Replaced callipers - long brake pedal and reduced braking

[Hereward]

2005 Mark 5 Golf 1.6 FSi

I replaced one front and one rear calliper, bled and went for a drive. Brakes now don't start to bite until way past the normal point and also require more shove.

I bled the callipers again - no air at all.

Is it possible to damage seals in the brake master cylinder during manual bleeding? With the engine Off I firmly pressed down the brake pedal multiple times with my hand to seat the pistons and bleed air into a bottle 1/3 full of brake fluid. Could this have flipped internal seals?

Per my below pic I also note that the front pads are only contacting the outer half of the front disc. Is that a factor?



Cheers for any advice.

[Dave.]

The old pads will have sat slightly different in the old calipers Vs the new ones, so you're not getting full contact.

You're basically rebedding in the pads, I few decent stops should sort them out.

[stevieturbo]

It should be near on impossible to damage the seals.

But surely it would be worth putting new pads in at the same time as new calipers ? Seems odd not to.

[GreenV8S]

stevieturbo said:

It should be near on impossible to damage the seals.

It's very possible if the master cylinders are worn, since the wear stops at the bottom of the normal range of travel, and bleeding brakes with the pedal will take the piston past that point. But if the seals have been damaged I'd expect that to lead to a sinking pedal, not just a long travel.

[GreenV8S]

Hereward said:

Per my below pic I also note that the front pads are only contacting the outer half of the front disc. Is that a factor?

Very much a factor. It implies the discs have worn away the inner part of the pad so you have less contact area and lots of flexing as you apply the brakes. The problem can compound itself when the rusty section of the disc causes accelerated wear on the pad, leaving that part of the disc free to corrode even mode.

It's also possible you haven't bled the calipers properly - in extreme cases you may even need to bleed them off the car to chase air pockets out, But I'd start by replacing the discs and pads and see if that solves the problem. Also bleed the brakes all round when you do this, not just the calipers you replaced.

[Panamax]

Hereward said:

I replaced one front and one rear calliper

Why?

And it seems weird to have been working on those brakes without replacing discs and pads.

[Hereward]

Thanks a lot for all the replies.

I have a replacement car already and this car was destined to be sold for £500 or scrapped. I put it through its MOT hoping for an easy pass but it failed on two binding brakes. Hence I was hoping for a quick and easy fix by simply replacing the two offending callipers.

I will bleed the callipers again (good point about taking them off and manipulating their orientation to dislodge air), and also bleed the untouched callipers. If it's the master cylinder I will throw in the towel since access is a nightmare.

I was hoping to give the car a more dignified send off since it's been in the family for 15 years but it is what it is.

Cheers.

[Daryl357]

Check if the master cylinder has bleed nipples, if it does, then bleed them. Common problem on TT's of a similar age.

[stevieturbo]

GreenV8S said:

It's very possible if the master cylinders are worn, since the wear stops at the bottom of the normal range of travel, and bleeding brakes with the pedal will take the piston past that point. But if the seals have been damaged I'd expect that to lead to a sinking pedal, not just a long travel.

I've heard of people claiming such damage, but in over 30 years never seen it myself.

And all too often the same people claiming such damage, might change 3 or 4 master cylinders before their "problem" is fixed.....which would kinda point that the problem was never the master in the first place, but something they were doing

[Hereward]

Daryl357 said:

Check if the master cylinder has bleed nipples, if it does, then bleed them. Common problem on TT's of a similar age.

Ooohh, thank you. Access is appalling (engine is mounted to the offside of the engine bay) but I will go and have a look now. Actually I will look online for a picture first.

I bled everything again an hour ago and still have the late/low point of brake engagement.

[TwinKam]

Did the reservoir empty at any point while you were changing or bleeding the calipers?

[Daryl357]

Christ I can't believe I missed that the first time round, your pads are the wrong way too, the pad with the 3 pronged clip is to go inside the caliper piston, not the side facing outwards.

[Hereward]

Hereward said:

Daryl357 said:

Check if the master cylinder has bleed nipples, if it does, then bleed them. Common problem on TT's of a similar age.

Ooohh, thank you. Access is appalling (engine is mounted to the offside of the engine bay) but I will go and have a look now. Actually I will look online for a picture first.

I bled everything again an hour ago and still have the late/low point of brake engagement.

Daryl, thank you so much for this.

No bleed nipples (apparently on Mk4, not Mk5 Golf) but I pressurised the reservoir and cracked open the two master cylinder brake lines until they dripped then nipped them back up. That seems to have done the job.

MOT re-test at 0900hrs tomorrow!...

[Hereward]

Daryl357 said:

Christ I can't believe I missed that the first time round, your pads are the wrong way too, the pad with the 3 pronged clip is to go inside the caliper piston, not the side facing outwards.

OMG, then they have been like that for years, as fitted by the garage! The other pad, in the piston, is nice shiny metal prongs, having been protected from the elements in there.

It's pissing down now so I will leave as-is (until this plays on my mind to the point where I have to go out and sort it).

Cheers.

[stevieturbo]

Daryl357 said:

Christ I can't believe I missed that the first time round, your pads are the wrong way too, the pad with the 3 pronged clip is to go inside the caliper piston, not the side facing outwards.

Well spotted

[ChocolateFrog]

It's almost certainly still got air in the system somewhere.

[ChocolateFrog]

Daryl357 said:

Christ I can't believe I missed that the first time round, your pads are the wrong way too, the pad with the 3 pronged clip is to go inside the caliper piston, not the side facing outwards.

Good spot, schoolboy error.

[TwinKam]

I think you'll find that both inner and outer pads have 'clips', different shapes though, and will probably not both fit in the wrong locations.
You do need to change them though as, if they've been binding, they've probably overheated.

Generic picture of Golf pads with clips on all four pads...

The silver clips here will be on the inners, the black clips on the outers.

Edited by TwinKam on Sunday 17th November 22:30

[E-bmw]

Hereward said:

I have a replacement car already and this car was destined to be sold for £500 or scrapped. I put it through its MOT hoping for an easy pass but it failed on two binding brakes. Hence I was hoping for a quick and easy fix by simply replacing the two offending callipers.

.

Unfortunately, the quick & easy (and much cheaper) solution would have been to just service the offending callipers at zero cost.

As others have said, I suspect you have a combination of repositioned pads now bedding in again & some air still in the system.

The real solution now is new pads all round & re-bleed again.

[stevieturbo]

TwinKam said:

I think you'll find that both inner and outer pads have 'clips', different shapes though, and will probably not both fit in the wrong locations.
You do need to change them though as, if they've been binding, they've probably overheated.

Generic picture of Golf pads with clips on all four pads...

The silver clips here will be on the inners, the black clips on the outers.

Seems a silly and pointless design. But sometimes manufacturers just do that