Hey all,
I've been struggling with burning out my clutch at an alarming rate over the past 6 years. This clutch replacement will be the FOURTH new clutch I've had in 7 years, with the last two being in the past 2 years. This has all the while been since I stopped driving it hard at all and have been paying very close attention to my clutch habits (not riding the clutch by accident, not babying it too much, etc). This past clutch replacement I decided to do it myself...

... boy, has that been a nightmare. But, it's finally complete; however, the transmission will not allow me to shift into gear while it is running. I can shift gears while it's off, though, so it's not a shifter plate mounting issue. Ultimately, I've come to accept that this is also the reason my clutch has been burning out with in increasing frequency.

I decided to take a look at the hydraulics because of a spongy clutch pedal (which I had a little bit before this past clutch replacement), and, after a very long and forgettable story of back-and-fourth alternating between a pneumatic bleeding kit process, taking days away from it, then trying gravity bleeding, and repeating, I could gain no progress in the pressurization of the clutch hydraulics. There are ABSOLUTELY NO BUBBLES AT ALL in the hydraulics which I can especially tell when I [properly] use the pneumatic bleeder kit.

During all of this, I ended up replacing the clutch master cylinder and the clutch slave cylinder. No marked improvement. Plus, the free-play adjustment on the clutch is already maxed out to the point where the piston is about to fall out of the clutch pedal assembly! (And it's That was the only way to get much of any kind of pressure. I believe it to be the clutch hydraulics because the pedal sticks to the floor a bit (severity varies depending on the method used to bleed).

At this point I am so incredibly f*cked and helpless with this. There are NO hydraulic leaks. All but the hydraulic lines themselves have been replaced. Whatever the issue is, it's not easily found because this has evaded two Mazda dealerships (one with a rotary tech of 40+ years) and a highly recommended mechanic here in Phoenix, AZ (comes with the praise of Charles R. Hill from BHR). I've spent the past *6 months* trying to get this working and no matter what I do, nothing seems to make a difference.

Yes, I've searched this forum extensively and tried every possible suggestion short of the custom bleeder valves. (That's part of the reason it's been going on for 6 months) At this point, unless they're magic and run on unicorns and rainbows, I don't care about the special bleeder valves. I haven't had a daily driver for nearly a year now. I'm beyond desperate, but if someone has some creative ideas (both cause and innovative diagnostic processes), I'll try anything.


P.S. No, I won't bring it to a mechanic. I've only ever had one good experience with someone else working on my car and that was the rotary tech of 40+ in Minnesota. Everything else has been a total, colossal disaster: even down to all but 2 oil changes.

Thanks,
--Nick

 

What clutch are you using, what pressure plate, are you replacing all of that each time you swap the clutch, is your prolite flywheel in spec still, where are you sourcing all your parts from, is your clutch pedal busted partially, all questions that might provide answers

 

To both: they're from the Exedy OE[M] Transmission Clutch kit (MZK1002).

Yes.

No, actually. In order to attempt to prevent further clutch slippage in the future as part of daily driving, (although see below about true root cause findings) I switched to the ACT XACT Streetlite flywheel (600145). It's worth noting that I already had an ACT counterweight which I left installed when replacing the flywheel.

Amazon.com. (Yes, yes, I know, eye roll. I usually purchase from BHR, but long story short, I had to do it through Amazon this time.)

However, in these instances, the parts were both packaged and appeared consistent with the original product (since I've seen them before, unfortunately). The flywheel was still in its vacuum sealed bag, was not warped even slightly, and was machined to a perfect surface.

All products were in the same condition. I have no reason to expect or suspect they are not genuine and undamaged.

No. I have the reinforced-weld version of the stock OE clutch pedal assembly that has been modified and sold by Charles from BHR. The pedal integrity remains intact.


Based on all of the symptoms and troubleshooting I've done, it all keeps coming back to the clutch hydraulics. While the clutch fork is being moved approximately half-way to its maximum position, and ChatGPT was able to indicate that approximately 17-24mm (a bit past half-way) is ideal for the RX-8's transmission (didn't cross-check that fact yet though), I still believe the trouble is the hydraulics.

I am uncertain what more is left to do other than check the lines, which I am uncertain how to do in a scientifically reproduceable method. In pneumatic systems and leaks, one would spray soapy water on the lines/joints, but obviously pneumatic ≠ hydraulic. Unfortunately, the issue isn't terribly consistent with a leak since there's no visible fluid leaking from anywhere. Yet, no matter the process of bleeding, I am never able to obtain full pressure in the lines. (I suppose it could leak in air without displacing the liquid outside of the line somehow?) The pneumatic bleeding kit is overwhelmingly the best process, though, leading to the most pressure, but still mild-to-moderately insufficient.

There are obviously a lot of things I've tried, a lot of backstory, and a long period of time to which it all occurred. Then the history of the vehicle is incredibly long and mildly troubled (no engine issues, yet, amazingly, other than having a low, but acceptable, minimum compression ratio). So, please, ask questions you find are most relevant, otherwise I'll literally end up writing a 500-page book on it all.

 

Are you able to record a high-resolution video clip as close to the side of the clutch slave cylinder as possible while the clutch pedal is depressed? Or know of one already? I'd really kill to see what it should look like, and how far the clutch fork should be depressed in order to cause clutch disc disengagement relative to the total area it has to slide, so I can be confident in my results incrementally.

 

I would replace with stainless steel clutch line, and i would highly advise to bench bleed the complete assembly prior to install. I also recommend speed bleeders even when bench bleeding.

Ive done my clutch bleed a few times, from replacing lines or replacing the master and slave (both at different occasions), qnd just to put fresh fluid into the system and let me just say that this car can be (but not always) a nightmare to bleed the clutch. Speed bleeders and bench bleeding made a night/day difference for initial installation and future bleeding. The braided line helped the pedal feel

 

Bent clutch fork inside the gearbox, or otherwise not operating correctly? Clutch adjustment causing partial clutch operation at all times ?

 

I can agree, bench bleed is the best way to go. Otherwise it is painful to fully bleed the system while it is in the car. Recently I had one of my stock clutch lines balloon on me and acted like a one way diaphragm. I think it overheated resting on another line after some quick roadtrip fix to the heatercore hose. The only way I bleed now is by doing a positive pressure kit on the master and then a vacuum on the slave end. Basically flow/pump fluid through and close it off.

Ive also had issues with non Mazda master cylinders. I've seen it where the rx8 clutch pedal adjustment is not long enough for the aftermarket master cylinder. Probably just typical chinese tolerancing or lack of.

 

Yes, this much is... painfully... obvious, haha.

I have something similar that no one really commented on and has me curious: a pneumatic brake hydraulics bleeder kit and I've used it on the clutch hydraulic system several times*.

Why is a pneumatic bleeder kit such an underexplored option, both on here, and on the internet in general? It seems like a much easier and much, much more readily available option than changing out your bleeder valves with new ones 一 a product that has to be shipped, is moderately costly, requires knowledge on the necessary config/part number, and may only be used for that one application.

A pneumatic bleeder kit seems much more useful, available at every Harbor Freight, and can be very easily used on your brake lines, too. Yet using it on clutch hydraulics is virtually unheard of.

So, whats the major downfall of them that no one online seems to really mention?

(* Initially, I kept seeing air bubbles in a strangely and consistently repeating pattern. Later troubleshooting revealed that the sheer suction from the air compressor was causing the bleeder valve itself, when open, to suck air through the threads. I fixed that by adding threading tape to the bleeder valve.)

See, now this is very interesting to me because one common "thread" throughout this clutch saga (since it being replaced the second time) is how the freeplay adjustment on the clutch pedal has to be at its extreme maximum to even have any chance at depressing the clutch fork enough to fully disengage the clutch.

The service manual says 0.1 - 0.5mm* is the only range that should be needed. But its at like 15-20mm or so, practically falling out.

I'm pretty sure the cyclinders that were in there were OE though and the ones I replaced them with were German engineered.

(* Also interesting is how the RX-8's freeplay adjustment range is an exact multiple of 10 when compared to quite literally every other clutch freeplay adjustment out there: 1-5mm. Kinda bizarre.)

 

The one I have doesnt need an air compressor, it just has its own hand pump built in.

For the adjustment screw I was questioning just getting a threaded rod and rounding it off to replace it with a longer one. The other option would be to trim down the flange on the master cylinder to bring it closer to the pedal. Maybe someone on the forum has an OE master that they can measure the flange to cup distance. I sadly do not have any stock ones. Granted the resting points could be different so it probably is impossible to compare

 

What do you do to create a positive pressure? Just attach it to a supply of brake fluid?

In a pneumatic bleeder kit process, you put a separate HDPE plastic reservoir full of brake fluid turned upside down onto the top of the brake fluid reservoir. I assume this is the equivalent of your process' positive pressure on the master cylinder.

It's worthwhile to mention that I strongly suspect that whatever the issue is, it's not the clutch master cylinder, simply because it hasn't been replaced on my RX-8, until now, and I've owned it since 34k miles and I believe I had it first replaced at about 65k miles. The next replacement was at about 90k, and ever since then it's been in quick succession: 115k and now 135k. And that's with me starting to avoid ever driving it hard and not babying the clutch much (to avoid hesitation/partial [dis]engagement) after the second replacement.

Knowing that, but back to your point: My gut instinct is that, in my case, the clutch master cylinder is OE spec. I mean, it looks nearly identical to stock. Both included pistons (threaded rod) are identical in every way, especially length.

What might be of value to troubleshooting this is that right before I replaced my master cylinder I had over-adjusted the freeplay causing the piston to fall out of the master cylinder. When that happened, it leaked a fair bit of brake fluid (maybe 10-20mL) but didn't continue to leak after that. I didn't think much of it at the time, but I don't believe that is normal. The reason I replaced it was based on the behavior of the clutch pedal feel: it matched the symptoms of the master cylinder needing to be replaced.


"Talking" through this does have me becoming increasingly convinced that -- despite the master cylinder potentially having an issue that may have not been very pronounced yet -- the issue is with the transmission, maybe even the clutch fork. It boils down to this:
- Clutch master cylinder was replaced
- Clutch master slave was replaced
- Hydraulics of all of it was bled until it was air free continuously for a solid 30+ seconds using a pneumatic bleeder kit
- Clutch disc, clutch cover / pressure plate were replaced
- Flywheel (but not counterweight -- which was left in place) replaced with ACT Streetlite
- Transmission was cleaned thoroughly prior to re-install
- 2 quarts of Red Line 50304 MT-90 75W-90 GL-4 Manual Transmission and Transaxle Lubricant (MTL) into the transmission
- All brake fluid utilized was DOT4 spec
- Power plant frame (beam) installed to spec with the bolts from the transmission being installed "to the max" (far extreme location) in the sliding bolt hole. It was installed in the manner as described in the service manual
- Freeplay was [attempted to be] adjusted. Ultimately, I never could get it to where I felt the true "freeplay" nature that everyone describes and I attribute that to the fact that the original cause of all of these clutch failures was causing this indeterminate behavior of the freeplay.
- Clutch pedal max position (for normal engagement pressure, but not at the disc-level, I believe) was calibrated according to the service manual

Despite all of that, the main issue remains.

One thing I still don't have that I really wish I did was a video showing the slave cylinder and clutch fork being extended to their furthest positions so I can truly know whether the issue is in the hydraulics or if it's a clutch fork issue. What I do NOT understand, is why, after replacing the flywheel, clutch disc, and clutch cover, that the likely original issue (clutch disc partial [dis]engagement) went from bad to entirely dysfunctional. Obviously, sometimes the process of taking something apart and putting it back together can manifest such behavior at the end of life of a part, but I want to make sure that's not just a convenient excuse.