ok so a guy asked me a qusetion today that i couldn't answer, ,

i know a little about car but i am allways looking to learn more..

ok so say you in 4th gear at about 4 grand, you go to downshift into 3rd,

what causes the rpm's to jump up...

while your in 4th what are the other gears doing?? are they stopped or do they keep moving???

just wanting to know the answer ,any new knowledge is good for me thanks alot guys.

 

- You push the clutch in and the input shaft is free to spin at a different speed than the engine
- You move the shifter from fourth to third, the synchro's match speed and get your input shaft spinning at 6000 rpm or whatever
-You release the clutch, which forces the engine to speed up to match the speed of the input shaft

It's obvious from your question you don't rev-match when you downshift. A word of advice, if you rev match you can make the input shaft speed up to 6000 rpm in neutral before you put it in 3rd, which will save wear on the synchros and the clutch.

Also, all the other gears keep spinning too. It's just they are spinning freely on the mainshaft because their synchro's aren't engaged.

 

You may have to look at a diagram to understand this but all the gears are in mesh and rotating all the time. They are not locked to the output shaft untill you select them. You can only select one mesh at a time( a good thing).When you upshift you reduce the ratio/ multiplication and thats why the engine drops RPM. When you down shift you select a greater speed/ mesh multiple and to drive at that speed requires the RPM to go up. Even if you do not use the gas the RPM increases - thats because the car is pushing the engine . This is one reason why missing a shift and selecting a lower gear can be damaging. You can easily overspeed a clutch disc( and burst it) or overspeed an engine( the fuel cut off will do nothing to stop this) and bend push rods and maybe more.

 

This will help more than anything i can type. http://auto.howstuffworks.com/transmission5.htm

 

i get it guys thanks alot

 

great website