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Walter Moore

Is this a Centerforce I or II? Does it matter?

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I bought this clutch setup a couple of years ago on Ebay. The seller called it a Centerforce, but did not say if it was a I or II series. The label, which I could not get to photograph, just says Centerforce.

It was used, but as you can see not very used because there is still lettering on the friction disk.

Anyway, I was planning on installing my engine and transmission back into the car yesterday when I noticed that the transmission isolator is torn, so as long as I am opening my wallet again I decided to search the forums to make sure that the rest of the parts here were ok...

I discovered this thread:

http://www.classiczcars.com/forums/showthread.php?t=17781&highlight=centerforce

which indicates that with a Centerforce II you need the throwout bearing sleeve from a 280Z...

So I checked my throwout bearing sleeve and based on the measurements, and the information at this link:

http://www.zparts.com/zptech/articles/trans_swap%20parts/4tobear_specs1.html

it appears that I have the sleeve from a "type A 4 speed" transmission. Which is all well and good, except that the transmission is clearly a "type B 4 speed"!!! :sick:

(I know this because of the shifter linkage, and the fact that the PO had to cut the transmission tunnel to clear the shift lever...)

So, I mocked up a simulated installation using a straight-edge and my calipers. It looks to me that at the maximum movement of the pressure plate release levers my existing sleeve might slide beyond the end of the transmission's bearing surface, and get stuck... Not a good thing in my opinon.

Of the five different T/O bearing sleeves that the parts CD shows, Courtesy Parts lists only the 30501-N1600, which is for the 75 and later cars. Is this the correct sleeve for the Centerforce II?

The Centerforce clutch arrived from the Ebay seller with a re-surfaced flywheel. I wasn't planning on using the "new" flywheel, because I noticed that it doesn't have dowel pins to locate the pressure plate, whereas the original one does. (The Centerforce pressure plate mates with the dowels on the old flywheel just fine.)

So my questions are:

1. Is this a Centerforce I, or a Centerforce II? How can I tell?

2. Given that I apparently have the wrong T/O bearing sleeve, Which one do I need?

3. Am I correct in assuming that the dowel pins are important? (Or were they omitted from the later cars for some reason?)

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So my questions are:

1. Is this a Centerforce I, or a Centerforce II? How can I tell?

2. Given that I apparently have the wrong T/O bearing sleeve, Which one do I need?

3. Am I correct in assuming that the dowel pins are important? (Or were they omitted from the later cars for some reason?)

Walter:

The P/P in your pic looks exactly (including the color) of the Dual- Friction Centerforce II shown in the current MSA Catalog (Page 93). When I bought my Centerforce I, it was not orange, but did have the ring of counter-weights. You didn't post a clear pic of the disc that you have which should show obvious signs of two different friction materials used in it's construction.

See MSA Online Catalog Page

Yes, dowel pins are important in my opinion, and should be easy to acquire.

As for the collar, I've always heard that you had to use compatible fork and t/o collar, but that is with OEM clutch parts. Is the height of the CII pressure plate different than a stock 280Z unit?

I think I'd try to contact Centerforce to inquire further. Might be that they could advise,

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Yes, I noticed that the pressure plate looks like the picture of the dual friction unit, but the friction disk is clearly not the same.

Thanks for the suggestion about contacting Centerforce, I hadn't thought about that.

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Walter,

For reference, here are pics of a new Centerforce II pressure plate & disc. Its very obvious if you have a CF II disc, as there is a different type of friction surface on each side. If not, someone may have put in a CF I disc with a CF II pressure plate. I've never done this, but I don't know why it would not work.

Its very common to destroy the dowels when removing them, to surface the flywheel. Just be sure to order some new ones from Nissan. Always use dowels in the flywheel. As long as you're doing all this, it would be a good idea to have the fly & pressure plate balanced as a unit. Its easy to get a weight imbalance when mixing & matching flys and clutches.

Phred

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I wasn't planning on having the flywheel resurfaced. It was a little rusty, but had no gouges or groves. I sanded the rust and it seems ok. What indicators would there be if it needed resurfaced?

As for balancing, I can see that it would need to be balanced if it was resurfaced, as it appears to be a casting, and is thus likely full of small non-uniform air bubbles. But at the same time, I am sure that Nissan balanced it way back when it was made, and the amount of material that the clutch disks would have removed over the years wouldn't be likely to change the imbalance very much.

The pressure plate fits on the studs one, and only one way.

I work in the balancing industry, and have heard that racing teams tend to balance things as assemblies, but I doubt that Nissan balanced the flywheel with a pressure plate mounted. Car companies tend to balance the parts, not the assembly. Wouldn't the pressure plate have been balanced when it was made?

If you drill holes in the flywheel to correct the imbalance of the assembly with the pressure plate in place doesn't that just guarantee that the next time you replace the pressure plate you will HAVE TO re-balance the assembly?

I guess that I will just attach the pressure plate to the original flywheel, buy a new throwout bearing and sleeve, and see what happens...

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Walter,

The most common, (and easy) way to see if your fly needs resurfacing, is a straight edge check. Take a 12 inch rule (like from a combination square) or just a good carpenters square, and set it on edge on the disc face of the flywheel. Then use your feeler gauges to check how much wear has taken place on the disc area. Also note if there is uneven wear from the inside to the outside of the disc area. There is no magic number here, but I resurface if I see more than four or five thousands. If you have wear or an uneven surface, sure you can bolt on a new clutch. But you will have accelerated disc wear and possibly chatter till the new disc conforms to the old uneven surface.

I have balanced literally hundreds of flywheels and clutches on a Stewart and Warner electronic balancer. I would guess that 1 in 15 new clutches would be "balanced" out of the box. Also, the procedure for balancing a fly/clutch set is to first balance the flywheel. Then bolt on the clutch and balance again, by adjusting, or drilling on the clutch itself. Then you can change clutches without disturbing the fly balance. Additionally, a flywheel/clutch can be unbalanced to the point that it can hammer out the bearings, or spit a damper off, and you still may not feel the imbalance in the seat of your pants. Its your dollar, you be the judge.

Respectfully,

Phred

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Please note Phred's post. I cannot stress this fact that you need to balance the flywheel/PP combo. I believe you must also remove the "weights" from the PP in order to correctly balance the Centerforce II clutch.

The picture of the T/O bearings is not correctly coded. What is important is the distance from the face of the T/O bearing to the thrust side of the fork collar. This is the only measurement that matters. I would use the shortest T/O bearing collar you can find with this clutch. I barely had any freethrow in my pedal with my new Centerforce II clutch. After I ran it and got the fuzzy stuff on the disc, it works just fine. I has about 1 1/2" of freethrow!

My Centerforce II clutch unit works very well in my '71 240Z.

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Phred,

What is the recommended allowable imbalance in the flywheel - pressure plate assembly?

We don't have any small balancers in the shop at the moment, at least not that could be adapted to this purpose...:cheeky:

Where would you recommend that I could get this done? (What sort of shop I mean...) I have had a lot of clutches replaced over the years and have never been charged for balancing. I doubt that many places do this.

By the way, I checked the clutch surface with a straight edge, and to the best of my ability to measure, it is flat within .002" so I assume it doesn't need resurfaced.

Oh, and the friction disk that I have is clearly NOT the CF-II disk from your post, so I don't know what I have.

ZSaint,

You seem to be saying the exact opposite of what was said in the earlier thread I referenced above. From what I can see my existing T/O collar is way too short. It looks to me like it will have to move nearly an inch from its extreme returned position just to reach the clutch levers. (I could be wrong...) In any event I have what appears to be the shortest T/O collar ever made for a Z car.

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Just make certain you have a matched set of clutch arm and T/O bearing collar. They recommend the 280Z set-up for the CFII. If you can dummy up the tranny on your engine and try it before you hook up the exhaust, etc., it will help. Good luck.

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Walter,

There are probably a dozen ISO standards listing what MAY be an acceptable imbalance. In the real world it works like this. Basically, an electronic, dynamic balancer detects an imbalance in a rotating mass (crank, damper, fly,clutch) by the use of load cells under a support beam/roller. The imbalance, measured in grams, ounces, or whatever, is determined from its location from the center of the axis. Through the use of an indicating strobe, or CRT display, the location is pinpointed. Weight is removed (or added) to eliminate the imbalance. In the racing industry, there is really not an acceptable imbalance. We just work at it till the dials on the gauges don't pick up any more imbalance. ( as close to zero as possible)

BTW, you live in the center of the racing world. There are probably more racing engine shops per capita there than any where else in the world. Let your fingers do the walking!

Phred

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Phred,

So you try to get to zero imbalance? What is the resolution of your Stewart Warner balancer?

Thanks for the lesson about balancers, but it wasn't needed. I design balancers for a living. No offense intended on my part. I didn't take any offence in your reply.

I also know that there is no such thing as zero imbalance. There is just a level at which either the electronics can't detect the forces being generated, or some point at which it no longer makes any sense to try to correct what is left.

For example, at a tire shop they add weights to your wheels until the balancer displays 0.0 oz required. But in point of fact all aftermarket tire and wheel balancers sold in North America display zero imbalance as soon as the residual imbalance is less than 3/8 oz per plane. The smallest weight sold for aftermarket use is 1/2 oz, and they aren't very accurate, so once the residual imbalance is less than 3/8 oz there is no point in trying to correct the part further. Thus for a tire and wheel assembly, 3/8 oz at the flange radius is the commonly agreed upon "Standard" for a properly balanced part.

I just wanted to know what the comparable limit is for the flywheel/clutch assembly. If you always try to reach zero, then for you it is the resolution, or possibly the repeatability of your measurement system.

It looks like the balance holes on the two flywheels that I own are at about a 128mm radius. I guess that I could calculate the mass removed by each of those holes based on the density of cast iron and have some close approximation of the limit.

Again, thanks for all your help thus far. I do appreciate it, even if it seems like I am smarting off sometimes.

I am sure that Nissan lists the imbalance limit of the flywheel on their part print, but I have no way to get a copy of the print. I doubt that it would be in the factory manuals for the car.

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