[BrendanP]

Does anyone have a good idea how to replace the rubber dust seal on a GD rear caliper? A few months age I noticed the rubber seal was split, so I want to replace it. The seal has an outer lip which sits in an internal groove on the caliper cylinder, and an inner lip which seats in an external groove on the brake piston. The gap between the caliper cylinder and the piston is very small, and I don't think I can push the seal through the gap so that it locates into the groove in the cylinder.

The only way I can think of doing it is to wind the piston completely out of the caliper, position the rubber seal in the caliper, then wind the piston  back in through the seal. To do this I'd have to thoroughly clean the caliper, try and hold it horizontal so the brake fluid doesn't run out, and bleed it after the piston is back in position.

Has anyone succeeded in changing this dust seal without having to remove the piston?

[sundiz]

I've serviced few brake calibers without the internal handbrake. No experience with that system. But even with the simpler ones I had them all out of the car and taken apart on the table. After removing the seal it is good to check that the piston and the caliber is clean and there is no damage. Dirt and rust can do nasty things to slide surfaces.

[BrendanP]

I now want to replace the dust boot on my rear caliper, but what is the best way to fit it? I've attached a sketch of a cross-section through the caliper. The boot has an external lip which goes into a groove in the caliper cylinder, and an internal lip which fits around a groove in the piston. If I wind the piston into the cylinder as far as possible, does this expose the groove in the cylinder so I can push the boot lip inside it? If it doesn't, I don't think the gap between the piston and cylinder bore is big enough to push the rubber through it.

If I take the piston out, and fit the boot to the caliper first, I don't think the boot will stretch enough to push the piston back through the centre of the boot.

Any advice would be greatly appreciated.

[BrendanP]

OK, I'm answering my own question here. After finding a couple of YouTube videos I concluded the piston has to be taken out of the caliper. I took the caliper off the car to do this. It's worth checking that the bleed nipple hasn't seized up before starting this job, so loosen it and re-tighten it first. You don't want to let a lot of air into the brakes and then find you can't bleed it. Before disconnecting the hydraulic hose, wind the piston all the way in to minimise the loss of fluid. Keep an eye on the brake fluid reservoir to make sure it doesn't overflow. Clean off as much grime as possible before winding the piston out. Keep everything as clean as possible. The rear view of the piston shows the lead screw which pushes it outwards when the handbrake is on. The front view shows the corrosion on the front face of the piston, which is exposed to the elements. The photo of the caliper shows the black rubber hydraulic seal, and the shiny groove on front of it when the lip of the dust boot has to locate.

To fit the boot, push it over the front of the piston, and then along the piston until it hangs over the inner end. Offer it up to the caliper and push the lip into the groove in the caliper. Then, push the piston back into the bore, and wind it back in. Double-check that the boot is actually fully seated in the caliper body. If not, wind the piston out and try it again.

Refit the caliper, re-connect the hydraulic hose and bleed the air out. Looking at the photo of the damaged boot, it pretty obvious this has been caused by the boot being pinched against the pip on the rear of the brake pad . This is down to stupidity on my part by pushing the caliper back over the brake pads when it's a tight fit. I would recommend always winding the piston back into the caliper before re-fitting it, then it's a loose fit over the pads. Hopefully, when sliding over the pads, you can then feel the slot in the piston engage with the pip on the brake pad without the rubber boot getting in the way.

[ro0sau]

was your seal weeping fluid at all?

just serviced my gd and  found the rear right caliper is leaking.
no seal kits available in west aus. ex east managed to find one of 3 seal kits in australia

$400 + for a new unit so  i guessin around $250 from a wreck - which has no guarantee of not having the same issue.

my mech says he's never come across a leaking piston on any other i30, regardless of model or klms lol.
after a few obscure issues i've had with this car i'm now tempted to sell it on

[BrendanP]

No, the actual piston seal was fine, I only replaced the dust boot because it was torn and I didn't want dirt and water getting in. Of course, I could only buy the boot as part of a repair kit which included all the other rubber seals. Cost me about £10. I wouldn't expect to pay more than £100 for a fully reconditioned caliper over here (manual handbrake). My old i30 is 10 years old with 225,000 miles and none of the calipers on that have ever leaked.

You might be unlucky to have had some dirt get in which has scratched the caliper bore, or water has got in and corroded it.