Noise like a chattering when downshift to 2nd gear

[TheStig]

Tonight I was coming home from work and i downshifted into second at a stop light while slowly coming to a cruising stop...as i downshifted the car was under 2000 rpm in 3rd gear and i let off the clutch the car made this really loud chattering and knocking noise....i noticed it earlier in the day and it only does it when i downshift into second gear on the way to a stop and not in any other gears...I just recently had my new Dynomax UltraFlo muffler put on too and i guess i noticed it after a couple of days making this sound...could it be that the muffler is hitting something on the car underneath? or maybe the catback piping??? or could this be CV Joint related or transmission???? I have only done 1 of the 4 cv joints on my car for a note.... if anyone can help please

[drew1]

Are you feeeling any kind of jerking?

drew1

[Z-man]

Don't know where your sound is coming from, but you should NEVER use the engine to slow the car down! (IE: downshifting). When coming to a light it's best to just put it in neutral and use the brakes.

Even in the case of track driving, where you have to shift from a higher gear to a lower one for a turn, when you engage the lower gear, there should be no effect on the decelleratoin of the car (provided you're doing a proper heel-and-toe downshift).
Why not use the engine to brake? Simple: brakes are cheaper to replace than engines and trannys....

That said, I do hope for your sake that the tranny's not going....
-Z.

[TheStig]

I'm writing this at school now and I found the problem! When the car is warmed up, the muffler makes these interesting noises. During the downshift in 2nd gear i hear more like a vibration and it sounds like the muffler is hitting something and vibrating. I can also hear a humming noise at 2500 rpm and at 3500 rpm. The car doesn't jerk at all and it doesn't jolt while going around turns. I already had one tranny replaced in my car and I think I would know what a broken pinion gear would feel like... At least its the muffler making the noisy vibrations. I'll change the gear oil on it this weekend though just to make sure...anyone have reccomendations for oil?

thanks for the tips Z-man, I'll be more careful with downshifting from now on.

[Z-man]

Originally posted by EuroSpec944
... I'll change the gear oil on it this weekend though just to make sure...anyone have reccomendations for oil?

I just got swepco synthetic tranny oil: it takes a little of the notchiness of shifting out, especially in cold weather.

Synthetic tranny oil is better than dino juice oil since it won't break down as easily, and has higher tolerances. And it won't heat up the tranny as much under constant hard use (like on the track).

Good luck!
-Z.