Stumped! Help with rear brakes?

[robbbie]

Hi all,

Would love if anyone could shed some light on this - my head's been wrecked the past fortnight...

 

2010 Octy VRS TDi

 

1. Changed the rear discs and pads (Pagid brand). One of the slider pins got bent in the process (due to not having a proper wind back tool at the time) so 2 new slider pins went into the carrier. Both slider pins slide in and out perfectly when the caliper is removed.

I put back on the caliper and tightened everything up, ran the engine and had someone pump the brakes for me, only to find that the disc is being held by the caliper and it doesn't turn freely when no brake pressure is applied.

 

2. Changed the caliper out for a new item, bled the system and tightened all bolts up only to find the same problem. The caliper operates fine on the lower slider pin, but doesn't move in/out properly on the top slider pin.

 

Could the caliper carrier have gotten damaged internally and prevents proper function of the slider pins when everything is tightened up and any slack (from loose bolts etc) is taken up?

 

Is a standard Octavia or Golf or Jetta etc rear brake set up the same size caliper and caliper carrier? A local breakers likely won't have a VRS for dismantling.

 

Appreciate any input you might have.

Rob

[Guest]

Sounds like you used a gorilla on a 6' pinch bar!

[brad1.8T]

Did you clamp the rear flexible brake line during this process?  I'm thinking it's collapsed.  The master cylinder has sufficient pressure to go one way but there is insufficient negative pressure to pull it back.  You'd think it would affect both calipers though...

 

If you disconnect the hydraulics off the caliper does it move freely.

 

If you've bent the caliper carrier then it should be obvious when checked with a straight edge.

 

You could also check that the slider pins are parallel with a vernier or calipers

[robbbie]

Thanks for your input. Had another wrestle with the whole thing this evening. 

 

Established that the carrier is straight and normal. The caliper floats in and out easily when the piston is fully wound in (leaving some slack between the piston and pads). 

 

Also established that the discs I was sold are about 10mm smaller in diameter than the previous ones. Don't see this causing an issue tho as they don't foul anywhere and the drivers side is identical to passenger side and it's fine. 

 

I took out the piston and greased the threaded bar inside and replaced piston and dust seal. Pumped out the piston and wound it back in a few times to ensure it was able to move in/out easily. 

 

The only thing that hasn't been checked/replaced now is the flexi hose, like you said Brad. I never clamped it. Maybe it got pulled a bit too far sometime in all the work and has pinched half-closed inside the hose. 

 

Annoying if that's the root cause all along since the first day of the job... 

 

Edited 31 January, 2019 by robbbie

[paddypaws]

if the disks are 10mm smaller, are you sure the depth of the disk from the front face of the hub is correct? The disk might be laying to far forward or back from the correct position. Sounds like you have the wrong parts?

[robbbie]

2 hours ago, paddypaws said:

if the disks are 10mm smaller, are you sure the depth of the disk from the front face of the hub is correct? The disk might be laying to far forward or back from the correct position. Sounds like you have the wrong parts?

 

The same size disc went on the right hand side and that side is perfect. So I don't see the slightly smaller disc being a problem. 

 

I changed the flexi hose this evening, bled the system and am still having binding issues. 

 

So there's a new:

Caliper

Slider pins

Flexi hose

Discs & pads

 

...Gone in. Cannot figure it out ☹️

 

 

[robbbie]

Even tried the old discs and pads for the hell of it and ran into the same issue. Binding without proper release of the brakes.

[BashRacing]

Fit a new calliper carrier with slider pins

[robbbie]

Yep, did that. 

[robbbie]

Had another go today. Tried the old caliper, new caliper, old discs/pads. 

Nothing I did allowed the pressure to  release from the caliper. 

 

To summarise everything:

Replaced pads, discs, caliper, slider pins, flexi hose. Even placed a piece of box iron in the caliper and squeezed the piston onto it and the pressure didn't release. 

 

I'm now thinking there's an issue with abs/servo/master cylinder. 

[Me-109]

Would suspect an issue with the handbrake cable or self-adjuster since you have ruled out hydraulics at the caliper end. Try disconnecting the cables and then operate the footbrake a few times to check.

[Quiksilver_TR]

Does the handbrake mechanism move freely on that caliper......sounds like it might be sticking.

[J.R.]

On 02/02/2019 at 16:58, robbbie said:

To summarise everything:

Replaced pads, discs, caliper, slider pins, flexi hose. Even placed a piece of box iron in the caliper and squeezed the piston onto it and the pressure didn't release. 

 

I'm now thinking there's an issue with abs/servo/master cylinder. 

 

An obvious test would be to open the bleed nipple when the caliper is locked, if the pads release its a hydraulic problem, if they dont its mechanical.

 

Apologies if you have already done this, I did not read back through the whole thread.

Edited 5 February, 2019 by J.R.

[robbbie]

It's a tough one. 

I brought the car to my mechanic and he threw his eye over everything and put all back together etc. 

 

He brought it for a drive and didn't have any binding issues. I've since done about 13 miles and also haven't seen any binding like before. I'll be taking the car for a longer spin at the weekend and will see how it performs then. 

 

One thing I know that's different is when the mechanic was poking on it on his lift, the car is level as normal. But when I was doing work with the car on the ground and jacked up at the rear left corner, it's obviously off level when I'm doing the work/bleeding brakes etc. 

 

Long shot and basic but something that is different. 

[Ju1ian1001]

Have you been bleeding or doing brake work with the engine running? if so then then the hill hold will come on  and act like the brake is binding, it should happen on both sides though not just the left. you as the driver does not have much control over this as it's sensed electroniclly. This is just a theory though but worth checking as the brake is working normally now.

 

In normal driving if you stop on a hill and hold the foot brake on the hill hold will hold the vehicle on the rear brakes for a couple of seconds then it will release, it's basically there to help with hill starts hence the name hillhold.

[robbbie]

On 06/02/2019 at 21:03, Ju1ian1001 said:

Have you been bleeding or doing brake work with the engine running? if so then then the hill hold will come on  and act like the brake is binding, it should happen on both sides though not just the left. you as the driver does not have much control over this as it's sensed electroniclly. This is just a theory though but worth checking as the brake is working normally now.

 

In normal driving if you stop on a hill and hold the foot brake on the hill hold will hold the vehicle on the rear brakes for a couple of seconds then it will release, it's basically there to help with hill starts hence the name hillhold.

 

My car doesn't have hill-hold unfortunately.
 

On 05/02/2019 at 10:34, J.R. said:

 

An obvious test would be to open the bleed nipple when the caliper is locked, if the pads release its a hydraulic problem, if they dont its mechanical.

 

Apologies if you have already done this, I did not read back through the whole thread.

Yes, the pressure does get released when bleed nipple is opened.

The car is booked in with the main dealer for this coming Tuesday. We'll see if they can get to the root cause.