Rear brakes binding, cleaned everything, removed and replaced some very seized pads on both sides and replaced some quite tired discs on both sides. Passenger's side works perfectly, driver's side still binding. Rewinding the pistons I did notice that they were looking worse for wear but I already had discs & pads and was a bit too hopeful - need to replace or refresh the calipers.

Looking at calipers on autodoc, I can see TRW or "Lucas/TRW" brake systems as options. The only difference being that "Lucas/TRW" is twice the price.

I've got a 1.6TDI DDYA engine, 1KD code for brakes with 253mm rear discs. On the caliper itself enscribed is "VWAG, GNO, TRW" and the piston diameter is 38mm as seen on the calipers.

Both "TRW" and "Lucas/TRW" options match those fitment details. How am I supposed to know which one? Does it matter?

Cheers!

I've had this a few times over the years with various makes, as I tend to drive somewhat older cars.

As your pads wear, so the piston sits progressively further out of the caliper, and when you replace the pads and push the piston back in the teensiest bit of dirt or surface rust interferes with the usually metal to metal fluid-tight movement.

You can replace them, as you seem to be heading, or with care you can get the caliper off, remove the piston, CAREFULLY clean it and CAREFULLY reinstall it. More labour but less money and you gain better understanding of how the whole thing works!

Hopefully someone will be along soon who will answer your actual question.. good luck either way.

Edit: if you remove any muck from the caliper, does it have any identification marks, names or numbers?

Edited 4 April4 Apr by hubrad

14 minutes ago, hubrad said:

I've had this a few times over the years with various makes, as I tend to drive somewhat older cars.

As your pads wear, so the piston sits progressively further out of the caliper, and when you replace the pads and push the piston back in the teensiest bit of dirt or surface rust interferes with the usually metal to metal fluid-tight movement.

You can replace them, as you seem to be heading, or with care you can get the caliper off, remove the piston, CAREFULLY clean it and CAREFULLY reinstall it. More labour but less money and you gain better understanding of how the whole thing works!

Hopefully someone will be along soon who will answer your actual question.. good luck either way.

Edit: if you remove any muck from the caliper, does it have any identification marks, names or numbers?

I don't currently need the car, and I'm avoiding driving it while it has brand new discs & pads on since the stuck caliper is very obviously wearing down the driver's side disc incorrectly - it's seen about 10 miles since I replaced them - but looks to have done no damage other than half the diameter of the disc is the factory coat still. If I find I do desperately need it before I get a chance to replace the calipers then I will look at giving the pistons a clean.

Is it possible to clean the pistons without completely removing them? In my mind half the labour involved is going to be introducing air to the brakes and having to bleed, which is what I'll have to do if I replace the calipers, anyway. Can the rubber piston seal be pulled off the piston (while it's fully rewound) and cleaned?

I've tried to do it without removing the caliper and, as you say, having to bleed on refitting.

Wasted sooo much time over the years.. last time I just went straight to removing it, which is what I had to do in the end every other time!

It could also be the sliders on which the caliper is mounted that are corroded/sticky. Cheap enough and easy to replace.

By the way, it is not a metal to metal seal of the piston in the caliper, there is a rubber seal in the piston that actually makes the seal; any damage to that and you'll have a leak.

Cleanliness is next to Godliness......😉

4 minutes ago, SwallownAmazon said:

It could also be the sliders on which the caliper is mounted that are corroded/sticky. Cheap enough and easy to replace.

By the way, it is not a metal to metal seal of the piston in the caliper, there is a rubber seal in the piston that actually makes the seal; any damage to that and you'll have a leak.

Cleanliness is next to Godliness......😉

If "slider" is the guide pins on the caliper - both sides moved freely and the boots looked OK. If it's the mounting bracket, which I can't remember if the caliper should move along this - yes it's quite rusty and I didn't give it a thorough clean or grease (if there's anywhere sensible to grease contact points of mounting bracket + caliper). I focused on cleaning the contact points for the pads, which I did manage to get to a high standard - nice and smooth. I'd hate to have to remove the mounting bracket, the bolts are almost certainly seized and my ego can't take stripping another bolt head on this car

For which brake system I have, looking at llparts and previous forum threads while nobody mentions Lucas/TRW or calipers themselves it's often suggested that 1KD with 253mm discs will be TRW system, and given I can't notice any difference between the two parts I'm growing confident that I should be getting TRW calipers. Hopefully someone will chime in saying for sure.

I'll have a go at cleaning the caliper and contact points more thoroughly, and inspect the piston since that might allow me to actually leave the house this bank holiday weekend, but I'm suspecting the final solution will be replacing the calipers.

My experience of sticking pistons ...... I usually find that corrosion on the calliper body has pushed the DUST SEAL inwards so it restricts the piston movement. Pumping out the piston until it can be removed, then clamp the hose, carefully remove the dust seal and remove rust from the grooves in the calliper. I've seen them bad enough that you have to sacrifice the seal and fit a new one.

You can easily get a seal kit from the likes of Bigg Red, pistons too.

You could refit without the dust seal, it'd give you the use of the car until a seal or calliper is found?

Before doing the above though make sure the bleed nipple turns !!

If its the rear it could be the handbrake cable operating lever that's seized. Pistons don't release properly when handbrake is let off. I removed the lever etc and lubricated mechanism plus operated it until pistons were out a good bit and then wound them in again and kept repeating until it worked smoothly. As for identification have a look at https://brakesint.co.uk/ They have description of caliper like smooth/ribbed etc with all sizes and pictures.

Alasdair

3 hours ago, SwallownAmazon said:

It could also be the sliders on which the caliper is mounted that are corroded/sticky. Cheap enough and easy to replace.

By the way, it is not a metal to metal seal of the piston in the caliper, there is a rubber seal in the piston that actually makes the seal; any damage to that and you'll have a leak.

Cleanliness is next to Godliness......😉

Good point on the sliders, my old Corolla suffered with that.

Re internal seal, it's been a while since I did one so can't exactly remember, but pretty sure at least some had no rubber since early 80s, and the fit was so tight that just a brown mark of surface rust, 0000 wire wool to wipe it off, was enough to seize it all up. Happy to be wrong mind!

Edited 4 April4 Apr by hubrad

Updating this thread after I've done the job in hopes this can help someone else in the future.

Replaced both rear calipers, on Autodoc I filtered by "TRW" brake system and then chose TRW-branded ones - these were correct. And in fact they were refurbs of the OEM part that I pulled off the Octavia - happy days. Cost a bit more than other manufacturers, but going OEM never hurt anybody.

I spent a lot of time looking at what size banjo bolt/washer size is needed - nothing official online, the ones in the Halfords variety pack I bought looked too skinny (ID 12mm OD 14mm) - I was right, the washers I pulled off are ID 12mm OD ~17mm. I used ID 12mm OD 18mm Thickness 1.5mm washers - these worked fine. Don't go less than 17mm OD or the washer will be thinner than the flange of the bolt.

Also found it difficult to find a torque spec for the banjo bolt, you'll see anywhere from 20nm-40nm online for other makes of cars with 10 or 12mm bolts. I went by feel balancing "will this leak" with "will this snap", while also firmly tapping the bolt head with a ball-peen to seat the washers. Checked the torque after and both are coming in at around 35nm.

No leaks and the driver's side disc is now wearing down properly so that's solved the binding!