Had to merge in a hurry this afternoon. I didn't launch it - just had to do a quick 1-2 shift to finish the merge. Heard the "thunk" after I released the clutch. Seems to drive fine and what not - no different then normal.

I've read other threads where those with aftermarket clutches have similar noises after a quick shift - I'm guessing it was just the axle bouncing inside its mounts or something.

Ideas, flames, comments?

 

You are correct --- it's the differential abusing it's bushings in response to the quick drivetrain lash. If you do this alot you can purchase beefier poly bushings to arrest the movement before contact. WORKS sells them, as do a ton of other vendors.

 

What he said. ^^ It's a very common thread topic. Searching for clunk + shift reveals that it's normal; it's just the drive shaft bottoming out within the carrier bearing that holds it just in front of the rear differential. No worries.

 

Awesome - thanks guys

 

i posted on this about a month ago, somebody told me it was driver error i didnt believe it. I know realize that it is driver error, once you get use to throttleing / engaging the clutch through the gears it will go away, i dont mean feather the clutch in, im talking hitting the accelerator pedal .5 seconds before the clutch is disingaged, test yourself and you will notice you drop the clutch and hit the pedal a sec after. Hit the accelerator before you release the clutch and the thump will go away. I know 1st gear pull then shift in to 2nd happens super fast, but if you watch yourself you will understand what i mean.

It is "Driver Error" i didnt believe it at first now i know that it is.

I'm assuming its because the motor RPM's slow down so much and as soon as the clutch engages there is a partial speed difference between the flywheel and the ground, so as it hits the initial point, the engagment force causes the thump. So if you catch the engine speed up it wont do it no matter how hard you engage the clutch.

 

Diff Slap, its your diff boucing of the undercariage. I am getting the bushings soon because it bothers me.

 

it is your differential mounts , but im telling you its DRIVER ERROR

 

Knew there needed to be someone with a flame. It's as guaranteed as death and taxes.

Notice I never asked what was causing it - just what it was. I know it's driver error. Duh.

 

^ lol. I have a exedy twin plate with a ss clutch line and no restrictor pill... no matter what rpm, if you try to shift fast, it'll do that. When I had a stock clutch and stock everything else w/ the restrictor pill still in, it would only do that on hard 1-2 shifts. If you shift just a tiny bit slower, you can avoid it... however with my setup, it's quite hard to.

 

I hear that thunk shifting from 1st to 2nd when turning a corner.

 

If you come to accept that it is driver error, you will not order the harder mounts,

If you dont accept it you will simply order the mounts, that will prevent the thump, but you will continue driving the way you do.

 

I also agree that it can be avoided through better shifting technique. When I first started driving the Evo, I noticed this, and it scared me a little. Once I started to get use to the gearing, and rev matching, it doesn't it do it anymore. If you hear this sound often, it means you probably aren't shifting correctly, or maybe your bushings need to be replaced.

 

its not that your shifting is slow or bad. Its just that you have to find the sweet spot point where your clutch is engaging at a certain Throttle Position. Its not exactly rev matching, you just preven the lash by having the motor hook up smoothly. Think about it your rear diff is between the ground and the motor. Its always spining with the ground, but once the motor hooks up it can cause a lash from the difference in speeds.

You almost have to feather your clutch in to gear, with your pedal over half way down. I know it happens super fast, you just have to do it.

 

This is exactly right. The problem is the difference in Engine speed vs. drivetrain speed and the rate at which the clutch reconnects to the flywheel (if you drop the clutch or not). Rev matching will make the problem go away. Slipping the clutch will also help.

 

Imo (although technically it’s off topic) if you are trying to go as fast as possible in a straight line, this clunk is inevitable with stock bushings. It’s only driver error if you are not trying as hard as possible to accelerate at all costs (drag racing etc).