Howdy Chaps,

02 MCS, 65.5K miles. Just replaced slave cylinder to buy some time till cooler weather to drop my trans and replace the usuals (clutch, pressure plate, updated throwout bearing/guide tube, seals and pivot shaft bushings, etc).

Have perfect operating clutch on this predominantly highway mileage car except for the typical onset of graunchy and increased resistance of clutch pedal on depression as vehicle warms to operating temp and throwout bearing inner face fouls the guide tube(?). Got plenty of leg (and patience) here to overcome this annoyance but am I running risk of rupturing main or slave clutch cylinder or breaking the piston/pin on the latter working them this hard or do they have a little more reserve in them than I'm giving plastic credit for in this application?

Thanks in advance.

 

It's been my experience that a lot of increased stiffness could cause the seals in the master cylinder to leak, slowly sucking a little bit of air at a time until you only get have disengagement. But with my car, it was caused by a huge increase in stiffness caused by a ceasing slave cylinder. When my release bearing was rubbing, it got really hard! That caused my slave cylinder to cease. I would only worry if it got a lot harder than normal. Just change the slave and master as a pair to prevent headaches.

 

Howdy ACW,

Thanks for your response. Reason I ask is when I replaced my perfectly working slave as a precaution after this issue started, the internal bore was deformed, ie, larger, where it extended beyond the mounting boss which provides structural reinforcement.

So, as an enterprising southern lad, I reckoned if that combo of heat and pressure over time had caused it to swell nearly 10 thou of an inch then possibly the added pressure of me trying to boot this graunchy clutch pedal with a leg very up to the task then either this bore would split or that plastic piston/rod would fracture. Anyone had this happen??

Which, as an aside, though no consolation, unlike a brake caliper piston, at least this slave cylinder design will not sieze in operation as there is no real piston, per se, rather just a small disk with a very nominally sized o-ring around its circumference to seal the bore.

Very fragile, me thinks as an old skool'r, but I'm spoiled by over 2 decades of pushing this porsche 930 clutch - a bridge cable that's never broken.

 

Like you said, the slave will never cease in operation...but the additional stress on the system has caused, in 2 separate occasions, my master cylinder to blow a seal and start slowly sucking air into the system causing squishy pedal and a clutch that does not want to fully disengage. The first time it was caused by the clutch fork being bent and the second was caused by my slave cylinder being extremely stiff. So from what I've seen, the extra stress can cause the slave to rub internally or in other people's cases blow a seal and start to leak fluid...and the extra stress has caused my master cylinder to fail multiple times.

...long story short, if it's just a little stiffer, I wouldn't worry, but if it is a lot stiffer, then it has to be caused by something, whether it is the clutch fork being bent, the release bearing rubbing, or the slave cylinder rubbing internally, I think it will cause the seals to break before any internal components actually break. The seals are only rubber after all.

 

I'm having the same problem for a few months!

Any diagnoses to confirm where the problem is?

I'm on the fence to change clutch/flywheel/LSD, or clutch guide tube/fork/bearings, or slave/master cylinders. Don't know which way to go.

 

Howdy Fei,

In the absence of much wiser chaps chiming in than I, you'll note from KHeuvo's post here that the release fork arms are very short from the pivot point to where the pads engage the throwout bearing. Such a short radius from pivot to pad contact means you cannot capture the t/o bearing with the fork by using conventional ears in cradles like on a 911/930, because it needs lateral movement with in operating range of engagement/disengagement to "swipe" the pads across the contact face of the t/o bearing. The sweet spot for this compromised method of disengagement is very narrow. Anything outside of that range of operation results in side thrust and thus (likely) why Mini has elected to install not only a guide tube but coat the inner perimeter of the t/o bearing to minimize friction from the inevitable contact. So what's happening here? It's about wear on the clutch system - working angles and friiction.

This increased pedal resistance problem on mine is 100% heat related, ie, it works perfectly when the engine's stone cold...no squaking and heavy pedal, and in cool ambient operating temps (80ish for us) is manageable. But, throw in our typical mid 90's day with the a/c on and the resistance jumps way up. Why? Don't know directly but you have a big chunk of alloy bellhousing here which expands alot between two operating components - a slave and a release arm - which are very sensitive to any change in distance. Likely why Mini uses more complex hydraulics for this than a simple cable - it self compensates for distance changes. So when hot, the working gap grows and the fork is now appying pressure to the t/o bearing at even more of an angle, it drags on the tube, or whatever, increasing resistance and probably loading both of those cheap nylon pivot shaft bushing to produce a symphony of squeeks, squanks and groans.

What to replace? I can tell you, for a now middle aged complacent fart who once didn't blink an eye at pulling a motor and trans to install something simple, after viewing some of the various illustrated guides for trans pulls on these cars - mercy - I'm going to have a crate of spares to do everything forseeable on this 6 year old piece at one time. Besides the s/c fluid change, waterpump, thermostat, etc.. it'll be the updated guide tube, t/o bearing, both engine and trans seals, pivot shaft bushings, clutch and a pressure plate. As this machine's role has been just a (silly and fun) way to get to work...no track duty or abuse, doubt that dual mass flywheel'll need anything unless it's just fallen apart....haven't researched on this board whether that's happened yet.

None the less, my shop's not air conditioned and thus the reason for my first post on this, can I nurse this till October-ish time frame before the BIG DISMANTLE?

 

I thought I was just imagining it but on some of the 90+ degree days we have had my foot was actually getting tired and sore from driving. Now that the weather is back in the 80's all is well.

My car is an 03 MCS. I have 58,000 miles on it. I really want to put an LSD in the car the same time I do a clutch but I can't really do that until after dental school is over. Do you think its possible to operate this two more years this way? The clutch works perfectly other than what you have talked about on really really warm days.

 

Howdy k_h_d,

That would be the million dollar answer to the question of making it 2 months in my case and I'm sure there are chaps on this forum with shops/expertise who could answer that readily but are more engaged with other more challenging forums/threads than this one...don't blame them, can be that way myself occasionally in my areas of expertise and I accept that here as an infrequent post'r.

But 2 years though? Looking at the components involved, I'd say definitely not from even another perspective. This whole thing's about an operating relationshing (fork to t/o bearing) and the factory's former friction-relieving answer to interference between the sleeve in t/o inner face, which they've apparently addressed with the new plated sleeve and coated t/o bearing. This relationship isn't static, it changes. Being a "pusher" clutch, as the disk wears, the t/o moves away from the motor towards the fork, as the pivot bushings wear, not only does the fork move away from the t/o, it gets sloppy in its pivot. At the end of the day, you don't know where it's at but likely out of the aforementioned sweet spot now putting more thrust on the sleeve and inner t/o which have which have worn through normal use but are now being asked to really step up when they're at the end of their life cycle.

OK, I'm hip to that, but to quote the bank robber in Dirty Harry, "I got's to know" just how long I can pedal this clutch (plastic arm no less!) against a slave that has an o-ring no larger in circumference than a pencil lead activating a piston the size/thickness of a half dollar on a shaft with a little plastic ball on the end - no answer has been forthcoming.

I'll say this as an aside, though. We need every bit of clutch pedal travel we've been provided and with this increased load you may have noticed a little more effort's required to put it in 1st from a stop and shifts from 1st to 2nd. With this increased load you're not getting complete disengagement because of clutch component flexing and your syncro's are working harder as a result. So, even if nothing literally breaks in the interim, unless you adjust your driving style - slower more deliberate shifts feeling for engagement - you may find by the time you replace/get this stuff replaced, your trans may not have weathered the storm.