Clutch chatter causing whole drivetrain to rattle (100 mile update)

[facultyofmusic]

When go-karting today I noticed that sometimes in a low gear (such as first or reverse) the whole car vibrates as if it's gonna rattle itself apart. Turns out it's the drive shaft rotating back and forth with a stable period of oscillation if I depress my clutch just right. Here's a video of it happening:

https://youtu.be/3jnkE1cl7R8

I jacked the car up and investigated a bit. I noticed the diff gear backlash before but didn't think it would be an issue. How much backlash do y'all have in your rear diff? I can turn my wheel a little back and forth before the drive shaft rotates.

Is everything here normal? Or is there something wrong that I should look into?

[facultyofmusic]

Video of me turning the wheel with the drive shaft staying still:

https://youtu.be/TU4PD2c9Yik

[Norm B]

I think what you are seeing is a symptom and not the cause of your vibration. The backlash in your rear differential seems normal. The cause is clutch chatter. Were you riding the clutch during your go cart drive?

Norm

[Jeff Kleiner]

I’m with Norm and think you’re seeing clutch chatter.

Jeff

[Railroad]

I agree clutch issue. Is your clutch disengaging completely? Low and reverse would create more movement than higher ratio gears.

[facultyofmusic]

This only occurs when I'm purposefully sipping the clutch. e.g. trying to make tiny movements. I take this as normal then!

[Jeff Kleiner]

...I take this as normal then!

Actually no, clutch chatter is not "normal". The clutch should engage smoothly. Chatter is most often caused because the friction surface (flywheel, clutch disc or pressure plate) has been contaminated with oil. Since this is a new installation you may find that it will lessen after making some heat from use and a few miles ---fingers crossed ;)

Jeff

[facultyofmusic]

Oh... Damn .. fingers crossed then!!! Thanks everyone!

[facultyofmusic]

Actually, how long should I expect it to chatter before it goes away?

[Jeff Kleiner]

Actually, how long should I expect it to chatter before it goes away?

It might not go away.

Jeff

[Railroad]

The lower the rpm I try to take off with, the greater chance mine will chatter. A little more rpm, nice and smooth. It might be getting a little better. 1800+ miles.

[ggunter]

Do you have an organic disc or a ceramic disc. Ceramic disc's, are more prone to chatter then the softer more forgiving organic (asbestos) disc. Ceramic disc's like to grab all at once, hence for performance use.

[ggunter]

Also, if you have an excess runout condition with any of the clutch components it can cause chatter.

[facultyofmusic]

Do you have an organic disc or a ceramic disc. Ceramic disc's, are more prone to chatter then the softer more forgiving organic (asbestos) disc. Ceramic disc's like to grab all at once, hence for performance use.

I have the item from FFR 16420 "450HP 11" CLUTCH, 11", 4.6L/5.0L, 2001-2010 MUSTANG, 26 SPLINE HUB FOR TKO, STREET PRO". Not sure if that's organic or ceramic.

[edwardb]

Not to discount Jeff's suggestion that the clutch surface could be contaminated. Could be the case. But my experience is that a brand new clutch is more prone to chatter some until broken in. After maybe several hundred miles and obviously depending on how it's used I've found they smooth out. Nearly any clutch will chatter if the RPM's are too low when releasing. Suspect both of those could be contributors for you. Trying picking up your RPM's a bit. The clutch I've used on my Coyote builds is the Ford Performance M-7560-T46. It's a dual friction Centerforce part, sold by Ford Performance. Don't know if that's the same one FF is selling.

[facultyofmusic]

Hi Paul, I've started doing exactly that. If I bring the RPM just a little higher it doesn't chatter at all. It's been just 2 days but I've completely gotten used to going into gear without it chattering. Hope it smoothes out over time. :)

[facultyofmusic]

I think I've found the culprit. I put a camera down in my trans tunnel, made the clutch chatter on purpose by slipping the clutch just right, and here's the result:

https://www.youtube.com/watch?v=qf4W0XlWIw8

My theory is that the clutch chatter is unfortunately matching the resonant frequency of the drivetrain mounted on the elastic polyurethane mounts. As chatter continues the system vibrates more and more and eventually the left to right motion of the transmission gets severe enough to rattle the driveshaft's slip yoke. Try as I may I did not find anything loose in the drive train. The slip yoke does have a tiny tiny bit of play, not enough to be abnormal I think... it's supposed to "slip" after all.

What do y'all think? Any other ideas? Does that video look like something else is off?

[Mastertech5]

My clutch directions say to drive conservatively for 500 miles to "break it in". No dumping or slamming gears. I assume your flywheel is a steel one because these cars are so light if you have an aluminum flywheel the engine rpm will drop significantly when you apply the clutch because of the inertia is much less than a steel flywheel. Be patient it should come around. I assume you checked your driveshaft angles.

[facultyofmusic]

... Be patient it should come around. I assume you checked your driveshaft angles.

Thanks @Mastertech5! Yessir I have my pinion angle dialed in.

[Norm B]

Your drivetrain is responding normally to clutch chatter. My suggestion is to increase the revs before letting up the clutch. Try to avoid chattering the clutch for any reason. By chattering the clutch for testing purposes you could be making it permanent and be damaging components. It may go away with usage and a little wear. Let’s hope.

Norm

[Jim Stabe]

I have a new ACT clutch and it chattered like yours. I have about 200 miles on it now and it keeps getting better. Mine came with the 500 mile break in instruction also so just hang in there.

[ggunter]

An organic clutch ( asbestos) is gray black in color. A ceramic disc has copper colored pads. usually four or six pads each side.

[facultyofmusic]

Update: 105miles in on the car. Chatter has gotten better but it's not gone.

[CraigS]

Over the years I have fixed chatter in a number of cars. While stopped put the car in 2nd and start moving. Keep the rpm high enough that it doesn't chatter. Starting in 2nd will keep the slipping going for a little longer than in first. Do this twice. And then drive for 10 min normally. What you are doing is slightly increasing the wear rate on the clutch so it gets smoother faster, but not enough to cause any long term reduction in it's life. Doing it just twice also assures that you don't over heat the lining.