Rear Brake Piston Installation

[midlifecrisis]

OK, I give up. Literally, as now I have to go back to the dealer for yet another part.

During a caliper rebuild I removed the old boots and seals, lightly honed the cylinders, cleaned everything up, installed new boots and seals, then tore one of the new boots by forcing the piston back in.

I greased up the boot before hand, then pushed the piston in with my fingers while turning it clockwise.

What's the trick to get the piston back into the cylinder without destroying the boot?

Thanks!

 

[TyraNSX]

I don't know for sure if this works due to the parking brake mechanism inside the caliper with the threaded rod, but for a front caliper (no rod), use an air compressor with a "squirt gun/blaster" nozzle on it thru the brake line conection port or bleeder screw port. Lube the piston & boot with plenty of clean brake fluid & use air pressure to inflate the seated boot around the piston. Once it is over the edge of the piston all around you should be able to seat everything by hand. I once spent MANY hours outside in the winter trying to do what you are doing on my Scorpio. I finally got lucky & the threads on the piston eventually caught the rod & it was then easy to thread back in. Good luck & you have my sympathy.

 

[Daedalus]

Haven't done it on the NSX, but your frustration sounds familiar. What I've done in the past on other cars for various seals, including brakes, is to use a small rectangular piece of mylar rolled up into a slightly conical tube. Lube it up on both sides, slip it into the seal, then slip the piston into the sleeve. Once the piston is past the lip of the seal you can pull the sleeve out. Measure the piston diameter, calculate the circumference, then cut the mylar to be just a little longer than that in one axis, and about the same length as the piston in the other axis.

 

[midlifecrisis]

Well, I tried the air pressure suggestion, but still couldn't get the piston in place.

I don't believe the emergency brake bolt is causing the problem, since I don't feel it touching the piston yet.

I'll try the mylar sleeve approach next weekend. Hopefully that will do the trick.

Any and all other suggestions welcome!

Thanks.

 

[midlifecrisis]

I tried the mylar sleeve approach with no success. Afer inserting the sleeve into the cylinder, the front of the caliper body gets in the way when trying to insert the piston into the sleeve.

Does anyone know the procedure a certified tech would follow?

 

[ChopsJazz]

I feel your pain. I tore a boot too trying to do this years ago, but I had success after that one attempt. But I forget how...

I think patience will win the day. Good luck.

 

[midlifecrisis]

Success!

I revisisted the air pressure suggestion, this time mounting the caliper body in a vice. With both hands free, I put the piston in place and slid a 3/4" wood block behind it. While holding the piston firmly and dead center against the boot, I injected air through the brake line inlet, and POP! The piston pushed out about 1/2" before it hit the block, giving the boot room to expand outside the cylinder.

With the air still on, a little finesse got the boot all the way around the piston. It then went into the cylinder smoothly.

The fronts posed another obstacle - 2 cylinders sharing the same air chamber. I resolved this by doing both pistons at once, carefully sliding the 3/4" block in behind both of them. Once I had the first boot seated, I placed a larger block (1 1/2") behind it so it wouldn't blow the piston clear out, then used the 3/4" block behind the 2nd piston.

Patience (and precision) will win the day!

 

[TyraNSX]

Lots of profanity helps too! :smile: Be glad it's over with.