Caliper rebuilding, is it ok to use a press to enter pistons?

[fizeus]

Hi all,
I'm in the middle of a caliper rebuilding project.
Calipers has been cleaned and zinc plated and now i'm reassembling.
I also changed inner seals and new dust covers, all ATE original parts.
Before putting back the cylinders I used a bit of ate caliper grease in the caliper bore.

I have noted that cylinders are very hard to sit in the caliper bore and i had to use a press to accomplish the job.
The Ate gasket manual says that pistons shuold snap in the caliper easily but i had to place them in the caliper bore with a press tool.

Is this normal? Is there any tip or trick i forget?

Thanks in advance.

[DaveMcKenz]

Not normal. Suspect parts mismatch.
Good luck,
Dave

[DRACO A5OG]

Originally Posted by DaveMcKenz

Not normal. Suspect parts mismatch.
Good luck,
Dave

+1, you should be able to put in by hand if fill valve is open and you use brake assembly lube or brake fluid. Make the inner seal is the proper ATE one (lube that too).

[shrtshck]

Should not have to press fit the pistons, something is not right. I have done this and was able to press the pistons in by hand. Can sometimes take a few tries to get the piston aligned with the bore, if not they won't want to go in. Recommend removing the pistons, inspect that the seals are not torn, and try again.
Could clean up thee bore with some fine emory cloth, possilby there is some build up from the plating.

[DRACO A5OG]

OP, post some pics and/or measurements. This way we can stop guessing on your behalf.

[juanbenae]

agree with what's been stated above. if you warm the caliper by letting it sit in the sun for a while with the new seal in place with a cool piston it can work well. lube after it's warm and use a lath like piece of wood to span the entire piston and roll it some like a stadium wave as you apply downward pressure after yir sure the groove is set at 20*...

ive found only brake fluid was ever needed to lube them for insertion. then again ive got a tiny piston...

[porsche930dude]

yes should go in by hand twisting it helps. You can sand the bore but never the piston.

[Rawknees'Turbo]

Originally Posted by juanbenae

ive found only brake fluid was ever needed to lube them for insertion. then again ive got a tiny piston...

Yes, but you make up for that shortcoming with personality and technique (so I hear)!!!

[fizeus]

Thank you all for you help.
I disassembled the caliper again, cleaned with brake cleaner to remove the caliper grease and magically the piston has snapped in perfectly by hand.
The problem here seems to be the grease: if I reapply it the piston wont snap in because it produce high resistance.

I'll try to put the caliper in the sun to see if this helps.... i've probably used to mutch grease. Isn't it?

[DaveMcKenz]

Try just a little brake fluid.
Good luck,
Dave

[al lkosmal]

when you had them zinc plated....did the bores get plated too?

regards,
al

[juanbenae]

Originally Posted by Rawknees'Turbo

Yes, but you make up for that shortcoming with personality and technique (so I hear)!!!

[djpateman]

Be very careful what "grease" you are using. There is an ATE Brake Cylinder paste that is used for parts in contact with brake fluid. Most caliper grease is for lubricating external parts like pins, slides & pad edges; but must NEVER be used for internal applications.
I have rebuilt countless calipers, but never needed more than hand pressure to install a piston. Something was very wrong to require a press.
I find the best technique to installing rebuilt calipers & pads is to assemble everything as usual and bleed the system until the pedal is firm. Then remove the pads and replace with something just a little thinner. Use the pedal to push the pistons out just a little bit more. Remove the replacement pads and force back the pistons with a spreader JUST enough to install the new pads. Pump the pedal until you have a firm feel again. Then do a test drive. The purpose is to ensure the seals are properly set so that they do not retract the pistons too much after the brakes have been applied; this is a common problem after installing calipers.

[trond]

press or hammer, both will work equally well...

[fizeus]

Ok, that's my fault.
Greasing the bore seems to be a good idea but I used too much and this interfere with piston ability to slide down the bore.
I simply removed again the pistons, wiped excessive grease and, as suggested, used some brake fluid.

This has solved the problem.

P.S. I have used bremszylinder-paste, and this should be the right grease. It's simply a little dense when cold so this can interfere whit piston ability to slide down to the bore. I imagine that this grease has been made to work with high temperature.

[DRACO A5OG]

Great, that was easy

[juanbenae]

the caliper rebuild grease is snake oil IMO. really, just plain old new brake fluid was all it ever took to get mine seated. is the grease apt to float up to the top so it flushed out as you bleed the system, or does it just float around in there after you put the brakes back into service? neither sound desirable.


t

[Walt Fricke]

I once pressed the pistons in. Didn't work well on the car, as they wouldn't retract when the foot was off the brake. They were aftermarket stainless pistons, and they had been made a hair too large. Luckily the seller took them back and got ones which fit, so all was well. I should have known better than to have put the calipers to use that way, though.

So plating the inside of the caliper bore is something I would not consider doing. It doesn't have to be as perfect as the piston has to be.

And yes, a little brake fluid should be all the lube for the seal needed, because that is what will continue to be on the seal anyway once the car is driven.

But sounds like you got it, so all is well.

[chris_seven]

Using brake fluid to lubricate pistons instead of a 'caliper' grease is interesting and some work was carried out at Girling some years ago using a caliper test dyno that I was involved with.

Brake fluid generally has a lower level of lubricity than a typical caliper grease and this means that a small increase in force is needed to operate the brakes.

This translates to an increase in seal deformation and hence the energy stored by the seal resulting in an increase in piston retraction once the brakes are released.

We are no always told that 'pad retraction' is a good thing as it stops brakes from rubbing and improves fuel consumption but I generally feel that this is BS

I was always taught that piston retraction caused longer pedal travel and wasn't good on cars being driven hard.

We always fit 'residual' springs in all the caliper we rebuild for Trackday and Competition cars and we always use ATE Caliper Assembly Grease.

The influence of the assembly grease lasts for surprisingly long periods of time and produces measurably different test results.

I am sure that for most normal application differences are small but just worth considering for race cars.

I have never seen a caliper where the zinc has plated into the piston bore as the 'covering power' of most rack plating baths is quite poor in terms of the ability to plate into a relatively deep hole

[Walt Fricke]

Chris
One source of piston retraction is the almost inevitable knock back from rotor irregularity (or, if you will, runout). My race rotors use round cross section rings, so I'm guessing that has less retraction power than the ATE square cut ones?
But how do you set residual springs? Are they long enough to push the pad right up to the rotor when the pads are worn thin? Wouldn't that cause more friction against the pad when the pads are fresh and thick? I've read about these springs, but how they function isn't intuitive, at least not to me. I prefer that my pads don't touch the rotor except when I am on the brakes. I must be missing something.