Caliper cleanup question

[steveg]

I'm getting my Jag calipers ready for rebuild. Have cleaned off all loose grease and dirt using laquer thinner but they're still really grungy. I'm planning on painting them.
Do they have to be media blasted or is there another chemical I can clean them up with which won't etch the piston bores?
These are typical but all the pieces are similar.

 

[HealeyRick]

Steve,

Try purple "SuperClean" from your local auto parts store. Make sure you wear proper protection, especially hands and eyes, It's really strong. Not for prolonged exposure on aluminum parts. Make sure to follow the directions. Good luck!

 

[57_BN4]

Don't waste your time with anything less than methylene chloride, aka paint stripper. It attacks everything except rust and leaves an oil-free surface after water washing that is ideal for paint to stick to. Try it on some old gungy SU carbs, they'll look like they are NOS in about an hour. Andy.

 

[drambuie]

If you don't want to use toxic chemicals, buy a box of baking soda and a cheap media blaster...The baking soda is very fine and easy on surfaces. Just duct tape over the bores and fluid passages. Your parts will look New again! A air compressor fitted with adjustable pressure gauges, Blasting pressure set at about 90 to 100 psi and a cheap media blaster gun works just fine for small parts such a calipers and Carb bodies ect... Just do the blasting in a contained blasting box, very easy to make. You will use it over and over again on many other projects as well.

 

[BoyRacer]

The only way to get your calipers looking good is to media blast them using either sand or glass beads. Soda blasting is usually not aggressive enough to clean the crud off calipers. I prefer glass bead blasting. Even if you sand blast them, you are not going to damage anything. The seal is made between the square section O ring in the caliper and the piston. Even if you "etched" the bores by using sand, it will have no effect on your calipers working just fine. Just make sure you wash the calipers after you blast them using soap (I use dawn) and warm water.......agitate the caliper in a bucket ........this will wash out the glass beads.

 

[drambuie]

The only way to get your calipers looking good is to media blast them using either sand or glass beads. Soda blasting is usually not aggressive enough to clean the crud off calipers. I prefer glass bead blasting. Even if you sand blast them, you are not going to damage anything. The seal is made between the square section O ring in the caliper and the piston. Even if you "etched" the bores by using sand, it will have no effect on your calipers working just fine.

Hello Richard, One reason I like the finer soda blasting is because the coarse media types tend to pit smooth surfaces such as caliper bores or carb bodies which are critical...many times the naked eye can't see the pitting that takes place that could damage the O rings. Most likely the bores would be masked off but sometimes the sheer air pressure pulls back the masked areas. In any case, the calipers will end up being painted after blasting anyway! Take care.

 

[steveg]

Followup - Original with Meth-Chlor Paint Stripper vs Evapo-Rust:

Both were carefully pre-cleaned to remove dirt & grease; both soaked overnight and washed with Dawn and a bronze brush.

 

[57_BN4]

Careful with that evapo-rust stuff, it can ruin parts very quickly. I tried dipping the engine side plates and the generator fan in it overnight only to find a mass of small craters had appeared all over the parts. Apart from looking rather ugly, the metal inside these craters is 'active' in that it will start rusting immediately even if painted.

Paint stripper doesn't make things look as pretty because it doesn't attack the steel/iron but also it doesn't activate the surface so no problems with spiderwebbing under the paint. I'd recommend dipping any parts exposed to evapo-rust (and any coarse blasting media) in weak phosphoric acid to neutralise the surface before painting. Read about active and passive surfaces on Wiki https://en.wikipedia.org/wiki/Passivation_(chemistry)

Andy.

 

[steveg]

Careful with that evapo-rust stuff, it can ruin parts very quickly. I tried dipping the engine side plates and the generator fan in it overnight only to find a mass of small craters had appeared all over the parts. Apart from looking rather ugly, the metal inside these craters is 'active' in that it will start rusting immediately even if painted.

Paint stripper doesn't make things look as pretty because it doesn't attack the steel/iron but also it doesn't activate the surface so no problems with spiderwebbing under the paint. I'd recommend dipping any parts exposed to evapo-rust (and any coarse blasting media) in weak phosphoric acid to neutralise the surface before painting. Read about active and passive surfaces on Wiki https://en.wikipedia.org/wiki/Passivation_(chemistry)

Andy.

Would vinegar work?

 

[57_BN4]

Would vinegar work?

Don't think so as it is acetic acid. Coke might since it contains "food acid" which is phosphoric acid renamed to sound more palatable on the bottle label. The best stuff is any of those 'rust eater' solutions watered down a bit, enough so that the resulting liquid tastes kind of nice. [quickly inserts standard disclaimer!] If the phos acid is too strong it leaves a white fluffy residue on the surface.

Here is a pic of my generator fan after evapo-rust treatment.


Andy.

 

[BoyRacer]

Hello Richard, One reason I like the finer soda blasting is because the coarse media types tend to pit smooth surfaces such as caliper bores or carb bodies which are critical...many times the naked eye can't see the pitting that takes place that could damage the O rings. Most likely the bores would be masked off but sometimes the sheer air pressure pulls back the masked areas. In any case, the calipers will end up being painted after blasting anyway! Take care.

First, there is a huge difference between an aluminum carburetor and a cast iron brake caliper.
As for sand blasting calipers, what pitting could possibly damage the O rings? You don't media blast the calipers with the O rings still left in.
As for pitting the bores of cast iron calipers when you sand blast the outer portion, I don't even think it is possible to do so, even if you were trying to do so. And, even if it is possible to "pit" the bores, it would still not have any effect on the proper functioning of the calipers.
The brake fluid seal that takes place in the caliper is between the O ring seal in the caliper body and the smooth surface of the piston, not the caliper bore. The smoothness of the caliper bore that could possibility be affected by sandblasting is not critical and has no effect on the "seal" of the brake fluid.

 

[Healey Nut]

When I did mine I used my home cabinet blaster with glass bead . Removed the pistons and hydraulic lines .I did not separate the caliper . I stuffed the piston cavitys with a rag and covered it over with duct tape . Took a small strip of rag and rolled it up and twisted it and screwed it into the hydraulic line hole . Blasted them clean blew off all the residue , painted and rebuilt all good working fine no issues .

 

[drambuie]

Sure, we all know where the critical areas are in a simple brake caliper, being the smooth piston surface Rubber O Ring and the groove that the rubber O Ring is seated. I have seen the result of people concentrating blasting course media at the groove area in the bore because it Is a little harder to reach, resulting in pitting and eating away the groove area very badly...you would be surprised at something's people do! we all know rubber O rings should be seated in a smooth surface for obvious reasons.. Don't get me wrong Richard, I blast my calipers with glass beads as well, however I switch to soda media for the smooth bore areas. I too wash them in water afterwards and use compressed air to blow out the passages before prime and paint. Take care.