Hydraulic jack fluid.

[Dana67Dart]

I bought a rebuilt single pot master cyl and some lines and fitting to pop some caliper pistons out of a KH caliper.

I would rather not use brake fluid due to its paint eating characteristics (ask my sister how I unknown this)

I have a bottle of Jack oil I'll never use so i figured it would work well.

I will never use the master for anything else, and the calipers will be fully rebuilt.

Any reason not to use the jack oil?

I am fully aware of the many techniques to minimize the fluid everywhere.

Thanks for your input

 

[abdywgn]

how about an air nozzle in the brake hose port?

 

[Dicer]

Nope, no problems. I have used power steering fluid, ATF and engine oil. Cooking oil will work also...for jack oil.

 

[RustyRatRod]

You could probably use water. Go for it.

 

[1MeanA]

It will be fine but you might have better luck with a grease gun. You just need threaded adaptors.

 

[Dana67Dart]

how about an air nozzle in the brake hose port

One 1/2 might come out under air pressure, the other I'm probably going to have to drill out one piston.

Caliper has been open to the atmosphere for some time

 

[1MeanA]

One 1/2 might come out under air pressure, the other I'm probably going to have to drill out one piston.

Caliper has been open to the atmosphere for some time

You have to block the pistons that move to stop them coming out of the bores while you work on the stuck piston.

 

[65TerrorCuda]

Brake fluid, no problems yet. Cured the leak too.

edit: oops, thought we were talking floor jacks. my bad

 

[Dana67Dart]

It worked perfect on 3 out of 4 pistons.

Minimal mess and super easy

The 4th is really stuck. Tried an 18" pipe wrench to twist the piston not a budge.

Soaked in PB blaster for a week, heat and soak and heat and soak etc.

The other piston of that half was pretty clean inside but had some rust between the outer seal and the inner seal.

This is the piston that squished my finger last week. So come hell or high water I'm getting it out!

 

[1MeanA]

Did you try and push the stuck one back into the bore? As you probably found out when using air, the pistons can be little rockets if there are no blocks to stop them flying out the bores. This is the video I watched before rebuilding my calipers a few years back. I did find that air is not enough pressure on the stuck pistons.

 

[DFX 340 Duster]

@hemi71x

Jim, any suggestions?

 

[Dana67Dart]

I came, I saw, I kicked its ***!


Dana 4 Caliper 1

Piston on the right was the stuck one.
Finally got it to turn, then hydrologic pressure and twisting.

The one on the left is the other from the same 1/2.

Rust in the usual place.

The other 2 pistons are really good but I'll probably replace all 4

 

[slantsixdan]

You're reminding me of the time, decades ago, when I set up a completely unstable pile of cinderblocks and bricks and caliper, put two long HD screwdrivers across from each other in the piston groove, and stood/jumped on the screwdriver handles to pry the extremely stuck pistons out from a pair of KH calipers. For some strange reason (probably the stupid luck that sometimes favours dumb teenagers) I got all eight pistons out and didn't break any bones.

 

[Dana67Dart]

@hemi71x

Jim, any suggestions?

That's funny, if I did not prevail today I was going to reach out to Jim!

 

[Dana67Dart]

Did you try and push the stuck one back into the bore

Yep, 3 of 4 moved #4 no way in hell!

I did not bother with air, hydraulics worked like a charm, and it only goes as fast as you clamp the piston into the MC. Very controlled.

The #4 piston took considerable persuasion. But once I got it to spin and applied some hydrolics pressure I got it to walk out.

 

[hemi71x]

@hemi71x

Jim, any suggestions?

WOW, boy, that is one mangled up piston that you got out of that caliper.

Yes, i have had some stuck pistons in some of the calipers that i have rebuilt throughout the years.

I taught myself a method in getting them out hydraulically by pumping grease behind the piston to get the stuck, frozen, piston(s) out of their bore.
I made myself a grease gun fitting screwed onto the screw flare nut end of a hydraulic brake hard line on the caliper.
You want to limit the travel of the piston that wants to come free first and all that i do is limit the travel of that piston in the jaws of the vice and and a block of wood.
I pump in the grease and open the jaws of the vice a bit at a time until the stuck piston starts to come out.
Kinda hard to explain in print, but i got every stuck piston out that i ever ran across.

My rebuilding days of calipers are over.
They have gotten to expensive, replacement parts wise to buy, and it's just not penciling out for me anymore in rebuilding them, and then trying to find buyers for them.
Jim V.
hemi71x

 

[Dana67Dart]

Thanks for the tips.

I started with grease gun but my tube was empty.

The master cyl worked great.

I used a c clamp to limit the travel

 

[Dana67Dart]

WOW, boy, that is one mangled up piston that you got out of that caliper

Got a question...

Any idea what these marks are on the bottom of all 4 pistons?

Each has 2 distinct grind marks

 

[hemi71x]

Got a question...

Any idea what these marks are on the bottom of all 4 pistons?

Each has 2 distinct grind marks
View attachment 1716481796View attachment 1716481797

I'v got a lot of old pistons with that mark on the bottom of them, too.
Never gave it a thought.
Most likely just a machining marking from the company that manufactured them in the beginning.

 

[Dana67Dart]

I'v got a lot of old pistons with that mark on the bottom of them, too.
Never gave it a thought.
Most likely just a machining marking from the company that manufactured them in the beginning.

all 4 were the same height. I saw that on some calipers there are 2 longer and 2 shorter. I wonder if the mark is an indication of that? I thought I saw that pistons with a round grove on the face that presses on the pad was the indication of long vs short?

 

[hemi71x]

That's because some pistons were previously replaced with parts store items in the lifetime of the calipers.
i too, have run across that same thing in the past.