Rubber boot around caliper piston

james250 · January 26, 2020

While changing out brake pads, I noticed the rubber boot that surrounds the brake piston on the caliper has a hole. Do I need to change the caliper now? What is the job of the boot? is it just to keep moisture out?I don't think it's directly sealing the fluid or anything because fluid isn't leaking.

Britprius · January 26, 2020

3 hours ago, james250 said:

While changing out brake pads, I noticed the rubber boot that surrounds the brake piston on the caliper has a hole. Do I need to change the caliper now? What is the job of the boot? is it just to keep moisture out?I don't think it's directly sealing the fluid or anything because fluid isn't leaking.

Change the boot as soon as possible as it not only keeps out moister, but also fine grit. This will damage the chrome piston, and seals leading to seized calipers, and leaks.
You can buy caliper boot, and seal kits on line quite reasonably even new pistons if yours appears damaged in any way.

John.

james250 · January 27, 2020

Thanks, how exactly do you remove and replace the boot iself? and does it need lubricant? Where can I buy replacement boot from?

Britprius · January 27, 2020

Replacement kits are readily available on eBay. As far as lubricant goes you can use a little brake fluid wiped round the boot to aid fitting. To change the boot remove the brake pads, and push the caliper piston in as far as it will go. The boot can then be pulled off the piston, and out of the retaining grove in the caliper.
It would be better to remove the caliper, and completely clean it after dismantling Then replace the seal, and the boot, but this would then require the brake system to be bled.

John.

james250 · March 13, 2020

So just to be clear, i push the piston in all the way back just like you do when installing new pads? I dont push it out by pressing the brakes? because videos i've seen that involve caliper re-build and changing of pistons show pushing the piston out until it comes out but then this makes fluid leak out. I'm assuming the seal inside seals the fluid from coming out right? so removing the boot wont cause fluid to come out?

Farqui · March 13, 2020

James, removing just the outer piston dust cover/boot will not cause brake fluid to leak out.

You need to be careful to get the piston pushed out just far enough to re-seat the new dust cover and no more.

The brake fluid is sealed by another inner seal.

More pic's; https://www.clublexus.com/forums/rx-1st-gen-1999-2003/602012-diy-lubricating-the-brake-slide-pins-and-replacing-rubber-dust-boots.html#post6808051

Good luck and let us know how you get on.

Cheers, Lee

james250 · March 13, 2020

Thank you, so the boot is seated in two grooves which are only accessible by making the piston come further out by pressing the brakes right? And then once installed then just push piston back like installing a new brake pad? Does the boot just sit in the groove? What is the metal ring? The is the inner seal that seals the fluid then the rubber boot and then there seems to be a metal ring. What is the metal ring for?

Oh and how do you avoid pushing piston out too much so that it doesn't come out of the inner seal?

Farqui · March 14, 2020

Use a spacer to stop the piston shooting out, like old pads/block of hardwood/similar

james250 · March 14, 2020

8 hours ago, Farqui said:

Use a spacer to stop the piston shooting out, like old pads/block of hardwood/similar

How thick of a spacer shall I use? Normally on the car the thickness is of two pads plus the thickness of the brake disc. So should I use two brake pads stacked together or will one brake pad be enough? Also, to press the brake for the piston to come out, do I need to put car on ignition? Because with car off the brakes start to go hard

Farqui · March 14, 2020

Be conservative and only allow space for 5mm at a time until the dust cover can be removed.

Your brake pedal going hard is because the booster isn't charging with the engine off. This isn't a bad and will mean you will have more control to gently ease the piston out.

Be careful tho as any miss calculation could easily have you pop the piston out.

Keep your pinkies out of the way too!

james250 · March 14, 2020

Ok thank you. What about that metal ring that comes with the caliper repair kit? I've got two new slider pin boots, the outer piston dust cover, the inner piston seal and also a metal ring. Do I need the metal ring or is that for changing the piston itself?

steve2006 · March 14, 2020

I can’t see a metal ring on the diagram, if you do find it replace it with the new one.

james250 · March 14, 2020

@steve2006 I think that diagram is of the back caliper. Below is a diagram of the front caliper and item number 47731A I believe is the metal ring I am referring to. Based on the diagram I believe the order things go in is the inner seal then the piston then the dust cover then the metal ring if I'm not mistaken? So I assume there is a metal ring somehow holding the dust cover compressed in?

Farqui · March 14, 2020

Yes, it looks like it's to secure the cover.

Get stuck in...

steve2006 · March 14, 2020

Sorry you are right, I assumed it was a rear calliper as it is only single piston where as I have 2 pot fronts on the LS400, the ring as confirmed is to retain the dust cover.