06_AP2Fletch

I always get the response of "It's normal" part of the s2000 whenever going into first gear and often you may get that thumping noise or at least you feel it to some sort to recognize it. Honestly it doesnt feel bad as far as anything happening damage wise, but I believe we all have that guilty conscience that everything is fine until something happens. I dont want to be in that predicament. So what is the cause of this thumping noise when going into first gear? what effect does it have on the transmission? is it due to low fluids or is it in fact normal? I am pretty good with my hands as far as changing out parts and adjustments, but I'd rather leave everything alone until I have a direct cause to fix... I've driven many cars as far as evos, 350s, you name it and have not ever had this experience until my s2000.

SheDrivesIt

If you have the car in neutral and the clutch engaged (foot off the pedal) the tranny spins. When you clutch in, the input shaft continues to spin and when you shift into gear, it connects the rest of the drive train. Since the wheels cannot move, all spinning stops when you put the tranny in gear. The thunk you hear is the lash being taken up in your drive traing between the transmission output and the stationary wheels.

RobEvans

All part of the s2000 experience haha

mr5parkle

i get the thumping too. i like to think it's normal.

when i put it into first and keep the clutch disengaged, i get a thump. immediately after, i put it in neutral then engage the clutch, then put it back into first w/clutch disengaged and no more thump. i think this behavior resonates with SheDrivesIt's explanation as the second attempt in putting it in gear has all the spinning parts stopped from the first attempt.

hope that makes sense

LeonV

Look up how a manual transmission works. Having a picture of a transmission up with labled parts helps with the explanation.

In neutral with the clutch engaged (foot off pedal), the engine spins the input shaft and countershaft, with the countershaft's gears in constant mesh with the free-spinning gears on the output shaft, which connects to the wheels. That is, the output shaft is stationary, while everything else spins at engine speed: output shaft gears, coutershaft, input shaft. When you push the clutch in to disengage it, power from the engine is disrupted to the input shaft and thus the countershaft. The input shaft and countershaft keep spinning (Newton's 1st Law) as friction in the bearings and on gear teeth slows them down.

Engaging first gear locks the free-spinning gear on the output shaft to the output shaft. This is accomplished with a syncronizer, which does just that, syncronizes gear speed to output shaft speed. With the car sitting still, the output shaft not rotating as it's locked to the wheels, the syncronizer will have to get the rotating gear and shaft speeds to match the output shaft, which is at zero RPM. This means that it must stop all rotating components: the gears, countershaft and input shaft. The clunk you hear is all of these being quickly brought to a halt.

This is why waiting, after you've pushed the clutch in, helps with the clunk. It allows time for the shafts to slow down before stopping them. The syncro does less work.

You've probably never noticed it before because of extra sound deadening in other cars, and possibly because of other design features. Perhaps the S2000 gearbox is a lot more free-spinning (less friction) than other boxes.

xviper

Ever been in a "conga line"? (It's a dance from decades ago.) You get a bunch of drunk people following each other at less than arms length, following the moves of the first person. Then the first yahoo suddenly stops without warning. The ensuing "clunk" is the sum total of all the knuckleheads banging into each other. That's the "lash" that's being talked about.
If it really bothers you that much, just shift into 4th, then immediately into 1st. The ratio of 4th is such that it can stop all the spinning in a somewhat dampened manner and you don't hear the clunk. Or just hold the clutch on the floor for a "3 count" before throwing it into 1st. The tranny fluid's viscose nature is enough to stop the spinning. It's basic mechanics, not rocket science.

LeonV

And FWIW, when at a stoplight for example, I'll push in the clutch as the light is about to turn for me but actually put it in 1st just before I get going. This "solves" the issue.

koy59agi

Check the rear differential mounts, almost every higher milage S2000 I have looked at needs the front mounts. You may need to actually take them out to see if they are in need of replacement. They seem rather flimsy in my opinion and I am considering using a more durable mount next time.

mazelmazelgoodthings

awesome explanation lol