Shutter/Vibration in 5th/6th Gear Around 40 MPH

[89Trooper]

Hey everybody! It's been a long time since I've posted.

I still have my 2015 Mustang GT - Automatic - 100% stock - about 80,000 miles.

It has developed a shutter (not sure what else to call it but you can physically feel it) when it's in 5th/6th gear going around 40 mph, especially when going up an incline.

If I get on it, everything works fine and it runs great. If I downshift with the paddle when I feel the vibration, the shutter goes away... or if I get on it a bit and it downshifts on its own, it goes away.

Anybody else experience this or any thoughts about what it could be?

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[shogun32]

when it's in 5th/6th gear going around 40 mph, especially when going up an incline.

Good God man, it should be in 4th or 3rd. Quit lugging the engine.

When was the last time the trans was flushed?

I would guess it's the lockup that is cycling and unable to reach/remain the desired state.

You've checked wheel bearings I assume. And drive shaft support bushings.

 

[89Trooper]

Tell me about it! But it's an automatic... I ain't got no control.

Now... when getting on it, of course it stays in each gear longer, but I'm talking about taking off from a light where people in front of you don't know how to move. The car goes through the gears in no time. This is nothing new and has never been an issue at all.

Trans fluid - never.

I won't turn away any suggestions, but remember, if I use the paddle to downshift at the same speed, the shutter goes away. I would think if it were the wheel bearings or the drive shaft support bushings, the problem wouldn't go away and I'd see/feel issues more often. Same with the trans fluid - wouldn't I feel problems in more gears/more speeds?

What about plugs/coils? Wouldn't problems with these be more noticeable at lower speeds/higher gears? Changing these is a piece of cake, but I didn't want to throw parts at it without getting some opinions, first.

My wife had a V6 Saturn and it had a bad coil - you'd notice it going slower but flooring it, you couldn't tell.

 

[shogun32]

Well spark plugs and fluids have a finite life. If you haven't done them per schedule do that first. You might even spot a problem when under the car. I would drop the trans pan and replace the filter while I was in there.

 

[Therealmattlex]

Mine is similar but I have the manual. If I come into a town and slow down to 40-45 to cruise through town in 6th it's fine. If I try to accelerate on the other side of town without dropping it down to 5th, I need to be extremely light on the throttle or it will do the same thing. I think it's just the load on the engine. It's never thrown a code or triggered a misfire.

 

[89Trooper]

Well spark plugs and fluids have a finite life. If you haven't done them per schedule do that first. You might even spot a problem when under the car. I would drop the trans pan and replace the filter while I was in there.

Will do! I'll start with spark plugs and trans fluid (and filter). Coils are easy enough to go back and do if the plugs don't solve the issue. I've done more research today about it, and coils seem less likely to be the issue. Thanks!

 

[89Trooper]

Mine is similar but I have the manual. If I come into a town and slow down to 40-45 to cruise through town in 6th it's fine. If I try to accelerate on the other side of town without dropping it down to 5th, I need to be extremely light on the throttle or it will do the same thing. I think it's just the load on the engine. It's never thrown a code or triggered a misfire.

Yes! It happens a lot using cruise... cruising in 6th is fine, but when it needs to pick up speed a little (using adaptive cruise) this shimmy will happen. But same with me - no code. And it isn't pre-ignition... that is more of a sound and doesn't shake the car.

 

[89Trooper]

I just remembered that these transmissions have adaptive learning and that if the battery is changed, the transmission needs to relearn its shift points. This started happening since I've last changed my battery... so worth a shot. I'll disconnect it for a few hours and let my car relearn when to shift.

I'll still try the other things soon... but this is free.

 

[89Trooper]

Here's an update: the battery disconnection was a bust (which I figured).

But this morning, it was cooler driving to work - mid 60s instead of mid 80s.

The shutter totally went away - I couldn't make it happen.

Driving home with warmer weather - the shutter is back.

So this definitely points me toward something air/fuel mixture related... and power produced at any given speed/gear.

So... spark plugs, fuel injectors, coils?, fuel filter?...

Thoughts before I start to spend some money?

 

[shogun32]

Thoughts before I start to spend some money?

fluids. And slap a computer on your OBD port and log the thing. The misbehavior will likely be very obvious.

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