Car buck/jerk near idle speed while in first gear.

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Rope-Pusher
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Re: Car buck/jerk near idle speed while in first gear.

Post by Rope-Pusher » Thu Apr 25, 2013 8:21 pm

When the damper in the hub of the clutch disk is worn, it's the torsional equivalent of having worn shocks. The springs in the clutch hub need to be damped.

Good to check on powertrain mounts as well - if they are worn or torn the powertrain can wind up and unwind in an uncontrolled manner.
'08 Jeep Liberty 6-Speed MT - "Last of the Mohicans"

havoktsx
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Re: Car buck/jerk near idle speed while in first gear.

Post by havoktsx » Mon May 13, 2013 10:20 pm

for tickles and giggles, i turned off vsa on my car and voila! jerking/bucking 90% gone in 1st and 2nd gear!

my guess is that the combination of DBW plus an aggressive vsa algorithm has something to do with it. with vsa off, the throttle cut-off seems gradual enough where the bucking is gone. why this is so i have no clue.

if your cars have a button or a way to turn off any type of vsa/stability control, try driving with it off and see if this helps.
08' Acura TSX ASM/Ebony 6MT

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ClutchFork
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Re: Car buck/jerk near idle speed while in first gear.

Post by ClutchFork » Sat Jan 11, 2020 11:09 am

My 2001 S10 does not buck when idling along in first gear, but the 1992 Mustang easily will buck. Mustang has 3.08 gear. S10 has 3.73 gear. I wonder if that makes a difference. But I used to have a 1995 F150 that would sometimes buck. Think that was geared somewhere around 3.30 or so.
Stick shiftin since '77
theholycow wrote:Why in the world would you even want to be as smooth as an automatic? Might as well just drive an automatic...

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Re: Car buck/jerk near idle speed while in first gear.

Post by ClutchFork » Wed Aug 05, 2020 12:00 pm

Just an academic questin:

Between a stock flywheel and a light weight flywheel, all else equal, which car would have the greater tendency to buck/jerk at very low speed in 1st gear? My guess is it would be the car with the lighter weight flywheel.
Stick shiftin since '77
theholycow wrote:Why in the world would you even want to be as smooth as an automatic? Might as well just drive an automatic...

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Re: Car buck/jerk near idle speed while in first gear.

Post by Rope-Pusher » Wed Aug 05, 2020 6:08 pm

ClutchFork wrote:
Wed Aug 05, 2020 12:00 pm
Just an academic questin:

Between a stock flywheel and a light weight flywheel, all else equal, which car would have the greater tendency to buck/jerk at very low speed in 1st gear? My guess is it would be the car with the lighter weight flywheel.
Owl things being equal, the flywheel with more rotational inertia would probably spin more smoothly, i.e. have less variation in rotational velocity. It is amazing to look at a flywheel under strobe lighting and see how unevenly it spins. Diesels are worse than spark ignition engines.

That being said, the clutch hub generally has a friction damper and some springs that serve to smooth those flywheel speed variations as they are fed into the transmission input shaft. Dual-Mass Flywheels (DMFs) are popular now, especially with diesel engines and/or in more premium products. The flywheel itself helps smooth the rotational velocity being fed into the transmission. Some transmissions, especially some 6-speed FWD transaxles have a lot of gears in mesh at any one time (twin intermediate shafts) and need a DMF to reduced their propensity to exhibit gear rattle otherwise.
'08 Jeep Liberty 6-Speed MT - "Last of the Mohicans"

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ClutchFork
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Re: Car buck/jerk near idle speed while in first gear.

Post by ClutchFork » Wed Aug 05, 2020 7:29 pm

Rope-Pusher wrote:
Wed Aug 05, 2020 6:08 pm
ClutchFork wrote:
Wed Aug 05, 2020 12:00 pm
Just an academic questin:

Between a stock flywheel and a light weight flywheel, all else equal, which car would have the greater tendency to buck/jerk at very low speed in 1st gear? My guess is it would be the car with the lighter weight flywheel.
Owl things being equal, the flywheel with more rotational inertia would probably spin more smoothly, i.e. have less variation in rotational velocity. It is amazing to look at a flywheel under strobe lighting and see how unevenly it spins. Diesels are worse than spark ignition engines.

That being said, the clutch hub generally has a friction damper and some springs that serve to smooth those flywheel speed variations as they are fed into the transmission input shaft. Dual-Mass Flywheels (DMFs) are popular now, especially with diesel engines and/or in more premium products. The flywheel itself helps smooth the rotational velocity being fed into the transmission. Some transmissions, especially some 6-speed FWD transaxles have a lot of gears in mesh at any one time (twin intermediate shafts) and need a DMF to reduced their propensity to exhibit gear rattle otherwise.
Ah yes, gear rattle. They used to get some of that in those early applications of ATF to manual transmissions.
Stick shiftin since '77
theholycow wrote:Why in the world would you even want to be as smooth as an automatic? Might as well just drive an automatic...

Rope-Pusher
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Posts: 11067
Joined: Mon Mar 16, 2009 3:44 pm
Cars: '08 Jeep Liberty
Location: Greater Detroit Area

Re: Car buck/jerk near idle speed while in first gear.

Post by Rope-Pusher » Wed Aug 05, 2020 9:01 pm

ClutchFork wrote:
Wed Aug 05, 2020 7:29 pm
Rope-Pusher wrote:
Wed Aug 05, 2020 6:08 pm
ClutchFork wrote:
Wed Aug 05, 2020 12:00 pm
Just an academic questin:

Between a stock flywheel and a light weight flywheel, all else equal, which car would have the greater tendency to buck/jerk at very low speed in 1st gear? My guess is it would be the car with the lighter weight flywheel.
Owl things being equal, the flywheel with more rotational inertia would probably spin more smoothly, i.e. have less variation in rotational velocity. It is amazing to look at a flywheel under strobe lighting and see how unevenly it spins. Diesels are worse than spark ignition engines.

That being said, the clutch hub generally has a friction damper and some springs that serve to smooth those flywheel speed variations as they are fed into the transmission input shaft. Dual-Mass Flywheels (DMFs) are popular now, especially with diesel engines and/or in more premium products. The flywheel itself helps smooth the rotational velocity being fed into the transmission. Some transmissions, especially some 6-speed FWD transaxles have a lot of gears in mesh at any one time (twin intermediate shafts) and need a DMF to reduced their propensity to exhibit gear rattle otherwise.
Ah yes, gear rattle. They used to get some of that in those early applications of ATF to manual transmissions.
It's more apparent as you go thru the drive thru lane to pick up some burger-whop. You can hear the sound bounce off the pavement below onto the building wall and in your open window.
'08 Jeep Liberty 6-Speed MT - "Last of the Mohicans"

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