Transmission "jerk"

[Rmodeler]

82 corvette This may have been discussed before, but couldn't find it. When putting transmission in drive, it jerks, especially if the rpm is up at all. At 5-6 hundred rpm it not quite as bad. It jerks and the back end squats. Shouldn't it go in smooth, without the jerk. I don't notice it going into reverse, just feel the back end raise up. Wife always complains about it(I know, don't let her ride in it.)

 

[zachh]

That is normal at higher rpms (around 1000), a small jerk. The jerk is just the pressure getting put on the rear suspension, thats why it sits down. If you put it in gear, hold the brake, and hit the gas, the higher the rpm, the lower it'll get. If there is a "clunk", thats just loosness in the rear end, driveshaft, trans, half shafts, and rear hubs.
Best Wishes
zachh

 

[gmjunkie]

Check for a Broken Transmission Mount and Worn or Missing Differential Snubber Mount too!!

 

[wishuwerehere82]

Mine has always done that even efter a tranny and driveline rebuild. It grabs into gear and squats the rear, even at idle. Definately not a smooth engagement like a normal passenger car. It wants to go!

 

[Rmodeler]

Thanks to all for the information. That was probably disappointing to spend all that money for the rebuild and still have the rough engagement. If they did that when new, it seems people would have complained about it. I was wondering if a rebuild would correct it, guess I'll save my money. The car has 40K miles on it and I'm the 3rd owner, runs great, except I have trouble with the idle staying high at times, one time you come to a stop and it will be 5-6 hundred, next time you come to a stop and it will want to run 1000-1200. Haven't had time to check it out completely yet.

 

[gmjunkie]

Thanks to all for the information. That was probably disappointing to spend all that money for the rebuild and still have the rough engagement. If they did that when new, it seems people would have complained about it. I was wondering if a rebuild would correct it, guess I'll save my money. The car has 40K miles on it and I'm the 3rd owner, runs great, except I have trouble with the idle staying high at times, one time you come to a stop and it will be 5-6 hundred, next time you come to a stop and it will want to run 1000-1200. Haven't had time to check it out completely yet.

Check out the Choke and fast Idle cam,it's sticking!!!My 78 L82 automatic don't slam when I put it in gear unless it is not warmed up!!! But it will squat when it loads the suspension!!

 

[wishuwerehere82]

Check out the Choke and fast Idle cam,it's sticking!!!My 78 L82 automatic don't slam when I put it in gear unless it is not warmed up!!! But it will squat when it loads the suspension!!

Crossfire injection doesn't have a choke, Junk.:L Remember?
The idle speed is controlled by the IAC motors on the throttle bodies. They open and close pintle valves on each TB to vary the flow of air into the intake, below the throttle plates. The throttle position sensor tells the ECM when the throttle is closed, and should be at idle. Then the IAC motors close off the air supply until the tach signal lowers to correct idle speed.
The system is not fast, sometimes taking a few seconds to equilibrate all that data. But a vacuum leak, old TPS, or a worn throttle shaft bushing can cause the idle speed to wander around a little.

Or.... it could be some dirt or gunk in the throttle linkages, causing them to stick and not return to the idle position.

That reminds me to go out and spray some carb cleaner on my linkages and throttle plates.

 

[gmjunkie]

Crossfire injection doesn't have a choke, Junk.:L Remember?
The idle speed is controlled by the IAC motors on the throttle bodies. They open and close pintle valves on each TB to vary the flow of air into the intake, below the throttle plates. The throttle position sensor tells the ECM when the throttle is closed, and should be at idle. Then the IAC motors close off the air supply until the tach signal lowers to correct idle speed.
The system is not fast, sometimes taking a few seconds to equilibrate all that data. But a vacuum leak, old TPS, or a worn throttle shaft bushing can cause the idle speed to wander around a little.

Or.... it could be some dirt or gunk in the throttle linkages, causing them to stick and not return to the idle position.

otfl Duh!!!! I knew That!!!!!I don't know what I was think'n!!:cool

 

[minifridge1138]

I had that same problem on my 1982. Your idle is the problem. Mine used to literally DROP into gear. The car moved forward an inch and the back end dropped 2 inches. I lowered the idle speed and the problem is gone.

Lucky for me, my car has a 4 barrel holley sitting where the CROSSFIRE used to be, so it was easy to adjust.

I'm not sure how to adjust the idle on the CFI, but lower the idle and your problem will go away. Although your 0-60 might be affected, too.

Good luck!

 

[wishuwerehere82]

The main problem with dropping the idle RPM on the crossfires is that the ECM won't let the RPM drop below 500 RPM. If it does, it will give it a double shot through the injectors, and the speed jumps up. This is the notorious "surging" that the crossfires are noted for. So 650 RPM is the spec. for the idle speed, with a TPS voltage of 0.525V.

 

[minifridge1138]

Well if the CFI won't let you get the idle low enough to eliminate the jerking, then i guess you'll just have to live with it. As I said in my first post, i have a carburetor and it is easy to adjust the idle. I don't know what idle i have though, because my tach does not work. Tuning a carburetor by ear is fun.

Good luck!!!