What exactly is clutch chatter?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Jan. 17, 2012 7:35 a.m. spitfirebill SuperDork

I need some input. My trusty Nissan pickup DD has started doing something I would call clutch chatter. As I let the clutch out, the truck shakes a little, but stops once the clutch is all the way out. It stared doing it occaissionally a couple of years ago, but now does nearly every time I cold start start or wehn ti very humid out. This morning though it felt like the differential was shuddering. The diff seems to be fine otherwise. I replaced the clutch witha Nissan item when I rebuilt the engine 4-5 years ago, but it only has ~30k miles on it since. I did not resurface the flywheel, because the"experts" told me it was better not to. Seems some people do more damage than good. Problem is, when I first rebuilt the engine it would not run right. Seems the MAF sensor and TPS had failed over the 4 years the truck sat in my back yard. On one early trip, I had to pat the throttle to rev the engine and slip the clutch out. Repeatedly, a lot. I was wondering if this could have damaged the clutch. The clutch does not slip at all when driving down the road.

What say ye? Time for another clutch? It is quite drivable as is.
Jan. 17, 2012 8:20 a.m. Curmudgeon SuperDork

Check the engine mounts. If they are stretched and saggy, the engine will shudder on its mounts, making you think the clutch is going south. The transmission mount can do this by itself, the back of the transmission can hop up and down.
Jan. 17, 2012 8:27 a.m. N Sperlo SuperDork

In reply to Curmudgeon:

+1. During clutch install (didn't resurface the flywheel) broke a mount, but since it was a 180 degree engine it wasn't so much a shutter, but a SLAM SLAM SLAM SLAM!
Jan. 17, 2012 10:09 a.m. spitfirebill SuperDork

I will check those. I definitely did not replace the front ones. I don't recall replacing the rear one.
Jan. 17, 2012 11:05 a.m. 1988RedT2 SuperDork

I had a Subaru that did that. The dealer politely informed me that it was quite normal, but for $2000. they could make it better. I politely told them to Berkeley off.
Jan. 17, 2012 11:25 a.m. 44Dwarf Dork

From what I've read most chatter is the result of a few overheated marcils in the clutch. Marcils are the thin sheet metal spring shims on the ends of the disk that the fiber is riveted too. When these are at different compressed heights and strengths you get slipper spots and sticky spots with in the disk as you let out the pressure plate. I'll look and see if i can find the article in the book shelf.
Jan. 17, 2012 11:27 a.m. belteshazzar SuperDork

so what is the problem when you hear a bearingy-type noise, but only when you're NOT pressing on the clutch.
Jan. 17, 2012 11:30 a.m. belteshazzar SuperDork

and in reply to spitfirebill, my '96 D21 did exactly the same kind of thing with the clutch. i never bothered trying to figure it out.
Jan. 17, 2012 11:30 a.m. nderwater SuperDork

I'm getting chatter (sorta like rocks in a soda can) only with the clutch out and the car in neutral. I realize that a clutch job is in my future, but I'd like to know exactly what the noise indicates is failing.
Jan. 17, 2012 11:37 a.m. Curmudgeon SuperDork

If there's a 'rolling whir' type noise in neutral with the clutch pedal out, try pushing the pedal in (disengaging the clutch). If the noise dies away slowly, it's the first motion shaft (input) bearing in the front of the transmission. RX7's do it pretty much all the time and I've heard it in other gearboxes which other than the whir continued to work just fine for a long time.

If the noise continues or gets worse when you push the pedal down, then that indicates a release bearing problem. Those will quite often fail catastrophically!
Jan. 17, 2012 11:38 a.m. 44Dwarf Dork

nderwater wrote:

I'm getting chatter (sorta like rocks in a soda can) only with the clutch out and the car in neutral. I realize that a clutch job is in my future, but I'd like to know exactly what the noise indicates is failing.

Your is likley the round spring in the "Shock Hub" are not up to snuff. 944 suffer from this badly as they were not springs but rubber barrels shaped units
Jan. 17, 2012 1:25 p.m. oldeskewltoy HalfDork

spitfirebill wrote:

I did not resurface the flywheel, because the"experts" told me it was better not to. Seems some people do more damage than good.

What say ye? Time for another clutch? It is quite drivable as is.

The shudder could accelerate the demise of other driveline parts.... The flywheel should almost always be machined, or replaced.... (and the whole unit[flywheel, and pressure plate] should get balanced as an assembly)
Jan. 17, 2012 1:52 p.m. HiTempguy SuperDork

1988RedT2 wrote:

I had a Subaru that did that. The dealer politely informed me that it was quite normal, but for $2000. they could make it better. I politely told them to Berkeley off.

Subaru's are special for a number of reasons. On certain models, they have a restrictor in the clutch line for how fast the clutch can be released. On ALL Subaru's, the input shaft (which the throwout bearing rides on) actually wears out. This causes the throwout bearing to catch and be a general pain in the ass. Almost every Subaru I've been in 2001 and older has this issue. A company makes a "snout repair kit" that involves a sleeve that goes over the shaft and a new throwout bearing. Only $150-ish.

Beyond all of that, I typically find chattering to happen due to a toast throwout bearing, especially if the clutch has been replaced with a cheap chinese one.