kentq

iTrader: (1)

Jeff20B, you think the RB pp is worth using with a different disc? I got the setup used but with very low mileage (barely any noticable wear). For what it's worth, the car weighs 2000 lbs. Sorry to the op for jacking the thread!

Kentetsu

I have never, ever, worn out a clutch. Over two decades of driving stick, agressively, on a daily basis, and even racing on weekends. All of those cars were well used, rarely with under a 100K miles on them. And I have never worn out a clutch.

Until now......

I installed a RB clutch (street/strip) when I put the new (used) motor in a few thousand miles ago. It has failed, and is now slipping so badly that I can't even drive the car in anything over 2nd gear. I am not happy. It will be replaced by anything but a RB clutch...



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Jeff20B

iTrader: (13)

kentq, you can combine almost anything you want. Tell me what you want to use specifically.

Kentetsu, do you have an HD disc? Is that what's slipping? Once these wear to a certain point, they slip because they lack marcels. When you measure one, keep in mind you're measuring fully compressed thickness. Compare to a stock disc that is uncompressed when you measure it. Big difference. I'm not sure how much a stock disc will compress once installed, but I can imagine my 8.6mm disc I just installed probably squeezes down to more like 8.0 which is still pretty good.

Oh and one more thing. Buy a new disc! It only hurts until you drive it for the first time. Then you wonder how you went so long without one.

Kentetsu

Yeah, it is an HD disc. New clutch is in the works.

PercentSevenC

RB/Clutchnet HD clutches suck. Similar story for Jeff's bro's RX-4: gone after about 5K miles. I tried a used one briefly when I was supercharged, also, and what was left of it wore down FAST. We measured it before and after, and I don't remember the exact numbers, but it was something like half a millimeter in 2K miles, and I generally don't abuse my clutches very much.

Jeff20B

iTrader: (13)

It was that old 215mm HD disc. I think is was 6.8mm when it began to slip with the reman p-plate. I suspected at the time if it had the SS p-plate it could have gone longer before slipping.

Uh oh, percent. Your REPU has a used HD disc. It will probably only last about 4k miles. lol It went from a nominal measurement of 7.5mm when I first started using it to 7.4 in only 500 miles. And that's the thickest part. Oh it may engage nice and smooth right now without a hint of shuddering, but once the high points wear down, it will probably begin to shudder regularly like they all do.

The new HD disc in my REPU is from Raybestos and it either has some sort of glue between the linings or lacks it. I can't recall, but I know one of our 225mm HD discs lacked the glue. It could have been the one from the RX-4 that lacked glue. Anyway my REPU has an awful clutch burning noise when you first start going when cold, and you smell clutch right after. It also burns it off even while warm if you have to slip it a normal amount (for the street) such as on a hill or what have you. It also begins to shudder a lot if you attempt to drive it spiritedly, making spririted driving a punishable offense. In other words sprited driving is unrewarding with an HD disc. You also have to pay attention each and every time you let the clutch pedal up for fear of burning/shuddering/stalling because it has a super narrow friction point. Lastly the REPU's clutch pedal travel is actually quite short so it feels like the HD disc is an on/off affair much like a puck disc even though it isn't. Of the times when it doesn't technically complain about slipping the clutch to get going or spirited driving etc, it is because it was burning silently and you can smell clutch right after. The HD disc is coming out and will be replaced by a stock disc.

And one final thing. Pedal effort is a little high with the FC p-plate and the short pedal travel. You have less mechanical advantage than say an S3 RX-7 which has a pretty long pedal travel in comparison. It's my hope that a stock disc will alleviate all the unpleasentries I'm currently experiencing with the clutch in the REPU. I really like the FC p-plate and the light steel flywheel. You S1 and S2 owners have a similar pedal travel and effort so I hope this info is useful.

Kentetsu

I hereby nominate Jeff20b to be our Resident Clutch Expert...

Jeff20B

iTrader: (13)

Hey Kentetsu, how is your clutchness going?

I recently noticed these Exedy cerametallic clutch kits at Atkins. http://www.atkinsrotary.com/store/home.php?cat=765

They claim to handle 400hp and are a streetable 3 puck. I did a little digging and some sites say the 225mm version for our 1st gen cars have 208ft/lbs capacity while other places say it's more. Likewise some say the clamp load number is 1808 but other plates say 1650 or something like that. Without a point of reference for our OEM and SS p-plates, I don't know how that translates to pedal effort.

Has anyone here tried the cerametallic?

So far the only searches on this forum that resulted in anything useful are Howard Coleman's Exedy cerametallic hyper single and then having outgrown it (passing the 400 ft/lbs mark) he switched to a twin disc version of same. He liked the twin disc for its lower pedal effort and higher torque capacity. Unfortunately for most of us these high grade clutch kits only work with a T2 tranny.

I'm staying with a 1st gen tranny for now, so 225mm is what I'm working with. The way I see it, I need to choose a clutch package that will hold at least 300rwhp and 200+ft/lbs with some overhead capacity. Clutches are rated at the flywheel so subtract 15% or so.

Looking around I see ACT is very popular with very few people reporting problems. They say the 6 puck is grabby but quite streetable. And upon doing a search on their site, this caught my attention.

It claims 343ft/lbs at only a 34% increase in clamp load over stock. Of course that's all in the pressure plate.

I already have a brand new RB SS pressure plate made by Exedy, which I suspect is what ACT paints yellow and calls their "Heavy Duty pressure plate" so I don't want to buy another one (as well I suspect their Xtreme pressure plate is just an Exedy RB "Race" painted yellow). I'd rather just buy the 6 puck disc alone since ACT sells them separately, unlike many other clutch sellers who insist you buy the disc and pp together; oh there's Centerforce, Exedy, Bully clutch, Spec, Fidanza (yes they're in the clutch game now too but they still sell their flywheels separately lol) and I'm sure there's many others. Only a few outfits like Clutchnet and ACT sell parts separately.

So if you've read all this and want to help me out, I'd like some opinions on ACT's pressure plates and 6 puck discs. Are the p-plates the same Exedy units as RB's, just with some yellow paint? And how hard are 6 puck sprung discs to drive, really?

I only have experience with HD discs and stock discs, and limited experience with centerforce dual friction. I've gotta say that so far the CFDF is my favorite, but unfortunately many people have had problems because it seems to be either hit or miss with them; they either work great or not at all. Plus you can't buy the disc outright; it has to come with their gimmicky pressure plate with the weight things.

I don't want to buy another pressure plate. I want to use my RB pressure plate with a disc that will hold the power and still be driveable on the street. Since Exedy doesn't appear to sell their cerametallic discs separately, I think my only option is an ACT 6 puck sprung disc. Thoughts?

elwood

iTrader: (1)

I'm running an ACT 6-puck solid disc, their extreme pressure plate, and their lightweight steel flywheel. I have no idea who actually made any of the parts, but the general quality seems to be very high. This is on a T2 tranny, so YMMV, but I've been very happy with the performance.

Maybe I'm insensitive to the whole thing, but after driving a lot of other piston engined vehicles with really heavy clutch efforts, this thing doesn't even make me blink.

Jeff20B

iTrader: (13)

I can tell you why. Your car is an '84. The pedals were redesigned along with lots of other interior changes for the '84-'85 cars. The pedals were made longer and I think the pivot point was moved. They also added a helper-spring (the '76 Cosmo had this and I should now because I swapped from autpo to a 5 speed in mine). This created a longer pedal travel and easier pedal effort. A pressure plate that feels heavy in an '81-'83 car feels like nothing in an '84-'85 car.

Because my car is an '81, I have to give these things careful consideration before making a purchase.

I went back and looked over the other offerings at ACT and searched on this forum a bit more. It turns out several 2nd gen owners didn't like the 6 puck discs while others had no problems, and could live with the driveability issues of 6 and even 4 pucks.

So given my past history with my car, the way I drive it, the amount of flywheel torque that I'm expecting, the general respect for ACT products found on this forum compared to other clutch makers, my budget, and the fact that I may one day need to switch to a T2 tranny instead (and spend the money on all the misc things like a starter, a modded driveshaft etc), I feel that my best choice right now would be ACT's performance street disc and NOT their 6 puck. The cost difference is only four bucks. It's intended to be a daily driver. Plus we all know a 1st gen is pretty light.

This is what I'm talking about.
The RX-7 225mm model probably differes from the picture a bit, but it does appear well made.

Can anyone comment on it? Any comments on the pressure plates? Thanks.

elwood

iTrader: (1)

Different pedal ratio -- makes sense. It also explains why some early FB owners complain about brake pedal effort, too.

Whisper

Yeah, I went with the ACT street performance clutch and HD PP, but I haven't put them on yet, so this comment is actually pretty useless.

Kentetsu

Hey Jeff-

Clutch swap has stalled while I recover from foot surgery. I had my right foot surgically modified to allow a greater range of motion on the gas pedal. But really, they cut a bone out that wouldn't reheal, then broke some other bones that I guess pissed them off or something, changed the angles on those, then bolted the whole thing back together again. They say I'll be fine. But what do they know? All I know is I'm on percocet, so, um, like, what was I saying?

I've got my flywheel sitting in the trunk of the Bimmer right now, waiting for me to find a place to resurface it. I'm thinking I might just keep her down for the winter, get some things cleaned up and swapped out, kinda take my time with it instead of always being behind schedule. Maybe I'll even send my carb over to Dennis to see if he can "freshen" it up a bit for me (not that it needs it, but I kinda feel like it deserves it).

The clutch I went with is the Exedy 10806:

Product Details
Exedy Single Plate ClutchEXEDY Organic ClutchEXEDY racing clutches with organic friction materials utilize only premium materials to provide maximum resistance to slippage and burst. EXEDY organic clutches can also handle modified engines due to the increased clamp loads. Drivability with EXEDY organic clutches is similar to that of stock clutches. Pedal efforts will be slightly higher due to the higher clamp loads. As with all EXEDY clutch discs EXEDY organic clutches feature high capacity spring center dampers designed to reduce drive train shock and impact.EXEDY Cerametallic ClutchEXEDY cerametallic clutches are designed to handle the abuse of high power modified engines. EXEDY cerametallic friction material can handle much more slippage than stock type disc assemblies. EXEDY cerametallic clutch discs feature spring center dampers to reduce the impact and shock loads placed on the drive train. This protects the transmission and the entire drive line system. All EXEDY clutch discs are equipped with thin cerametallic friction material (approximately half the thickness of a stock disc). Compared to other discs with thicker friction materials EXEDYs thinner layer of friction material reduces clutch disc inertia and improves transmission shift efforts and synchronizer durability. As with any cerametallic clutch system some compromise of startup drivability should be expected as compared to a stock clutch (i.e. chatter on light throttle low rpm startup). This characteristic is considered generally acceptable in modified performance cars.

Since I haven't installed it yet, all I can tell you is that it's real pretty. The pressure plate is totally different from the RB PP. The clutch disc has a sticker on it that says Daiken. That's about all I can tell you. I just went with Billy's recommendation, which always seems to work well so why fight it. lol.

Good luck on your latest project...


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Jeff20B

iTrader: (13)

Thanks.

I'd like you to post a picture of the kit at some point so I can see what the disc looks like. I can post a picture of the ACT disc so we can compare. I have a sneaking suspicion the ACT unit is just a repackaged Exedy, but maybe with yellow painted springs. My RB SS p-plate is an Exedy but it's a couple years old now. Maybe they changed their design a little.

Just a note. You know the Exedy 10806 is 225mm right? I recall there were some issues with the flywheel you had for a while being the wrong one, but you sorted that out. I can't remember whether you had to use an '83-'85 225mm flywheel or an '81-'82 215mm flywheel.

I've noticed ACT has dropped support for '82 and older kits in the 215mm size. Is there any other recent Mazda that still uses a 215mm disc that we could cross-reference? I only know of the 1.6L Miata that used a 200mm disc, which doesn't help. Then the 1.8L I think moved up to a 225mm. Or maybe the 4 cylinder 626 had a 215mm but was compatible with a 225mm? It gets confusing. ACT lists the same disc but a different pressure plate for all these models, which really doesn't help.

Jeff20B

iTrader: (13)

Yeah about that. The '79-'80 cars have even higher effort due to the small brake booster. But yes it did improve in the '81-'83 cars with the larger booster, then again in the '84-'85 cars with the longer pedal travel.

mar3

iTrader: (8)

Yet one more urban myth...I'll add my name as having personal experience with the CenterForce Dual Friction clutch set-up. You try 20+ drag race drop clutch passes anywhere from 2500 to 4500 rpm in 3 hours and see what's left of normal "HD" clutches...never even smelled clutch, just burning oil off the engine......quite embarrassing.

Kentetsu

Damn Jeff, you're right. The new clutch is a 225. How the hell did I screw that up?

Well, just one more delay to add to the list.

Jeff20B

iTrader: (13)

Good thing we caught this in time, huh? It's not like you're installing it today, right? Plenty of time to get the correct size parts.

Now the question is since ACT dropped support for 215mm, and there is no cerametallic for us in that size as well, what are you going to do?

Here is a possibility for you, and if it works you can thank me later. Since you still have access to the flywheel, grab the 225mm disc and limp (sorry) out there and place the disc on the flywheel. I bet you'll see that it actually just barely fits within the raised step, making full contact. This just leaves you needing a 215mm p-plate, which as it turns out, you already have and it's proven to work already. I hope this will be a bright spot in your otherwise dreary day.

Yes there will be a 5mm overhang of disc material past the pressure plate, but I tried this with a 215mm SS p-plate and a 225mm HD disc last year and it worked very well on the Camden powered 13B in my '81.

Jeff20B

iTrader: (13)

Did it fit?

The new ACT "Performance Street Disc" I ordered arrived yesterday. Part number 3000203 for '84-'92 or any other year which will take a 225mm disc. Note I couldn't find a confirmed 215mm ACT disc but I didn't try that hard.

I'm glad to say it looks like the picture above. Measures 224mm-225mm across (perfect).

About 7.93mm thick pre-break-in.*

The splined hub is just as beefy as a Clutchnet HD disc, but looks better made/more accurately machined.

The yellow springs are pretty beefy looking and include smaller springs within.

The copper content of the friction material is increadibly high; perhaps that's why these things are so expensive, using a semi precious metal like that lol. This copper sinks heat away allowing the disc to recover more quickly if overheated. Not bad!

The stamped upper cover looks like an Exedy, so you know it's going to be good quality.

It has an SFI Spec1.1 rating which the Clutchnet HD discs probably lack.

*Oh and probably the neatest feature is the "reduced marcel" between friction surfaces. You can squeeze it with thumb and forefinger and just barely see some minor movement.

Compare this with a stock disc and you'll understand that the ACT discs will have quicker take-up with still enough movement to reduce the tendency to shudder for smooth street and race driving.

Compare with HD discs which are rivited directly to the steel backing with no marcels and most have some sort of glue/epoxy making them truely solid. Perhaps that's why HD discs like to shudder so often. For example my HD disc would shudder more when hot, and not at all when first starting from a stop but would make a funny noise and then I'd smell clutch for a while. Stupid HD disc.

Jeff20B

iTrader: (13)

Glad I got an ACT. Now in which vehicle should I install it? I think I'll try it in the REPU. It will be a good test to gauge how much it differs from the HD disc previously in there. It's certainly heavy duty enough to handle towing without overheating during starts (high copper content), and its street manners ought to be a lot nicer than the HD disc.

I'm debating whether to use my new 225mm RB Exedy "street strip" pressure plate with it, or just a stocker again. Reason I might prefer the upgraded p-plate is, as I've just realized, the way SS p-plates are sprung, they tend to have their friction points lower to the floor than stock p-plates do. This works fine with non marcel discs like HD, puck etc, and places the friction point somewhere in the middle of clutch pedal travel. It is also fine with stock marcel type discs as the friction point is really low which can be adjusted up a bit if you want.

However if you use a stock p-plate with a non marcel disc, you're in for a nasty surprise. Because stock pressure plates were designed with a stock disc in mind, and when used together, the friction point is usually somewhere in the middle of clutch pedal travel. Not too high, not too low. But try to use a stock p-plate with a non marcel disc and it does all of its clamp and release action at the very top of its travel, rendering the other 90% irrelavent. Not very much fun to drive on, let me tell you.

My REPU had this type of setup briefly this summer and I just couldn't learn to like it. Stock p-plate, HD disc, light steel flywheel etc. Just no fun to drive it. I did like the pedal effort though. I'd like it to be that level of effort again but with a much lower and slightly wider friction point.

I might not be able to have it both ways however. It seems that I may have to choose between comfort and strength.

The OEM REPU setup was pretty strong from the factory. It had to be as this was Mazda's pickup with pick up. It used 9 pressure plate bolts instead of the usual 6. The only rotary in the lineup at that time that had a 225mm disc when all others were 215mm. The p-plate was more heavily sprung than the RX-4 and the other cars. The disc itself was also obviously built to a heavier standard I would assume. The only real problem with using the ancient OEM REPU parts is finding new ones. They were designed for this one model only. They had a funny offest as this was Mazda's only way to fit a 225mm disc inside of a flywheel originally designed for 215mm and still maintain the 30 pound weight. Remember this was the early '70s. Heck the 3rd gen used a pull type clutch because it was the only way for a clutch with reasonable pedal effort to hold the level of torque they were making by the early '90s. Now look at the RX-8; same old 240mm disc as the T2 and 3rd gen, but back to a push type clutch and it holds the power of the Renesis fine. My bro's hasn't blown up yet, although it is worn and pedal effort is higher than I'd want in a daily...

Clutch tech has come a long way and I'm doing my best to keep up.

I might need to choose strength because the plan is to use a 5" SC with a -10 pulley for maximum boost in a minimum RPM range for better low end power up to where the SC runs out of breath with a -10 (like 6.5k or something). Stock ported 4 port 13B so it has maximum low RPM torque off boost. Nice thing is stock ports run out of breath by around 6.5k as well. Early heavy 9.2 compression rotors for less detonation and more rotational weight. Hey it's a truck! Exhaust will follow RB's example and consist of dual long primaries with one 2" presilencer on each pipe like the RB "streetport" system. Then I'll collect to a single 2.5" and on into an RB universal 2.5" muffler. If it's still too loud after that, (remember this is not one of their somewhat restrictive but also quite powerpulse mufflers), I'll need to add a Magnaflow oval or something. Plenty of room under the bed.

So I think I'll have to choose strength over comfort, but then I'll never have to worry about clutch stuff again.

Kentetsu

Wow Jeff, that's a whole lot of info right there!

Sorry, I haven't made it out to the garage while the wife has been home with the car. In some pain, on heavy pain killers, makes me sleepy.... I'll be back on the ball soon though.

I was wondering, what if I were to consider a lightweight flywheel? Would that change my situation at all, considering I've got an '82 with the goofy weight? Not sure how all that works with the weight balancing of the flywheel anyway, doesn't that thow the balance off itself? Might make more sense to me sober. G'night...

Jeff20B

iTrader: (13)

In my experience the oddball front weight of the '81-'82 engines doesn't matter. All you need is the '79-'82 rear weight. Send me a PM.

I personally like light flywheels. I'm currently in the planning stages for my '81 FB's next engine project which includes a superlight steel flywheel. Only 8 pounds and 215mm only. I already have an RB street strip pressure plate in 215mm, slightly used, but would like to get a stronger disc for it because a 7" SC and 3" exhaust are in its future. Having examined my new ACT 225mm disc, I've been on the lookout for a 215mm version and I just found one this evening! Mind you ACT has dropped support for the '82 and older rotaries so I haven't found their HD or Xtreme pressure plate yet, because they are model specific, but the 215mm disc was found in several models including some Fords (probably with Mazda trannies as corporate cousins or whatever). The link to Summit is here. http://www.summitracing.com/parts/ACL-3000205/

Even the part numbers are similar 3000205 = 215mm & 3000203 = 225mm

What is the part number for their 215mm rotary HD pressure plate? Anyone?

Have you considered Fidanza for your flywheel? I looked that up too. 161991 for '86-'91. Doesn't actually matter because it is the NA version and can be used all the way back to '74. Looks like that's the only way we'll get an 8 pound flywheel these days because the superlight steels are no longer made. One thing to note the Fidanzas are 225mm only. They have step spacers already machined into the outer edge. 215mm pressure plates will not fit. Compare this to RB's aluminum flywheel that is compatible with both sizes. 225mm requires longer bolts and spacers. RB's aluminums also weigh 11 or 12 pounds, so something to consider. RB's light steel flywheels weigh 13 pounds.

PercentSevenC's car has the same 8 pound superlight flywheel model that I'm going to use. His car has a centerforce dual friction clutch kit. The pedal effort and friction point are both actually pretty good. I took it for a quick spin yesterday and really liked the feedback and driveability of the setup. It's my hope that an ACT disc with its limited marcels will behave similarly to his CFDF setup which also has limited marcels in its own right; the dual friction disc basically only has one set of marcels on the pressure plate side. The flywheel side just has some fiber pucks solidly attatched to the steel backing. Drives really nice!

Please don't fall under the impression that these so called superlight steel flywheels are easy to come by as I've only ever seen just these two in my entire experience with rotaries thus far. I don't know anything about their manufacturer, any of their specs, where they came from etc. Something of a mystery.

Jeff20B

iTrader: (13)

Ok I finally found what I was looking for. The ACT HD p-plate is MZ-016 and Xtreme version is MZ-016X. It's no longer manufactured but distributers still might have one or two on the shelf. Happy hunting.

As for my car I've given it a lot of thought today and I think I'd like to try out my centerforce I or II pressure plate (got it used so not sure) on the superlight flywheel with a stock disc. If it slips I'll get a Fidanza and throw in the ACT disc and the Exedy RB SS P-plate.