Car shakes when downshifting

[DsmKid98GST]

My 2600 is probably close to a year old and has close to 20000 miles on it. The flywheel was bought brand new also and is equal with the clutch in miles / time driven on. This started happening yesterday. As I downshift the car shakes violently. It doesn't do it so much when i shift normally, but I notice it a little bit when I do slower shifts.

I did a search and i came up with this thread http://www.dsmtuners.com/forums/showthread.php?t=115332&highlight=car+shakes
but it never came to a conclusion.

The clutch does not slip as going up the RPMs and the only time it won't shake violently is when I downshift way below a gear starts and it doesn't need to drop down in RPMs. I had a shop install it when I got it installed and i havn't had a problem proir to this one with the clutch. Any help or information will help a ton since i'm planning on running the car at the track tomorrow.

Thanks,

 

[talontuner1997]

if you dont think its the clutch check the throttle position sensor

 

[96gstdsm]

To me it definately sounds like clutch chatter. I have a little clutch chatter with my 2100 setup, but i have had that ever since the install. It only happens to me when i downshift at low rpm's If i rev match and down shift from higher rpm's it will be a nice smooth downshift with no jolting. It could be from hot spots on the flywheel or pressure plate surface possibly, or a warped disc or even like the throw out bearing i have heard can cause clutch chatter. When the flywheel was installed was it stepped to the correct step height for the clutch? I would think if not this would have been happening right from the beginning but possibly over time it caused some warping or hot spots.

 

[DsmKid98GST]

I just had the TPS adjusted two days ago to smooth out my idle and fix my idle surge. Could a TPS cause the clutch to do this on every downshift? If so how?

I don't know if it was steped to the correct height, but the mechanic that installed it when i got the car did a fine job and the clutch worked great until just recently.

 

[silver bullit]

Are you dumping the clutch without rev matching the engine when you down shift?

 

[DsmKid98GST]

I do not dump the clutch persay. I more gradually release it to help me slow down as I come to a stop.

 

[JayRolla]

Are your motor mounts in good shape??

 

[96gstdsm]

I do not dump the clutch persay. I more gradually release it to help me slow down as I come to a stop.

If you rev match when you downshift though there is no vibration correct?
I know one of the causes of clutch chatter can be the throw out bearing. Those are very prone to be problamatic for our cars, especially if it was one from i believe the ACT clutch's before they switched over to the plastic sleeved ones like the oem tob.
My tob went and i did not notice any jolting though so i don't know first hand about this begin a cause. Mine just made one hell of a racket when it was dried and cracked.

 

[silver bullit]

I do not dump the clutch persay. I more gradually release it to help me slow down as I come to a stop.

That is what the brakes are for.
The cost of a clutch+labor if you cant do it yourself far outways the cost of new brakes unless you like to rip the tranny off to fix the clutch.

You answered your own question look:
"My 2600 is probably close to a year old and has close to 20000 miles on it. The flywheel was bought brand new also and is equal with the clutch in miles / time driven on. This started happening yesterday. As I downshift the car shakes violently. It doesn't do it so much when i shift normally, but I notice it a little bit when I do slower shifts."

When you drive normal it does not do this, so if you drive normal than no problems.
If you slowly release the clutch in combination of "use the clutch as brakes",using the clutch to slowly slip it in then you will over heat or premature wear on the clutch. Oh if you slowly shift then you are probly letting the revs drop to idle then letting the clutch in, which causes the car to shake violently.

 

[DsmKid98GST]

Are your motor mounts in good shape??

transmition and front motor mount are replaced the side ones are not.

 

[DsmKid98GST]

That is what the brakes are for.
The cost of a clutch+labor if you cant do it yourself far outways the cost of new brakes unless you like to rip the tranny off to fix the clutch.

You answered your own question look:
"My 2600 is probably close to a year old and has close to 20000 miles on it. The flywheel was bought brand new also and is equal with the clutch in miles / time driven on. This started happening yesterday. As I downshift the car shakes violently. It doesn't do it so much when i shift normally, but I notice it a little bit when I do slower shifts."

When you drive normal it does not do this, so if you drive normal than no problems.
If you slowly release the clutch in combination of "use the clutch as brakes",using the clutch to slowly slip it in then you will over heat or premature wear on the clutch. Oh if you slowly shift then you are probly letting the revs drop to idle then letting the clutch in, which causes the car to shake violently.

Thanks for the help, I guess old habbits are hard to break. I learned to use the clutch to help me slow down from my parents when I was 16 in my first car. Nobody has corrected me using this method, but i will practice not using my incorrect technique for the remainder of this clutch and future clutches.

Could you explain rev matching? It sounds pretty self explanitory but, I want to make sure I'm doing it right.

As for the part that is going bad - would you say it's the throwout barring? 96gstdsm listed alot of good possible parts, but, that sounds like entire clutch assembly haha which I don't have the money to replace at the moment.

 

[96gstdsm]

Thanks for the help, I guess old habbits are hard to break. I learned to use the clutch to help me slow down from my parents when I was 16 in my first car. Nobody has corrected me using this method, but i will practice not using my incorrect technique for the remainder of this clutch and future clutches.

Could you explain rev matching? It sounds pretty self explanitory but, I want to make sure I'm doing it right.

As for the part that is going bad - would you say it's the throwout barring? 96gstdsm listed alot of good possible parts, but, that sounds like entire clutch assembly haha which I don't have the money to replace at the moment.

About the tob i think it would be a slim chance that that would be the problem here. Although it is listed as a possible problem, you would usually hear a grinding noise coming from the tranny area. It kinda sounds like marbles bouncing around when it goes bad. At least that is how it was for me. It sounds to me like you must have some warping. Or could just be loosened bolts on the flywheel.

The best way i believe to rev match is by doing a double clutch technique. I just throw it into neutral so that the transmission also slow's down so i dont put anymore stress on the tranny. With it in neutral i just tap the gas a little bit to get the rpm's up to the desired rpm level for when i downshift. Say if i am driving at 2k rpm's at the moment, if i want to downshift you figure it would probably go up to about 3500k or so. So just tap the gas with it in neutral to bring it to that point and then downshift into the desired gear. You can also do it by just pushing the clutch in and putting it into the desired gear without putting it in neutral, which is of course faster but the transmission wont be able to slow down so will put more strain on it that way. Once you get used to doing it it is like second nature.

---Ryan.

 

[jeffrey]

Yeah, don't go downshifting all over town. When it is time to stop, pull it out of gear and use your brakes. The violent shakes are because your wheel speed and engine speed are far out of sync and since the car weighs so much, the engine has to instantly match speed when the clutch is disengaged.