Alfa Romeo Forums banner

1 - 18 of 18 Posts

·
Registered
Joined
·
183 Posts
Discussion Starter #1
My rear calipers were seized, and there was quite a bit of rust which was contacting the pistons and holding them in place. The pistons are OK, but the bores they ride in have some visible rust. The rust was on the pad-side of the seal--not in the area where there was brake fluid. I didn't split the calipers, but splitting them sure would make it easy to get in there with a brake hone and clean out that rust. I've gone over it with 500 grit paper and the pistons fit fine with no interference, but how far should I go with rust removal? Is there a way to inhibit rust after they're re-assembled?

Thanks
 

·
Administrator
Joined
·
12,581 Posts
Brass sleeving the caliper is an option.

Pete
 

·
Registered
Joined
·
183 Posts
Discussion Starter #3
Brass sleeving the caliper is an option.

Pete
I don't think they're out of spec yet, although I don't know how to get a caliper in there to measure. Just wondering whether anyone else has run into the rusting bore problem and if there's a relatively simple solution.
 

·
Administrator
Joined
·
12,581 Posts
I don't think they're out of spec yet, although I don't know how to get a caliper in there to measure. Just wondering whether anyone else has run into the rusting bore problem and if there's a relatively simple solution.
You can hone them.
Pete
 

·
Administrator
Joined
·
12,581 Posts
OK, but doesn't that involve splitting them? Most of what I've read here says that's not something one is supposed to do.
Splitting the calipers is not something to be worried about. You will need to replace a small rubber o-ring that seals the 2 halves. That is all.

Good luck
Pete
 

·
Registered
Joined
·
4,306 Posts
I've read that a few times as well about not splitting the calipers but I don't recall the reason. I always split them every time I've rebuilt and have never had any problems. The seal is actually a square cut section ring rather than a regular o-ring but honestly I just re-used it since there was nothing wrong with it. It's not something that's going to wear out but I imagine you could find a match if you needed one.
 

·
Super Moderator
Joined
·
10,622 Posts
My rear calipers were seized, and there was quite a bit of rust which was contacting the pistons and holding them in place. The pistons are OK, but the bores they ride in have some visible rust. The rust was on the pad-side of the seal--not in the area where there was brake fluid.
The pistons do not ride in the bores - they ride on those square-cut O rings. So if the pistons are really unrusted, and the O rings are OK, then rust on the bores is no more significant than rust on the exterior of the caliper. Brake cylinders on drum brake cars are the opposite: there, the bores are the sealing surface, and the piston surface is pretty much irrelevant since the seals ride in the bore.

Admittedly, if the rust on your calipers is so thick that it interferes with the piston, it needs to come off. If only for the sake of cleanliness, you should attack the rust with a wire brush and remove all debris from inside the caliper. While you have it apart, install new O rings, lubricate with brake assembly lube, and call it a day.

The key to preventing frozen calipers is to use the car regularly, change brake fluid regularly, and avoid humidity (easier said than done).
 

·
Administrator
Joined
·
17,043 Posts
"Back in the day" it was advised to not split the calipers so they could go to a rebuilder unmolested. Essentially, if they needed more than seal replacements 'they' would rather you just swap them out for new or rebuilt units.

As for rust in the bores, the pistons & seals do not ride along the bores (like the pistons & rings in the engine do). Instead, the seals fit into recesses in the bore and the piston slides along the seals. The seals grip the pistons so the outside surface of the pistons must be smooth & clean (no rust/pits/scratches). It is the grip of the seals on the pistons that causes them to retract slightly when the brake pedal is released.

So, as long as the bores & the recesses clean up & the pistons are serviceable then they can be rebuilt. If needed, go ahead & split the calipers. Replace the square section seal between the halfs if you can. Examine the bolts closely - they should not have damaged threads or be stretched.
 

·
Registered
Joined
·
1,704 Posts
FWIW

About two years ago, before I fell in love and decided "nothing but the best!" for my baby, I didn't know about this prohibition on splitting calipers and - using the info found here - split all four of my calipers because three of them had stuck pistons. I bought rebuild kits and went to Harbor Freight and bought cheap Chinese caliper hones. I honed off the rust and found no pitting; I then reassembled the Calipers using the rebuild kit, caliper grease, the original o-rings, and the IAP template. They have never leaked and stop fine.

If you consider replacing them instead, I would probably consider buying the VW Bus big ATE's to replace the fronts, rather than stock. i doubt if they cost any more, and you are upgrading rather than just refurbishing .
 

·
Registered
Joined
·
1,879 Posts
If I lived in the US, I'd be boxing up all the calipers and sending them off to member/user PMB_performace to have them professionally rebuilt and restored. Seems like a cheap way to get peace of mind for the next forty years. Indeed his pricing nearly works out competitively sending them from Australia, it's just the shipping which can be a bear.

Have a search for some of his theads or posts on caliper rebuilds/splitting etc. all the info you need is in these.
 

·
Administrator
Joined
·
12,581 Posts
Probably the easiest thing on a car to rebuild is a caliper (a non handbrake caliper that is). There is nothing that is scary or should not be pulled apart.
Pete
 

·
Registered
Joined
·
2,076 Posts
You will need to replace a small rubber o-ring
Not just any rubber. Must be brake fluid compatible. EPDM.

You might be able to get the bridge seals from PMB Performance.

Or maybe Porsche pn 901.351.928.10, VW pn 311.615.277 would work.
 

·
Registered
Joined
·
97 Posts
One thing I found out is that the bolts are NOT Torx. They take a Ribe (AKA Polydrive) socket. This is similar to a Torx, but different enough to allow the Torx socket to ruin the bolt. (AMHIK) You can order the Ribe sockets online. It will take 2 different sizes for the front & rears.

Check out this link:
The Ultimate Brake Caliper Restoration Guide

Good luck, cadet!

-Ralphie
 

·
Registered
Joined
·
7,754 Posts
Professional brake people take all the guesswork out of the proposition. It is the best money you can spend on a car and it is done right. I use King Kaliper in Peabody MA. Calipers are their business. They can do ANYTHING, including removing broken bleeders and have seen it all.. The parts come back like new and the price is ridiculously cheap. The service is impeccable with easy communications and no long term waits. They keep their front desk phone person informed so there is no hassle chasing down the guy doing the work. They do all the equipment for the City of Boston so there isn't a challenge they aren't up for. I had my Lancia Fulvia rears done by them and they came out perfectly and hospital clean..click here. Home
 

Attachments

·
Registered
Joined
·
82 Posts
Early on in my Alfa education I was faced by the warning that you do not split callipers on an Alfa. I didn't listen and decided that it was a no brainier to split clean and reassemble the callipers. I progressed in the types and methods of doing restoration work and to the best of my knowledge and understanding I believe the following to be the issues and my methods for addressing it and resolving the "do not split warning."

The warning about rebuilding Alfa callipers relates to the flat mating surfaces of each half and the small square cut o-ring between the calliper halves. The seal must be able to withstand living in brake fluid, once compressed during assembly it will flatten down and expand in the recess it lives in providing a good seal for the brake fluid that passes between each half. I went to Wriason Seals and had some made. Natural rubber or a natural rubber mixture of compounds that is brake fluid rated needs to be used.

The flat mating surfaces on each calliper half must have the integrity of the plated zinc surface in tact. Without zinc plating, under normal circumstances, the metal would react with the electrolytes (moisture) and begin to corrode. If for example a calliper is reassembled with no plating, the mating surfaces will quickly start to rust and eventually the forces at a molecular level will create enough force to break the retaining bolts clamping the calliper halves together.

I chose to split my callipers and glass bead them, that's when I discovered the plating as I could see it being etched away by the action of the glass beading. I dipped them in a solution of iron phosphate to provide the first barrier to corrosion and to provide the base for good adhesion of powder coating material. I masked the mating surfaces and piston bore then powder coated them. The next step which I have to complete is use a wire wheel to remove the phosphate coating and create a smooth flat surfacing for plating. I plated all my fasteners using a kit from Caswell, this will be adequate for plating the surface and the piston bore (plating the piston cavity and outer surface is not required it happens), the callipers will weather better if they are fully zinc-ed, I chose to powder coat for the external surface of the calliper.

I've made the assumption that zinc plating is used by Alfa. Stock Alfa callipers are plated without a brightener thereby creating a dull gray finish you cannot see very easily as it looks like bare metal. The bright gold reconditioned callipers that are available will likely be zinc plated with the addition of a zinc brightener (yellow chromate) which changes it from dull gray to a bright golden colour and also increases the corrosion resistance of the zinc plating.

Zinc coatings provide a continuous, impervious metallic barrier that does not allow moisture to contact the steel. Without moisture, there is no corrosion. Zinc plating is a sacrificial anode which works by introducing another metal surface with more negative charge to it, more anodic surface. A metallurgical bond is formed between the zinc and steel creates a strong adhesion between the two materials. The zinc plating inhibits/reduces the formation of rust on either of the mating surfaces. Current will flow from the newly introduced anode and the protected metal becomes cathodic creating a galvanic cell. The oxidation reactions are transferred from the metal surface to the Zinc (galvanic anode) and will be sacrificed in favour of the protected metal. The zinc corrodes before the metal does, sacrificing itself for the benefit of the metal. The resulting corrosion of the Zinc creates an oxidation or patina providing an additional layer of protection.

Sacrificial Anodes are highly active metals that are used to prevent a less active material surface from corroding. Sacrificial Anodes are created from a metal alloy with a more negative electrochemical potential than the other metal it will be used to protect. The sacrificial anode will be consumed in place of the metal it is protecting, which is why it is referred to as a "sacrificial" anode. The zinc corrodes at a lesser rate without the consequences of metal on metal corrosion and with the benefit of improved corrosion inhibiting properties of the oxides produced.

In a nutshell it all boils down to a liability issue, failing to properly recondition the callipers. The assumption is that a car owner/hobbyist that works on his own vehicle doesn't have the ability to re-plate their callipers. For a retailer supplying rebuilt callipers, liability is eliminated/reduced by ensuring that the mating surface will not react and corrode to the wet environment they live in, causing a critical failure.

That's my understanding and methodology I'm using, I feel safe about it and it seems to resolve what I perceive as the reason for the "do not split warning." A zinc plating kit, power supply to control the current (regulates the deposition rate), patience, research, and attention to detail, it can be done in your work shop. An operating temperature for the dip tank at 110 deg F, with 0.14 amps per square inch of part surface, and a 20 minute plating time is all you need. There's lots of good information at the Caswell web site.

Ciao for now
Franco
 

·
Registered
Joined
·
7,754 Posts
Franco..dead spot on..We reap the benefit of a lot of years of experience and research before the internet... THANK YOU fro sharing your experience and research. Now I know why people like King Kaliper and others just don't give back a squeaky clean caliper but it is also plated in some solution.
 
1 - 18 of 18 Posts
Top