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Old 06-23-2016, 01:32 AM   #1
DrvLikHell
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1996 SL2
Default Engine rocking excessively between on and off throttle while moving in gear

For starters, it's a 1996 SL2 5MT with 135k. When in gear and moving in first gear, if I let off the gas and then get back on the gas lightly, it bucks/bounces while doing so. It's the worst in first and gets less bad as you go higher. It's bad enough to where I don't let off the gas in first without hitting the clutch. It can be ok if I sloooowly let off the throttle and let it get to the point of engine braking gently. In 5th, it's not a problem, but I can feel it sorta bounce lightly when I let off the gas. The lower the gear, the harder the bounce. I'm fairly (99.9%) certain by the feel of it that it's not electrical/fuel, it's mechanical.

I replaced the "dogbone" mounts about a year ago in hopes that it would solve the problem. No change at all. I have very little engine vibration at idle. In that respect, my Saturn is much smoother than every other SL/SW of comparable age/mileage that I've been in. So I'm not sure if one of the other motor mounts could be the problem. I replaced both of them about 10 years ago, however, the car hasn't seen many miles in that time since it was a spare car that spent most of it's time sitting.

The other things that come to mind as possible culprits are worn CV joints, worn splines at the axle ends, and my least favorite, something worn inside the transmission like an input shaft or output shaft gear or something. Some of you will say don't worry about the transmission internals because they're tough, however, I have/had a bad habit of pulling the shifter out of gear without pushing in the clutch. I'd pull it out just as I'd let off the gas, but sometimes I could feel some friction while doing so. Not sure if that could cause any problems or not. Also, I don't ride with my hand on the shifter, and I don't sit at lights with the clutch held in. I only have that one bad transmission habit.

I'm hoping this isn't something that I cause with my driving style/habits because my RX-7 had the same problem, except it was worse. It would buck violently if I went off and on the gas in first gear. And that was with solid metal motor mounts.

If any of you guys (or gals) have any ideas or experience with something similar, I'd be glad to hear it. For reference, my friends 1998 SL2 5MT with 160ish felt much tighter on and off the gas compared to mine when I drove it. And that was when he had a bad top motor mount.
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Old 06-23-2016, 02:04 AM   #2
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1996 SC2
2006 VUE 3.5L
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Did you releave the tension on the cradle to dog bone mount bolts? They need to be loosened and then reset. There is a service advisory that covers this. Behind the right wheel on the rear dog bone mount. Bolts to up through the cradle.

-Robert
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Old 06-23-2016, 11:05 AM   #3
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Default Re: Engine rocking excessively between on and off throttle while moving in gear

I think I get the picture... but please clarify:

Do you know the engine is rocking abnormally, as the Title of this thread implies; have you observed that while it is happening? Or is the only known symptom the fact that the car is bucking/jerky when shifting?
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Old 06-23-2016, 06:17 PM   #4
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Quote:
Originally Posted by RobertGary1 View Post
Did you releave the tension on the cradle to dog bone mount bolts? They need to be loosened and then reset. There is a service advisory that covers this. Behind the right wheel on the rear dog bone mount. Bolts to up through the cradle.

-Robert
I think I did that when I replaced the dog bone mounts. They were a pain to get out and I remember loosening a lot of bolts. I'll do it again just to be sure though.

Quote:
Originally Posted by billr View Post
I think I get the picture... but please clarify:

Do you know the engine is rocking abnormally, as the Title of this thread implies; have you observed that while it is happening? Or is the only known symptom the fact that the car is bucking/jerky when shifting?
I haven't visually observed it. Without removing the hood and driving with my head out the window or mounting a camera somewhere under the hood, I don't know how I would go about doing that. Also, it's not during shifting that it bounces/bucks. I can shift nice and smooth, it's when I don't shift but let off the gas and/or get back on the gas that brings about the bouncing/bucking. So I guess you could be right, it may not be the engine that's rocking, if it's a CV joint or excessive clearance between gear teeth or something then the engine would be sitting still while the other part is rocking.

Here's an example: Going down a slow street in 2nd gear, coming to an intersection where I'm going to make a right hand turn. There's a yield sign so no stop is required. I let off the gas to check for traffic to my left (bounce, bounce), decelerating to about 1400rpm, still in gear, not hitting the clutch, make the right hand turn, hit the gas (bounce, bounce, bounce) and off we go.

Or in parking lots creeping around in 1st gear without stopping while looking for a parking space, I have to hit the clutch as I slow down or else it'll buck terribly once I hit the gas again, like an old worn out 1970s Alfa Romeo.
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Old 06-23-2016, 08:34 PM   #5
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Default Re: Engine rocking excessively between on and off throttle while moving in gear

Check the throttle cable, make sure its housing is firmly anchored at both ends (firewall and TB).
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Old 06-25-2016, 12:35 AM   #6
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Quote:
Originally Posted by billr View Post
Check the throttle cable, make sure its housing is firmly anchored at both ends (firewall and TB).
I checked it, it's solid.

Perhaps I can try to take a video to better explain it in case my explanation is confusing.
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Old 06-25-2016, 10:34 AM   #7
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Default Re: Engine rocking excessively between on and off throttle while moving in gear

I think I understand what you are describing. Is there any indication of the TPS signal bouncing around during these episodes?

Just four easy-to-reach screws to remove the hood? Yeah, I still think taking a peek at things while it is happening could save you a lot of guessing here.

PS: don't sprain your neck trying to look from out the window, just mount a little flag on the engine that sticks up high enough to easily see through the windshield; see how its motion changes during the bucking.
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Old 06-25-2016, 10:51 AM   #8
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1998 SC2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Sounds suspiciously like a hesitation on throttle position change. If the throttle is full closed and then this happens when it is cracked open that is a tip in hesitation and not engine/transmission mounts.

Before rushing off to start playing with sensors the ignition system must be letter perfect and the exhaust completely leak tight, soap bubble test is required to demonstrate this.
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Old 06-25-2016, 11:30 AM   #9
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2007 ION-2 Quad Coupe
Default Re: Engine rocking excessively between on and off throttle while moving in gear

You probably have a bad top right engine mount a.k.a. "torque angle mount" or "TAM" for short. Park your car on a level surface, shut the engine off and leave the transmission in first gear. Don't engage the park prake. Then pop the hood and rock the car back and forth. You'll see the engine move excessively as you rock the car if you have a bad mount.

There are two designs of this mount available. The frowny mount and the solid mount. You want the solid one. See the linked pictures below.

Frowny mount (what you DON'T want)


Solid mount (what you DO want)


The general consensus is that the OEM solid mount is best (p/n 21012185), but it costs a lot more than a solid aftermarket mount (~$90 vs ~$20). Personally, I don't feel the OEM mount is worth the extra cost, but YMMV. There are many threads discussing this mount so do a search and read for yourself so you can make an informed decision.
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Last edited by ruley73; 06-25-2016 at 11:36 AM.
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Old 06-25-2016, 10:34 PM   #10
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Quote:
Originally Posted by billr View Post
I think I understand what you are describing. Is there any indication of the TPS signal bouncing around during these episodes?

Just four easy-to-reach screws to remove the hood? Yeah, I still think taking a peek at things while it is happening could save you a lot of guessing here.

PS: don't sprain your neck trying to look from out the window, just mount a little flag on the engine that sticks up high enough to easily see through the windshield; see how its motion changes during the bucking.
I don't have a scan tool to check the TPS signal, however it doesn't do it when not in gear. It also doesn't do it as I'm engaging the clutch. Regardless of whether I start engaging the clutch before or after I touch the throttle, it doesn't do it then. Or, to make it easier, I should say it only does it in gear with the engine fully engaged to the transmission. Also, if my shifting is a little off, as in not so smooth, the jerk is exacerbated by what feels like excessive drivetrain or engine movement.

Hood removal requires an extra set of arms, which I never have. I live out in BFE and no one ever comes to see me. Except tomorrow, maybe. If so I'll see about giving the visual a try. Interesting idea with the flag.

Quote:
Originally Posted by OldNuc View Post
Sounds suspiciously like a hesitation on throttle position change. If the throttle is full closed and then this happens when it is cracked open that is a tip in hesitation and not engine/transmission mounts.

Before rushing off to start playing with sensors the ignition system must be letter perfect and the exhaust completely leak tight, soap bubble test is required to demonstrate this.
It's not universally on throttle position change. Only when solidly in gear. I have a very small exhaust leak at a fold at the edge of catalytic converter towards it's rear passenger side, but it was doing bounce/rocking/jerk this long before it developed the leak.

Quote:
Originally Posted by ruley73 View Post
You probably have a bad top right engine mount a.k.a. "torque angle mount" or "TAM" for short. Park your car on a level surface, shut the engine off and leave the transmission in first gear. Don't engage the park prake. Then pop the hood and rock the car back and forth. You'll see the engine move excessively as you rock the car if you have a bad mount.

There are two designs of this mount available. The frowny mount and the solid mount. You want the solid one. See the linked pictures below...
I'm familiar with the mounts having done all of mine previously. I'll try the in-gear rocking, and I may pull the upper mount to have a look for damage to the damper material.

Thanks for all your suggestions guys. I'll report back shortly.
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Old 06-25-2016, 11:51 PM   #11
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

I don't know if there's an official way to upload videos on this board so I just put it on Vimeo. Here's the link: https://vimeo.com/172265282

It's in 1st gear, in my garage, not on a slant but I think this gets the idea across pretty good. I don't think the car is supposed to move that much? Also, the airbox is missing a screw or two on the bottom so it moves more than it should. And as the video description says, that "squash" sound is from the half full gas tank sloshing around.

Let me know what you guys think.
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Old 06-25-2016, 11:53 PM   #12
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1998 SC2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

You have failed dogbone mounts.
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Old 06-26-2016, 12:40 AM   #13
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Quote:
Originally Posted by OldNuc View Post
You have failed dogbone mounts.
As I said in the second paragraph of my original post, I replaced the dogbone mounts with new ones in June of last year. At that time, replacing them made no difference in the issues as described. It was exactly the same with the new mounts. Now, a year later, the issue has been getting worse.
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Old 06-26-2016, 12:49 AM   #14
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1998 SC2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Have you replaced the transmission mount?

Have you actually inspected the dogbone struts?
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Old 06-26-2016, 01:13 AM   #15
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

I replaced the transmission mount about 15k miles ago (though 15k miles was also 10 years ago).

I inspected the dogbones pretty good when I installed them. They're the second gen version that basically looks like flat iron wrapped around some bushings where my original dogbones were quite different in design and looked much stronger. I've checked them since then they look fine. I could take them out and have a closer look, but I doubt there's anything wrong with them because changing them out a year ago made zero difference in the rocking movement.
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Old 06-26-2016, 11:07 AM   #16
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Default Re: Engine rocking excessively between on and off throttle while moving in gear

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Originally Posted by DrvLikHell View Post
I replaced the transmission mount about 10 years ago).
Age is a factor. It warrants inspect/replacement.
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Old 06-26-2016, 01:28 PM   #17
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1998 SC2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

If that is a 10 year old aftermarket transmission mount then it is likely shot.
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Old 09-11-2016, 03:53 PM   #18
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

I replaced the transmission mount with a Westar and while it transmits much more engine vibration through the car, it stopped 90% of the bouncing. I inspected the old mount and the rubber had started to separate from the metal bottom plate.

However, while the car was up on jack stands I took a closer look at the axle/transmission movement and there is a lot of play from inside the transmission. With the car off the ground and in first gear, the wheels will move forward and backward together about an inch or two. Most of this movement comes from inside the transmission and I can hear it clicking in there as I rotate the wheels back and forth. There is also a small bit of play from the interior joint on the passenger side axle. There's likely nothing I can do about the play in the transmission except to replace/rebuild it and the play in the axle is only 15%, or less, of the total play. So I guess that's as good as it gets for now.

I also ordered a new top engine mount from Westar just because the current one is an aftermarket mount and it's 12 years old.
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Old 09-11-2016, 04:48 PM   #19
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1999 SC2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

Just replaced all my mounts, minus the load bearing tranny mount, with performance replacements. Motor doesn't move at all when playing the throttle, and doesn't move much when in first gear, also doesn't flop around anymore when letting off the gas, or from a bad clutch drop.
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Old 09-16-2016, 02:23 PM   #20
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1996 SL2
Default Re: Engine rocking excessively between on and off throttle while moving in gear

I should probably change the title of this thread since I've got the engine pretty solidly in place now with the new mounts. But I don't think titles can be changed.

Now it's just that the car rocks back and forth while in gear because of play in the axles/transmission.
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