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Old 09-14-2010, 11:06 AM   #1
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1968 24' Tradewind
Louisville , earth
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Post fly wheel change issues...

Many of you will remember my episode this summer with the truck about shaking me to death. Well, removing the old dual mass fly wheel and replacing it with a single mass unit took care of that. BUT it left me with a rumbling noise out of the transmission when sitting in neutral with the clutch up and underway when the RPMs dropped below about 1500. Unsettling indeed. The first mechanic said I needed to replace the transmission, I decided to try and limp home from Alb which I did. The mechanic here dropped the transmission out and took it apart (the thing looked brand new inside after 230+K miles) but couldn't find anything wrong. Put it back together: same noise.

So now I am at about my wits end, I cant afford the $4k for a replacement transmission and I need that truck to be reliable. So today I posted the story on Ford Truck Enthusiast. Almost immediately, someone comes back with the diagnosis of "gear roll over". Said it was a common consequence of changing out a dual mass flywheel with a single mass one. Told me to add an extra quart of automatic transmission fluid to the shifter. Does this sound right?


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Old 09-14-2010, 05:44 PM   #2
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Somewhere , South Carolina
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All engines create pulsations in their crankshaft/flywheel output to the transmission, if coupled directly to the trans, a lot of gear noise is created.

The Dual Mass Flywheel (DMF) is designed to minimize gear noise among the other normal clutch things it does, but to accomplish that is has a LOT OF PARTS in it, typical for a Ford 7.3L about 120 individual components down to the rivet. I have taken several apart.

A correctly functioning DMF and a non-worn out transmission are the quietest combination that your truck could ever have.

This is accomplished by two seperate functions inside the DMF, first a torsion damper comprised of a series of coil springs that ALL of the engine power is transfered to and by its ability to be compressed and rebound, it smooths out the power pulses significantly. The second element is that the secondary (friction side) of the DMF is considered to attach its weight directly to the input shaft this adds flywheel effect to the input shaft and it also minimizes the pulstations that trigger the gear noise that you do not want to hear.

The DMF needed a public relations campain manager shortly after it hit the 7.3L engines with all of the tales of woe and doom, many of which were related to miss-understanding of its functions and CORRECT service procedures, for example you NEVER want to dip or spray a lot of solvent or cleaning solution on the Ford DMF due to the internal friction torque limiting clutch inside the DMF.

Several aftemarket clutch companies responded to the DMF shortcomings and offered a Solid Flywheel (SF) conversion. The SF system cannot exactly match the filtering capabilities of the DMF so under some loads/RPM/gear conditions you hear more noise than normal from the DMF. The trade off is cost vs less cost, 120 pieces vs a solid cast iron SF and a simpler disc that does a darn good job for most all customers. The internal clutch of the DMF also limited the power that can be transferred to the trans which has saved many trnasmissions, but ticked off a lot of the power hungry Powerstroke owners, this also drove the SF segment.

Fact: The company that built your Ford DMF made the last production run, no more will be built.

A DMF cannot make up for the noise a worn transmission creates, it will not make gear teeth grow back or fix worn bearings.

The tech support for the clutch company that supplied the parts should have been contacted PRIOR to the teardown of the transmission.

If your supplier has multiple clutch systems, was the correct system chosen for a replacement clutch? Some are replacement SF systems and sometimes a more agressive and stronger system is chosen which may have an even cruder simple torsion damper that is more noise prone, but strong as you will ever need.

I do not recommend seeking a solution to your problem by adding more or a different type of oil, just use the type and qty. that Ford spec'd out.

Also, make sure that all boots at the shifter are in place and not popped out of place.

Your question is not a new one to the clutch industry, and FWIW, I do not work for the compan that made the DMF.
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