slalom44

[QUOTE=tof,Jun 28 2007, 10:30 PM] Anybody who knows what a "layshaft" is probably has the correct answer.

FISH22

so you think i pulled that out of my ass?

raymo19

If you have the clutch pedal fully depressed and the car moves forward when you put it in gear your clutch is not fully disengaging. The "thump" will be more pronounced and frequent if that is the case.

Catahoula01

Have MY07. Also experiencing "thump" while shifting into 1st, sometimes. It really bothers me, but I always thought like many it was like a factory thing, so I've never taken my car to the dealer for inspection.

Kinda like that bumper defect on the passenger side. Although, I did have that fixed.

SpitfireS

This is how the S2000' gearbox looks like inside.
Simplified obviously.

Black gears mean they are fixed on the axle.
White gears mean they are free rolling.
Synchro rings, sleeves and hub lock them (white gears) onto the axle when you select them.

At idle, in neutral, clutch out: the whole primairy shaft is spinning at idle revs.
So is the reverse set (3 gears), 1st and 2nd gear set (2 gears each)
Note: 1st gear has the highest ratio (IOW it is the strongest).

Engine at idle, trans in neutral, clutch out:
When you select 1st gear right after pressing the clutch you will notice a "thumb" because all spinning parts come to a sudden stop and the kinetic energy in those parts is enough to (via 1st gear - the strongest gear) move the car a little.
When you select 2nd gear first, you will not feel the thumb.
IMO because 2nd gear ratio is less (not as strong as 1st) and maybe 2nd gear synchro is less "aggressive", IOW it has a smoother "grab".

IMO, if your clutch disk is dragging a bit (not enough grease on the splines, damaged splines, clutch not dissangaging enough) you will notice a "thumb" in all gears (or at least 1st or 2nd or 3rd) if you select them right after pressing the clutch pedal.

RED MX5

Rust on the input shaft splines can cause the clutch disk to bind, and this can produce a pretty heavy "thump" as the gears disengage (under certain conditions), and I suppose it could also make the car move forward when first gear was engaged. That's the problem here. We don't really know what these people are hearing. Some of them are probably rushing the shift from neutral to first, some may have a clutch that isn't fully disengaging or is dragging, and some may be hearing something else entirely. The descriptions here don't seem consistent to me, so I think we're looking at a variety of issues rather than a single problem.

SpitfireS is also correct. Going directly from neutral with the clutch out, to first, will produce greater loading than if you go to second before first, and that's the first "fix" people should try (becuase it's free). When you come out of neutral, engage second gear before engaging first and see if the "problem" goes away. If it does then you have solved the problem, and it was operator error. If engaging second first doesn't help then you may have other issues.

raymo19

^ Yeah I probably should have clarified that a bit. If the car bumps forward a bit no big deal but if it creeps forward until you brake you need to consider a clutch problem. Idle speed shouldn't move you much on a level surface.

Roxy

Thanks very much to SpitfireS for some technical information that is pretty clear to even someone like me that doesn't have a lot of tech skills. Concerning a few people's suggestions that we are not all talking about the same problem; having read a lot of posts about this subject already, I AM CERTAIN THERE ARE MULTIPLE PROBLEMS WITH A SIMILAR THUMP, SOME OF WHICH ARE TRULY CLUTCH PROBLEMS, AND SOME OF WHICH ARE ALL CAUSED BY A DRIVE TRAIN MOMENTUM ISSUE THAT IS COMMON. One of the reasons I posted this thread even though there are lots of other similar ones, is to hopefully clear up this ambiguity. So, to be clear, the problem I have and that I believe is the common problem most people have to which the term "infamous thump" refers, is a sound and vibration seemingly coming from the rear of the car that sometimes happens when shifting into first gear from a stop. As I described in the opening post, the first time it happened to me, I thought someone had slightly tapped my rear bumper. The problem I have does not make my car move. The problem I have does not happen in higher gears; I have maybe heard it, barely, when shifting from 1st to 2nd a few times, but only because I was bothering to listen closely. I don't think I would have ever noticed if I hadn't been tipped off by the louder thump from stop to 1st. Thanks for all the posts so far, and if anybody has any information about what distinguishes these similar problems we seem to be talking about, please post. Thanks everyone.

RED MX5

Well, in every case, it's got to be either a clutch issue or a driver issue.

If it's a driver issue, shift into second first.

If it's the clutch, it could be rusty splines, or the clutch may not be disengaging fully because of problems in they hydrolics.

It could also be excessive slop in the driveline somewhere, but I'm not sure that listing all the things that might be described as a "thump" will narrow things down much for most people. If the second first shifting doesn't stop the thumping, and the owner can't diagnose the problem, then it seems to me that the car needs to be checked out by a competent mechanic.

I'm not aware of anything that would cause anything that could be described as a "thump" that hasn't already been covered.

If it is a "common" problem as you say then I have to believe that it's an operator error, because I've never driven an S2000 that thumped the way you describe. My car is seven years old and has never exhibited any symptoms like the ones (any of them) described in this thread.

Roxy

bump for more opinions or suggestions? anyone?