How to compress REAR brake piston

[Nanonevol]

Roy Batty link above doesn't work. RRoller or anyone remember what tool is referenced?

[RRoller123]

no idea, been too long.... I used a large handheld metalworking file to fit in the slot.

[AriK]

Try this link
http://www.fiatspider.com/f15/viewtopic ... brake+tool

[DieselSpider]

I just use a piece of 3/16" thick bar stock, file, flat bar or whatever else is handy and fits in the slot to screw them in.

If the brake fluid was really bad or the rubber hoses failed I will unscrew them to remove the pistons completely and be sure to flush out the back of the pistons to clean out the self adjusters located inside them.

[Nanonevol]

Thanks, I have the advantage of having the caliper out of the car and had it all apart for cleaning and new seals. I don't understand why it's so hard and why there is not a specific tool available for this. Or is there? I'm brainstorming a way to fabricate one.

[DieselSpider]

Thanks, I have the advantage of having the caliper out of the car and had it all apart for cleaning and new seals. I don't understand why it's so hard and why there is not a specific tool available for this. Or is there? I'm brainstorming a way to fabricate one.

There are some tools out there but any old mill file or piece of bar stock along with a Crescent type wrench to turn the file/bar stock will do it so most don't bother with any fancy special purpose tool. Its not hard or complicated unless we make it that way over engineering a more complex than required solution. "Keep it simple" is the key thought here.

[Nanonevol]

Thanks, I think you're right - If it takes more than reasonable force there's something wrong which is the case with one of my rears. The right side screwed in as expected - I actually used a vice grip on the small end - but the left was much more difficult and won't go all the way compressed. And when I squeeze the lever for the emergency brake nothing happens so I think there is something wrong with the mechanism inside the piston. I'm going to take it apart and look at it but I'm thinking I need a new caliper.
I think you can tell I'm a stubborn SOB.

[DieselSpider]

If the groove for the pressure ring or seal was not cleaned out completely then the pistons will be hard to turn in however that would have been apparent while rebuilding them. If you did not pre-lubricate the piston and seals with brake fluid then they can sometimes also be quite difficult to turn in. The self adjuster mechanism will simply not activate and adjust for wear if it sticks however if the threaded pin inside the caliper or the threaded center of the adjuster is dirty that could make them difficult to turn in too. Cleaning up the adjuster pin and mechanism inside the piston is very often overlooked.

Be aware that there are loose ball bearings inside the piston that are very easy to loose. Be sure to pay attention to how it all goes together too as I have not found a good diagram to jog ones memory.

[Nanonevol]

Thanks Diesel Spider for walking me through this. I took my troublesome one apart but the inside of the piston looked so pristine (and complicated) that I left it alone. It went back together fine this time for some reason. I think it's a no-no but I actually lubed the seal a bit with brake grease. It was a desperation move. Anyway I won't be looking for a new caliper which is good. New springs and sliding pieces should come today from A/R.

[DieselSpider]

Its ok to lightly lube the outer seal with brake grease however the piston ring should only be lubrcated with brake fluid. One might be amazed how much easier the pistons go in with just a few drops of brake fluid smeared on the square cut o-ring.