Lost Stopping Power

[particlewave]

A couple months ago, I took the car out for a drive and had significantly reduced stopping power (pads are relatively new). I flushed the brakes and that helped a little, but not much.

The booster appears to be ok and it is getting 18 in/hg of vacuum (the pedal is not hard and it passed the “hold pedal and start car” test).

My only thought is a stuck caliper. Earlier this summer, the car did get put away wet and the rotors rusted a bit and froze to the pads...

Any other thoughts would be greatly appreciated!

[rfuerst911sc]

By chance do you have an IR temp gun ? Even a cheap one from Harbor Freight would work . If possible find an open stretch of road that you can drive and coast on . After driving for a bit coast to a stop without touching the brakes . Set the parking brake and hit all four rotors with the IR gun . If you have a hanging caliper you should easily see a temp difference . When was the last brake fluid flush ? Any chance water in the system ? Brake fluid is hydro scopic so it's possible .

[rfuerst911sc]

Ooops I didn't see that you flushed the brakes recently sorry about that .

[JimmyBad]

Any fluid loss from the reservoir? Brake lines in good condition?

[blue62]

Originally Posted by particlewave

A couple months ago, I took the car out for a drive and had significantly reduced stopping power (pads are relatively new). I flushed the brakes and that helped a little, but not much.

The booster appears to be ok and it is getting 18” of vacuum (the pedal is not hard and it passed the “hold pedal and start car” test).

My only thought is a stuck caliper. Earlier this summer, the car did get put away wet and the rotors rusted a bit and froze to the pads...

Any other thoughts would be greatly appreciated!

your rubber? lines between the hard line and the calipers can have issues.
They can swell inside and cause problems with the brakes releasing acting like a stuck caliper.
Or they can soften causing them to swell when you apply the brakes thus less clamping force at the caliper.
From you description:
You may possibly have the second problem.

[particlewave]

Thanks guys.
The lines all look good (checked them at flush) and no fluid loss.

I have an IR temp gun and planned to check the rotors, but I’ve never heard of a caliper getting stuck open. The hydraulic pressure seems like it would be too great.

Could it be something to do with the master cylinder or pressure valve?
I should also add that this cropped up over night. It was not gradual.

I really have to press very hard to slow down from 35mph. It feels like someone greased my rotors.

[piper6909]

Originally Posted by particlewave

Thanks guys.
I’ve never heard of a caliper getting stuck open. The hydraulic pressure seems like it would be too great.

Yes, they can get stuck open. Depends how long you had it sitting. Keep in mind that the fluid pressure get distributed to all the other pistons, so you really won't build in so much pressure to get the one piston unstuck. Unless you're really standing on it and locking up the other wheels.

Since you've already checked the booster and your pedal isn't hard, your next suspect is one of the calipers.

[blue62]

Originally Posted by particlewave

Thanks guys.
The lines all look good (checked them at flush) and no fluid loss.

I have an IR temp gun and planned to check the rotors, but I’ve never heard of a caliper getting stuck open. The hydraulic pressure seems like it would be too great.

Could it be something to do with the master cylinder or pressure valve?
I should also add that this cropped up over night. It was not gradual.

I really have to press very hard to slow down from 35mph. It feels like someone greased my rotors.

the rubber seals that are on the plunger in the master cylinder could have an issue and no longer making a proper seal with the master cylinder barrel thus allowing fluid to bypass or the barrel could be pitted causing the same result.

If this was the case your pedal would eventually go to the floor under pressure if you held it long enough.
you could try to test that theory by starting the car apply the brakes hard and hold them for a good period to see if your pedal goes towards the floor.

The only other things I can think of without looking at the car are.
Some sort of obstruction in the master cylinder. (not very likely) but possible.
If they are floating calipers a caliper could be moving farther the its design feature.
But you have done a visual right? so any problem there should be evident.

Or back to - one or more of the soft lines swelling under brake pressure.
This is not something you can usually see on visual inspection.
Usually take a hands on feel test as someone applies the brakes while you feel each hose in turn for swelling. Also it is not very common. But does happen.

[Racer Boy]

Could something have gotten on the rotors and pads? If it were me, I'd pull the pads, sand the surface of them, and use brake cleaner to rinse them off. Then I'd do the same thing to the rotors, using a scotch pad with brake cleaner.

[JayG]

This may sound silly, but try a different set of pads.
I had a similar problem and did 3 full flushes, changed the master cylinder and still the brakes sucked.

I put in a old set of factory p[ads and BAZING!!! Brakes were great.

I had cooked the old pads (which were fairly new)

A shade tree mechanic way of cleaning the rotors is spray them with water and let them rust a bit, then do some driving and use the brakes. You will have clean rotors

[mikesz]

I had issues similar I have a 99 and got the water issue in the brake booster. I replaced it and got the retro kit to eliminate problem. Was a real fun job. If you take off the vacuum line and stick your finger in you can feel if there is water or a rag and screw driver to absorb.

[particlewave]

I came across your posts when researching, Mike.
I stuck some clear vinyl tubing attached to a small pump down in there and nothing came out.
Also stuck my endoscope in there...looks immaculate.

I’ve yet to find a description of a problem that matches what I’m experiencing.

[maytag]

You're one of the smarter guys on this board, so I scratch my head trying to imagine something you wouldn't have already thought of. But I'll suggest some things I'm thinking, in the hopes it'll jog a thought.

Does your car have PSM?

RacerBoy and JayG seem to be thinking along the sames lines as I am: "Glazed pads". What pads are you using, and did you heat them (coming down a conyon, or?) prior to the symptoms appearing. I've been known to "deglaze", when my budget required it. Use a palm sander on the pads and even on the rotors. You're not trying to change the shape, just remove the top glazing that's there. Organic pads are notorious for this. (I've done the same with clutches, fwiw)

Do we understand correctly that this more or less happened "overnight"? and your fluid flush was done to mitigate, not done before, right? I ask because a mis-mix of brake fluid can cause obstructions in the master-cylinder or the lines or the calipers. (DOT 5 doesn't mix with other fluids, for instance,and will create nasty gel in the lines) You hadn't topped-off the fluid recently, or anything, right?

From there, I think I'd be pulling all 4 calipers, inspecting visually, probably cleaning thoroughly, maybe a seal kit if there's one available (I assume there is, they're Brembo) and then this is where scope-creep would take over: I'd be doing pads, rotors, steel-braided lines, etc. Then a complete flush. That oughtta do it, haha. (Sounds like a fun winter project?)

[maytag]

hmmm.... another idea. Spray a light mist of red spray paint on your rotors, then go out and ease into the brakes gently, even just in the driveway, and then get out and look at what paint remains vs what's gone. You'll get an idea about pad-to-rotor contact.

[particlewave]

Originally Posted by maytag

hmmm.... another idea. Spray a light mist of red spray paint on your rotors, then go out and ease into the brakes gently, even just in the driveway, and then get out and look at what paint remains vs what's gone. You'll get an idea about pad-to-rotor contact.

I like this. Between it and the temp gun, I should be able to determine if one wheel is grabbing more or less than the others.

No PSM and car is a ‘99.
“Overnight” isn’t exactly right as I don’t drive it daily, but it was fine one day and had this problem the next time I drove it (noticed on first brake press when backing out).
I suppose it could be glazing, but I haven’t driven it hard in a while. The way it feels and my gut are both telling me it’s something mechanical, though...

The flush was done after the issue cropped up. It didn’t seem like a fluid issue, but it needed to be done anyway (I may have imagined the slight improvement after fluid change). The reservoir had been opened around the time the problem began to check the fluid moisture level, but nothing added.

I haven’t had much time to address it because of the move. Now we’re here, the weather has been great, and I can’t drive.
I hope to have time to hit it hard soon and get it solved.

[JayG]

Changing the pads is the easiest and fastest thing to check
You can even try with an old set of pads ( I keep a set on hand, just in case)

[Gilles]

Originally Posted by blue62

your rubber? lines between the hard line and the calipers can have issues.
They can swell inside and cause problems with the brakes releasing acting like a stuck caliper.
Or they can soften causing them to swell when you apply the brakes thus less clamping force at the caliper.
From you description:
You may possibly have the second problem.

I had this issue before with the rear brakes on the Alfa transaxle, they were 'balloning' (blistering..?) under pressure, but otherwise look normal without pressure.

How old are your rubber brake hoses? You may want to replace them, as they do age and are not too expensive..

PS: just remember that I also had the same failure but with an old slave cylinder rubber hose (also on the Alfa..)

[Topless]

A 20 yr old car so jammed caliper, failed master cyl, or internally failed brake lines are all possible. I am not a total fanboy of aftermarket SS braided brake lines but would consider replacing with OEM as just good maintenance at this point. Was there any noticeable discoloration when you flushed the brake fluid? This will often reveal contamination or failed seals.

Normally when pads get replaced the caliper pistons will visually move during the process. I want to see them move freely to make sure nothing is binding.

Process of elimination:
1. Crappy pads
2. Aged out brake lines
3. Caliper piston binding
4. Failed master cyl.

What else?

[particlewave]

I took it for a test drive today. Results:

1) After a 10 minute drive with some hard braking, front drivers side rotor was at 210f, front passenger 145f (oddly with a 1cm band in the middle of the rotor reading 190f), rears 90f (50f outside).
2) Braking power is still there, I just have to press a lot harder (pedal not hard or soft, feels normal).
3) The front end wandered a bit under hard braking, but only a couple times (didn’t seem significant).
4) Brakes lines are not swelling under pressure, but I’m going to replace them anyway.

Maybe low vacuum?
I think I should order a good manometer as I don’t fully trust my current one.

[maytag]

You've got something on ther pad on the passenger front.

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