# What are those symptoms of DMF failure?



## MRO1791 (Sep 2, 2016)

Barry Allen said:


> Driving today I was cruising about about 40-50 mph. When unloading and loading the throttle I noticed some intermittent "clunking" feeling or what could be described as a shudder. The engine was already at near full temperature due to a prior drive and the outside temperature.
> 
> What were those symptoms of the failure of the dual-mass flywheel?


When my DMF failed, it made the clutch pedal have a weird feel, like it was grinding when pushed in, and there was quite a racket from the engine, and the lower the RPM, the LOUDER. When you study what and why DMFs exist, it begins to make sense that the noise would be worse at low RPM. The DMF is besically a damper between the engine and drivetrain put there to absorb rotational speed variations caused by the low RPM, high torque that is prevalent in Diesel engines (it's also why you generally don't see them on gasoline engines). 

I had one on my truck, that was acting up, and it was first noted by a slipping clutch, at less than 45K miles! Now, I know how to drive a manual, and while it sure seemed to match a worn out clutch, it was not the case, that DMF had not failed yet, per se, but it had excessive play between the 2 fly wheel masses, which is how they start to go. I replaced it with a much better standard single mass flywheel, and dual disk clucth.. it is a truck, and it is louder for sure now that the DMF is gone, but I'm OK with loud when I know it won't come apart and destroy the bell housing and leave me stranded on the side of the road. 

For the Cruze, mine failed at just over 12K miles, the dealer wanted to tell me it was a worn out clutch, and if they were to inspect it and find it was the clutch, I'd be paying since the clutch is only covered for 12K, (I was like maybe 100 miles over)... In any case, I assured them it was not the clutch. I told them it was the DMF, based on my experience with the truck, but there is more.. (I have a separate thread on this somewhere as well). I think it's possible my DMF suddenly failed following a reverse start of the engine.. Yep, it is possible for a Diesel to start and roll backwards.. I might have let up the clutch too soon in the start sequence, and the engine turned briefly, then starter shut off (thanks stupid neutral safety switch). The noise and vibration was bad, real bad.. what is worse.. the engine did not shut off with the start-stop button! I had to hold the brake, and use the clutch and reverse gear to stall out the engine and stop it.. Yes, that was super crazy, and it was like only a few seconds.. After that incident, when I started the car, it started noramally, but began making a new rattle sound.. that was the now failed DMF. 

I hope that helps you with figuring out what is going on with yours, I will say this, I'll be looking to traditional single mass flywheels, and probably have to look to the EU to get one, when I need to replace the clutch or the DMF fails again. I have no confidence in the concept of a DMF, and I'm OK with a little bit extra gear rattle from the transmission.


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## 6speedTi (May 18, 2018)

MRO1791 said:


> When my DMF failed, it made the clutch pedal have a weird feel, like it was grinding when pushed in, and there was quite a racket from the engine, and the lower the RPM, the LOUDER. When you study what and why DMFs exist, it begins to make sense that the noise would be worse at low RPM. The DMF is besically a damper between the engine and drivetrain put there to absorb rotational speed variations caused by the low RPM, high torque that is prevalent in Diesel engines (it's also why you generally don't see them on gasoline engines).
> 
> I had one on my truck, that was acting up, and it was first noted by a slipping clutch, at less than 45K miles! Now, I know how to drive a manual, and while it sure seemed to match a worn out clutch, it was not the case, that DMF had not failed yet, per se, but it had excessive play between the 2 fly wheel masses, which is how they start to go. I replaced it with a much better standard single mass flywheel, and dual disk clucth.. it is a truck, and it is louder for sure now that the DMF is gone, but I'm OK with loud when I know it won't come apart and destroy the bell housing and leave me stranded on the side of the road.
> 
> ...


My diesel Cruze is at the dealer for the same symptoms. 15,600 miles. I had the engine start issue were it raced and couldn't turn it off. Rattling noise very obvious. When accelerating it rattles. They are pulling the transmission to see what's wrong with it. I'll find out soon enough. Thanks for the information.


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## 6speedTi (May 18, 2018)

6speedTi said:


> My diesel Cruze is at the dealer for the same symptoms. 15,600 miles. I had the engine start issue were it raced and couldn't turn it off. Rattling noise very obvious. When accelerating it rattles. They are pulling the transmission to see what's wrong with it. I'll find out soon enough. Thanks for the information.


UPDATE.......
Dealer service department just confirmed that the clutch and flywheel will be replaced. Slave cylinder is OK. Clutch is one whole unit. Disc, pressure plate and throwout bearing.

UPDATE:
My Cruze is back home today. Dealer replaced the Clutch assembly package. They replaced the Flywheel and the Slave Cylinder as well. All is good on the drive home. I had the recall done on the particulate regeneration filter frequencies. I'll find out soon enough if this affected my fuel economy.


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## 6speedTi (May 18, 2018)

I found this very good video on REV HANG as they call it. It explains the differences between mechanical and electronic throttle bodies. Also explains between multiport and direct injection. I can tell you from my experience with the sonic 1.4 liter that I no longer own that rev hang was really noticeable that I brought it to the dealer thinking something was wrong. They found nothing wrong and did not or could not explain why the rev hang. The problem with rev hang I don't like is you lose closed throttle engine braking. So on my Cruze diesel I noticed rev hang is hardly noticed because it is a direct injection engine. The video explains this. So if your a manual transmission enthusiast the days of free spirited driving up shifting and downshifting have fell victim to emissions compliance. Feel free to post this video on other topics since it affects both gasoline and diesel engines.


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## Barry Allen (Apr 18, 2018)

6speedTi said:


> So on my Cruze diesel I noticed rev hang is hardly noticed because it is a direct injection engine.


My experience is no diesel engine has any appreciable engine braking because they don't have throttle plates. Well, they do, but are partially used only for emissions - they serve to close off some of the intake in order to draw a vacuum so EGR can be sucked into the intake stream.

Driving my Cruze, I notice there is no engine braking when I lived off the throttle in 6th or 5th gear. 4th gear starts to have some and I have to dump down to 3rd gear when exiting a freeway to get any engine braking - and even then it has to be supplemented with application of the brakes. Prior gasoline cars I owned I could dump to 3rd gear and get lots of engine braking - enough to slow for almost any highway off ramp without having to use the brake pedal.


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## JPinSTL (Jul 9, 2018)

Barry Allen said:


> Driving today I was cruising about about 40-50 mph. When unloading and loading the throttle I noticed some intermittent "clunking" feeling or what could be described as a shudder. The engine was already at near full temperature due to a prior drive and the outside temperature.
> 
> What were those symptoms of the failure of the dual-mass flywheel?


I had a "shudder" that got progressively worse and I was SURE it was a DMF issue as it was throttle/load related. Ease on the throttle, especially on a hill, where the torque would build and you'd feel it. Multiple dealer trips and the run around. Took it back to the dealer I bought it from and the mechanic did a ride along, did a drive with a vibration sensing meter, seemed to know what he was doing. They decided it was a bad CV Joint, ordered a new half shaft assembly, and a couple weeks later they swapped the part and all was well. Been vibration free for the last few months.


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