Hey!

 

I have a 2007 Octavia with a strange brake issue. The rear left brake disc is overheating due to a sticking caliper, and changing the caliper has not solved the problem. Handbrake wire, pads or sliders don't seem to be the issue. When we open the pressure nipple, only some drops of fluid drip out, no "fountain" of brake fluid. When the caliper has a grip on the disc, it can be released by adding some outwards pressure to the top edge of the outer brake pad. One thing that is strange, is that adding outwards pressure to the bottom edge of the brake pad makes it stick a bit more. The disc can be pulled around manually, but it sticks too much, and after driving, the temperature is far over 100 degrees celsius. There's still some snow here in Norway, and applying some to the disc made it boil with an audible "frying noise" (sorry my limited vocabulary).

 

We were recommended to try grinding down the sides of the pads, so they could move more freely against the caliper, but this didn't help.

 

I'd like to highlight that we've changed the caliper, and handbrake wire is not the issue, as I've seen this has solved the issue for some.

 

I'd be thankful for all suggestions! I'd like to save myself the 1200 kroner, around £100, for a diagnosis if it can be avoided. And some have said that the ABS-lamp would be on if this was an ABS issue.

Edited 28 March, 20197 yr by stjerneblaa

Brake fluid is incompressible (unless contaminated) and you would not expect to see a "fountain of fluid" the tiniest amount of one drip is enough to release the residual pressure, that is why pressure vessels are tested hydraulicly and not with pressurised air.

 

If the dragging brake releases when you open the bleed nipple you have found the problem but not the cause, I would look to the ABS system and/or the master cylinder, I remain sceptical about all the anecdotal quotes of flexible hoses creating an internal pressure valve, theoretically possible but I know what I have always found in the past to be causing residual pressure and it was never the hoses or lines.

 

One exception was a very heavy hydraulic clutch on a Mini, it was caused by internal corrosion of the metal pipe, the clutch was only heavy when operated at normal speed, if you very slowly pushed it down it was as light as it should be.

@stjerneblaa - As @J.R. has suggested but not said, I'd suspect the ABS valve on that corner is sticking. I have absolutely no idea how to prove that though!

2 hours ago, J.R. said:

Brake fluid is incompressible (unless contaminated) and you would not expect to see a "fountain of fluid" the tiniest amount of one drip is enough to release the residual pressure, that is why pressure vessels are tested hydraulicly and not with pressurised air.

 

If the dragging brake releases when you open the bleed nipple you have found the problem but not the cause, I would look to the ABS system and/or the master cylinder, I remain sceptical about all the anecdotal quotes of flexible hoses creating an internal pressure valve, theoretically possible but I know what I have always found in the past to be causing residual pressure and it was never the hoses or lines.

 

One exception was a very heavy hydraulic clutch on a Mini, it was caused by internal corrosion of the metal pipe, the clutch was only heavy when operated at normal speed, if you very slowly pushed it down it was as light as it should be.

 

Thanks for your reply! The brake does not release when opening the nipple, sadly. 

11 minutes ago, KenONeill said:

@stjerneblaa - As @J.R. has suggested but not said, I'd suspect the ABS valve on that corner is sticking. I have absolutely no idea how to prove that though!

 

Ok, anyone got ideas about how to test the ABS-valve? Would the ABS-light be on if that was the case?

No need to check, from your previous posting the brake does not release when the nipple is opened so you simply have a mechanical problem, much easier to find and remedy.

 

Strip, clean and re-assemble the caliper with new seals, replace if there is significant corrosion of the piston and/or bore.

Just now, J.R. said:

No need to check, from your previous posting the brake does not release when the nipple is opened so you simply have a mechanical problem, much easier to find and remedy.

 

Strip, clean and re-assemble the caliper with new seals, replace if there is significant corrosion of the piston and/or bore.

 

The caliper is new, and the problem is still there.

Remove the pads/ caliper, rewind the pistons, then clean up the carrier, particularly the surfaces that the pads slide against. A small file or grit paper probably to remove the corrosion that builds up on these. Insert the pads and check there is sufficient clearance/slop to allow the pads to move and slide freely, you may need to dress the pad backing plates with a small file as sometimes they are a tight fit. Use brake grease (Ceratec) lightly applied on the sliding surfaces between carrier and pads. Refit caliper. Before pumping the piston out, check the caliper slides back and forth together with the pads easily.

 

 

Edited 28 March, 20197 yr by xman

15 minutes ago, xman said:

Remove the pads/ caliper, rewind the pistons, then clean up the carrier, particularly the surfaces that the pads slide against. A small file or grit paper probably to remove the corrosion that builds up on these. Insert the pads and check there is sufficient clearance/slop to allow the pads to move and slide freely, you may need to dress the pad backing plates with a small file as sometimes they are a tight fit. Use brake grease (Ceratec) lightly applied on the sliding surfaces between carrier and pads. Refit caliper. Before pumping the piston out, check the caliper slides back and forth together with the pads easily.

 

 

 

We have not tried cleaning the carrier, but we filed down and put grease on the sides of the pads to move and slide freely. However, the caliper is pinching on the pads, it's not just the pads that are stuck on the disc. The caliper slides perfectly before hitting the brakes, when the caliper pinches and sticks.

 

Sorry for my poor English, what does dressing the pad backing plates mean? 

 

Should we screw the piston all the way back into the caliper before putting it on?

 

Thanks for all the response so far!

Edited 28 March, 20197 yr by stjerneblaa

30 minutes ago, stjerneblaa said:

What does dressing the pad backing plates mean?

This means lightly sanding or filing the back plates so that the surface that makes contact with the piston (or caliper) is smooth, and at 90 degrees to the sides of the back plate.

2 minutes ago, KenONeill said:

This means lightly sanding or filing the back plates so that the surface that makes contact with the piston (or caliper) is smooth, and at 90 degrees to the sides of the back plate.

No, not at all, don't sand/file the back of the pad backplates! Its the edges/ tabs that contact the (clean) carrier need filing down so that the pads are nice and loose. Corrosion and gunk builds quickly on the carrier slides, they need filing back to metal and protected with brake grease. Its fairly easy to assess what needs filing, simply put the pads in and check the clearances and their ability to move

 

I'm fairly certain, 90% of sticking brakes is due to pads/calipers jamming on corroded carriers.

12 minutes ago, xman said:

No, not at all, don't sand/file the back of the pad backplates! Its the edges/ tabs that contact the (clean) carrier need filing down so that the pads are nice and loose. Corrosion and gunk builds quickly on the carrier slides, they need filing back to metal and protected with brake grease. Its fairly easy to assess what needs filing, simply put the pads in and check the clearances and their ability to move

 

I'm fairly certain, 90% of sticking brakes is due to pads/calipers jamming on corroded carriers.

 

Ok, I’ll file the carrier. The pads have been filed and grease has been applied, and they do move freely against the carrier. Thanks again. 

Make sure there is no damage to the slide tubes or that the caliper bolts have been cross threaded (unlikely).

 

Have you changed the brake fluid? If its been over 2 years, maybe time to change and flush out any debris that might have formed.

5 minutes ago, xman said:

Make sure there is no damage to the slide tubes or that the caliper bolts have been cross threaded (unlikely).

 

Have you changed the brake fluid? If its been over 2 years, maybe time to change and flush out any debris that might have formed.

 

The caliper slides perfectly, brake fluid changed. What does “cross threaded” mean?

17 minutes ago, stjerneblaa said:

 

Ok, I’ll file the carrier. The pads have been filed and grease has been applied, and they do move freely against the carrier. Thanks again. 

 

Don't file the carrier, caliper or the rear of the pads. It is just the lugs (ringed in the picture) on the backing plate that can be badly cut leaving burrs behind. You just need to remove the burrs so the edges are smooth on the lugs where they make contact with the carrier. 

 

 

4 minutes ago, stjerneblaa said:

 

The caliper slides perfectly, brake fluid changed. What does “cross threaded” mean?

 

crossed threaded is where the bolt hasn't been screwed in correctly and mangles the thread up.

 

9 minutes ago, CWARD said:

 

Don't file the carrier, caliper or the rear of the pads. It is just the lugs (ringed in the picture) on the backing plate that can be badly cut leaving burrs behind. You just need to remove the burrs so the edges are smooth on the lugs where they make contact with the carrier. 

 

 

 

Thanks, I will try that, and keep crossing fingers some of these suggestions helps! 

It was the problem I had with mine sticking, a few others have had the same problem. A simply fix but one that shouldn't need doing in the first place.

1 minute ago, CWARD said:

It was the problem I had with mine sticking, a few others have had the same problem. A simply fix but one that shouldn't need doing in the first place.

 

Yeah, and best of all - it’s free! Cheers

16 hours ago, xman said:

 

 

16 hours ago, xman said:

No, not at all, don't sand/file the back of the pad backplates! Its the edges/ tabs that contact the (clean) carrier need filing down

Which just goes to show the issue(s) with using a technical term that admits to more than one definition!

This still isn't solved, I'm gonna look check the things you've kindly suggested this evening. I talked to the workshop today, and they gave me a tip on how to check whether this is an ABS-issue. They told me there are four screws that can be untightened to disengage the ABS. So now I'm trying to figure out where under the hood I can find the ABS. This is a bit embarassing, but I can't find any images showing where this unit is located. Any help would be helpful! 

Update: I didn't have time to check the brakes myself, so I got some assistance from the garage. Basically, they did placebo surgery on the bugger, and when they put it together again, the brakes weren't sticking. The mechanic said that maybe something was clogged somewhere and was released during testing. 

 

However, now we have another issue. The brake pedal is "soft" and sinking slowly further and further down when we compress the padal. When released and stepped on a second and third time, it reacts normally. If I release and then wait some seconds, it gets soft again. Another issue is that when we brake, the right side seems to grip the discs before the left (the one that used to stick), the car pulling to the right for a short moment before it evens out. Can this be due to unevenly adjusted caliper pistons?

 

We are 100% sure that all air has been released correctly from the system, so that doesn't seem to be the problem.

 

Very thankful for all help :-)

Edited 4 April, 20197 yr by stjerneblaa

Sounds like air in the brake system and a simple bleed would solve it but your garage should have suggested this. 

10 minutes ago, CWARD said:

Sounds like air in the brake system and a simple bleed would solve it but your garage should have suggested this. 

Yes, they told me the air had been taken care of.

Are the rear pads new? As the pedal with feel a bit soft until the pads are fully bedded in.