Jerky Cav Drivetrain - MikeC
92J (1989-92 shape) Cavalier 2.0i 8v manual. (GL not SRi)

The drivetrain is very jerky and it is very difficult to drive smoothly in traffic. Purchased at 88k, its now done 143k and its no worse or better. Makes no difference whether engine or weather is hot or cold.

When you are in gear and accelerate the drive jerks and chunks noticeably (noise and feel). Similarly when taking your foot off causes it. It doesnt jerk when varying an open throttle, only when closing fully or opening from closed. It also happens when changing gear up or down. It happens in all gears even fifth & reverse but is most obvious in 1st/2nd because of greater torque. Not sure if it is a mechincal or ECU problem? It requires an extremely light foot, sometimes it will do it when I havent knowingly moved my foot.

I can get round the problem by dipping the clutch and bring the revs up when wanting to speed up in slow moving traffic and by keeping the throttle open (slightly!) whilst changing gear, not ideal I know, the clutch is now starting to judder!

Ive lived with this so long I dont want to spend any money on it but if any of you know a simple cure I would be grateful as it is so annoying arrrgggghhh!!

MikeC
Jerky Cav Drivetrain - Dynamic Dave
My initial thought would be worn engine mounts, or maybe worn front suspension bushes.

Looking at the engine on tickover, would you say it is quite motionless, or moving around?
Jerky Cav Drivetrain - Dave_TD
I had this on my old MkII Cav, (if you check previous threads you'll see I had most recognised problems with that car!) it turned out to be engine mounts.
The way to check this is to get someone to floor the throttle then immediately back completely off it while you look at the engine with the bonnet open, mine used to jerk backwards by about 15 degrees, so hard the (carb) air filter housing would hit the bonnet! At its worst point the whole front of the car would "jump" about 2" upwards every time you took up drive.
If you're lucky, the mounts will have failed and you can get them replaced. If you're unlucky, the part of the engine the mounts fix to will have broken, and you'll need to find somebody who's very good at welding to bodge it together again.
Jerky Cav Drivetrain - RogerL
Check out main lead to starter which is used by alternator to charge battery and earth straps. Faults in either of these leads can give faults as the engine rocks backwards and forwards due to torque.

Faulty engine mounts can be diagnosed by revving engine and releasing throttle to get engine rocking backwards and forwards and listening for thumps, if mounts are faulty.
Jerky Cav Drivetrain - Dave_TD
IIRC, the first sympton of worn engine mounts was that the car used to keep wearing out the asbestos gasket at the bottom of the exhaust downpipe, as it flexed back and forth.
Jerky Cav Drivetrain - MikeC
Thanks for the ideas guys, I looked at the engine whilst it was revved today and its hardly moves at all, just very slightly but no more than a couple of mm. The engine of my previous car (a Clio) rocked a lot and the engine mounts squeaked but that never had a jerky throttle response.

Today the Cavalier drove much smoother and didnt once jerk noticably in 32 miles. Perhaps because I washed it on Sunday, or it knows Im getting tempted to trade it in for an HDI 306!

Ill have another look at the rocking when it next gets bad.

Thanks for your help.
Mike.

 

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