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Possible cause of "THUNK" at start
After driving for a while and the car is getting hot, whenever I place the car into neutral waiting for the traffic to move and then try to shift into first when the traffic starts, I usually get a big "thunk" noise. I can avoid this "thunk" by threading the shifter into first very-very slowly.
Other people experienced this on this forum, so it is not big news but I think I have an explanation. Today it was an exceptionally hot day and after stopping the car in may garage I let it run for a few minutes to cool it down. Transmission was noisy as usual. Pushing the clutch I heard the shaft spinning down really slow. It took a few seconds for the tranny noise to cease. The explanation for the “thunk”: when we try to engage the first fast without letting the primary shaft spinning down the synchro stops the spinning suddenly and this gives the “thunk”. On this thread https://www.rx8club.com/showthread.php?t=59487 there is a detailed explanation of the phenomena. |
If it takes more than 1/2 a second or so for the tranny noise to stop after you have depressed the clutch pedal fully, your clutch is not completely disengaging and this is VERY bad.
This will cause clutch failure. The reason it clunks is because the first gear synchro (all of them in fact) are relatively hard and don't grab with light pressure as well as they might in some other cars. You don't notice the clunk on ither gears because the gear assembly is already spinning. |
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Originally Posted by MazdaManiac
If it takes more than 1/2 a second or so for the tranny noise to stop after you have depressed the clutch pedal fully, your clutch is not completely disengaging and this is VERY bad.
This will cause clutch failure. The reason it clunks is because the first gear synchro (all of them in fact) are relatively hard and don't grab with light pressure as well as they might in some other cars. You don't notice the clunk on ither gears because the gear assembly is already spinning. This would be the case if he was sitting at the light with the clutch in the whole time. I think that he is not. That the clutch is out and in neutral, then depressing the clutch and shifting into first right away will result in a thump as the tranny shaft has been spinning with the engine the whole time....I dont know the specifics, but this is something that has happened in every manual I have owned. Confirm for us that you are or are not holding the clutch in at standstill. |
drive a bimmer....it'll do the same. no worries
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Mine has always spun down by the time I shove it into first.
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