930 Caliper Rebuild (Process)

[ncseahawk]

Well, Here goes, have been watching posts etc for quite a while. Have even contributed to a few threads but this will be on e of the first times I am attempting a how to.

To set the scene. I got a pair of rear 930 calipers for near nothing a few months ago hoping to find a project that I could handle but also one that would help me upgrade the p-car.

First off these things were UGLY xxx UGLY when I got them. The pictures do not do justice to the amount of caked on paint. It was everywhere.

[flatsixjunky]

Hello, I'm new here also and I'm in no way telling you what to do, just trying to help. Maybe you should try giving this a read:

http://www.pelicanparts.com/techarticles/911_caliper_rebuild/911_caliper_rebuild.htm

flatsix

[ncseahawk]

The first thing to do after reading similar pelican threads was to go get some stripper.

I have seen others suggest some sort of media blasting and still believe it to be a good idea, on the other hand I don;t have enough time to track down these sorts of things.

Instead I decided to use some aircraft quality stripper. Its a chemical item. Comes in a spray can. Foams up upon contact with surface. Wait about 30 minutes and you can begin taking off the paint.

The first coat of red came off pretty quickly, the second a yellow coat was less easy to remove.

Stings like a biatch at fist. Now I can hardly even feel it. I'm not sure if that is a good thing though.

[ncseahawk]

FlatsixJunky, Got it. I am attempting to add something to the community.

So...

Today I finally broke the caliper down into its assorted pieces for more cleaning.

Took a breaker bar to get the main threads loose. But they finally gave way without me having to resort to flame. PB Blaster had minimal effect.

So, breaking them parts down allowed me to begin to address all the little nooks and crannies these little babies have, fins and all.

[ncseahawk]

Now with all the parts in a bucket, I can spend my evenings with a dental tool trying to remove all the tiny bits of paint.



Does anyone know why the pistons appear to be of different metal composition. The seals appear to be OK and I'd rather not take the pistons out if they are in decent condition and the right parts.

[ViR2]

did you leave pistons and seals in when you used coating remover?

[ncseahawk]

Yes, the pistons and seals remained in when I used the solvent.

They caked in red paint, including the inside of the pistons and the seals. So much infact that I could not tell that rubber seals were present at all.

After removing all the paint, the seals and the pistons appear to be in very good condition with no nicks, burrs, dents, etc...

I'll post close-ups later

[mede8er]

I'd be surprised if the paint remover didn't compromise the integrity of the seals...at least the dust seal should probably be replaced, if not both....

[javadog]

If the calipers were mine, I'd pull the pistons and seals and rebuild the whole caliper, not just remove the paint.

Just my 2 cents,
JR

[GaryR]

Originally Posted by javadog

If the calipers were mine, I'd pull the pistons and seals and rebuild the whole caliper, not just remove the paint.

Just my 2 cents,
JR

I would hope so, considering the thread is titled "930 Caliper REBUILD (Process)". New seals, clean/inspect the pistons and bores, etc..

[ncseahawk]

But of course I am going to take out the pistons and replace the seals, scrapers, etc...

Now I have to find a compressed air source to do so. Any suggestions, Harbor Freight, HD, Lowes.

[WERK I]

Originally Posted by ncseahawk

............
Does anyone know why the pistons appear to be of different metal composition. The seals appear to be OK and I'd rather not take the pistons out if they are in decent condition and the right parts.

I believe the pistons are stainless steel. Check the piston bores for pitting/corrosion.

[DW SD]

Are you going to have the calipers re-annodized BLACK as they were delivered from the factory? Seems as if your stripper has removed the annodizing.

Note for future rebuilders: You can use soda blasting to remove paint and it will not harm the annodizing, if you are careful. Maybe the annodizing had been previously removed?

NCSeahawk,
When I read your comment about not removing the pistons, I had assumed you decided against a proper rebuild. Good to see I misinterpretted your comments.

While a simple project, functional, reliable brakes are absolutlely a critical safety component, as you know.

Keep us posted!

Doug

[jcge]

Originally Posted by ncseahawk

Now I have to find a compressed air source to do so. Any suggestions.

If you only want to remove the pistions, (and aren't looking to buy a compressor) get a schrader (tyre) valve fitting and head to your local petrol station and use their tyre inflating hose to pop the pistons out of the caliper and into a rag (held facing away from you)

[ncseahawk]

JCGE,

Good solution. Thanks for that. I'll give it a go tomorrow nite.

[mede8er]

Be extremely carful popping those pistons out, they come out at a very high velocity...

[boostfix]

I recently rebuilt my 930 calipers (fronts) with the seals and scraper rings from Pelican. It was my experience that one or two pistons tend to move more freely than the others. To ensure that they all get moving with the compressed air and allow final extraction by hand I cut a wooden block of the correct thickness and placed it between the pistons (in place of the rotor and pads). This blocks the early moving pistons and allows the compressed air to work on the stubborn pistons. If one comes out early just fit it back in and continue. They come out with some force so be careful. If they go flying you run the risk of damaging the piston. Not sure what type of metal they are but there appears to be a coating of some type on them. Don't forget to get a tube of Dow 111 (silcone grease) as an assembly lube. The bigest challenge of the whole process was getting the old scraper rings out without scraping the cylinder bore. The manual talks about collapsing the steel retaining ring of the scraper ring with a punch to remove. Getting the new scraper rings properly seated was next challenge! Good luck.

[mede8er]

Here's how I do it...wood wedges...then I spin them out the rest of the way...

[ncseahawk]

Good photo. I'll try and recreate with scraps in the garage. Pics to follow.

Love this board

[ncseahawk]

Alright. I went down to the gas station last night as recommended to use the coin operated type air hose.

Sadly, enough pressure was not generated to even get the pistons moving in any fashion.

I figure I will just have the machine shop that files the old mounting holes down and re-drills as per VCI techinque to do it.

I'll update accordingly.