LS1 jerks right before complete stop. Help
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Teching In
Joined: Jul 2011
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thanks mario Pretty descriptive answer I appreciate that. So I don't want any play in the sway bar. And im assuming the rubber would be cracked and show signs of wear. So u feel like the problems are connected?
Teching In
Joined: Aug 2007
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From: Central Illinois
I'm not sure if the problems are connected, but that's what I would do. If the noise is coming from the rear, that's where I'd start. It's hard to diagnose things over the Internet. You'll be able to see the sway bar connections and mounts. It will have an end link on each side and mounted to the rear end. Mine has a broken end link and I can hear it pop on stops and turns. Check the control arm bushings for cracks, or if they are really bad they can be rotted almost away. The torque arm will be mounted to the rear end with two large bolts and to the trans in a mount. Check that mount and the trans mount for any excessive play or torn rubber.
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Teching In
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Such a good answer I couldn't be more appreciative of the answer. I'll have to check some things then. The cars in storage but I have good access to it. I definitely appreciate all the help. I read the forum often learning new things. Sounds like bushings mounts and shocks are the main thing to look at
Joined: Nov 2003
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From: Wichita KS / Rancho San Diego
Sometimes when the car downshifts when slowing to a stop it it will kind of "clunk" into gear and that clunk is transmitted through the driveshaft and sounds like it's coming from the rear end. It's "normal". My car used to do it more noticeably than it does now for whatever reason ...
Go on the automatic forum and do a search for "clunk" and you'll find some old threads about this. This may be what you're experiencing.
Go on the automatic forum and do a search for "clunk" and you'll find some old threads about this. This may be what you're experiencing.
Start with the simple stuff, go to Advance or one of the other stores and have your car scanned for free. Post up some codes if you have any, sometimes you won't have a code thrown but have one pending. Vacuum leaks will absolutly cause bucking when you come to a stop. It could be as simple as the EGR tube right by the throttle body is loose. Anyway, go scan your car!
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Teching In
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thanks guys I'm happy with all the info received. I have learned a lot over the weekend so I'll know how to check everything. Somehow never thought about getting it scanned I'll do that first thing out. I can get a free inspection check on the suspension so wouldn't hurt having pros look at it whether I find something or not. Looking forward to spring fellas. Kills me not being able to drive it lol
My car (a '98 auto as well) has done the whole bucking from 5mph>0mph thing since I bought it @102K in 2004. I always imagined it was the torque converter releasing from lockup. Ideally I think it should probably open earlier so the transition is smoother. It really feels like engine braking (the drag from shifting into low gear on a manual in lieu of using the brakes) is suddenly being released. My car doesn't make any noise when this happens, but it could just be that the shock is causing something like the exhaust to clunk against the body on your car (especially if a hanger/isolator is rotted away). As a side note, remember that if it's engine related, the sound can easily be transported to the rear by the exhaust.
I had my transmission rebuilt by Aamco @150K miles and this condition never changed. There is also another oddity I have noticed, which may be a fact of life, or a sign of a trouble. It's not easy to induce the problem, but if a large, harsh bump is encountered at moderate-to-high speeds around a tight corner (like say, a drainage gutter across the corner crosswalk), the transmission will be thrown for a loop from the harsh impact. It will prematurely upshift or downshift at that moment (I can't recall exactly), but only if it was about to do so already. Because it's premature, this will cause drag and it's not very enjoyable when it happens. I was wondering recently if this might be caused by a bad tranny mount, or even a bad engine mount? If so, it occurred to me that it could be causing the clunky shifts when coming to a stop. Is this easy to check for?
I had my transmission rebuilt by Aamco @150K miles and this condition never changed. There is also another oddity I have noticed, which may be a fact of life, or a sign of a trouble. It's not easy to induce the problem, but if a large, harsh bump is encountered at moderate-to-high speeds around a tight corner (like say, a drainage gutter across the corner crosswalk), the transmission will be thrown for a loop from the harsh impact. It will prematurely upshift or downshift at that moment (I can't recall exactly), but only if it was about to do so already. Because it's premature, this will cause drag and it's not very enjoyable when it happens. I was wondering recently if this might be caused by a bad tranny mount, or even a bad engine mount? If so, it occurred to me that it could be causing the clunky shifts when coming to a stop. Is this easy to check for?
Well, my suspicions were confirmed. The main tranny mount which sits atop the center tunnel brace is torn. I noticed this while swapping out the O2 sensors today.
I also took apart the IAC (idle air control) valve/motor. I tried to clean it, but I think it was just too jammed up with oil and deposits to ever work again. It looks fine and the plunger moves now (it was completely jammed before), but I think it may have stripped out internally pulling it apart or it just may have been stuck from the start. The plunger had about a half inch of carbon deposits from the bad PCV valve I just replaced, so the whole thing was clearly not working for some time now. I have to pick up a new one soon (I unplugged it for now as it just idles increasingly high when plugged in, but at 1200 RPM in park or neutral and 950 RPM in drive or reverse when it's unplugged with the plunger left extended) and I'll report back if that has fixed the high idle.
This is important, as I suspect that the engine fighting the brakes (the high idle is like having your foot on the gas and the brakes at the same time) may be cause for the abrupt transition to a stop. It also meant having to hold my foot down on the brakes harder than most other cars to hold still at a stop. Granted, this was with the idle at 800 or 850 RPM, which I just took to be normal. But foot off the brakes, the car would speed up as would RPMs, which I expect to go away with the new IAC. The new transmission mount will surely cure the shifting in bumpy conditions, but I'll have to report back if the jerkiness before a complete stop (like the OP) goes away.
I also took apart the IAC (idle air control) valve/motor. I tried to clean it, but I think it was just too jammed up with oil and deposits to ever work again. It looks fine and the plunger moves now (it was completely jammed before), but I think it may have stripped out internally pulling it apart or it just may have been stuck from the start. The plunger had about a half inch of carbon deposits from the bad PCV valve I just replaced, so the whole thing was clearly not working for some time now. I have to pick up a new one soon (I unplugged it for now as it just idles increasingly high when plugged in, but at 1200 RPM in park or neutral and 950 RPM in drive or reverse when it's unplugged with the plunger left extended) and I'll report back if that has fixed the high idle.
This is important, as I suspect that the engine fighting the brakes (the high idle is like having your foot on the gas and the brakes at the same time) may be cause for the abrupt transition to a stop. It also meant having to hold my foot down on the brakes harder than most other cars to hold still at a stop. Granted, this was with the idle at 800 or 850 RPM, which I just took to be normal. But foot off the brakes, the car would speed up as would RPMs, which I expect to go away with the new IAC. The new transmission mount will surely cure the shifting in bumpy conditions, but I'll have to report back if the jerkiness before a complete stop (like the OP) goes away.
Thread Starter
Teching In
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discovery I took a look under the car and found that the u joints are both questionable. One is definitely messed up. I can move the driveshaft quite a bit. I bought some new ones that are pretty pricey so I will check back in if this fixes the issue.
Thinking the same thing. My bird had an auto and was supposedly rebuilt and had a shift kit when I bought it. When i would come to stops it would give that little surge when downshifting to first gear. Never found anything wrong with it. Check with the previous owner to see if it has a shift kit. They shift a little stiffer with them and that could be what youre experiencing.
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Teching In
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good news! Put it brand new u-joints and a new axle seal last night. The joints on it were in crappy shape. The axle seal was also leaking so fluid change was done also. After replacing these things the jerk is completely gone. im sure it was the joints that did it. Thanks for everyone's help on here, hopefully I continue to expand my knowledge of these cars, and pass it on to others 
