Ferrari Mailing List: Brake caliper piston rust removal

[Douglas Anderson (dnt]

Yeah, WD 40 is good stuff.  Really not lubricant per se.  WD stands for Water – Displacement.

 

BRAKE caliper pistons

Caution:  the piston may have a large square groove and a weird square “O” ring.  When all is happy, and the brakes are applied, the brake pressure presses the piston which presses the brake pad towards the caliper and squeezes the caliper.  In the process, the large square O ring tips towards the caliper, is now distorted in its square groove and isn’t happy. 

 

In the caliper squeezing state – the unhappy distorted square O ring wants to return to its ‘at rest’ position in its square groove.  When the brake pedal is released the distorted O ring pulls the piston back to it near previous, minus a millionth of a mm wear, location.  When the piston returns to its at rest position it releases the pressure from the pad and allows the pad to slither back a few thousandths of an inch away from the caliper which keeps the pads from dragging on the caliper.

 

HOWEVER – 308 rear brake caliper piston maximum caution should be exercised.  The pistons ‘work’ the same as above from their at rest position to working position BUT the initial setting for the rear caliper to pad MUST be set up manually.  How much?  .008” on both sides or .02 mm. 

 

So why be careful?  Because the initial piston to pad to caliper set up is a monkey motion Allen (?) bolt set in a series of interference washers and must be released by unscrewing the bolt going thru the caliper from the backside. 

 

If the pads are forced back into the caliper as you can do with the front brake calipers there is a good chance the monkey motion bolt arrangement will be striped and now . . . . and now you have a one way piston towards the caliper motion.  That is there will be no piston back off clearance once the brake pedal is released and the pads simply get tighter and tighter. 

 

Ever seen a blue caliper disk?  Pretty.  But pretty awful as it can actually stop the rear wheels from turning.  Such a fine bit of engineering.

 

So if you screw up the rear caliper pistons – that’s and expensive fix – but hey, that’s the brakes.

 

Doug

 

From: Ferrari <ferrari-bounces+dnt=dock.net [at] ferrarilist.com> On Behalf Of Rick Moseley
Sent: Thursday, February 17, 2022 6:03 PM
To: DOUG <dnt [at] dock.net>
Cc: The FerrariList <ferrari [at] ferrarilist.com>
Subject: Re: [Ferrari] Rust removal

 

Or EvapoRust

On Feb 17, 2022, at 17:30, Clarence Romero Jr. <clyderomerof4 [at] gmail.com> wrote:

WD-40 

Clyde Romero

 

If you have no enemies

You have no character ! 

 

Scars are tattoos with better stories!

When you're out of F-4's you're out of fighters!

 

 

 

On Feb 17, 2022, at 8:22 PM, Dominic Carri <zigzagzoot [at] comcast.net> wrote:

Just wondering what seems to work best to de-rust brake calipers and loosen pistons?

And if any heated discussion occurs I have 4 calipers and 4 5 gallon pails so I’ll run a test for certainly what will be ‘inconclusive’ results!
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