak because of this.

-Wes

[AdventureSubaru]

http://www.ebay.com/...984.m1439.l2649

Got one of these on the way. Hopefully this is a quick and easy one. Anything unique to putting new MC in for subaru? Bench bleed, mount, bleed right rear, left rear, right front and left front and theoretically... drive away right?

[Fairtax4me]

You've already bled the lines? If you're good you can bench the MC and after you hook up the lines push the pistons in on the calipers, this pushes the air out of the top of the lines into the MC. Do it right and all the air will be pushed up and out into the reservoir.

[AdventureSubaru]

New MC is here! Gonna get on this today as the weather is actually warm out! Fingers crossed that this goes smoothly.

[AdventureSubaru]

You've already bled the lines? If you're good you can bench the MC and after you hook up the lines push the pistons in on the calipers, this pushes the air out of the top of the lines into the MC. Do it right and all the air will be pushed up and out into the reservoir.

What's the advantage? Just less mess?

How difficult will this be to learn? I've bled lines the usual way but never tried this way? Just remove the caliper and squeeze the pistons in the usual bleed order?

[AdventureSubaru]

Getting fairly stuck here. If I apply much more force, I think I'm going to snap the rear bleeder screw. Options?

[1 Lucky Texan]

Getting fairly stuck here. If I apply much more force, I think I'm going to snap the rear bleeder screw. Options?

try tightening, then loosening. sometimes helps

other than that - I dunno

[AdventureSubaru]

Yeah. Did that with some WD-40. Got a few squirts out of it and snapped the bleeder screw. Luckily this was as I was tightening it down and we had no bubbles. So 1 down. 3 to go. I have bled them in the past at the point that the brake line meets the caliper with good results. So I may have to resort to that if I snap a bleeder.