I picked this up as a mostly complete project, so I don't have all the details about the components used. So I've been working on an FD that has this bad shudder when engaging the clutch from a stop. Not a "clunk", it's much more severe. The entire trans shakes/moves and things are contacting each other. Can't say exactly what as I cannot simultaneously run myself over and work the clutch at the same time. The entire car shakes and is borderline undriveable in 'city' driving. Otherwise the car drives great.

Engaging the clutch harder/more rpm makes it more violent while really slipping the clutch makes it almost disappear. (Like it would take me a full minute to get up to 5 mph kind of slipping).

Here's what I've looked at so far:
*Clutch/pp looks to be OEM. Definitely disc-style not pucks. Flywheel did not look aftermarket, but couldn't see much from the inspection plate.
*Engine mounts look good. Lifted engine and pried/inspected for cracks. None found. Even tried using c-clamps to hold the engine mount arms to the subframe. Just resulted in more chassis vibration. Drivetrain shake was same.
*PPF was removed and inspected for cracks, but none were found. Torqued it to spec.
*Driveshaft does not seem have abnormal play in either the front or rear u-joints.
*JDM trans does make some funny noises, but I think it is unlikely it has that much internal resistance. Yes it has fluid.
*Just rebuilt clutch master, slave looks newer. New SS line. System makes and holds pressure.
*Car does it while on jackstands, so none of the suspension components are in play.

Things to look into:
*Diff mounts are suspect, but I've heard they are a 'clunk' not this level of shaking.
*Engine torque brace/trans brace/diff brace - May solve they symptom, but the stock drivetrain definitely didn't shake this much. So, I'd like to solve the root problem. And I'd prefer not to trade chassis vibration for drivetrain.
*Bent clutch fork?
???

Sorry for the novel, but I've been working on this for a while. Any input is appreciated and thanks in advance.

 

I highly doubt it is the diff bushings or a bent clutch fork.

We had a car come into the shop a while back with similar issues. It turned out to be someone had forgotten to torque the flywheel nut. This allowed the flywheel to pull off the e-shaft a little every time the clutch pedal was depressed.

Put the car on a lift (or jack stands), look through the inspection plate and have someone depress the clutch pedal, if the flywheel moves rearward this is the issue.

 

Interesting. I'll have to check next time I have a helper. Wouldn't a loose flywheel also cause a vibration with the clutch in vs clutch engaged with the trans in neutral? I didn't notice much difference, but wasn't really looking for it. Engine and trans are a 99+ j-spec (more on that later) so I don't know what was done to it prior to shipping. Maybe they pulled off some goodies before shipping.

Really, all the symptoms are the same as a lighweight flywheel/aggressive clutch combo, but as far as I can tell, that isn't the case.

I guessed the diff bushings could be bad allowing the diff to mis-align the driveshaft and cause extra binding, but that's a bit of a stretch.

Or the clutch fork is bent to a weird shape that doesn't allow a smooth clutch engagement. Again, takes a lot of imagination.

 

I'm with Banzai on this one. A full face disk should not be chattering. Sometimes a cluth will chatter if the flywheel is severely scourched or worn. I would perform the test Banzai mentioned and see what you get. Unfortunately, you may need to pull the tranny to inspect the clutch and flywheel.

I dont think diff buahings could cause this. Mine were toast when I purchased my car and I had no chatter from a ACT SS disc and HD pressure plate.

 

Thanks for the replies. Just wanted to make sure I wasn't missing any of the simple things before dropping the trans. If I find anything interesting, I'll report back.

 

There was just another one of these threads recently. If the drivetrain shutters when engaging and then as you pick up speed stops, my money is on a bent PPF. This is what happened to me. I'd engage the clutch and the car would shutter like crap. With the car in motion and under speed, no problems.

Check to see if you have a bent but not cracked PPF.

 

Sounds promising. Any suggestions on how to test it without buying a new one?

 

I'm currently having a similar problem. Here is the thread I started and the one David is refering to: https://www.rx7club.com/3rd-generati...-next-1021821/

In my case I'm almost sure the PPF is the problem, however I have not confirmed it yet cause it's winter down here.

 

Great info! Sounds very familiar.

Had some time this weekend and here's an update. Wedged the clutch pedal down and tried prying/moving the flywheel and couldn't find any movement. Doesn't rule out a warped/abused unit, but nothing indicates the flywheel nut is loose.

For ***** and giggles, I fabbed up a solid engine torque brace. It's adjustable, so i could pre-load the engine in either direction or try to leave it in it's stock location. An attempt to counteract any static pre-load imposed by a bent PPF.

The brace did transmit a noticeable amount of vibration to the chassis, but it made the shudder much less severe than before. No real difference depending on which direction it was pre-loaded. But pre-loaded seemed to work better than just attaching it wherever the engine sat naturally. It improved it so much that I actually drove it for a couple days and found inspiration to keep working on this car.

Continuing the search for a local, straight PPF.

 

Do you have any update about your problem cause in my case it was not the PPF?

 

I can update, but unfortunately no fix.

Tried a different PPF. Inspected both side by side with no visible difference between the two. No change between the two different PPF's. It's possible they were bent exactly the same way without deforming the paint whatsoever, but seems pretty unlikely.

I'm going to try to align the ppf per the FSM, but I don't have a setup to measure it exactly.

Having driven it more, I can slip the clutch at about 2k and get it to engage pretty smoothly. I suspect there is a plain-looking, but stronger than stock pressure plate and/or lightweight flywheel making it difficult to get going. I've got an OEM setup ready to go in. Just haven't gotten time to do it.

Driveshaft is still a suspect, but it didn't seem bad during the on-car inspection. I'll know better once it's out.

Will report back if I find anything interesting.

 

Finally got it all back together and the problem is solved. Turned out to be the flywheel was warped and had some hotspots. Runout was > .040" (max spec is .008"). Everything else looked ok.

Replaced the old stuff with a re-surfaced stock flywheel and oem clutch/pp and it is super smooth now.

Thanks for all the help!

 

Crap! I have changed my clutch last weekend and didn't check the runout. It should be ok as I resurfaced the flywheel last year and I still have the same problem then before resurfacing it. However I should have verified the runout while the trans was out just to double check.

Anyway that's a good news for you dude.

 

Thanks. and sorry you're still having issues. The other componenets I was looking at were the driveshaft u-joints and really trying to align the PPF according to the FSM. It was just checking the ground to frame rail, adding 3" and then tightening the PPF bolts. But maybe it made a difference? :shrug: Also, I was playing with another engine mount and there was enough road debris in the threads to stop the nut half way up. That's about all I got.

Good luck getting yours solved.

 

With your new flywheel and PP/cluctch combo did you notice any vibration on the jackstands?

Thanks!

 

The vibration was completely gone when I tried it on jackstands.