908 Magnesium Brake Calipers Restoration

[914-6gt]

Just wanted to highlight and share with you all a few 'before and after' photos of the PMB restoration of my 908 Mag Calipers. Eric did a wonderful job bringing these very rare racing calipers back to life.

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The 'after'...

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Thanks again Eric!

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[718RSK]

Very nice, did you guys re-chromate the caliper halves?

[Neunelfer]

I'm not really qualified to answer the coating question. I believe it's the Dow coating but Armando's mag. guy didn't really say when we spoke with him.

Knowing it was the original finish, we did try the chromate but, on our sample it didn't turn out as we expected. I tend to think it will only work with calipers or various mag. bits fresh out of the forging. Over the years, the porosity and corrosion cause the chromate dip to have a fuzzy effect. Aside from an industrial polish first, that's the only way it might work.

For this reason we went with Armando's friend who does mag. finishes. Again, I don't think he likes to tell people what he's using. With a lot of these guys, their secret is their livelihood. He "did" run the calipers through an industrial polish (we found all of the beads clogging up the various journals when we went to assemble them), so, perhaps on the next set we'll experiment with a glass bead and a heavy industrial polish and shoot for the chromate again.

It is my belief that these were a very shiny silver with a rainbow hue from the chromate when new. We "did" see quite a bit of rainbow on one of the calipers which was the driving factor.

Here's a picture of the rainbow we saw:



Here's a sample of magnesium billet.



For a complete photographic history of the process, you can review the Facebook Album here:

https://www.facebook.com/media/set/?...0238192&type=3

[914-6gt]

I'm not really qualified to answer the coating question. I believe it's the Dow coating but Armando's mag. guy didn't really say when we spoke with him....

Gary Arentz in San Andreas, CA stripped and Chromate treated the 908 Mag bodies. I'm not clear on what exactly is the chemical process he uses. For those interested, you may want to contact Gary directly and ask; (209) 754-4496.

[914-6gt]

For additional reference, here are a few photos of the other pair I have---to be restored also...

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If I'm not mistaken, this other set of 908 Mag calipers retain their original Mag finish.

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Note the 'hallow' pins in this other pair...

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...to be continued...

[914-6gt]

A 3rd pair of 908 Mag calipers that appeared on eBay in 2012. Sorry, these photos are not very good...

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Note how the alloy pistons were flipped in this pair...

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[Neunelfer]

Those pistons are not flipped in that pair. The soft radius on the inner edge and the lack of knockback provisions means they were machined specially for that pair. They are hard anodized as well. The aluminum 908 and mag 908 pistons I've seen have no coating. They weren't concerned with longevity for these calipers or their internal components.

We have 908 pistons in both raw or hard anodized for anyone interested...

[914-6gt]

Yes, I see that now, the ones you just restored had a different piston, see below...

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[Neunelfer]

Yup... those were indeed installed upside down when we got them.

[gled49]

This finish on the inside of the Mag chain covers, can not be reproduced to the best of my knowledge. When exposed to the elements it turns real dark with traces of the bright finish in corners and crevasses. Of course where protected from the elements and soaked in oil it is preserved