Zeus single pot. Pistons not retracting

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Grayjay66
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#1 Zeus single pot. Pistons not retracting

Post by Grayjay66 » Sat Jul 13, 2019 9:22 am

66 fhc, I replaced my original front left calipers with Zeus single pot stainless leaving original Dunlop on right front.

Simple bolt off and then Zeus bolt on . All seemed well. Drove around 6 miles and found Zeus side hub warm. Thinking I had a bearing problem, put the car up, took tire off and found Zeus wheel locked up , could not turn by hand. Original Dunlop side wheel turns with light touch. Zeus Pistons are not retracting.

Loosened outboard Zeus pot 4 bolts, wheel turning with drag, loosened inboard side and wheel turns freely.

Took both pots off, checked and I could hand press the Pistons back. Remounted , wheel turning freely. Bled brake line and wheel locked up again with pedal pressure established.

So since the Dunlop side is behaving normally and the Zeus side is not, it would seem the problem is with both of the Zeus calipers/pistons or I have a one way block in the brake line somewhere between the calipers and the line T to the right front. I did replace flexible section last Nov.

Any ideas as to cause?

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abowie
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#2 Re: Zeus single pot. Pistons not retracting

Post by abowie » Sat Jul 13, 2019 9:28 am

Grayjay66 wrote:
Sat Jul 13, 2019 9:22 am


So since the Dunlop side is behaving normally and the Zeus side is not, it would seem the problem is with both of the Zeus calipers/pistons
Sounds like it. Are they new? Used? Rebuilt?
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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Grayjay66
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#3 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Sat Jul 13, 2019 9:38 am

Brand shiny new Zeus. Original du lops on right side. I bought a second pair of Zeus but now will not put on until this is resolved.

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abowie
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#4 Re: Zeus single pot. Pistons not retracting

Post by abowie » Sat Jul 13, 2019 10:00 am

Sorry but when I originally read your post I thought you had put a pair of Zeus calipers on the front.

You can't run different calipers on different sides; it doesn't work like that.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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Doug Buchan
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#5 Re: Zeus single pot. Pistons not retracting

Post by Doug Buchan » Sat Jul 13, 2019 12:07 pm

"You can't run different calipers on different sides; it doesn't work like that."

I think he means that he changed the cylinders on one side to Zeus which wouldn't be advisable IMO.
Zeus clearly states they are only sold in sets of four.
Doug
'67 ots

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Grayjay66
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#6 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Sat Jul 13, 2019 1:22 pm

The Zeus piston not retracting on the left front while the dunlops are on the right front, has nothing to do with the piston manufacturer being mixed .

I intended to change out both sides but was testing the Zeus before committing to the second pair, and was not concerned about the test drive as the swept pad area is exactly the same. Mis matched swept pad area is a very bad idea., unless you are driving a dirt track sprint car.

I forgot to mention once the Zeus locked up, even after opening the Zeus side bleed nipple, the Pistons would not release, leaving the wheel locked up.

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Grayjay66
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#7 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Sat Jul 13, 2019 1:51 pm

Also to clarify, the Zeus are single piston 2 1/8th as are the original dunlops.

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Geoff Green
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#8 Re: Zeus single pot. Pistons not retracting

Post by Geoff Green » Sat Jul 13, 2019 4:27 pm

You have done the testing I would to determine what components are causing the problem. Time to call the vendor or manufacturer. Perhaps the piston seal (square cut o-ring) is installed backwards.

Pad swept area is different from piston diameter. Piston diameter determines the pressure and pad swept area determines the friction to stop. Both have to match side to side. I would not mix components on an axle.

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Grayjay66
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#9 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Sat Jul 13, 2019 5:02 pm

I agree about not mixing components although in this case piston diameter and pad area are the same so not a big concern for a short test drive.

I viewed it as a bit of an experiment to drive it with Zeus on one side and Dunlop on the other just to see if it did result in pull to one side or the other ( differential friction). Stopping From 40 mph there was no pull.

Although when I returned home the Zeus side hub was warm. Zeus do not have a positive retraction spring as do the Dunlops. And as I found the Zeus are binding.

Thank you for suggestion of the possible internal seal problem.

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