Zeus single pot. Pistons not retracting

[PeterCrespin]

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

Probably because you don’t and it isn't, so far...

Shims are sometimes used on the two caliper-to-upright bolts. I think I’ve only ever needed a couple and don’t recall ever seeing them on any modern car or bike. The uprights are forged, which leaves critical points needing turning, boring, spot-facing etc. The calipers are cast, and they too require finish machining, which is not the same level of precision as, say a crank journal or cylinder bore. So it can happen that tolerances build up and this type of mounting lug requires shimming to get the caliper perfectly aligned to the disc.

From S2 onwards, the brake cylinders are machined integral with the caliper so can never be misaligned, whereas in your earlier brakes they are separate parts. However, because the four cylinder attachment points are all machined parallel/perpendicular, the separate cylinders can also never be misaligned to the caliper, so you never need shims there.

Since you appear to have ruled out a few typical scenarios, people are considering more unlikely possible causes. It is barely conceivable that a standard brake setup on undamaged uprights (ARE they straight?) could be so out of line that pushing unevenly on pads would cause a piston to jam. But you may as well formally rule it out rather than not check and miss something

[tinworm]

Thankyou Peter, that's exactly what I meant. It could be that a small amount of caliper carrier misalignment could jam your pistons (or pads) The old Dunlop cylinders with 50 odd years of use could be more forgiving (of misalignment) than the freshly manufactured Zeus .
I have never seen a Zeus - although I believe they are made quite close to me !

regards Barrie

[Grayjay66]

i remounted and bled today , without even being fully bled the brake bound up again.

I did note when I took the outboard cylinder/ piston off the car completely, draining all fluid, the inboard was still binding.

Do you think I am correct in thinking then the problem has nothing to do with the hydraulic or vacuum ie master, slave , reaction valve, vacuum servo? Ie any part that creates or could trap pressure?

I noted also with the inner binding , when I backed the 4 bolts off by 1 to 2 turns the binding was eliminated.

The car has never been wrecked or off roaded . The wear pattern on the new pads seems even .

How would I check the carrier for being straight? The problem is on both sides.

I think we are like Drs looking for the most common presentation of the most common problem. This one is a bit beyond I think.

I'm going to try shims between the carrier and the mounting face of the Zeus on the thought if it is the rubber seal perhaps it has a limited travel that a bit more spacing would help. Not a long term solution but could Id the problem. I could just take the seals off and try too.

Thanks again for thinking about this.

[MarkRado]

Compare the Dunlop (which has no issues I understand) vs the Zeus, both mounted to the caliper as well as side by side on the bench. There must be a difference to be detected.

[Grayjay66]

Good suggestion.

[Grayjay66]

Today I tried placing shims between the face of the Zeus and the carrier. Still binding. Tried removing the dust seal completely on the thought that was bunching up. Still binding.

Decided I was done messing with these Zeus. Put my old Dunlops back on and they work fine no binding , full stop. May be originals but at least 20 yrs old but they work. Will need a companion pair for the other front that had corrosion in the cylinders.


Unless Zeus can come up with a reason why these do not retract on my car, I have no longer have use for the Zeus if someone wants them . 2 1/8 single piston stainless.

[Grayjay66]

Btw I did compare the Dunlop to the Zeus and they appear to be dimensionally the same.

The internal difference is the spring retract internal to the dunlops vs a seal in the Zeus.

My friends tell me I should have gone with Wiwoods in the first place. Maybe so.

[Grayjay66]

Looking back when I very first put on the LF Zeus I had my old worn pads in. Ie more piston travel. With new pads in , less piston travel . In both cases the binding occurred during bleeding before even starting the car. I noticed if I backed off the 4 bolts the binding released . I think this is because the whole cylinder piston body moved back, the Pistons remained in the same position.

There must be a mechanism in the Zeus that moves the "rest" position of the piston out as the pads wear. If this mechanism is not allowing even a very small retraction, that would explain why, with the brake lines completely disconnected, the binding remains.

I've posed this to Zeus who have said they are going to do some more testing. It's a mystery to them also.

[tinworm]

I am interested in what you call the spring return on the Dunlops - there is no spring internally - there is a 'gripper' which works on a small rod - this reduces knockback. The only thing that eases the piston (and allows the disc to rotate ) when pressure is released is the cylinder seal returning to its original shape. I mentioned before that the cylinder must be square to the disc , the reason being that if it is misaligned the piston can jam in the cylinder. You can see this happening when pushing back a piston (to fit new pads or something) the piston can jam.The same thing can happen if the carrier is not aligned squarely. Also pads can become sticky due to rust build up/dirt etc - but I assume this is not the case here.
You can dismount the caliper, support it on something and using a block of steel to take the place of the disc - watch the pads (with someone else to help you) close up on the block - this should tell you something as you can see more of whats going on. The block should drop out when the caliper is inverted (when brake released). A disc which has worn to a taper at its outer edge may not help matters ...
You must be missing something!
Regarding pads they must be loose in their housing - so file/remove material until they are - do the Zeus cylinders have the location/pullback boss in the centre of the piston? If not it does not matter - the pads must be loose and not snug.

Barrie

[Grayjay66]

Barrie thank you for taking the time to think about this.

Actually the Dunlops either have a return spring washer or a return spring internal. These springs cause the retraction not the seal.

I think sometime in the 70's brake design changed to a seal retraction. My long time mech remembers the Mercedes brakes in those days came with seals marked as to the proper way to insert them. Apparently they were slightly angled which aided in the distortion and rebound to retract the piston.

I have mounted the four Zeus cylinders around a total of 16 times or more and they always bind. The Dunlops I've remounted 4 times and they always work. It seems unlikely that just by coincidence the Zeus have never been on square. I did consider this canting jamming problem and rerun the bolts in one half turn on each bolt in sequence and visually check the contact with the carrier.

The pads are always very slightly "loose" when I put them in even before I tried filing the outside edges.

I've not considered a tapered rotor as an issue. A uniformly worn rotor would act no different than a worn pad, forcing the piston to travel a bit farther.

The Zeus do not have an internal rod like the dunlop. They are also different in that the dunlop piston has a full flat face contacting the pad, the Zeus piston only has its outside circumference contacting the pad with a hollow center.

If I take the caliper (carrier) off it will be because Im
mounting Wilwoods

I am waiting however to hear back from Zeus if they come up with something.

[tinworm]

Yes I see what you mean - Dunlop called it a retractor pin- so I read. I also read that when disconnected the cylinder still retracted, according to Dunlop that's when they realised the seal was just as efficient at the job and that was the end for the pin arrangement.

Best of luck with your Willwoods

Barrie

[abowie]

Best of luck with your Willwoods

Barrie

I bought a set of Willwoods maybe 10 years ago and was underwhelmed by the poorly manufactured "adapter" brackets supplied with them. I didn't use them.

Have a look at Coopercraft; their calipers bolt directly to the uprights.

I have 3 series 1 E types and have owned one other. I have had Willwood, Coopercraft and Volvo calipers. I'll be honest. In my view brake "upgrades" are not necessary. The standard braking system, working properly, is more than adequate unless you plan to race your car.

[Grayjay66]

Thank you for the suggestion on Cooper crafts, I had heard of them but never did any research.

I went with the Zeus initially because the repro Dunlops were more expensive and the Zeus were stainless eliminating the corrosion in a steel cylinder that started this whole saga.

Now it would seem the Wiwoods I'm looked at are the less expensive.

I do not think more is necessarily better particularly if more stopping power on the front leads to significant front bias.

I still have a nagging feeling it could be my master or slave/vacuum but discount that as even when disconnected the Zeus do not retract. Plus the Dunlops work.

Anyway Zeus has said they will do more testing trying to recreate the problem.

I hope the fires did not affect you in Australia too badly. We had fires here in Ventura not long ago . It was hard evacuating and leaving the Jag and all else not knowing if any of it would be there when we came back.

One Brit club member came home to find his Etype melted draped over the lift he had left it on. another found his house gone but firefighters had pushed his cars out and saved them.

I at one time also had 3 series I otherwise known as foolish person, syndrome

[SpeedieJag]

Another option for upgraded brakes is Fosseway Performance in the UK. I friend with a 64 FHC just installed their front brakes and he couldn't be happier. They also make numerous other upgrade items.

http://www.fossewayperformance.co.uk/cl ... -upgrades/

[AshM]

Another vote for Fosseway - big fan of their stuff...

[Bill Michigan]

Grayjay66

As a former engineer I’ve really enjoyed following this thread. I applaud your perseverance and the efforts of this community to identify the source of the Zeus binding.

Most of the questions, suggested things-to-try, and possible causes seem to have (appropriately) been in two categories:
1. The “usual suspects” (master cylinder issues, etc.)
2. Differences between the Dunlop and the Zeus units

Those areas were certainly the best ones to start with, but at this point in the troubleshooting process, let me suggest a shift to a third area of analysis:
3. Differences between Zeus-installed and Zeus-unmounted (or partially unmounted)

Two of your observations seem like a "Eureka!" moment and point to that 3rd line of “study”:

“When I very first put on the LF Zeus I had my old worn pads in. Ie more piston travel. With new pads in , less piston travel . In both cases the binding occurred during bleeding before even starting the car. I noticed if I backed off the 4 bolts the binding released.”

“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.”

At this point, I suggest temporarily setting aside these still-valid questions:
What is the difference between Zeus and Dunlop units (design-wise)?
Does the Zeus have a design weakness that could result in binding?
Does this particular batch of Zeus units have a quality problem?

Instead, I suggest focusing on this question:
What conditions change when the Zeus unit is unmounted?

Then, list all the possible “downstream” effects of those changes
A. Mechanical changes
1. The mounting bolts are removed
a. Forces on the caliper are relaxed
aa. The pistons are no longer forced into mis-alignment
ab. The bores are no longer distorted
Etc.

B. Hydraulic changes
1. Unmounting opens a hydraulic passage (for example)
2. Etc.

C. Passage of time (during unmounting, getting a much-needed beer, etc.)
1. Unit cools down
a. Thermal distortion of bore relaxes
2. Brake fluid seeps out
3. Etc.

D. Orientation of caliper changes
1. Check valve opens (for example)
2. Etc.

Once the mechanism/cause of the binding is pinpointed, THEN you can determine if that’s due to a design difference, a design flaw, etc, and then select your corrective action.

Good Luck!


Bill

[Grayjay66]

Bill, you may have guessed I was an engineer which is why I've continued to fuss with these vs just moving on. I'm still at the same net place I was when I first mounted the Zeus , bled and they bound. Lots of experiments between then and now but no different result.

The problem is as yet I cannot determine the cause of the binding.

The caliper(carrier ) is the same for both. The new and old pads are the same, the rotors the same, the brake lines, master, vacuum , slave all the same. The design is different, Dunlops relying on a spring, Zeus a seal for retraction.

Zeus after confirming my original set worked on their test stand, sent me a new set with same result on my car - binding. Once Zeus bind they stay bound even with outboard side In my hand, and inboard still binding on the rotor.

There are not many reasons why a piston disconnected from the hydraulic system will not retract.
I suspect three remaining things , 1 the retraction seal is in backwards if that is even possible or 2 the retraction seal is not at spec for rebound elasticity. 3 ) the pistons (all four) are being wedged in place for some unknown reason. The fourth possibility is of course why they bind, but I do not know what that is. I'm betting on 4.

Yesterday though my house water heater failed, and tonight the dryer will not start. More important problems so the Jag will sit a bit longer....

[Series1 Stu]

If you've had 2 sets of calipers and they both show the same problem AND Zeus have given them a clean bill of health then it's clear to me that the problem lies elsewhere.

My view is that there's a restriction somewhere between master cylinder and calipers that the Dunlop calipers can overcome but the Zeus calipers can't. It could be as simple as a very tight bend in a brake pipe.

Regards

[Grayjay66]

Possibly, however if true that would mean somewhere there is trapped pressure.

With the bleed open and brake lines disconnected the Zeus stay bound.

How can that be explained?

[Bill Michigan]

Yesterday though my house water heater failed, and tonight the dryer will not start. More important problems so the Jag will sit a bit longer....

Well now, there's the problem, Grayjay66 -- Your priorities are all mixed up!