Clutch Porn

The chirp is more like the sound of a belt sqeal , I think. I'm used to how to drive it on the street, But Mine is Strip/Weekend Warrior. I wouldn't start messing with how the Pressure Plate graps or dial in too much slipage, or you may end up toasting the flywheel.

There is a scientific way to dial the clutch in. It requires reading both the driveshaft speed and engine speed during a run. You compare both RPM's to determine the amount of slippage.

The system can be either part of a complete data collection system, such as the Innovate LM-1, or can be in built into a tach, such as Autometer dual channel with playback. Both are expensive options.

4th gear is where the clutch is most likely to slip. You can back off the pressure until it starts to slip in 4th gear, then add a turn. This will give the smoothest launches, yet still hold on the top end. Of course, this also means the most slippage and least clutch life.

Mine has 800lbs of static pressure, and I have one turn of preload. It has NO problem holding up to the nitrous in 4th gear. The only time it slipped in 4th gear, was after 3-4 years of street/strip abuse, and the disk was very worn and the facing was starting to chip away. Still, even with a disintigrating disk and excessive pressure plate clearance, I was able to turn up the preload to where it would still make a full pass and hold in 4th gear.

Many racers will only have a couple hundred pounds of preload, where the car will barely pull itself at idle with a cold clutch.... but, rev it up and get some heat in the thing, and it takes off! (those guys do a lot of clutch maintenance, and rev it up to where the centrifugal kicks in)

I think 800lbs will work just fine for you at the track, but -may- seem a little low on the street when cold. I installed a new disk, and set at one turn, works just fine on the street. You may want to turn yours down a little, and try it.

Good luck, and keep us informed! All us sintered iron guys need to keep in touch and share our experiences.

Mike

Here is the "wear and tear" update.

Today I dropped the Scattershield in order to send it back to Ram to have it rebuilt with the counterweight option that I regrettably did not know about when I purchased the pressure plate. The first thing that I did was to remeasured the PP distance and found that it is now 1.990, where it was originally at 1.975. So after 200 or so street miles and 25 runs, I am certainly due to remove a couple of the .010 spacer washers. This wear was becoming evident at the track because the I needed to increase the static pressure to overcome the additional slippage.

Because of the slipping nature of this type of clutch, there was a dust coating found on various parts. Here is the tranny snout:



Inside the scattershield:



Clutch before being disassembled from the flywheel:



A couple of pics of the sintered iron disc--it still looks good on both sides but you can see the heat marks on the metal center:





Now for that bad news. I have an interesting 3 point burn pattern in both the PP and the Flywheel. I can feel the wear in those 3 points in the flywheel, particularly at the lowest part of the contact circle. There it is burnt blue an is a few thousands difference compared to the part of the flywheel that the clutch does not ride on. Note that this Ram Billet steel flywheel was freshly blanchard ground at the start of the this year's race season. Obvious it be ground again before reassembly. As for the PP, since it is being sent back for the CW mod, it will of course also be renewed.

Here are pics of the heavy burn marks that I am describing:





Removing those 6 studs shown on the flywheel became a chore in itself. Although they were initially installed finger tight, 242 locktite was used on the threads as recommended by Ram. In order to remove them, I had to first heat the pressure plate and studs with a propane torch. Once I got them hot enough, the studs spun out, but still with some effort.

As you can see (from my limited experience,) sintered iron clutches will require periodic maintenance and will not be an "install and forget it" type deal like the typical replacement clutches. The PP will need to be measured periodically to determine clutch disc wear and you may need to remove the PP once in awhile to remove the spacing washers (at least for the Ram unit) to correct for clutch wear. This is not the same thing as doing the static adjustment which can easily be accomplished through a small opening in the scattershield with an allen head socket.

The sintered iron dust is abrasive and can affect the longevity of your pilot and your throw out bearing. My pilot bearing is a special shielded roller bearing and my throwout bearing is the premium type that can be greased. Luckily, those items still look good.

Wow, mine's never been burnt up that bad... even after 2-3 years of continuous use. Hopefully, after you get this figured out, it won't slip so bad. I've never encountered such pronounced burn areas like you have. Something has to be warped and not flat, I would think...

Good Luck!

Dennis,
You might want to do what I am doing. On the bottom side of the bellhousing, drill a small access hole to be able to get a feeler gauge in between the disc and flywheel to ensure .090 clearance when clutch is depressed. Also, be sure to index your bellhousing.
You shouldn't be have ANY slippage with that disc. As the disc heats, it should actually grab better. Adjust it to hook and stay hooked and dial -in the rest of your drive train to handle the shock under launch. Set your .090 clearance, and go with it. You also might want to consider a flywheel with removable clutch surface. My iron disc was .030 new, after one season it is .015. In my case it looks like a new insert and disc every year. 4500RPM launches really munch on everything. I guess this is the price we pay for abusing them. As you can see in my pics the wear isn't too bad, I mean as far even wear. I had the massive dust inside the bell too. Imagine the light show inside on a launch!!!

P.S. while driving it on the street, try not to slip it too much to get going. Just dump it. Short shifting with nitrous is bad too. I've been through 4 clutch set-ups within the last 2 years....So, I do know how to tear 'em up! hehe. Now I'm figuring out how to make 'em work! LOL. This access hole just might be the key to my success.

Here is the reply from the Ram technician after sending him my photos. I highlighted the the last sentence:

Dennis,

These discs are good for 60-80 passes and one thing we do find when folks try to drive them on the street is there such an agressive disc that they have to be slipped allot to engage smoothly. This is typical wear pattern on a sintered iron setup.

Doug
RAM TECH

Well doesn't that just suck big ones . . . . . . .

Not sure what I am going to do at this time, although one area I can improve is how I put the car on the trailer (where I probably slip the clutch the most.) Might be time to invest in a hoist.

Those long, hard slips through 3rd and 4th gear are what are causing all that heat. Anything you do on the street or trailer are MILD in comparison.

Get the flywheel surfaced and put everything together so it doesn't slip too bad, and things should be fine. Mine has had EXTREMELY long life. As long as you don't have it set up to slip a LOT, those setups will last a long time. Mine had no trouble going TONS of street miles and well over 100 drag strip pases.... and I don't even have shims to remove! (plate was set up deeper) RAM has to say what they did in their reply to you, as they have no control over how people set them up. Top fuel cars only get ONE run out of those disks before they need service.

Triple check everything when put it back together in order to see if there is any way anything might be bottoming out or binding when in use, as there is no way your clutch should have been slipping with over 1000lbs of base pressure! I run less pressure than you, nitrousing into the 10's, and mine is still on the tight side. Hopefully the centrifugal weights will do something, but I don't see not having them making THAT much of a difference at your rpm range. (but, I could be wrong)

Good Luck!

Again, I stress to check your bell housing alignment to the block. By the looks of the input shaft on the trans, it looks like there has been some binding that Mike is speaking of. Aftermarket lakewood sheild and line boring of the block will have a direct effect on this measurement. The most amount it can be off is .05. Have you been having any shifting issues?

Mike, are you using the stock type Z-bar linkage? Mine is the stock type. I have what appears to be lots of play in the fork when the clutch was adjusted. I could move the fork enough that I could almost pull the contact rod out of the dimple in the fork. I am using the fork that has the hardened spring clip, not the wire type that was found on the early cars. The motor is chained down and the Z-bar linkage has no slack. Try as I might, I just can't where a slippage problem would originate. I will be cautious when it is all reassembled.

The scattershield was dialed in and was less than.05". There is no signs of binding when looking at the cleaned up inputshaft and snout. I did drag my finger over the dust prior to taking the pic. NO shifting issues--as a matter of fact, with this clutch and the use of Mobil 1 synthetic the tranny shifted better than ever in the forward gears. Reverse had a little grind.

I did have some slippage in 3rd and 4th which appears to be the main culpret--I increased the pressure to counter act it. I then experimented in both directions. When I felt it slip, each time I let off. By then, I am sure the damage was done and the wear was excessive (as evident by the need to remove a couple of spacer washers.) Counterweights are supposed to help in the higher gears, but as Mike alluded too, it may be RPM dependent. Mike (and others) said that I should never had slippage with over 1000lbs pressure. Mine was only safe when there was something like 1160lbs. Try as I might to find a problem with my junk, I just haven't found the source of my problem. What are the chances that the PP I received had problems in the first place? I did annotate the issues I had on the Ram return form.

This time around I will make a hole in the PP in order to check freeplay. Pretty sure that Ram specified .060 with this setup, but I can certainly find it again on their site.

From what I've learned, I will be even more cautious in dropping base pressure, although I never went to the lower extreme.

Thanks Mike and FatNfast. Your input is greatly appreciated. I will put the info to good use and hopefully my next go around will be better--it would be nice to at least make it to the end of the racing year before replacement.