Help Please 2014 B8.5 Brake Drag?

[777GE90]

My B8.5 has been sitting for most of this past year, with the odd supermarket run and quick spin on the motorway every now and then.

Unfortuntely, it seems to have developed what I think is a brake drag problem. When driving, sometimes I notice the car seems to struggle to put the power down like it used to and sometimes even gives a slight twisting sensation. Initially, I couldn't figure out what it was, when I took the car on the motorway it was making buffetting sounds and my first thoughts were it sounded like the undertray was flapping about, but having recently been to a garage the undertray seemed to be secure under the car.

Last week when driving, I noticed loud noises while the car is moving and so after a bit of experimenting, I felt the car was coming to a sudden stop if I let it coast, even down slight down hills. This immediately made me realise that the brakes seem to be applying.

I verified this by taking the car on a run, parking it up and then placing my hand over each wheel, 3 of the tyres were cold but the front right wheel was very warm. So I am pretty confident that all of these issues are related to that front right tyre brake dragging.

But I'm no expert and not really sure where to go from here. Would replacing the caliper resolve this (I'm assuming the bad piston is part of the caliper) or could other issues cause this as well?

 

[spartacus68]

Hang fire before you go replacing calipers.

When was the last time the brake fluid was changed? It's meant to be every 2 years. Over time the system will absorb moisture. Back to the problem at hand, at this time of year, then the brakes won't heat up, so road salt, moisture and brake dust just sit.

So my money is on siezed brake sliders. The brake sliders need to be lubed to allow the caliper to move as the brake pads wear.

If you've driven and coasted to a stop and it's hot that's a sure sign, however it could be corrosion on the piston bore. A torn dust sleeve will allow moisture to cause surface rust and friction, again not allowing the piston to retract.

If you're not mechanically minded, then by all means replace the caliper. It's probably the most convenient way to get an instant result, but if you are able, then a rebuild is satisfying, and will save you a small fortune.

Often just a brake dismantle, wire brush the caliper, file the carrier, regrease the pad clips and backs of the pads can pay dividends.

Bigg Red sell rebuild kits with 'o' ring seals, new dust sleeve, sliders, etc. For the right grease, then Pro Slip is excellent.

I still use red grease when rebuilding calipers. Even if you don't to a full dismantle, you can remove the brake disc and pads, extend the piston by pressing the brake, then applying a little red grease under the piston bore dust sleeve.

On the A4 you will need VCDS for rear electro-mechanical handbrake. There are a few videos on a YouTube that bypass it, but I'd go with the software approach.

On bleeding, a thorough flush with DOT4 brake fluid I said advised. Work from the corner furthest from the brake fluid reservoir, keeping the reservoir topped up as someone else pumps the brakes. Remember and wire brush the brake nipple to remove corrosion before you unlock. Use the right spanner too. Use to much force and you sheer the nipple, then you're in a world of pain.

Anyone contemplating new discs and pads, then Zimmermann discs and pads are hard to beat.

 

[777GE90]

Hang fire before you go replacing calipers.

When was the last time the brake fluid was changed? It's meant to be every 2 years. Over time the system will absorb moisture. Back to the problem at hand, at this time of year, then the brakes won't heat up, so road salt, moisture and brake dust just sit.

So my money is on siezed brake sliders. The brake sliders need to be lubed to allow the caliper to move as the brake pads wear.

If you've driven and coasted to a stop and it's hot that's a sure sign, however it could be corrosion on the piston bore. A torn dust sleeve will allow moisture to cause surface rust and friction, again not allowing the piston to retract.

If you're not mechanically minded, then by all means replace the caliper. It's probably the most convenient way to get an instant result, but if you are able, then a rebuild is satisfying, and will save you a small fortune.

Often just a brake dismantle, wire brush the caliper, file the carrier, regrease the pad clips and backs of the pads can pay dividends.

Bigg Red sell rebuild kits with 'o' ring seals, new dust sleeve, sliders, etc. For the right grease, then Pro Slip is excellent.

I still use red grease when rebuilding calipers. Even if you don't to a full dismantle, you can remove the brake disc and pads, extend the piston by pressing the brake, then applying a little red grease under the piston bore dust sleeve.

On the A4 you will need VCDS for rear electro-mechanical handbrake. There are a few videos on a YouTube that bypass it, but I'd go with the software approach.

On bleeding, a thorough flush with DOT4 brake fluid I said advised. Work from the corner furthest from the brake fluid reservoir, keeping the reservoir topped up as someone else pumps the brakes. Remember and wire brush the brake nipple to remove corrosion before you unlock. Use the right spanner too. Use to much force and you sheer the nipple, then you're in a world of pain.

Anyone contemplating new discs and pads, then Zimmermann discs and pads are hard to beat.

Well it's a good point, the brake fluid has not been changed in 4 years, but that shouldn't cause the calliper to start sticking like this? I guess it may be worth getting it changed at some point, does the under tray need removing for it?

Where are the brake sliders normally? Do they sit behind the piston? I wouldn't say I'm mechanically minded, but certainly capable of taking things apart and putting them back together, my only problem is I lack tools or anywhere decent to do the work. In terms of doing it myself, I guess I'd have to buy a rebuild kit and then hope I'm capable of doing it lol, that's why was thinking just replacing the calliper is easier. But I'll have a look on Youtube and stuff.

 

[spartacus68]

Brake fluid absorbs moisture, so if it's 4 years old, then it needs changed. Both my daughter's are practically master mechanic trained now from an early age of helping their old man pump brakes over the years! I haven't used a self bleeder kit, I just drag in an apprentice. Also this is weather critical. Brakes invariably take longer than you think, so on the street is no use in January. Ideally a drive, with space. A garage, even better.

The brake sliders are on the caliper. No need to drop the undertray to access. You will need to jack the car, but you'll need an axle stand for safety. If you've no tools, then stop, depending on what you find.

If you're dismantling front brakes will need a G clamp to push back the piston, wire brush, hammer, decent socket set (Halford Professional set) is excellent and comes with a lifetime warranty, claw grips, decent long handled flathead screwdriver, needle nose pliers, Torx bit set, copper anti-sieze grease, red grease, lithium grease for brake pins or sliders, rubber mallet, 21mm ring spanner if you remove brake carrier, M9 Allen key bit for sliders, torque wrench, 1 litre DOT 4 brake fluid, rubber tube.

In terms of videos, check out Dave Sterl and Fixitsam on YouTube.

Looking at one of Dave Sterl's videos today points to the dust sleeve around the piston as the usual culprit. With corrosion on the caliper it forces the dust sleeve to expand so it doesn't seat properly, which causes it to stick. The brake sliders are definately worth investigating, but the dust sleeve would be my next port of call.

 

[Dippy]

I can't comment on the drag, but I always have my brake fluid changed every 2 years and I always notice an improvement afterwards.

 

[777GE90]

Well I opted to take it to the garage given the freezing conditions, ended up replacing the front and rear brake pads too as they were pretty low. Garage managed to clean / unsieze the piston so pleased I didn't need to buy a new caliper. It actually feels great that the car now coasts smoothly until it looses momentum, rather than coming to a sudden and short stop.

Have left the brake fluid for now as tempted to give that one a go myself, but going to wait a few more months till it's warmer outside to do that anyway, the car is going to be sitting most of this year I suspect, given I am working from home now.

Thanks for your help all!