View Full Version : Doin' The 4+3 Off-Throttle Herky-Jerky

04-08-04, 09:50 PM
Hi Guys--

When the revs on my '86 4+3 Z51 fall far enough (in gear) the car sets to "bucking" about as though the entire driveline was having some sort of fit. Besides being embarrassing--especially considering I learned manual transmissions about 35 years ago-- I'm wondering whether this all suggests a bad driveshaft/rear end/u-joints/whathaveyou. Thanks!

04-08-04, 10:27 PM
Oh, I should note that this circumstance is accompanied by a fair amount of thunking and clunking in the drivetrain, also happens on light to neutral throttle at lower speeds (25-30mph in fourth,say), and disappears under any acceleration. Thanks again.

04-08-04, 10:28 PM
I too have had this problem w/ my 86 4+3 vette
mine had the same problem before i put a milder cam in it. I had a cam w/ a 106 LSA, and it would buck like hell, i constantly had to be in the throttle. I put a cam w/ less duration in it, and a 110 LSA, and the probem went away. The rear end/u-joints would not cause this.

04-08-04, 10:28 PM
Sounds like me when I first discovered that quirk in late model vehicles! :L

Having driven, as you say, standard transmissions all my life, then finding myself chugging and bucking at stop signs when I tried to drive it the old way, was certainly embarrassing. :o

It was then I discovered that all of the newer vehicles with their respective emissions systems, do that. Sometime when you're out cruising and the traffic is light, put the car (any car) in neutral, or disengage the clutch, and watch your tach - the revs stay up over 1000 rpm or so until you come to a complete stop. After the vehicle comes to a rest, the revs will come down to normal idling speed. ;)

04-08-04, 11:08 PM
Well, now at least I don't feel so bad. Thought it was only me and my 4+3 and I too grew up driving all sorts of standards. :Steer

Remember having to double clutch the old ones, before syncronizers? :(

04-08-04, 11:10 PM
If you remember that Gordon, then you remember the phrase "Grind me a pound of that!", used when someone wasn't proficient with a clutch. :L

04-08-04, 11:24 PM
Ouch!! Do I ever! Just sold my '52 Chevy PU w/granny 4 speed and no syncs and the guy I sold it to couldn't seem to grasp why he had to double clutch it, so all I could do was grit my teeth as he ground a pound away driving down the road.:(

PS - I think we've 'dated' ourselves here. :D

04-09-04, 08:18 AM
Yes, I fall in the same category. I took drivers education at the age of 14 in a standard shift car. Working summers on my Granddad's ranch I had mastered a clutch long before that. I got my drivers license in 1963 and have driven almost nothing but a stick ever since. Even my four door sedans have sticks.

That said, I have never experienced what you describe with my 4+3. With any car, if you feel that coming or it starts, just kick in the clutch and find a gear/rpm combination that won't do it.

If you did not experience this before and it has come on lately, you should check motor mounts, trans, driveshaft and jackshafts and anything that could cause excessive slack.

04-09-04, 02:30 PM
happens on light to neutral throttle at lower speeds (25-30mph in fourth,say).
Yeh, that'll do it! You just can't lug these engines down like the old non-emissions straight sixes and flatheads of years gone by (and why would you want to?)

04-09-04, 05:25 PM
The main problem I run into is when I'm in a school zone, I can't keep a steady throttle under 20 MPH in 1st or 2nd without riding the clutch or coasting with the clutch engaged. Was this meant to be? I have a hard enough time keeping it under 50, but that's because of a malfunction in my right foot! :D

25-30 MPH in 4th?

04-09-04, 06:46 PM
I've had the problem for few years now and just tracked it down. I had the scan tool connected and found that it runs fine at 900-1300 in fourth 25-35 mph as long as you don't feed it any fuel......give it justa little and bucking time! Well the EGR is off on coast and seems to come on too soon when the throttle is opened. it dilutes the fuel mix and causes what is known as lean surge! If you are programing your own proms it could be fixed rather easily. otherwise its just nice to know that nothing really bad is happening.

04-09-04, 06:59 PM
That's some info, Ernie......Dang, but this site is amazing!!!!