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Old 21st August 2019, 10:28   #1
Blink
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Question Acid for refurbing

Mild acid gobbles up rust if you leave a part soaking in it for long enough, i.e. 18-24 hours ish.

The vital question is, can it be used on brake calipers - i.e. submerse the whole thing in a bath after removing pistons & seals etc. Would the acid enlarge the un-rusty piston bore, thereby ruining the caliper, or would it just go for the rust?

Has anyone ever tried it?
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Old 21st August 2019, 10:29   #2
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This stuff - https://www.amazon.co.uk/Phosphoric-...3D1NRYBJRP3BE9
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Old 21st August 2019, 10:51   #3
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Quote:
Originally Posted by Blink View Post
Would the acid enlarge the un-rusty piston bore, thereby ruining the caliper, or would it just go for the rust?
Chemical type rust removers are usually based on inhibited phosphoric acid. The inhibitor prevents the acid from attacking fresh metal after the rust has been removed/converted to ferric phosphate and such. The acid is certainly not dilute or weak. In fact it's typically around 80% concentrated, so not to be messed with. It will take your eyes out if they get splashed (so wear goggles and neoprene gloves).

As to whether it would attack a clean piston bore in a rusty caliper, I suspect not. Not to any extent that would affect its operation. The metal surface may stain/blacken, but it shouldn't be etched. The product referred to in the above link is only 45% strength, so weaker than the industrial rust removers my old company made, but it should be suitable. Basically follow the instructions to the letter.

An impressive alternative to acids is the electrolytic method which does quite amazing things and in many ways is preferable to chemicals.
There are a few threads here on using a car battery and bucket for de-rusting parts. You can also find videos on YouTube.

EDIT: YouTube videos: https://www.youtube.com/results?sear...c+rust+removal

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Last edited by T-Cut; 21st August 2019 at 10:56..
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Old 21st August 2019, 11:09   #4
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For mild rust removal I've used normal vinegar, also for carbon removal on inlet / exhaust valves.
It takes a while to work on the item, but it wont kill you / poison you and is a lot more forgiving than some other products which can cause pitting if left too long.
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Old 21st August 2019, 12:13   #5
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I guess if you are expecting to see a smooth shiny surface after the rust removal you are going to be disappointed.---
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Old 21st August 2019, 12:16   #6
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Quote:
Originally Posted by T-Cut View Post
Chemical type rust removers are usually based on inhibited phosphoric acid. The inhibitor prevents the acid from attacking fresh metal after the rust has been removed/converted to ferric phosphate and such. The acid is certainly not dilute or weak. In fact it's typically around 80% concentrated, so not to be messed with. It will take your eyes out if they get splashed (so wear goggles and neoprene gloves).

As to whether it would attack a clean piston bore in a rusty caliper, I suspect not. Not to any extent that would affect its operation. The metal surface may stain/blacken, but it shouldn't be etched. The product referred to in the above link is only 45% strength, so weaker than the industrial rust removers my old company made, but it should be suitable. Basically follow the instructions to the letter.

An impressive alternative to acids is the electrolytic method which does quite amazing things and in many ways is preferable to chemicals.
There are a few threads here on using a car battery and bucket for de-rusting parts. You can also find videos on YouTube.

EDIT: YouTube videos: https://www.youtube.com/results?sear...c+rust+removal

TC
I've used the 45% stuff in the Amazon link and it works well if left for 18-24hrs. Not very economic for larger parts (@ £20 for 5L) but a caliper 'should' (?) fit inside a cut-off 6 pint milk thingy, with maybe 3 litres of acid.

I've seen/read about the electrolytic method before but never tried it. Maybe I'll give it a go with a caliper in a milk carton.


Quote:
Originally Posted by Odd Job View Post
For mild rust removal I've used normal vinegar, also for carbon removal on inlet / exhaust valves.
It takes a while to work on the item, but it wont kill you / poison you and is a lot more forgiving than some other products which can cause pitting if left too long.
I've tried white vinegar and it does work well - slower than acid but cheaper, £10 for 5L here.
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Old 21st August 2019, 12:19   #7
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Quote:
Originally Posted by COLVERT View Post
I guess if you are expecting to see a smooth shiny surface after the rust removal you are going to be disappointed.---
The castings aren't exactly smooth when they're new so I'm expecting a bobbled but rust-free surface. They'll be painted anyway.
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Old 21st August 2019, 17:32   #8
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Electrolytic method every time for me.
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Old 21st August 2019, 19:32   #9
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just did my 800 callipers and left them in a citric acid bath for a day and a half, beware the acid attacks chrome so my pistons were damaged but getting renewed anyway
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