Knockin/Grinding when engaging clutch quickly/jerking car/potholes
Hello,
1998 Corolla CE Manual
About two months ago, I replaced the fourth gear in my transmission, as well as the clutch disc, pressure plate, and throwout bearing. The flywheel had one spot in it that was barely within spec, but I didn't bother having it resurfaced.The car has been driving well, with the transmission being somewhat picky about what RPM's it likes to shift at in each gear.
Today I was teaching my girlfriend how to drive a stick, and (obviously) the clutch took quite a beating with many dumps and a fair amount of slipping.
After I took back over driving the car, I immediately began to notice a dull/muffled thumping/grinding coming from what sounded like the right hand drive shaft area whenever I would go over a manhole (bump.) I slowed down and drove the car around the block, and found that when I jerk the car (go from coasting to bumping the gas, or sometimes when braking) the car makes the same grinding/thumping noise, as if the engine is sliding back and forth. It does the same thing over potholes. When I go from a stop and engage the clutch quickly, it also does it. I've crawled under the car and can't find anything that seems out of the ordinary. Bouncing the car on the suspension by hand doesn't repeat the sound. My conclusion is that it must be somewhere in the drivetrain, but I am totally stumped as to what it could be. Any help greatly appreciated!
Last edited by Corolla1027; 01-05-2012 at 07:46 AM.
It could be your CV shaft. Did you check that it is still firmly seated in the transmission? Also the inner joint sometimes gets worn out and can clunk when accelerating.
Do you mean the drive shaft? I checked them both and they're still seated fine. I considered CV joints, but I just think it has to be related to the clutch somehow because it got dumped so many times. Perhaps the clutch getting dumped was impacting the joints? I've never had CV joints go out on me, but I can't imagine that they would make this much noise. Thanks for your reply.
It sounds like you could have a failed motor mount(s). The preceding events could certainly explain the cause of failure, or at least the "last straw", and your description of the symptoms fits like a glove. Inspect them all carefully for any torn rubber, or any sign of being "out of place".
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If it were a motor mount, wouldn't I be able to replicate the noise by bouncing the car up and down? Is it possible for the right hand inner CV joint to fail and make this type of noise?
Motor mounts are very hard to reproduce. The best way is via visual inspection or removing the mount and inspecting it.
I'd probably start with the motor mount first, and then look at something in the drivetrain/suspension.
The two mounts you need to look at are the front lower mount (near the radiator), and the top passenger mount.
The front lower can be inspected with a mirror and a flashlight from below the car. Check if the rubber is sagging/torn. This can be replaced by putting a jack under the engine to hold it up, and then removing the 3 bolts holding it to the frame/engine.
The top passenger mount needs to be removed to inspect it. Remove the washer fluid reservoir bolt, move the washer fluid out of the way, put a jack under the engine, and remove the 5 bolts holding it to the frame and engine. If you decide to replace this, get the mount from Toyota. The aftermarket mount usually does not fit properly.
On my car after 10 years both of these mounts were in bad shape.
If it were a motor mount, wouldn't I be able to replicate the noise by bouncing the car up and down?
No, you wouldn't. If inspecting them doesn't turn anything up, you could try applying the park brake, then torque the driveline in 1st and reverse ( carefully let out the clutch with some light throttle until it almost stalls ) while a helper watches for excessive movment on the mounts, or any other signs of trouble. Be sure your assistant stands to the SIDE in case the park brake doesn't hold, and use caution and lots of space in front and behind.
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"The thing about quotes on the Internet is you can't confirm their validity"
We tried that, but we really don't know what to look for. What is excessive movement?
Some more details:
The rattling disappears at higher speeds. When going 60, the noise is only there when tapping or releasing the accelerator.
The rattling is very prevalent when in lower gears driving around side streets (more bumps?)
The rattling is also still there at times with the clutch pedal pressed.
I took off the top passenger motor mount, but I really did not know what to look for. It's quite different than all the other mounts. The other mounts I think I will be able to tell because the rubber is visible, but this one is all inside a metal casing. The metal bolt hole where the engine attaches moves smoothly in all lateral directions with pressure. What should it feel like as far as up and down? Does anyone have a picture of what a healthy/bad one would look like?
Any other ideas?
Last edited by Corolla1027; 01-07-2012 at 10:20 AM.
This is the passenger mount. The rubber is messed up at the top, but to me it doesn't look like that affects anything. Is anyone familiar with these mounts?
Well dang! The weaknesses of e-diagnostics show once again. You describe it as a rattling this time, could it possibly be the exhaust joint gasket / swivel at the bottom of the manifold? These can rattle, squeak, etc, not so sure about the dull thud noise though. It is the correct location based on your first description. Based on the low speed = worse, it would be because the transmission and engine torque up more in lower gears, both on accell and decell. BUT, there is equally more torque on the drive axles as well, so don't rule that out either. Have you jacked up the front and tried rotating the wheels while in gear to look for play in the CV's etc?
Also, look for any signs of movement at the control arm bushings.
__________________
"The thing about quotes on the Internet is you can't confirm their validity"
Well guys,
I am totally stumped. I have the front end off the ground and cannot find anything. I've rotated the tires in and out of gear. Also started the car up, and when engaging the clutch the noise is not present like it is when it's on the ground. I'm about to throw my hands up and take it somebody. The only other thing I can think to do is replace both of the other mounts and the CV shaft, but I really doubt that either of those are the problem.
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