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 Post subject: Re: Clutch Question
PostPosted: November 4, 2018, 12:08 pm 
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It is hard to understand your description as you never mention the pressure plate. There three different components to address: a pressure plate, a clutch disc, and the flywheel. The pressure plate does not need to be a mustang plate even if the clutch disc is a mustang disc. Use a zetec pressure plate with the mustang clutch disc. The pressure plate must match the flywheel. A 2002 focus pp for a 9-7/16 clutch is $37 on rockauto.

Your clutch thickness is typical. The marcel spring between the facings compresses when installed so the driven thickness is .320. This is what the thickness would be for a puck type clutch with no marcel spring.


SHOULDS: With the pp bolts finger tight, there should be no gap between the pp ring and the flywheel friction surface but there will be a gap between the pp cover flange and the flywheel clamp surface, clutch or no clutch. If this is not the case, I expect the issue is the pp not matching the flywheel. It appears you have a flywheel with a protruding pp cover contact surface for the pp that sticks out above the friction surface. The mustang pp is designed for a level surface between friction and pp cover contact.

How much diff will the right pp make? I don't know but it is a good place to start.

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 Post subject: Re: Clutch Question
PostPosted: November 6, 2018, 3:25 am 
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"With the pp bolts finger tight, there should be no gap between the pp ring and the flywheel friction surface but there will be a gap between the pp cover flange and the flywheel clamp surface, clutch or no clutch. If this is not the case, I expect the issue is the pp not matching the flywheel. It appears you have a flywheel with a protruding pp cover contact surface for the pp that sticks out above the friction surface. The mustang pp is designed for a level surface between friction and pp cover contact."

The relationship between clutch finger travel & pressure plate travel is not linear, but proportional (it's a lever-and-fulcrum system), where (at least, in this case) the relationship is a ratio of roughly 4:1. In other words, if there were no gap between the flywheel friction surface & the pressure plate friction surface (with no friction plate installed), the fingers would have to move inward 1.320" just to accommodate the thickness of the .3300"-thick friction plate when installed between the pressure plate & flywheel.

The fingers don't have anywhere near that total amount of travel so, without this gap, the pressure plate could never be installed. Unfortunately, the gap is only 0.1325". Owing to the aforementioned 4:1 relationship, even with this gap, just installing the friction plate is enough to force the clutch fingers to move inward nearly a full inch, almost into contact with the friction plate.

One issue seems to be that there are substantial dimensional differences among various manufacturer's clutch parts, and none of these are specified by the sellers/manufacturers. There's simply no way to know. Today I looked three different friction plates, for example, all for the identical application, and they are very different in design, as well as in several of their dimensions (such as hub height/diameter, damper spring number & arrangement, etc.). The same seems to apply to pressure plates.

When I purchased my clutch parts, I used the same application-specific parts as all the others who have done this same combination, with success, in the past.

- My pressure plate is a Sachs unit, badged as a Ford Motorcraft item, specified for a 1999 Ford Focus Zetec 2.0 (that's what my engine is).

- The friction plate is a 9" Exedy unit, specified for a Mustang II, selected to match the input shaft of my Mustang II-sourced, T5 WC (V6 version) transmission.

- The flywheel is a Fidanza aluminum unit, specifically for this version of Zetec. I did have the opportunity, today, to confirm its dimensions vs. a stock, Zetec steel flywheel. Its friction surface height is identical to the OEM unit.

I've noticed that for everyone who's also done this, there seems to be perilously little travel available for the pressure plate's fingers to travel. The fingers on all the applications I've seen point fairly steeply inward, toward the friction plate hub, rather than being either parallel to the pressure plate's outer surface, or somewhat proud of it (which seems common in other installations on different engines).

It certainly seems to be a universal issue when mating a T-5 to a Zetec, although others have been "lucky" (one builder employed a used-but-serviceable friction disc, which probably saved him from this issue). In my case, fractional differences in available parts seems to have worked against me.

That's my luck, by the way - this picture exemplifies my luck, for which I am famous among all who know me -

Attachment:
my luck.jpg
my luck.jpg [ 27.35 KiB | Viewed 278 times ]


In my case, when the pressure plate & friction plate were installed & torqued properly, the pressure plate's fingers moved inward to such an extent that they were facing very steeply inward, almost touching the friction disc's center, with only 0.286" of remaining finger travel remaining. In my opinion, that was insufficient to allow the clutch to release when the fingers were compressed the remaining 1/4". This small remaining amount of travel would only have permitted the pressure plate to release 0.0071"....nowhere near the 0.200" or so I calculated it needed to actually release the clutch.

I made up a test rig (essentially a manual, lever-activated clutch release bearing), and tested this.

I was correct - when the fingers were compressed to the point that they were hard up against the friction plate, the clutch did not release.

As an experiment, I made up some 0.095" shims of hardened T-6061 aluminum (the same material as the flywheel), and installed them between the pressure plate's 6 mounting pedestals and the flywheel. The shims duplicate the area of each of the pressure plate's clamping surface areas exactly, so the contact area between the pressure plate & flywheel is the same as it was before.

The hardened steel dowels are still in place, and are fully engaged in the pressure plate.

The shims were enough to cause the clutch fingers to move outward to where I thought they should be, roughly at the same level as the outer surface of the pressure plate. This increased the available clutch finger movement to over 1".

Another test with the manual test rig proved the clutch now releases properly & fully, yet clamps with full pressure when released. It gives a very reasonable amount of travel for the hyraulic throwout bearing (a RAM 78136) to work properly.

Without the shims, the RAM unit would have been forced to use the very last 1/8" of its 1" available travel to release the clutch, and the unit's "snout" was almost in contact with the friction plate hub (this must NOT be allowed to happen, for obvious reasons - only the RAM unit's bearing can be allowed to make contact).

With the shims, the clutch now releases at about the halfway point of the RAM's travel (from full engagement to full release only requires about 1/8"-1/4" of travel, but this now occurs halfway along its travel, rather than at the extreme end of it).

I know this seems like an over-simple (and unusual) solution but, as it stands, the only other option would be to buy several different brands of pressure plates, in the hopes that one of them would provide sufficient clearance for the clutch to work.

My buddy (another Locoster, and a very accomplished mechanic) and I examined my solution together. He was initially very skeptical, but on going through it in detail, we can't find a fault with it. There doesn't seem to be any compromise whatever in strength, parts alignment, or balance of the flywheel/clutch assembly, and the hydraulic RAM unit can now work as it's supposed to.

As a bonus, its installation now meets RAM's requirements, without the use of any adjustment shims, perfectly. RAM specifies a bearing surface-to-clutch finger clearance of 0.150" to 0.200". My setup, with the shims, provides a clearance of 0.170".

Can anyone see any real problems with this solution?

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 Post subject: Re: Clutch Question
PostPosted: November 6, 2018, 4:30 am 
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So when you stated (and confirmed) that you had a MII "clutch assembly" you really just meant the friction disc, and when you said you have a Zetec "flywheel" you really meant flywheel and clutch/pressure plate? That's a pretty crucial difference when trying to help diagnose this remotely via text descriptions...But it does make more sense.

I'll post more on this later, but according to your previously stated dimensions, you just lost almost all of your clamping force by shimming. And no, you don't need anywhere near .200 of pressure plate travel to release the clutch. One of the most important sanity checks you can do, is ensure that the math and the measurements are in agreement...Yours are not.

What you really need to at this point is a new condition stock Zetec friction disc to dimensionally compare to your MII friction disc. Namely the friction surface thickness, and the hub protrusion from the friction surface.

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 Post subject: Re: Clutch Question
PostPosted: November 6, 2018, 8:00 am 
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Those parts should have worked fine as-is. Yes, a diaphragm pp is just a big spring with an overall ratio for the range. I think the flywheel you have is not exactly as it should be but the shims address the issue. Case solved imho.

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 Post subject: Re: Clutch Question
PostPosted: November 6, 2018, 1:03 pm 
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Depending which of the provided numbers are correct, as .100 PP compression was initially stated by measurement but the later math from corresponding measurements (that you thought was calculating the PP release travel) supports .200 PP compression, that means somewhere between 95% and 47.5% (respectively) of the clamping has been lost with a .095 shim, and it will only get worse with wear...Which will happen very quickly if the PP compression is indeed as originally measured.

Since the flywheel and pressure plate are now stated as both being standard directly compatible components, by far the most likely culprit is the odd man out. I'd guess it's some combination of the hub on the disc simply protruding out further than on the OEM disc and/or the disc friction surface being slightly thicker than on the OEM disc. Either way, considering only 1/8-1/4 inch at the bearing is all that is required to release the disc after shimming, and there was already a >1/4 inch gap between the spring fingers and hub previously, then even accounting for the motion ratio change through the spring travel, the amount of shimming required should be minimal.

If shimming it, only do so that absolute minimum amount necessary until the clutch fully releases just before the springs contact the hub and then set a clutch pedal stop at that point. I'm thinking in the .005-.010 range for starters.

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 Post subject: Re: Clutch Question
PostPosted: November 6, 2018, 5:46 pm 
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Thanks for the info!

I agree. The 0.995" shims were intended as an initial test value only, to provide a baseline.

Now, after empirical testing, I know that shims (of some thickness or other), will provide enough space for the clutch to release properly. What remains to be determined is what the minimum thickness is.

I had already intended, for my next attempt, to try 0.50" shims, and see if I can get clutch release. With 0.0995" shims, I have finger clearance of 0.7910" clearance from the disc face - therefore, the 0.0995" shims moved the fingers out 0.5040" to (0.7910 minus 0.2870).

So.... that would indicate that 0.0500" shims, the fingers should have total clearance of 0.3995" vs. the un-shimmed clearance of 0.2870". Hopefully, that will be enough for full clutch release without having too much free play. As the spring fingers have a total (uncompressed-to-fully compressed) travel of 1.1800", using the last 0.3995" of it for clutch release would still leave 0.7805" of available finger travel to ensure a solid clutch engagement.

I can try shim material in the .005" range, but I doubt it will allow any clutch release. I'm going to try some 0.010" stock, if I can find something that thin. Hopefully, release will be possible.

One thing I have to keep in mind is the hydraulic release bearing - it should not operated at the very last fraction of an inch of its 1" travel. There's a very thin snap ring to help prevent over-travel (and seal blow-out, which would ruin the bearing seals & friction disc), so operation at its extreme is best avoided. If I can get clutch release with the thinner shims, while still being in the "sweet spot" on the hydraulic bearing, all should be good, I think.

We'll see what happens with the next test....

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 Post subject: Re: Clutch Question
PostPosted: November 8, 2018, 8:04 pm 
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Okay - here's the skinny.

My new test rig is far more precise than the old one, and now I can actually take accurate release point measurements.

Also, with no shims, the clutch DOES release (just).

Here are some measurements (NO shims installed), taken from the upper surface of the pressure plate to the upper surface of the fingers (***These measurements all reflect how deep the fingers are below the pressure plate's surface, as (unless the PP bolts are slacked off completely), the fingers are always well below the PP's surface***):

0PP torqued down, no depression on fingers: ........................................................................0.4125" below PP surface
Fingers depressed to actual clutch release: ......................................................................... 0.5985" below PP surface
Fingers depressed to hard bind on friction plate (clutch no longer released, due to binding):.......... 0.6565" below PP surface

This gives a maximum workable finger movement range = 0.1860", which means over 81% of the hydraulic throw out bearing's 1.000" range will be unusable. It will be working off the last 0.1860". Measurements for fitting the hydraulic release bearing will have to be extremely precise, as allowing it to go an extra 0.058" will result in a hard bind of the fingers on the friction disc (and a seriously binding clutch, not to mention chewing up & destroying both the fingers & the friction disc).

What I need to figure out now is how to deal with the hydraulic release. It's measurements are taken from the top surface of the fingers. The bearing has 1" of travel from that point on., with the clutch installed & torqued down. That pretty much ensures that when the clutch pedal is depressed, the hydraulic's bearing will force the fingers hard up against the friction plate, so I have to figure out a way to prevent that.

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http://zetec7.webs.com/


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 Post subject: Re: Clutch Question
PostPosted: November 9, 2018, 2:38 am 
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Further to that, I have to consider that the RAM unit travels 1" for ever 6" of travel of the clutch pedal (confirmed by RAM and Wilwood). Due to space limitations, I've had to reduce my clutch pedal travel to about 4", so it will line up with the height of the brake pedal. RAM techs advised this isn't an issue, as 3/4" of travel for the RAM unit should work just fine.

However - there is no spring return for the RAM unit. It relies on finger spring pressure to push it back. If this doesn't happen, it simply pumps up to whatever level the fingers are at & stays there except for the small remaining amount of travel.

In my case, with no shims, this means the pedal can only travel about 1" total. That would seem to be a problem.

Shimming turns out to have a couple of measured benefits. One, it moves the release point away from the friction plate a bit, so binding between the fingers and the friction plate can be avoided. Second, it appears to increase the span of movement of the fingers over which release & clamping occur.

At this point, it comes down to whether or not diaphragm springs increase their clamping force gradually across their range of motion, or whether they have constant clamping pressure all the way through their range of motion.

If it's the latter, shimming should work without compromising clutch clamping force.

If it's the former, I'm in a world of hurt. Pedal travel of only 1" ain't gonna cut it...

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Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit.

http://zetec7.webs.com/


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 Post subject: Re: Clutch Question
PostPosted: November 9, 2018, 7:12 pm 
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Shim the pressure plate so the fingers protrude .250 from the cover with a new clutch.Potential error; see following post.

Swap the clutch for a shim that is 0.290 (duplicates worn out clutch) to check the finger height with the pp shims. Measure from the bellhousing matting surface to the fingers. Ensure the bellhousing depth is at least this distance with the RAM so the ram does not reduce the clamping load as the clutch wears by pressing on the fingers.

As for a spring, much older clutch systems operated with a gap so the bearing was not contacting the pp levers unless the pedal was pressed.
Many of the newer systems actually have a spring that pushes (lightly) on the fingers at all times and the bearings are made for it. Here is a pic of mine on the f23 where I had to remove the spring and boot to verify clearances.

If you determine you need more bearing travel for the pedal travel, fit the next size larger bore master contrary to the instructions which expect more pedal travel. Verify you do not run out of travel in the ram if it has a stop like my f23 does.

If you can't shim to .250 above the cover for whatever reason then do the best you can.


Attachments:
f23 001.jpg
f23 001.jpg [ 179.62 KiB | Viewed 140 times ]

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Last edited by Miatav8,MstrASE,A&P,F on November 10, 2018, 7:55 am, edited 1 time in total.
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 Post subject: Re: Clutch Question
PostPosted: November 10, 2018, 7:54 am 
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Rather than change part of what I said that could cause it to be missed, I will leave my potential error in the above post in bold and reference this post.

The issue is my recommendation to shim to .250 above the pp cover because even though many covers appear to be the same, there are many subtle differences. For example, with my f23 bell depth, I could use the cobalt pp without shims or any older v6-60 pp with a shim due to differences in the cover height and ultimately finger height.

So a better rec is to first measure the finger height of an pp that is not installed to know where you are starting. That may be somewhere above but I didn't see it.

I looked up a focus hyd rel bearing and it has a spring to maintain contact with the fingers at all times.

Here is an easy way to measure the engine side, using a carpenter square and a 6 inch dial caliper to the pp cover. Then just add from the cover to the fingers. Also a pic of my two similar looking covers that had different requirements.


Attachments:
pp 002.jpg
pp 002.jpg [ 164.91 KiB | Viewed 109 times ]
pp 006.jpg
pp 006.jpg [ 224.24 KiB | Viewed 109 times ]
pp 007.jpg
pp 007.jpg [ 181.3 KiB | Viewed 109 times ]

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 Post subject: Re: Clutch Question
PostPosted: November 15, 2018, 1:06 am 
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I’ve had some success, I think.

In the end, I used 0.054” shims between the pressure plate and flywheel, which allows a bit over .500” of travel for the fingers. It’s shy of what the RAM unit is designed for, but workable, I believe.

Rather than make the shims, I bought stainless steel washers. It turns out there’s a remarkable variation in thickness of these. I knew they weren’t consistent, but the variance surprised me. I ended up sitting on the floor of the store, with a bucket of washers & my Mutitoyo digital calipers, dividing washers into several piles of different sizes on the floor. I can tell you that this brings some strange looks from other customers! In the end, I came home with some that miked out at 0.049” and some at 0.054”. I used the latter.

As a possible explanation for the source of the problem in the first place, my buddy was doing a bunch of research on Focus Zetec clutches, and came across a thread indicating that there was a brief period of North American Focus Zetec production where the OEM clutches used thinner friction discs than normal, and pressure plates to match.

It’s probably one of those items where you need the car’s VIN number to ensure you get the correct part. As I never had the original car, I don’t have a VIN number.

Anecdotal references seem to indicate these friction plates were more than a millimeter thinner than “normal” clutch discs. One of those pressure plates, coupled with a “standard” thickness Mustang II friction plate, would certainly explain my issue.

Anyway, I’ve done the measurements & calculations dozens of times, as well as doing “empirical” testing, and it looks good. The special spacers provided with the RAM unit weren’t quite enough to accommodate the revised position of the bearing release unit, so I turned a .280” thick one on my lathe out of marine brass. It allows me lots of combinations to set it up accurately. I got the required clearance to within 0.0005” and even for my old OCD self, that’s “close enough”.

Next, I have to figure out the hydraulic hose routing...

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Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit.

http://zetec7.webs.com/


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 Post subject: Re: Clutch Question
PostPosted: November 15, 2018, 7:45 am 
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I ended up sitting on the floor of the store, with a bucket of washers & my Mutitoyo digital calipers, dividing washers into several piles of different sizes on the floor. I can tell you that this brings some strange looks from other customers!
Heehee... Yeah, the staff at the local Ace Hardware is kinda getting used to me... :mrgreen:

:cheers:

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