[krustissimo]

Hi all, I'm looking for a bit of advice about a rattling sound my '92 manual cab recently developed. I think its probably not a coincidence that it started a few drives after I used it to teach my daughter to drive stick. Like all of us when we were learning, she did a few bad starts including one particular really lurchy one that I'm afraid might have done some damage!

 

So now there's a kind of rattle that happens when I hit the accelerator from low RPMs. It happens in gear when pulling out but it also happens when stopped in neutral with the clutch either up or down. You can also hear it going from 1st to 2nd gear but then it is a little less noticeable. It only seems to happen in the low 1-2k RPM range and only while spinning up the RPMs. "Rattle" is the best description I can give: maybe I feel it a little in the accelerator pedal but its hard to be sure. Seems to be more noise than physical, so far. At higher RPMs or after a second or so holding a stable RPM it goes away.

 

So I pulled out the clutch (btw car only has 30k miles) and found the pressure plate has worn much more around the perimeter than in the center. Its quite a lot: there's a ~1cm wide, maybe 1mm deep, rounded trench that runs around almost at the outer edge. The rest of the plate is flat and it returns to flat at the very outer edge probably just outside the friction disc's contact area.

 

I used a dial indicator to measure the flywheel's runout and it seemed totally fine (~1 or 2 thou) at the three radii I checked. However I'm pretty sure it must be a bit dished based on how it looks with a straightedge and from the pressure plate outer wear. I didn't take the flywheel out, just cleaned and scuffed it up and reassembled with a a new friction disc, throwout bearing (old one was sticking), needle and pilot bearings. I did manage to get my hands on a new pressure plate but I decided not to use it yet since it is hard to find a green stripe one and I figured I'd save that unicorn until I know for sure what the problem is.

 

I put it all back together and the problem didn't go away. It maybe sounds a tiny bit different (higher pitched?) but its still basically the same as before. I'm thinking this has got to be a dual-mass flywheel failure, perhaps at an early stage. When the clutch was open I had pushed and pulled on the flywheel and it would move a centimeter or so before weakly returning to not-quite-where it started. But I don't have any specs on what it is supposed to do and this seemed more or less correct from what I found online for other cars.

 

I'd be fine with replacing the flywheel but damn they are insanely expensive! Like $2400, which is 3 or 4x what a DMF costs for other cars. And I don't even know for sure that it is the flywheel causing the problem. I'm thinking if I have to replace it maybe I'll try the Spec SP86S steel flywheel since that is "only" around $600. But I can't find any info on that model, only posts about the Fidanza lightweight aluminum one that seems too light and apparently causes gearbox noise.

 

Anyone have any ideas for what else it could be besides the flywheel, or thoughts on how to fix this without spending crazy money on more overpriced parts?  Thanks!

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[vliegwielolaf1234]

I would check the exhaust , maybe one of the hangers (rubbers) broke , heat shields , that kind of stuff .

Are the engine mounts still oke , all rubber parts used ore not they wear with age .

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[krustissimo]

I don't think its engine mounts: they look fine and not squished so far as I can tell. Also I don't see any connection between engine movement and the sound. The exhaust I had to take off and put back on for the clutch so I know the hangars are fine there.

 

It might be something other than the flywheel though. I was just listening to the sound with the hood open and I'm wondering if it could be something like balance shaft bearings or the water pump. Its really hard to tell where on the engine the sound is coming from.

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[dlearl476]

$10-$15

   

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[krustissimo]

That's a good idea, I'll get one of those! Today I had the sudden inspiration that it might actually just be engine knock since the gas is pretty old: the car is definitely a bit of a garage queen. But better gas didn't fix it: I put in 10 gals of fresh 93 octane over the 3 or so gals left in the tank. It is running a lot more powerfully but it didn't affect the spin-up noise.

 

I don't think its related but I'm getting an intermittent squealing sound, too. That one comes and goes randomly (mostly on cold start-up) and I figured its probably just belts slipping from getting brake fluid on them during the clutch and brake fluid changeout. My pressure bleeder cap didn't seat well and it made quite a mess. But now I'm wondering if it could be something like the water pump pulley, which I recall can sometimes seize up. I'll open up the timing belt cover tomorrow and make sure everything in there looks OK.

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[dlearl476]

When was the last time you changed your water pump? i thought mine was loose belts, too. Until it froze up. 

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[krustissimo]

I checked the water pump today by running the engine with the belt covers off. The pump is a few belt changes old but it doesn't seem like its having any issues. Unfortunately you can't hand-spin it with the timing belt on; all I could do was watch it rotate under engine power and listen for bearing rattle or whatever. The balance belt also looked fine; possibly a hair tighter than it ought to be but basically all in decent order there.

 

When I ran the engine with no covers or air filter it almost seemed like the sound was coming from up the air intake/MAF sensor tube. But its really hard to be sure. Its just a brief chunk or click at the moment you throttle up and I have to do it again and again and try to figure out where it originates.

 

I also noticed another thing probably unrelated: when I throttle up to say 4-5k RPMs (just a guess since I'm outside the cockpit), at the highest speeds the timing belt twists a little as it enters the main timing sprocket at the distributor cap. I hope it is supposed to do that because it is a bit unsettling to watch.

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[unknown4u]

Can you make a little film?

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[tejon007]

It seems your initial suspicions could be correct. Inexperienced driver over-working, even abusing the clutch. Add in your description of the new sounds...yes, it could be a DMF flywheel failure.



Use the new stethoscope and positively track down the DMF sounds and especially the water pump noise.



Once you diagnose the problem(s), you'll know the path to the fix. Personally, replacing the DMF with a single mass flywheel doesn't bother me, but it's your car and understand the single mass is likely to transmit more vibration and could impact your transmission life too.



Best wishes for the fix.

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[krustissimo]

My best guess is still that its the flywheel, too. I haven't gotten a car stethoscope yet but I will try that asap and also post a video once I'm back home in a few days. I'm thinking I'll also briefly run it without the alternator/AC belt to eliminate any of those spinny items as a possibility.

 

But if it isn't, say, the AC clutch, aside from the flywheel all I can think of would be maybe some internal bearing or journal (which would really suck) or perhaps something in the head or variocam system (which would also really suck, but maybe a bit less).

 

The thing about the single mass flywheel is there are only two options that I've found: the super-lightweight aluminum ones (Fidanza 12lb or one from Spec of unknown weight) and the Spec SP86S steel one. I think the Fidanza would be too light for me but there are (ironically) no specs available from Spec! I don't even know if it uses the same flywheel bolts and whether it is compatible with the standard clutch or only works with a Spec clutch. Guess I need to give them a ring.

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[tejon007]

Lightweight flywheels can be a nice performance increase on a stock street-driven car (we run one on our 914). But, I have to agree with you that if you go too light, it's not good (BTDT). IIRC the 914 is running a 12.5 pound flywheel - but, it's in a car that's quite a bit lighter than the 968.



Haven't used a single mass or Lightweight flywheel on a 968 or 944. Maybe someone with that experience can chime in...

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