freeing up a seized brake caliper
 

What is the best way to free up a seized brake caliper piston? It's on a 300D. Thanks

Unfortunately there are only two options.rebuild the caliper with new seals($~40Cdn)or replace with a rebuilt($~60Cdn).Rust inside the caliper causes the seizure.Brake fluid absorbs moisture and holds it (for a while)then it makes it's way to the lowest point in the brake system(the calipers or wheel cylinders).This is why it's critical to flush the brake fluid once a year.If you're on a tight budget and need a temporary fix try to seat the piston back into the caliper with a C-clamp.Then fit new pads($~30Cdn)and you should get a few thousand km before you have to really fix it.Good luck:)

Hey thanks a lot for your help!:D

Glad to help out a fellow hoser,eh:D

My seal kit cost about $20 from the dealership. If you just reset the seized caliper, it will not release full brake pressure when you let off the brake. This will cause rotor warping, overheating, uneven and rapid pad wear, lower MPG and possibly other serious problems. If you reset the caliper, you are forcing the piston back onto more, unrequited, rust and it will be harder to remove next time; also will require more force to opperate (seized to a greater extent). I would not do this unless you don't plan to keep the car for more than a few more months (I'd say six tops).

To rebuild your caliper, it's not much more trouble than changing your pads. Once you have your wheel off, remove the caliper and brake-line. Remove the pads and use your C-clamp to hold in the NOT-seized piston, while applying 20-30 PSI of compressed air into the brake line connection on the caliper. Remember to keep your fingers out of the pistons way. It should just pop-out, if it's not seized really bad. If it wont come out, try increasing the pressure. PB-Blaster, available at Pep-Boys, is a great penetrating oil, and if you continue having trouble, try it. When the piston is removed, repeat for the other side (if it's not seized it soo will be) unscrew the bolts that join the left and right parts of the caliper. Lightly use a brake cylinder hone ($10) and light sandpaper to clean off the rust buildup on the piston and inside the cylinder for both sides. Carefully clean the cylinders and replace the o-ring type seal inside the cylinder wall. Replace the piston and fit new piston seals. Reverse obvious to reinstall. Then bleed your brakes and replace fluid with fresh new fluid. You car will drive much better and happier.

If you love your car, please do this.
Good luck.

ATLD
Adam

Hey ATLD:

Can you describe the compressed air deal a bit more in detail? Is there a fitting necessary from the air hose to the brake line? Thanks....

Don

There is a better way than compressed air -- use the brake pedal!

Remove caliper, clamp the "unstuck" side, then step on the brakes hard. This generates more pressure that is safe to use with compressed air, and won't blow out as the pedal will hit the floor when the piston is free. If you get carried away with the compressed air and the piston is really stuck, you get quite a blast when it does let go.

The usual reason an MB piston is stuck is that someone left under-thickness rotors on the car, the backing plate on the pad jammed up on the anti-rattle spring, and the piston is cocked in the bore. They can often be freed just by tapping on the upper edge to straighten them out in the bore.

Don't bother to hone the bores, and never, never use abrasives on the piston. If they are rusty or corroded or have crud on them that won't come off with brake cleaner, get rid of them. The bore and piston are both chrome plated for corrosion resistance, and the coating is thin enough that honing or cleaning with abrasive paper will remove it. The caliper will again seize in short order. The piston will no longer seal properly on the bore, and won't retract properly if it isn't very, very smooth (shiny bright). I'd also not take the caliper halfs apart -- they need to be very closely aligned for proper operation, and getting them re-sealed can be a pain.

Caliper re-build is very easy -- pull piston, remove square seal with a plastic or wooden pointed tool, no metal picks!, clean well with brake cleaner (no abrasives, please), wipe down with brake fluid, coat new seal with brake fluid and insert in slot, align piston (the heat shield won't fit if the piston is rotated, easy to see), press piston back into bore, attach new dust boot, and clip heat shield into place.

The piston can be removed by prying straight up with two screwdrivers from the sides of the caliper using the dust boot lip.

Peter

Thanks for the advice. Will be tackling this job soon.

Don

brake
 

If one piston is free pack the bore in the cylinder with grease and reinsert
the piston. Block the holes with bolts and PTFE tape as described above.
Now use a G Clamp to force the free piston into the housing in the caliper.
This will force the second piston out. If a G Clamp isn't strong enough for
the job use a pair of metal bars, one through the hole in the caliper and
the other on the outside. Bolt the bars together and tighten the bolts in
turn to drive the piston in. Alternatively use a bolt at one end of the
bars and a bench vice at the other.

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davis
Car Auctions

http://webhollis.com/albums/Funny-Forum/OldThread.jpg

Sometimes its just far easier, and safer when it comes to the brake system, to spend the $50 on a rebuilt caliper.

AHHHHH!!!!!! I just had flashbacks of reading "Great Expectations" in high school. That looks like Miss Havisham ... she just needs a rotting wedding dress.

:eek:

Now I got to find the "Pretty girls thread" to get that image out of my head.

Force, where can i find a rebuilt for $50?????

Use a brake cylinder hone to get rid of the rust.

Sears item #00904656000
Mfr. model #4656
price $3.97 while supplies last

Replace calipers in pairs! Do not replace just one side. The new/rebuilt caliper actually requires MORE pressure to activate and the increased pressure will "blow-out" the old side in a very short amount of time.