Zeus single pot. Pistons not retracting

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

Post by Grayjay66 » Sun Aug 25, 2019 8:00 am

Ah but what is your guess as to what is the cause given the hydraulics are working with the Dunlops.

And the Zeus open to nothing but atmospheric pressure does not result in a no drag fully released condition.

The square seals are the only thing that cause the Zeus pistons to retract, so not much else that can fail. I do not know and Zeus has not answered, if it is possible to install the seals backwards.

All a great $700 mystery.

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

Post by abowie » Sun Aug 25, 2019 9:37 am

I hate to say this, but my money's with Peter's.
Andrew.
881824, 1E21538. 889457..oops
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1954Etype
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#23 Re: Zeus single pot. Pistons not retracting

Post by 1954Etype » Sun Aug 25, 2019 9:49 am

abowie wrote:
Sun Aug 25, 2019 9:37 am
I hate to say this, but my money's with Peter's.
Having fitted numerous Zeus calipers, I have to say that unless these are faulty in some way, I too would agree.
Angus 65 OTS 1E11497. 67 FHC 1E33656

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Series1 Stu
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#24 Re: Zeus single pot. Pistons not retracting

Post by Series1 Stu » Sun Aug 25, 2019 10:13 am

Don't most brake calipers just release and rely on the movement of the wheels to push them back very slightly? I know that the early disc brake systems had spring return calipers but this was quickly superseded (read, cost reduced).

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Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
'69 Daimler 420 Sovereign
'94 X300 XJR basket case

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

Post by Grayjay66 » Sun Aug 25, 2019 1:00 pm

It has been interesting in researching this problem.

We all including me think there should not be a problem but there is. The most common presentation of the most common problems have all been checked and eliminated as to possible cause. The brakes are not fully releasing.

My analogy is place a book on a table. The table represents the disc. The book a pad. Now place 10 more books on top and try to slide the stack. Not easy and represents the pad with hydraulic force applied. Now remove the 10 and slide the remaining book , much easier and represents the pad with no hydraulic force, it also represents a pad with no force causing it to lift away from the disc.

The Dunlops on the 66 have a spring causing the pad to move off the disc. Visually it looks like around 1/16 inch. Some bright soul figured out the spring was not necessary the pads only need to move a very very small distance from the disc. The reflexive seals would pull the piston back and the pads would react to the disc movement and in theory move off the disc.

In the Zeus the pads are not connected to the Pistons so disc motion is all that causes the pad
to lift off the disc or at least leave slight but not zero friction.

This set is leaving enough friction to heat the hub after only 5 or 6 miles. The pad does not apply force to itself so the Pistons must be the source of the force, but why?

People have all kinds of opinions from if it's warm but not hot don't worry about it because these design brakes always have drag, to something is wrong with the seals, to has to be some other magical problem that only manifests itself when Zeus are on the car.

Zeus has been good and will have a look . I just wish they were closer. I'd love to watch the test.

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

Post by Geoff Green » Sun Aug 25, 2019 2:40 pm

I assume from your first post you are using the ZEUS FRONT STAINLESS STEEL REPLACEMENT CALLIPER 2 1/8th
Part Number: Z2125 which will use the factory type brake pads.

Yes when the caliper piston retracts the disc knocks the pads back on "modern" brakes however the Dunlop pistons with return springs also pulled the pads away from the disc. the movement away from the disc is very small.

Some issues that keep pads contacting the disc when foot not pressing on brake pedal.

Master cylinder not releasing internal piston keeping fluid pressure up. Test by loosening brake line.

Metal brake line crushed and not releasing fluid pressure. Test by loosening brake line.

Brake hose not releasing fluid pressure due to internal hose layer blocking passage. Test by loosening brake line.

Brake caliper piston not retracting due to mechanical sticking (rust). Test by loosening brake line.

Brake caliper piston not retracting due to square cut "o" ring not working or installed backwards. Test by loosening brake line.

Brake pad sticking on caliper mount/pad guide. Test by lightly filing edge of brake pad.

There are other remote causes which can be determined by asking; does this effect one side or both sides or all front and rear. Brake pedal pivot, brake balance warning switch, ABS unit to name a few.

Awaiting the report from Zeus.

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

Post by Grayjay66 » Mon Sep 30, 2019 6:52 am

Zeus has tested the calipers and taken them apart with no faults found. They sent a set back, so should have them to try again soon.

Zeus has been really good to deal with. The Vendor in Ohio, I would not buy bubble gum from.

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

Post by abowie » Mon Sep 30, 2019 7:26 am

At the end of the day the most important thing about a car is that it will stop when you need it to.

Were I you, after all the trouble you have had, I'd take my car to a professional brake place and get them to sort it out for you. Then your car works as it should and you and yours are safe when you drive it.
Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
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#29 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Mon Nov 04, 2019 4:47 am

After traveling for several weeks was able to put the new set Zeus sent on the left front along with Zeus on the right front. So all Zeus now.

Now right front are working fine, no heating. The left front inboard is binding causing cylinder housing, disc and hub to be very hot after a mile or so. Outboard cylinder body is significantly cooler so likely is not binding.

I think in medical terms my car has some sort of new tissue rejection issue.

Anyway will take off and remount and try again. Crossover hard line from outboard to inboard is clear in both directions.

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#30 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Tue Nov 05, 2019 3:59 am

SUCCESS! All 4 cylinder/Pistons are now working as they should.

On the one sticking, I loosened the 4 retaining bolts by 3 turns removed the retaining clip and pulled out the pad. I found a 1/16 square slight gouge at the fore and aft edge of the pad. I also found these pads are built around a circular metallic part with 3 rivets. Two of the rivets were canted leaving an edge above what should be a flat surface for the piston to push against.

I filed the rivet heads down and each of the 4 pad edges slightly. I then reinstalled the pad making sure it was all the way forward. I retightened each of the 4 bolts 1/2 turn at a time to keep it even. Re bled and after driving my test route found no heat on the hubs or any of the cylinder bodies!

I still do not know why the original sticking problem occurred but all is now well.

Being a Jag, never long problem free, I did find a slight fuel weep at a banjo bolt. Easy fix.

Thank all of you who responded for your thoughts and suggestions and particularly to A.C. at Zeus who was really helpful.

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#31 Re: Zeus single pot. Pistons not retracting

Post by rswaffie » Tue Nov 05, 2019 9:16 am

:dance: :drinkingcheers: :swerve:
Richard

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Now running-in my diy nut ‘n’ bolt restoration. :wrench: :hammer: :fingerscrossed:

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#32 Re: Zeus single pot. Pistons not retracting

Post by PeterCrespin » Thu Nov 07, 2019 9:49 am

So the pads are the same as for the first piston set and were probably the culprit then as well?
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 97 XJ6L

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#33 Re: Zeus single pot. Pistons not retracting

Post by Grayjay66 » Thu Nov 07, 2019 6:23 pm

For the first set of cylinder/Pistons, I tried both the used pads and the new pads and binding occurred with both. I did not do any filing of the pad edges during those trials.

Zeus found nothing wrong with the binding set on their test stand. Zeus did say all along I needed to have Zeus on both wheels, so maybe doing that was the general key. Although why that would make a difference , I do not know.

It's still a mystery to me however in this long thread someone mentioned filing the pad edges so when I saw the slight gouge marks , I filed. Whether that would have worked initially cannot now be determined. Something worked. I doubt it was the rivet heads as the Zeus piston only contacts the pad on the circumference.

I learned a lot about brake systems.

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