6c GTi bleeding the brakes

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Graham1701
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6c GTi bleeding the brakes

Post by Graham1701 » Mon Jun 29, 2020 5:19 pm

Hi,
I have decided to order some new brake flexis to try and sort my sticking brakes. However I have read in various places you cannot bleed the brakes in the conventional manner. You need to do it with the computer plugged in. Is this correct?
I was hoping I could bleed them with someone pumping the pedal and me on the bleed screw. Will this not work? Thanks.

Kind regards,
Graham

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iichel
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Re: 6c GTi bleeding the brakes

Post by iichel » Mon Jun 29, 2020 6:14 pm

You can bleed them just like any other Polo 6R/6C.

For a full flush, I would probably recommend to get a computer to bleed the ESP unit itself.
If you don't run it completely dry, the good old pump the pedal should work as well.

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Re: 6c GTi bleeding the brakes

Post by RUM4MO » Mon Jun 29, 2020 8:31 pm

Just make sure that you don't drain the system out, ie make sure that you keep the master cylinder reservoir well topped up while replacing each flexi brake line. Problem begin when you allow air to get into the ABS valve block, that is when you need to activate the ABS pump to flush air out of the ABS block.

I always use a Gunsons Esibleeder.

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Re: 6c GTi bleeding the brakes

Post by veteran » Tue Jun 30, 2020 11:39 am

Graham1701,

You describe your problem as being one of "sticking brakes". I wouldn't have thought, therefore, that changing the brake hoses would make any difference to that, as instead it's more likely to be something to do with the discs (disc runout issue?) or the sliders on each caliper not working well enough. However, I know only too well how niggling and sometimes intractable brake issues can be, particularly on the 6C/6R Polo. Solving brake issues can be a bit of a black art sometimes.

Of course, if the vehicle is quite old and the hoses are bulging to any extent, that could indicate a breakdown of their bores and resulting partial blockage of the fluid. (I'm assuming that the 'flexis' to which your refer are those at the roadwheels and not some others that might exist between the fluid reservoir and the ABS unit?). Incidentally, my experience when changing the front hoses on my previous car, a Golf, was that there was very little loss of fluid at the pipe/hose junction, provided I ensured that there was an airtight seal at the lid of the fluid reservoir (as the seal prevented atmospheric pressure from allowing fluid to freely flow out when the pipe/hose joint was undone). To ensure that that was so on the Golf I temporarily used some clingfilm on the reservoir's screwlid. That's probably unnecessary on these Polos though, as I'm pretty sure that 6C/6R Polo reservoirs are not permanently vented ones. All the same, if you do the job yourself, do make sure the reservoir lid is tightly done up before you start undoing any pipe/hose unions.

I've had more than my share of brake-noise issues with my own Polo, as it happens, and about a year ago I finally ended them by re-servicing the calipers and removing any Copaslip that had been used on the sliders, replacing it with just a smidgen of Textar Ceratec. The latter is non-metallic. Copper grease used on caliper sliders is notorious for causing both poor braking and sticking when the brakes are released. Pro garage mechanics now avoid its use, except on minor, exposed parts of the calipers. Also, the stock VW-fitted pads on 6R/6C Polos often aren't the best examples, some being more prone to brake squeal than others. I myself removed the OEM pads on mine and fitted a Pagid set instead. You'll probably find, as I did with mine, that anti-squealing is, with most pads now, dealt with by the inclusion of thin-film plastic/rubber backings on the pads. Slapping copper grease on the backs becomes unnecessary.

Whilst I was at it (a job that took me more than just one day to do), I did a full flush/change of the system fluid, something that would have been advisable this year anyway. This included a good bleed of the clutch slave cylinder as well. For the full change, and after advice via these forums, I decided to invest in a meter-fitted pressure vessel (from Laser Tools) with which to do the system flush. I used this, part-filled with the full amount of new fluid required, plus some more, at the reservoir, putting positive fluid pressure into the system. It then made bleeding at each caliper an easy, one-person job.

The overall result of doing all of this was that brake noise and clutch noise - loud 'clanks' - that had been bedevelling my Polo disappeared. All three changes - the slider lubricant, the pads, and the system flush - all helped in this, but on reflection I think that possibly the use of Ceratec, rather than Copaslip, made the biggest difference.

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Re: 6c GTi bleeding the brakes

Post by Graham1701 » Tue Jun 30, 2020 6:23 pm

The Ferodo pads I have fitted do have a tin plate bonded to the back of the pads. This also folds over at the points where the ears are on the pads where they slide in the caliper carrier. Both pads are free in the carrier. I smeared a little bit of white brake slider pingrease on the sliding pins after I wiped them clean. They are the type of sliders that are always partially exposed. More so as the pads wear down. I also put a little grease on the slider rails on the caliper carrier, but I have since wiped this off since I took it apart again to investigate the sticking caliper. My instant thought always is what have I done wrong? I compared the new discs to the old as best I can and they appear identical. I was going to clean the old ones up and refit them to see if it made any difference. They have been sat outside so a little rusty now. Would clean up though. It really is bizarre.
It is the flexible hoses that go to the calipers I'm thinking of changing.
It doesn't even stick that badly but as the disc and pads expand with heat it gets worse to the point that if I do a hard stop I can feel the car pull to the left. The Abs is functioning though. Will have another look at the weekend and see if I can get to the bottom of it. I've changed discs and pads on various vehicles before (including hydraulic citroens) and never encountered anything like this, other than an obviously sticky caliper piston. Thanks again.

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Re: 6c GTi bleeding the brakes

Post by veteran » Tue Jun 30, 2020 11:16 pm

Ferodo pads with tin backings, that's a new one on me. Recipe for plenty of squealing, I'd have thought. Instinctively, one would view that with a bit of suspicion. For your GTi, could you not find better pads than Ferodos?

As regards the discs themselves, although they can often, after a while, look fine to the naked eye, they can either wear unevenly or warp and so require replacing. To see if they've warped, you'd need to use something like a sensitive dial gauge against each one, to double-check the so-called 'runout' when the disc is rotated in situ.

You raise a quite plausible reason for sticking when you mention the caliper pistons themselves. Pistons can indeed seize. If you were prepared to dismantle the front calipers once more, you could try squirting a modicum of brake-cleaning fluid where each piston moves against its external rubber seal (just temporarily pull back the seal with your fingers a bit) and then exercising the piston. A second person would be handy for that, and you'd have to be very careful that you didn't move the piston so much as to spill brake fluid out from behind it. I can never remember whether it's on the front brakes or the rear ones where the pistons actually wind in and out, rather than move in a straight line, as it were (and so you have to use a special tool that engages in notches in the piston top in order to manually move it in and out). But if you're familiar with that, you'll know what I mean. I'm simply suggesting that the sticking may be being caused by one or more piston having partially seized, particularly if you're getting pulling to one side during braking. A bit of lubricant as I've suggested, indeed even a smearing of ceratec around the exposed piston rim, to assist movement of it in its bore, might be all you need.

If you (or someone else) were to mistakenly allow air to enter the ABS unit during a flushing of the brake system or during a bleeding operation, then that might conceivably give rise to some weird performance of the brakes, with attendant noises. For any DIYer who thinks that that may have happened, I'm led to believe that, in the VCDS package, there's an air-purging routine for the ABS unit, which could put that right. I suspect that that's what you were hinting at earlier on.

An afterthought: If you're definitely intent on replacing each front brake hose, then between the disconnection of the old one and the introduction of the new one might be the time to try to free up the piston. Provided up top you've the reservoir lid at that point firmly on, there'd not be much loss of fluid when you disconnect the old hose and indeed you could probably stopper any loss by temporarily fitting the caliper nipple's rubber dustcap over the end of the rigid pipe. With a wind-out tool, you'd then be free to manually lubricate and exercise the piston, with no fear of instead somebody operating the brake pedal too zealously and causing an almighty mess. You could then make the new union with the new hose, with a view to later bleeding the brakes, once the piston and new hose for the other side have been similarly done. Just a thought

Graham1701
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Re: 6c GTi bleeding the brakes

Post by Graham1701 » Wed Jul 01, 2020 4:11 pm

The Ferodo pads I fitted were exactly the same design as the TRW oe ones I removed. Which did not squeak or stick.
I will bear in mind everything you have said and update when I have hopefully made some progress (fingers crossed). Thanks again.

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Re: 6c GTi bleeding the brakes

Post by veteran » Wed Jul 01, 2020 10:53 pm

Just because brake pads look the same it doesn't necessarily mean that they perform the same. Formulations of the friction material will vary slightly from marque to marque.

From what you've told us, my hunch is that you've more than likely got a sticking caliper piston. So, freeing those pistons up should see your issues disappear. Of course, if you're renewing the brake hoses on the fronts (followed by bleeding to ensure you end up with clean fluid), then that will help and then won't be something you'll need to worry about as time moves on. It's conceivable, I suppose, that someone - either you or a servicing workshop - may have at some stage abused the brake hoses (such as letting the calipers hang on them, or using a hose clamp), causing some internal damage to them.

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