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Thud when pressing accelerator

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prwood
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prwood

Re: Thud when pressing accelerator

Post by prwood » Tue May 21, 2019 7:21 am

Yesterday I managed to film a bit of footage while driving where you can actually hear the sound several times. I had the camera aimed at the instrument cluster so you can see the vehicle speed and RPM in case that's relevant. The video was shot while in stop-and-go city traffic.

In the video, I was narrating whenever the sound occurred, except for the very first time which occurs just after the video starts.

[youtube][/youtube]

Since my videos of the mounts themselves don't seem to point to any issues with them, and since I couldn't actually duplicate the sound while parked, I'm hoping this live recording will be more useful for diagnostic purposes.

The occurrence of the "thud" and the degree of severity seems to depend on engine speed, vehicle speed, and how the accelerator pedal is pressed. If I were to give "steps to reproduce the condition," it would be something like this:

1. Set transmission to Drive.
2. Press accelerator.
3. Accelerate to 10-15 mph.
4. Release accelerator.
5. Allow car to coast at 10-15 mph and allow RPM to drop to 750.
6. Apply moderate pressure to the accelerator. RPM should jump from 750 to ~1500-2000 with < 5 mph change in speed.
7. "Thud" should occur.

Note: In step 6, if very light pressure is applied, RPM increases more slowly and no "thud" occurs. If heavy pressure is applied, RPM and speed both increase quickly and no "thud" occurs. When the issue does occur, my observation is that the RPM has increased at a higher rate than the vehicle speed.

Thinking through this logically, if the engine speed increases without an immediate corresponding increase in wheel speed, there must be an issue with something between the engine and the wheels, aka the transmission and drivetrain:
- Torque converter?
- Transmission fluid?
- Gearbox?
- Driveshafts?

Not sure what to check next.


Cars I've owned:
- 2015 to current: 2001 Volvo V70 2.4T
- 2007 to 2015: 2002 Subaru Legacy L Wagon
- 2003 to 2016: 2001 Toyota Corolla LE
- 1999 to 2003: 1994 Toyota Camry LE

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abscate
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Re: Thud when pressing accelerator

Post by abscate » Tue May 21, 2019 8:14 am

The torque converter is the item that lets engine speed and tranmission/vehicle speed vary, so I think your intuition is on track about that being the part to explore.

Its pretty subtle. I hate saying this, but you might have to wait for it to get worse.


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Re: Thud when pressing accelerator

Post by gcha8e » Tue May 21, 2019 8:53 am

In order to rule out engine block movement as the issue here's a cheesy idea. Eliminate all the play in the upper mount. My method would be to jam a piece of rubber or two in the space(s) between the rubber bushing and the mount. A utility knife and a hack job on the sole of an old flip flop or shoe sole would do the job. (any chunk of stuff). Im not sure how firmly the engine should or could be secured this way, or if that is wise, but you seem determined to nail this down! :D

Other thoughts, sorry if some of these were covered:
does the issue occur at any and all engine temperatures?
Is it more likely or more severe going up or down a steep hill?
The same in reverse/forward?



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prwood
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Re: Thud when pressing accelerator

Post by prwood » Tue May 21, 2019 9:12 am

abscate wrote:
Tue May 21, 2019 8:14 am
The torque converter is the item that lets engine speed and tranmission/vehicle speed vary, so I think your intuition is on track about that being the part to explore.

Its pretty subtle. I hate saying this, but you might have to wait for it to get worse.
I agree that the sound is pretty subtle. What can't be conveyed on video is the physical sensation that accompanies the sound, which is really more noticeable than the sound when I'm driving the car. If I had to describe the physical sensation, I'd say it feels like a sudden jerk at the same time the thud occurs.


Cars I've owned:
- 2015 to current: 2001 Volvo V70 2.4T
- 2007 to 2015: 2002 Subaru Legacy L Wagon
- 2003 to 2016: 2001 Toyota Corolla LE
- 1999 to 2003: 1994 Toyota Camry LE

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prwood
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Re: Thud when pressing accelerator

Post by prwood » Tue May 21, 2019 9:17 am

gcha8e wrote:
Tue May 21, 2019 8:53 am
In order to rule out engine block movement as the issue here's a cheesy idea. Eliminate all the play in the upper mount. My method would be to jam a piece of rubber or two in the space(s) between the rubber bushing and the mount. A utility knife and a hack job on the sole of an old flip flop or shoe sole would do the job. (any chunk of stuff). Im not sure how firmly the engine should or could be secured this way, or if that is wise, but you seem determined to nail this down! :D
I've been thinking about doing this. My thought was actually to get a can of Great Stuff (polyurethane spray) and spray it in there to fill all the voids. If it doesn't help, I can chip it off, it's just going to be messy.
gcha8e wrote:
Tue May 21, 2019 8:53 am
Other thoughts, sorry if some of these were covered:
does the issue occur at any and all engine temperatures?
Is it more likely or more severe going up or down a steep hill?
The same in reverse/forward?
* It seems to occur at all engine temperatures.
* It seems slightly less likely to happen going up a hill.
* I haven't found a place where I can safely drive in reverse long enough to see if it would happen. :-)
^ That reminds me, however, that I *do* get the same, or very nearly the same type of thud and jerk when I shift into reverse from park......


Cars I've owned:
- 2015 to current: 2001 Volvo V70 2.4T
- 2007 to 2015: 2002 Subaru Legacy L Wagon
- 2003 to 2016: 2001 Toyota Corolla LE
- 1999 to 2003: 1994 Toyota Camry LE

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gcha8e

Re: Thud when pressing accelerator

Post by gcha8e » Tue May 21, 2019 9:25 am

Yes, don't make a mess. Use a chunk of rubber. Drill a hole in it and secure it from falling out with a twistie tie or zip tie.



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Re: Thud when pressing accelerator

Post by mark99tj » Tue May 21, 2019 11:31 am

I had a clunk something like as well. It seemed like I would get it when accelerating and hard braking. After having a lot of noises when I got the car, I replaced all the motor mounts, and a lot of suspension parts. I kept chasing this final clunk. While I was ordering some other maintenance stuff from IPD (I mostly order from FCP, but IPD has some things that FCP does not), I ordered the Upper Engine Stabilizer Poly Bushing Kit for $11 They were super simple to install and once I did, my clunk went away. I have a very quiet car (2002 V70XC) now, with almost all the bushings and replaceable parts imaginable in the front end.



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prwood
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Re: Thud when pressing accelerator

Post by prwood » Wed May 22, 2019 8:20 am

Since I'm considering the possibility of a torque converter issue, I'm trying to get an accurate check of the transmission fluid. I've watched oragex's video:

[youtube][/youtube]

I've got the turbo engine which makes it harder to access the ATF dipstick to begin with, let alone when the engine is hot. I actually tried to get to it yesterday after I had been driving for 30 minutes as recommended, and I guess I must be a lot more skittish about getting burned because I couldn't even get close to the dipstick before I had to pull my hand away. I thought about using one of those heat resistant "ove-gloves" that we use for handling hot pans in the kitchen, but even that only goes up just past my wrist, and I have to go in nearly up to my elbow to reach the dipstick.

I *did* take a reading when the engine was cold this morning, but apparently that type of reading is unreliable. Nonetheless, here it is:
IMG_2827 copy.jpg
IMG_2827 copy.jpg (830.44 KiB) Viewed 188 times
It seems bad that the level would be up to the top "hot" line when the engine was cold, but should I disregard this reading and make another attempt to get a reading when the engine is hot? Or is this enough of an indication of a problem?


Cars I've owned:
- 2015 to current: 2001 Volvo V70 2.4T
- 2007 to 2015: 2002 Subaru Legacy L Wagon
- 2003 to 2016: 2001 Toyota Corolla LE
- 1999 to 2003: 1994 Toyota Camry LE

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Re: Thud when pressing accelerator

Post by RickHaleParker » Wed May 22, 2019 8:49 am

prwood wrote:
Wed May 22, 2019 8:20 am
It seems bad that the level would be up to the top "hot" line when the engine was cold, but should I disregard this reading and make another attempt to get a reading when the engine is hot? Or is this enough of an indication of a problem?
That could be the source of your Thud. It may be producing excess pressure, oil starvation or foaming. Overfill can damage the transmission. Correct the fluid level, at the least you can put that concern out of mind. Siphon some off with a clear hose. Then add some back if needed.


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abscate

Re: Thud when pressing accelerator

Post by abscate » Wed May 22, 2019 10:00 am

Its worth a shot, but the transmission level in the sump climbs when the engine is shut off, just like the engine.

It really needs to be checked per the procedure.

When was the last drain and fill?


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