Evora Wilwood Clutch Master Cylinder Group Buy - Page 3 - LotusTalk - The Lotus Cars Community
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post #41 of 53 (permalink) Old 05-21-2019, 08:29 AM Thread Starter
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Originally Posted by brgelise View Post
Resurrecting this thread as I came in from last session at track yesterday. When I went back to car to leave 30 minutes later, pedal was soft halfway way to floor. Pumps did not help, but it recovered immediately when I stuck my foot behind clutch pedal to let it refill. BTW all fresh ATE 200 fluids but i did drive the pi$$ out of it that session with a passenger. Suspicious that MC may be getting tired or I just plain cooked the fluid again...hehe

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post #42 of 53 (permalink) Old 05-22-2019, 10:54 AM
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Whaddya think, super hot or cylinder getting tired? Came right back up when foot went under to pull at top of travel.

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post #43 of 53 (permalink) Old 05-23-2019, 04:01 AM
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The soft MC problem has always confused me. Perhaps someone with more (admittedly mine is very minimal) knowledge of fluid/hydaulic/flow dynamics can clarify.
The MC is located approx. 10ft from the hottest constant source, engine compartment; air anywhere in the system will give a mushy pedal, and it seems logical that the fluid would be the hottest (boiling out air?) in the engine compartment, or secondarily in the caliper regions when severely using the brakes. So wouldn't the slave cylinder be more of a concern? Or simply the heat in the engine compartment is too great at times for the fluid to accomodate?
Most who have raced cars know how often brakes get mushy as car gets hotter, and a part of prep was always bleeding calipers frequently since this was where the air was; pedal firmed up and out we went for next session. The MC hadn't failed.......
The fluid doesn't really flow when brakes applied, so it would seem difficult to generate such a high temp in the MC itself, so far removed from high heat source? Would seem if MC is the culprit, it is so because of poor design/manufacture that fails to seal properly under pressure. If so, failure should occur at any time not just when car is used heavily and high heat is generated?
This is why I asked for info on the 400 MC performance, since 400 has same part # (see "Evora 400 Problem" thread). Anyhow, just scratching my head.........

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post #44 of 53 (permalink) Old 05-23-2019, 05:47 AM
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The soft MC problem has always confused me. Perhaps someone with more (admittedly mine is very minimal) knowledge of fluid/hydaulic/flow dynamics can clarify.
The MC is located approx. 10ft from the hottest constant source, engine compartment; air anywhere in the system will give a mushy pedal, and it seems logical that the fluid would be the hottest (boiling out air?) in the engine compartment, or secondarily in the caliper regions when severely using the brakes. So wouldn't the slave cylinder be more of a concern? Or simply the heat in the engine compartment is too great at times for the fluid to accomodate?
Most who have raced cars know how often brakes get mushy as car gets hotter, and a part of prep was always bleeding calipers frequently since this was where the air was; pedal firmed up and out we went for next session. The MC hadn't failed.......
The fluid doesn't really flow when brakes applied, so it would seem difficult to generate such a high temp in the MC itself, so far removed from high heat source? Would seem if MC is the culprit, it is so because of poor design/manufacture that fails to seal properly under pressure. If so, failure should occur at any time not just when car is used heavily and high heat is generated?
This is why I asked for info on the 400 MC performance, since 400 has same part # (see "Evora 400 Problem" thread). Anyhow, just scratching my head.........
A number of good points. You are correct that the MC is in a relatively cool position.
While the Brakes and Clutch share hydraulic fluid, this sharing is on the non pressurized reserve side, so hot fluid from one will not actually migrate to the other.
Be it brakes or clutch system, the fluid does 'flow' rather than just transmit a pressure pulse, the flow is not continual though but rather a 'tidal' back and forth by the amount of volume change under the piston and as the line diameters are very small ... I estimate fluid moves about 3 to 4 feet each way in the clutch line with pedal movement.
Boiling fluid in the system with air will create a vapor pocket, system is sealed so air does not just boil away, gas bubbles will work up to 'higher' ground, that is the MC as its above the SC; maybe its those that do the MC in???

I never had an issue with my S1 car and after recall to add insulation I added an extra layer full length from SC to the Damper, I never understood the factory additionally of only a few inches at the SC side. My 410 had not exhibited any issues at 7500 miles and to day I have not added insulation other than the now standard factory partial wrap. I do have an Tilton/BOE MC at the ready on my home office shelf, just in case.

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Last edited by Julian73; 05-23-2019 at 05:52 AM.
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post #45 of 53 (permalink) Old 05-23-2019, 06:18 AM
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Thanks Julian. My perceptions I boiled the fluid in the clutch slave where it runs right next to the front bank of the exhaust manifold. I was actually kind of proud of myself for getting into it that good on day 1. Brakes were totally solid all day so it was definitely the clutch tubing. The trick is to put foot under clutch pedal to let it refill. Works every time....so far.

scv hit my thoughts on this issue. People changing MC for clutch issues...

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post #46 of 53 (permalink) Old 05-23-2019, 08:49 AM
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Originally Posted by scv View Post
The soft MC problem has always confused me. Perhaps someone with more (admittedly mine is very minimal) knowledge of fluid/hydaulic/flow dynamics can clarify.
The MC is located approx. 10ft from the hottest constant source, engine compartment; air anywhere in the system will give a mushy pedal, and it seems logical that the fluid would be the hottest (boiling out air?) in the engine compartment, or secondarily in the caliper regions when severely using the brakes. So wouldn't the slave cylinder be more of a concern? Or simply the heat in the engine compartment is too great at times for the fluid to accomodate?
Most who have raced cars know how often brakes get mushy as car gets hotter, and a part of prep was always bleeding calipers frequently since this was where the air was; pedal firmed up and out we went for next session. The MC hadn't failed.......
The fluid doesn't really flow when brakes applied, so it would seem difficult to generate such a high temp in the MC itself, so far removed from high heat source? Would seem if MC is the culprit, it is so because of poor design/manufacture that fails to seal properly under pressure. If so, failure should occur at any time not just when car is used heavily and high heat is generated?
This is why I asked for info on the 400 MC performance, since 400 has same part # (see "Evora 400 Problem" thread). Anyhow, just scratching my head.........
This was brought up on TLF, since the RHD cars don't seem to experience MC failures as often as our LHDs. One theory is that the heater core hoses traverse the left side of the front clam area, very near to the MC. Since there's little to zero airflow in that area, it's possible that the MC just soaks up the heat over time, causing wear and tear on the seals.

My personal opinion is Lotus just picked a not-so-great but cost-effective MC from someone else's parts bin. And when they couldn't source the metal ones any more, they proceeded to get plastic ones from a different bin. Failures are entirely up to luck/chance/gods/etc.

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post #47 of 53 (permalink) Old 05-24-2019, 03:57 AM
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Well, all good info.....Julian I'm amazed at the amount of fluid movement you mention, far more than I would have thought.......the migration of air to the highest point is noted, and known; I wonder if bleeding MC when pedal softens might be of value?? And, I probably overlooked the amount of heat transfer through fluid from both clutch and brake systems.......
Also, good to hear of your 4xx experience, as mine is same with 5000 miles..have not wrapped line at slave/engine area yet, but have material and will do next time pan off. Hoping Lotus addressed this issue on 4xx series.......

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post #48 of 53 (permalink) Old 05-24-2019, 04:05 AM
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This was brought up on TLF, since the RHD cars don't seem to experience MC failures as often as our LHDs. One theory is that the heater core hoses traverse the left side of the front clam area, very near to the MC. Since there's little to zero airflow in that area, it's possible that the MC just soaks up the heat over time, causing wear and tear on the seals.

My personal opinion is Lotus just picked a not-so-great but cost-effective MC from someone else's parts bin. And when they couldn't source the metal ones any more, they proceeded to get plastic ones from a different bin. Failures are entirely up to luck/chance/gods/etc.
Heat soak from cooling lines a possibility, I suppose. Though,I would think must be a pretty shoddy MC to fail to handle this amount of temp. Most modern cars have MC in engine bay, varying proximity to very high heat sources (engine etc), yet perform.....your personal opinion may be spot on........

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Last edited by scv; 05-24-2019 at 04:08 AM. Reason: addition
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post #49 of 53 (permalink) Old 05-24-2019, 05:10 AM
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Interesting point on the LHD vs RHD! They did that heat wrap service item for the slave line in the engine bay, I wonder if it would help to wrap the exposed line at the front, or if all the heat absorption is happening inside the sill?

We've dismantled failed versions of both the plastic and the old metal cylinders at the shop... in short, the mechanics don't think highly of either one. Either Greg's Wilwood or BOE's Tilton kits are going to be a big upgrade in quality. I swear; for Lotus to go all the way and use things like AP brakes with race-quality stainless lines and fittings, and then cut corners with things like this.. I mean, I get it, the brakes are flashy and a selling point, but it's still sometimes confounding.

Best thing you can do is use a high quality brake fluid (Castrol SRF, Motul 660, ATE200, etc) and bleed the slave cylinder regularly. A motive bleeder is fantastic for this.

As to whether your soft clutch problems are air bubbles or bad MC seals, examine the fluid after bleeding.. if you've got lots of rubber particulate floating in there, that's probably your answer.
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post #50 of 53 (permalink) Old 05-24-2019, 06:56 AM
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Well, all good info.....Julian I'm amazed at the amount of fluid movement you mention, far more than I would have thought.......the migration of air to the highest point is noted, and known; I wonder if bleeding MC when pedal softens might be of value?? And, I probably overlooked the amount of heat transfer through fluid from both clutch and brake systems.......
Also, good to hear of your 4xx experience, as mine is same with 5000 miles..have not wrapped line at slave/engine area yet, but have material and will do next time pan off. Hoping Lotus addressed this issue on 4xx series.......
5/8 bore MC 1" stroke = 0.307 cu in of fluid moved through a 0.12" ID line == 27 inch

No heat transfer between brake and clutch systems, each have their own MC's that only share a remote fluid reservoir, and fluid doesn't return back into the reservoir (except when new pads are installed and fluid is pushed back).

Someday I will heat wrap slave cylinder, full length of line in engine bay and line at MC.

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post #51 of 53 (permalink) Old 05-24-2019, 07:10 PM
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A Clutch Pedal going to the floor from boiling fluid, presumably at the Slave Cylinder, would NOT come back up and function normally by just lifting the pedal.
The air in the system, causing a mushy pedal from boiling fluid, would have to be bleed out to get a normal functioning system.
Since lifting the pedal seems to rectify the problem, I assume that the problem lies in the Master Cylinder, that refills when the pedal is lifted opening the refill orfice.
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post #52 of 53 (permalink) Old 05-25-2019, 03:36 AM
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5/8 bore MC 1" stroke = 0.307 cu in of fluid moved through a 0.12" ID line == 27 inch

No heat transfer between brake and clutch systems, each have their own MC's that only share a remote fluid reservoir, and fluid doesn't return back into the reservoir (except when new pads are installed and fluid is pushed back).

Someday I will heat wrap slave cylinder, full length of line in engine bay and line at MC.
Good/valid point on separate MCs and fluid motion-my horizon has been broadened!.....think I will follow your lead on stocking Tilton MC, and should opportunity arise, change out even if OEM still functional...
Derek o Bass notes bleeding slave regularly, and sounds appropriate, in addition to info on OEM MC internals.............I was hoping the 4xx had a different part /number from S1.......perhaps Lotus applied some "input" to supplier to improve construction/design of OEM?????? One can only hope.........time may be helpful as 4xxs accumulate miles and reports surface -or not.

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post #53 of 53 (permalink) Old 05-25-2019, 01:41 PM
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Plastic MC has been the same at least since I started collecting parts lists with the July 2012 edition; That is A132Q6017S through at least the Oct 2018 list; the A signifies 1st edition, i.e. no modifications to the part, whereas the metal version moved to a B rev early on.

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