Zeus single pot. Pistons not retracting

[Grayjay66]

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.

[abowie]

I hate to say this, but my money's with Peter's.

[1954Etype]

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.

[Series1 Stu]

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 I know that the early disc brake systems had spring return calipers but this was quickly superseded (read, cost reduced).

Regards

[Grayjay66]

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.

[Geoff Green]

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.

[Grayjay66]

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.

[abowie]

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.

[Grayjay66]

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.

[Grayjay66]

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.

[rswaffie]

[PeterCrespin]

So the pads are the same as for the first piston set and were probably the culprit then as well?

[Grayjay66]

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.

[Grayjay66]

I spoke too soon. I drove 6 miles. Parked the car, came back 10 minutes later and found the knockoffs too hot to touch on both sides. The brakes are still binding.

I quit the car through the holidays and started again today thinking what else could be the problem. I checked reaction valve works. Backed off the brake pedal stop nut by 3/8 inch to give the piston more movement. Drove again , still hot after 1 mile.

So rear dunlops work, a single Dunlop front paired with a Zeus works, Zeus side binds. 2 front Zeus bind. Same with new Zeus set that Zeus provided. Very happy with Zeus as a company.

Master and/or slave problem seems unlikely given dunlops are working.

I don't want to throw more money at it replacing master/slave which would cost more than simply putting dunlops back on.

Given the 5700 views with no solution , this does seem to be a unique problem.

[PeterCrespin]

I think you said ages ago during one of your diagnostic stages that the reaction valve or servo (I forget which) was 'open to atmosphere'. I.e. you felt it/they could not be causing the problem because they were no longer hooked up. I assume you are aware, however, that depending which connection(s) you undo, making the servo open to atmosphere is a prime cause of binding if only the back connection, or the relevant reaction valve connection is open?

Clearly it's not a Zeus problem, so in your shoes (or 'pads', geddit?) I would disconnect your vacuum hose at the back of the manifold, plug the manifold, and not reconnect until your problem is solved by whatever means.

If, having undone and plugged the manifold connection, you are no longer able to reproduce the dragging, you have your diagnosis. \

If, on the other hand, it appears to make no difference, I would still leave it unhooked as a way of removing one blind alley you might be tempted to follow.

There is only a finite number of components in the system, and applying stepwise logic you are bound eventually to discover the incorrect part(s) or procedure causing unwanted continuing pad pressure.

[Grayjay66]

Thank you for the suggestion. Today I did the following:

After leaving the car sit overnight, all engine off, I jacked the front up and tried to turn the left front wheel It was binding.

I then disconnected the manifold vacuum line - still binding. Pumped brakes , seemed binding was slightly worse.

Took off reaction valve - still binding.

Put reaction valve and manifold line back on. Still binding

Opened bleed. Still binding.

Took off brake lines to outboard caliper draining all brake fluid -still binding.

It would seem with the front outboard caliper completely isolated from the rest of the system that completely relieves any possible pressure on the Piston and therefore pad.

I've now taken both calipers off the left front , cleaned every thing , filed slightly the edges of the new pads and remounted. Tomorrow I will bleed and try again.

I'm beginning to suspect the Pistons are not sticking in the cylinder but perhaps the clearances for the Pistons vs the carrier may be slightly off. Given the tech improvements if so it is likely the carrier is a slightly smaller diameter, and the pistons are wedging themselves in.

I cannot force the Pistons back after removing the pads while they are still mounted. After taking them off the car the Pistons retract easily with thumb pressure.

It is odd the old dunlop on that side worked just fine, yet the Zeus are binding. Making me think it is not the master, reaction valve, slave or vacuum.

Thank you again for thinking about this. I hope you can continue to follow along.

[tinworm]

Just in case... you have shimmed the caliper correctly ie it is sitting square to the disc with equal shims on both mounting points?

Barrie

[Grayjay66]

I did not change any shims on the carrier. Just unbolted the Dunlops and bolted on the Zeus.

[chrisfell]

My Zeus Calipers required 5mm of shims to get the disc central in the caliper. Zeus normally supply shims to fit.

My OE calipers (Girling, not Dunlop - my car has S2 uprights) bolted up with no shims.

Is this the problem?

[Grayjay66]

in my case the disc is central to the carrier. The Zeus cylinder/piston body Bolts to the carrier .

I'm not clear about what you actually shimmed.

Placing shims under the 4 bolts of the Zeus would move it out from the carrier and disc forcing the Pistons to move further , which is equivalent to having pads that are thinner due to wear.

Zeus made no mention of needing shims or that was even a possible source of the problem.