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Shaun @ Tru6's Avatar
 
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Restoring a set of Turbo Calipers

I was given a set to restore a few months ago but they were in such bad shape, we ended up Cerakoting them vs restoring to original anodized condition. Those turned out beautifully but when I received another inquiry on restoring a set, I was eager to see how they would turn out.

Calipers as received. Notice how the piston housings are darker than the bridges. Turns out they are different aluminum alloys so they anodize differently and take up color differently. Did a fair amount of testing with various processes to even out the color but they will never match 100%. My anodizer does a lot of military work and we ended up using some special chemistry for a certain black helicopter. I, and more importantly the customer, are happy with the results.

















After disassembling, the seals and scraper rings had to be removed before stripping the old anodizing off. Seals pull out easily. Factory technique for removing the rings is to dent them with a small chisel or punch. I made one and it worked ok. Better process was to grab the lip of the ring with a small pair of wire cutters and twist. Doing that a few times shrinks the ring and they pop right out.








Caliper pieces stripped of anodizing. As with window frames you want to be as gentle as possible with the stripping solution as it will start to attack the bare aluminum while other areas still have anodizing. Better to chemically strip as best as possible with minimum attack and then physically remove any remaining anodizing. The goal for these was when the piston bores were clean, they came out of the stripper.







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Last edited by Shaun @ Tru6; 01-23-2019 at 04:58 PM..
Old 01-23-2019, 03:25 PM
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Remaining anodizing was removed in the media cabinet and then the whole top side of each piston housing was evened out. From there they went into the tumbler for a while to create a good clean surface for anodizing.











Even though there is practically no chance any media could be left in the passages after being tumbled, I spent a good 10 minutes on each caliper making sure they were perfectly clean.

First use Cerakote hanging wire and then with welding wire and then water pressure and a final check with light in both light and dark room settings. There is a greater chance of debris being in the calipers passageways when they were made than now.










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Old 01-23-2019, 03:34 PM
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I thought I had taken pics right after anodizing but apparently not. Next step is to remove the anodizing over the PORSCHE lettering. These are sand cast and machined so even though this was done at the factory when first made, this proved more challenging than I anticipated.

Tools used. The pneumatic pen spins at 56,000 RPM. An amazing little tool.




Taped up and started filing away. Very uneven surface on this particular half.




After a little work and then cleaned up with the wire brush on the pen.







Finally time to get the seals and scraper rings in. Tumbled/polished the pistons and then lubricated the seals with Sil-Glyde, worked perfectly, I used a bearing press disc with some duct tape to press them in place. The pistons are stepped to reduce contact with the pads which reduces temperature transfer from the pads to the fluid. Front calipers, the step is on the lower side, rear calipers the step is on the top side.














All done.




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Old 01-23-2019, 03:48 PM
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All hardware was stripped of plating, tumbled and then replated in yellow zinc. Got the pistons in and the pad plates with retaining springs. Sil-Glyde worked nicely on getting the springs in. New screws for the plates.




















Hardware ready to go. The brass banjo fittings polished up nicely.







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Old 01-23-2019, 03:55 PM
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Thats some PMB level of detail right there.
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Old 01-23-2019, 04:07 PM
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Beautiful work. I have a 930 and the front brakes have been dragging so I replaced the seals and scraper rings. The pistons and bores were clean so didn't do any work on them.

Question for you: the pistons are very tight in the bores although I've run them through the bores w/o seals and scraper rings and all pistons moved freely. After replacement, they are still dragging. The rotors are somewhat worn on especially on the outside. Is it possible that with new pads and worn rotors that the pistons are getting cocked in the bores and dragging?
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Old 01-23-2019, 04:44 PM
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Pretty cool Shaun! That cerakote is spot on.
Old 01-23-2019, 05:08 PM
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Spectacular. Itís art. Major caliper envy.
Old 01-23-2019, 05:16 PM
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Quote:
Originally Posted by spoke View Post
Beautiful work. I have a 930 and the front brakes have been dragging so I replaced the seals and scraper rings. The pistons and bores were clean so didn't do any work on them.

Question for you: the pistons are very tight in the bores although I've run them through the bores w/o seals and scraper rings and all pistons moved freely. After replacement, they are still dragging. The rotors are somewhat worn on especially on the outside. Is it possible that with new pads and worn rotors that the pistons are getting cocked in the bores and dragging?
I don't think so. First I would check to make sure your steps are oriented correctly. If they are then I would next check to make sure the rotors are in spec. If they are, I think it might be prudent to disassemble the entire caliper and check the passageways to ensure they are clear.
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Old 01-23-2019, 05:29 PM
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Pretty cool Shaun! That cerakote is spot on.
Thanks! These are anodized using a special military chemistry. The set I did in Cerakote a few months are here. These the customer finished building.
















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Old 01-23-2019, 05:34 PM
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I don't think so. First I would check to make sure your steps are oriented correctly. If they are then I would next check to make sure the rotors are in spec. If they are, I think it might be prudent to disassemble the entire caliper and check the passageways to ensure they are clear.
Thanks for the response. I did blow out the passageways with electrical cleaner which leaves no residue as well as high pressure air. When installing the pistons, they had to be exactly straight otherwise would hang up going into the bore after sliding through the scraper rings. I don't think the calipers were overheated as I've never abused the brakes.

The steps are on the bottom side like you mentioned.
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Old 01-23-2019, 06:18 PM
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Amazing work, my ocd is satisfied.
Old 01-23-2019, 08:22 PM
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Quote:
Originally Posted by Shaun @ Tru6 View Post
Thanks! These are anodized using a special military chemistry. The set I did in Cerakote a few months are here. These the customer finished building.



































Thatís some fantastic work right there! As soon as I get back to the states Iíll be getting these rebuilt and back on the car. Shaun does fantastic work and the costumer will be very happy with the product. He takes some serious pride in his work and goes above and beyond to ensure it is done right.


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Old 01-24-2019, 12:10 AM
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Not only is Shaun's work exceptional but his customer service matches his work.
Old 01-24-2019, 01:45 AM
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Very nice work, indeed.I wish I had a set that I could send you.
Considering these are sand castings, the anodizing turned out exceptionally well and appears to hide the surface irregularities superbly. Type II or hardcoat? Hard to tell from the photos.
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Old 01-24-2019, 03:53 AM
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damn you shaun! anther temptation.
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Old 01-24-2019, 05:01 AM
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Built them up this morning. A few quick pics before getting these packed up and shipped out.






















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Old 01-24-2019, 07:23 AM
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Fantastic work by Shaun once again! Both sets of calipers look fantabulous!!!!

Do the pistons typically need much tumbling or polishing? Their anodized surface is usually very resistant to attack, as long as nobody has mangled them like this



The rule of thumb for the piston steps is they are oriented to be perpendicular to the rotor. If you were to draw an arrow in the direction of forward travel around the rotor, the arrow should hit the step perpendicular. On the Ate calipers it's 20į that gets the piston in the right position



However, on the 930 calipers the steps can be aligned parallel with the edge of the pad box. Just make sure you point the steps to face the direction of travel. That means on the front calipers the steps point up (calipers are mounted in front of the axle) and the rear caliper has the steps facing down because 930s have the calipers mounted behind the axle.


The purpose of the step is to reduce tapered pad wear. Apparently the step allows pad outgassing without the pad coming off the face of the rotor. Without the step the pad tilts away from the rotor face and you get tapered pad wear. It's not insignificant pad wear either. It's actually very substantial if the brakes are used hard like on the track. Later calipers on other cars like the 944 Turbo, 928 S4, 944S2, 964, etc. that have calipers with different sized pistons accomplish the same thing without the need for stepped pistons. The differing piston diameters take the place of the stepped pistons.

Keep up the great work Shaun. Very impressive level of detail and beautiful results.
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Old 01-24-2019, 07:25 AM
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Seriously excellent work!! They are beautiful. Trying to locate a passenger side big fin caliper for my ride so I can do this project. These pics are pure car porn!
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Old 01-24-2019, 08:12 AM
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Thatís some fantastic work right there! As soon as I get back to the states Iíll be getting these rebuilt and back on the car. Shaun does fantastic work and the costumer will be very happy with the product. He takes some serious pride in his work and goes above and beyond to ensure it is done right.


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Thank you James! Email me or give me a call when you get back, I can give you some tips on building them. Stay safe!
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Old 01-24-2019, 11:40 AM
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