I think that most of the SMF conversions are a financial decision, more than any other reason.

Peeps who don't know, are told by a repair shop, " You need a new flywheel. You can buy an OEM for $800-1200 or you can put in a SMF for $300"

Not knowing that the DMF is available to them at a more competetive price.
It's commonly known that some shops buy the DMF for $550-650 and pocket the diff.

And there's the guys that just make all their decisions with their wallets. Not knowing they can do the clutch/FW with OEM parts, for about $300 more than the SMF. Then they put up with the rattle, and potential wear issues of the ZF tranny

 

One of the most important things to remember with DMF and ZF's is there are 5 gears .... USE THEM ALL. Starting in second gear was not and still is not the right proceedure.... sorry.

 

What are the specs for a dual mass flywheel?

I will be changing a zf5 trans on a truck the that previous owner said the clutch was just changed and DMF tolerance was checked.

Since the rear trans case snapped off shortly after this work I want to take a close look at the flywheel/clutch while everything is apart.
Can anyone recommend where to buy a replacement DMF.

 

Just type Ford DMF into the google box. Plenty of info out there. There's a shop on Ebay that sells them pretty cheap, also.

 

How would you test DMF to understand it worn out.Cracks or discoloration is simple enough, any idea about spring pressure or friction material wear/failure.

 

Here is information about dual mass troubleshooting



What is the DMF's function? It is designed to isolate torsional crankshaft spikes created by diesel engines with high compression ratios. By separating the mass of the flywheel between the diesel engines and the transmission, torsional spikes can be isolated, eliminating potential damage to the transmission gear teeth.

Engine-side flywheel damper springs The damper springs that are visible on the engine side of DMF are designed to dampen heavy torsional spikes that occur when the diesel engine's torsional frequency matches the torsional frequency of the transmission. When torsional frequencies match (have the same amplitude), severe damage can occur to the transmission if not isolated. DMF's isolate the torsional frequency match between the engine and transmission to an r.p.m. range below the operating range of the engine (usually between 200-400 r.p.m.). These damper springs only work hard when the engine passes through 200-400 r.p.m. at vehicle start up and shut down.

DMF damper springs and/or damper springs nylon retainers usually fall because the diesel engine is not running correctly. Bad fuel injectors, worn pistol rings, bad valves, etc, will change the resonant frequency of the engine. A change in the resonant frequency of the engine can force the torsional frequency match between the engine and DMF to fall within the operating range of the engine. This forces the damper springs to work continuously, resulting in failure.

Friction Ring The friction ring located between the inner and outer flywheel is designed to allow the inner and outer flywheel to slip. This feature saves the transmission from damage when torque loads exceed the vehicle rating of the transmission. The friction ring will wear out if excessive torque loads are continuously applied. Loading the vehicle beyond the rated load capacity is often the root cause of friction ring failures in DMF's.

Center Bearing A sealed double row center ball bearing carries the load between the inner and outer halves of the DMF. The leading cause of center bearing failure is often related to out of balance vibration caused by not aligning the pressure plate with the DMF dowel pins. The center bearing may also fall if the clutch pilot bearing is destroyed by a worn transmission input shaft (see Pilot Bearing) or if the rated load/towing capacity of the vehicle is exceeded.

Pilot Bearing The pilot bearing supplied with most DMF's is a caged needle roller bearing. If it fails, the transmission input shaft must be repaired or replaced. If the input shaft is not repaired correctly or replaced, the lack of input shaft support will result in DMF center bearing failure. Go to page top

Diagnostic Charts For Dual Mass Flywheels

<CENTER><TABLE width="95%" border=1><TBODY><TR><TD vAlign=top width="18%">Symptom

</TD><TD width="82%">Damper springs and/or damper springs nylon spacers are failing on the engine side of the DMF after short service life.</TD></TR><TR><TD vAlign=top width="18%">Solution

</TD><TD width="82%">

Service diesel engine. Correct bad fuel injectors, poor engine compression, etc. Make sure engine idle is set to factory specifications. IMPORTANT: Changing the turbo boost will change the torsional frequency of the engine which can damage the DMF. Go to top of page

</TD></TR></TBODY></TABLE></CENTER>
<CENTER><TABLE width="95%" border=1><TBODY><TR><TD vAlign=top width="18%">Symptom

</TD><TD width="82%">Clutch slips after short service life.</TD></TR><TR><TD vAlign=top width="18%" rowSpan=5>Solution

</TD><TD width="82%">Check the friction ring between the inner and outer halves of the DMF. This check should be made with the DMF installed and the clutch and bell housing removed:</TD></TR><TR><TD width="82%">1. Partially insert two pressure plate bolts on opposite sides of the DMF's pressure plate bolt holes.</TD></TR><TR><TD width="82%">2. Block the engine so that it cannot turn.</TD></TR><TR><TD width="82%">3. Place a pry bar between the two pressure plate bolts. Try and rotate the outer portion of the DMF relative to the inner portion of the DMF. It does not matter if you pry clockwise of counter clockwise. NOTE: All DMF's have eight to eleven degrees of free rotational movement before the friction ring engages. You are checking for movement after initial free play.</TD></TR><TR><TD width="82%">4. If the outer half of the DMF will rotate with hand pressure on the pry bar, the DMF friction ring is worn out. The DMF will slip and must be replaced. Go to top of page</TD></TR></TBODY></TABLE></CENTER>
<CENTER><TABLE width="95%" border=1><TBODY><TR><TD vAlign=top align=middle width="18%">Symptom</TD><TD width="82%">DMF center bearing fails after short service life.</TD></TR><TR><TD vAlign=top align=middle width="18%">Solution</TD><TD width="82%">Check the DMF for missing dowel pins. Failure to use the O.E.M. dowel pins will set up a vibration that will destroy the center bearing. Check the DMF friction surface for heat cracks and/or hot spots. Check the pressure plate for hot spots and the disc friction material for friction material separation. Both are signs that the truck is being used beyond it's rated capacity and/or the clutch is not releasing properly due to a worn or faulty hydraulic clutch release system. The DMF is designed to protect the transmission. It is also designed as a wear component and will fail if O.E.M. vehicle capacity is ignored. Go to top of page</TD></TR></TBODY></TABLE></CENTER>


<CENTER><TABLE height=48 width="95%" border=1><TBODY><TR><TD vAlign=top align=middle width="18%" height=19>Symptom</TD><TD width="82%" height=19>DMF pilot bearing fails after short service life.</TD></TR><TR><TD vAlign=top align=middle width="18%" height=21>Solution</TD><TD width="82%" height=21>Check the transmission input shaft pilot bearing surface. If this surface is scored or otherwise damaged, the shaft must be repaired or replaced. Failure to do either will ultimately result in the DMF's failure. Go to top of page</TD></TR></TBODY></TABLE></CENTER>

 

If the DMF is so important to the longevity of the transmission, then why aren't they used behind the Cummins/ NV's or the GM diesels? Both of them have used aluminum case transmissions and Dodge continues to do so (you can't even get a manual in the GM trucks anymore). I think it comes down to what the automakers call Noise, Vibration and Harshness or NVH. I think the ZF is a noisy trans and the DMF was a good fix without having to redesign the transmission.

PLC, have you ever owned a 7.3 with the ZF? I've owned 2 of them. Both with 35" tires and my current one has 250K on the original clutch and transmission. I regularly start out in second gear, without slipping the clutch and using no throttle. The only time I use 1st gear is with a load on, or if I need slow speed.
If you start out in first, you run out of RPM's before you go anywhere so you have to immediately shift to 2nd anyways. You lose a lot of momentum which is not good in front of a line of traffic.

You are not hurting the transmission at all to start out in second. It is geared low enough to allow it, especially considering the torque available from the 7.3.

Jason

 

And I have to answer that with I know several people here in town that have Dodge Cummins powered trucks and transmission trouble.

One of them had three transmissions before he traded his truck off under the lemon law.

I always use first gear.
Even though I tow and haul heavy loads, I got 250,000 miles out of my original clutch.
And it was actually the throw out bearing that made me change it when I did.

 

But can you trace the causes of those transmission failures from engine harmonics and power stroke shock loading? Not just poor design? There have been numerous revisions and updates made to the NV transmissions behind both the gas and diesel engines. And lets not forget that the 4500 was brought in to replace the Getrag 5 speed that should have never been behind the Cummins in the first place.
For every instance you hear of a low mileage manual trans failure in one of these and you have 10 that have been in service way beyond their expected life. I have a friend with an '89 Cummins with the original Getrag that has almost 700K miles on it with 2 clutches and new trans bearings at 500K. The first half of the its life was spent in the woods as a logging crummy. He put a service bed and converted to DRW. With a compressor, welder, crane, tools, and parts, I'm guessing the weight at around 14K lbs. So, this truck has been used and abused.

I've never seen a clutch setup like this used in the HD truck market. And with some of the engines approaching 2500 lb/ft torque, I can imagine the torsional spikes would be tremendous. Why wouldn't they?

Jason