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Slight jerk when releasing acceleration


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Bertimus

Got my 88 back from an extensive tune-up a week ago, haven't really had a chance to drive it until today. On the freeway at higher speeds (70+ mph), I noticed it would very slighty jerk when releasing the acceleration. It accelerates perfectly, the jerk only happens when going from acceleration to coasting. Any thoughts would be greatly appreciated 🙏🏽

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Danpatters583

Im having the same issue. It flashed the engine light at me once. I checked the codes and it is complaining about the vehicle speed Circuit. So im guessing it has something to do with the vehicle speed sensor. I can't confirm yet. I haven't had a chance to look at it. 

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Bertimus

I will be taking it to a mechanic on Friday, I will post updates!

Edited by Bertimus
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Danpatters583

Sweet! Let me know what they say. 

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Ronnie

I wonder if it could be caused by a worn engine strut commonly called the Dog Bone? It helps control the rocking back and forth of the engine. It is common for the rubber bushings in it to wear out allowing the engine to move more than it should.

 

Here is a photo if it. It is mounted between the engine and the radiator support.

 

31Mdix3KnGL._AC_UL320_.jpg

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2seater

In addition to the aforementioned dog bone, is it the TCC unlocking? It can be monitored in diagnostics.

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Bertimus

@Ronniei will definitely mention to the mechanic, thanks!

 

@2seater, how does one monitor it in the diagnostics?

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2seater

Okay touch screen guys, can you answer Bertimus question? I know there is a screen that shows the TCC indication but I am not a regular user.

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Ronnie
10 hours ago, Bertimus said:

how does one monitor it in the diagnostics?

Start the engine and make sure it is up to normal operating temperature.

 

Enter diagnostics. Wait for any codes to be displayed. Then select ECM when asked. The photo below shows the ECM diagnostic screen. While driving watch the triangle over TCC in the bottom left corner. The triangle will illuminate when the ECM is calling for the TCC to lock and go off when it unlocks.

 

 

diagnostics_book-12.jpg

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Bertimus
1 hour ago, Ronnie said:

Start the engine and make sure it is up to normal operating temperature.

 

Enter diagnostics. Wait for any codes to be displayed. Then select ECM when asked. The photo below shows the ECM diagnostic screen. While driving watch the triangle over TCC in the bottom left corner. The triangle will illuminate when the ECM is calling for the TCC to lock and go off when it unlocks.

 

 

diagnostics_book-12.jpg

Awesome! I do not get any codes though, no issues are detected so far

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2seater

Thanks Ronnie👍
 

The TCC should unlock when you lift off the throttle, no matter the speed. It does so because the ECM thinks you might be braking next. It will re engage immediately upon reapplying throttle above a certain threshold. 

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Bertimus

I will try that as soon as I get a chance! 

 

But I made an interesting observation today:

 

The slight jerk very much seems to only happen when the road is level or on a decline. I did not notice it on inclines. And like before, it doesn't not happen at all at slower speeds.

Edited by Bertimus
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2seater
8 hours ago, Bertimus said:

 

But I made an interesting observation today:

 

The slight jerk very much seems to only happen when the road is level or on a decline. I did not notice it on inclines. And like before, it doesn't not happen at all at slower speeds.

Analytical mind at work🙂  That does lend support for the engine/trans moving around. Has your mechanic checked the drive axles for play? Usually axle issues give a noise or vibration indication and are generally very reliable, so just a question at this point.

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Nittany

Bertimus - I will share what works for me:  drive your Reatta in Drive not Overdrive!!  Think about it ... GM added an overdrive which works great at saving fuel when driven at 55 - 60 mph over great distances.  That should be the only time that we use OD, the rest of the time the Reatta was designed and engineered to operate in Drive!

 

I could be wrong (I often am wrong according to my wife!) but most drive ability issues fade into the sunset when we use the transmission as designed!!  

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Bertimus
4 hours ago, 2seater said:

Analytical mind at work🙂  That does lend support for the engine/trans moving around. Has your mechanic checked the drive axles for play? Usually axle issues give a noise or vibration indication and are generally very reliable, so just a question at this point.

@Ronniedid mention that the rubber bushings in the engine struts (aka dogbones) are prone to wear, causing rocking. Haven't seen my mechanic yet, that will be on Friday, I'll will keep you guys updated!

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Ronnie

Nittany is right about putting the transmission in Drive to avoid so much locking and unlocking of the converter.  I dislike lockup converters for my style of driving in my Reatta. Most of my driving is through curvy mountain roads and rarely on the interstate.

 

I dislike the locking and unlocking of the converter as slow speeds so much that I put a switch under the dash that turns the TCC lockup off. That causes a code E039 in diagnostics but it doesn't display a warning on the dash and it doesn't effect how the transmission shifts. If I do drive on the interstate I flip the switch and the TCC operates normally.

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Bertimus
36 minutes ago, Nittany said:

Bertimus - I will share what works for me:  drive your Reatta in Drive not Overdrive!!  Think about it ... GM added an overdrive which works great at saving fuel when driven at 55 - 60 mph over great distances.  That should be the only time that we use OD, the rest of the time the Reatta was designed and engineered to operate in Drive!

 

I could be wrong (I often am wrong according to my wife!) but most drive ability issues fade into the sunset when we use the transmission as designed!!  

@Nittany, I have the same mindset as you, I usually have her exclusively on drive! So this jerking motion happens in drive, I'm pretty sure in overdrive as well, I will check that as well!

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Ronnie

It's easy to check to see of the dogbone or something in the driveline is causing the problem. Just start the engine and put your foot on the brake in the driveway. Shift the transmission back and forth between drive and reverse. Listen to see if you hear a clunk.

 

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2seater

Loosely related but if you are having changes made to your Prom, such as fan settings, you can also modify the lockup settings. My present chip will only engage the converter clutch above 55mph

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  • 3 weeks later...
Bertimus

Checked out the engine struts and mounts. They were okay. The car was lifted and revealed that the transmission was worked on/upgraded by a previous owner. Thicker/stiffer springs are most likely the culprit of the slight jerk. Totally normal and harmless as far as one can tell.

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