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Shudder when downshifting and whine at 65 mph.

zanethan

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#1
So a new phenomenon has started occurring on my '15 ST with about 5500 miles. No mods.

When downshifting the car will shudder briefly after I release the clutch if I don't rev match (downshifting to slow down). It typically takes about a full second after I've released the clutch before I feel the shudder. Also, it shuddered once with the clutch pedal pressed in when I shifted to first. Any thoughts to this? Slave cylinder going bad maybe?

Additionally there is a whine at roughly 65 mph (63-67). It's only at this speed. It's been doing this for a while and I was wondering if it was normal gear whine, or if it could be the output bearing issue several others have had.
 


Intuit

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#2
Questions first, opinion second.

Address Questions:
Check the condition of all motor/trans mounts. Unfortunately a visual inspection may not find anything unless they're first removed. There's kind of a transition period between when the engine goes from injector-off to idle. I haven't experienced it with this vehicle, but those I've driven in the past, it is a noticeable shift... which incidentally, can feel like a shift.

Does the noise change depending upon:
the roadway, engine load, vehicle weight shift, or brake application?

Opinion:
Brakes are designed to slow and stop the vehicle. Use them instead. Unless you are going down a very long hill or mountain and are attempting to keep from overheating the brakes, it is unnecessary to use the clutch to slow down the vehicle. You are placing undue wear on the clutch components, engine, CV components and transmission. Brakes on the other hand are designed for the purpose of stopping the vehicle, and are much cheaper to maintain over the long run. Limited use of engine braking is something that can be debated for multi-ton loads but not for passenger vehicles. We are in a valley meaning, if you're not going down a hill, it is because you're going up one. I witness people riding their brakes for as long as a minute down hills all the time. This is bad. Even riding behind these people, I usually don't find it necessary to apply my brakes for more than a few seconds at a time. An infrared temperature reader at the bottom of the hill would probably confirm that their brakes are blazing hot while mine are only warm. There are racing fundamentals that foster the idea of always staying in a gear. We're of course not racing though.
 


Quisp

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#3
Does it bump forwards when in gear with clutch depressed? Mine did this before clutch slave failed. Felt like someone tapping my bumper gently with their car when I was stopped.
 


OP
zanethan

zanethan

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Location
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Thread Starter #4
Questions first, opinion second.

Address Questions:
Check the condition of all motor/trans mounts. Unfortunately a visual inspection may not find anything unless they're first removed. There's kind of a transition period between when the engine goes from injector-off to idle. I haven't experienced it with this vehicle, but those I've driven in the past, it is a noticeable shift... which incidentally, can feel like a shift.

Does the noise change depending upon:
the roadway, engine load, vehicle weight shift, or brake application?
I had considered the rear motor mount as it's a weak link in our cars. As far as the injector-off to idle I'm not sure that would be it as the shudder occurs after the engine speed is back up. So it would be shutting off injectors at higher than idle RPMs.

The noise does seem to change with roadways but I'm unsure if that's just due to road noise covering up the whine. It's pretty consistent in all other regards.

I did do some digging on this and typically do use brakes but occasionally I downshift if I know I'll need to slow down just a few (5-10 mph) and don't want to lug the engine by staying in a higher gear. Basically I'm braking and downshifting at the same time to match the ideal engine speed for my decreasing actual speed if that makes sense. At any rate I agree that brakes are cheaper to maintain so I'll alter my driving style but this wasn't occurring until now so I'm thinking something's up.

Something related yesterday as well. While on the interstate:
-I down shifted to 5th to pass a semi. (Rev matched and no issues).
-Passed the truck and up shifted to 6th.
-After about a full 2 seconds after shifting to 6th (Foot completely off the clutch) the car shudders while accelerating in 6th.
I tried to duplicate it again but was unable to do so. I should also note that the road was wet when this occurred.

I've been driving manuals for over a decade (not saying I'm a pro but I have a decent amount of experience) at this point and have never felt a vehicle shudder like this.
 


OP
zanethan

zanethan

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Thread Starter #5
Does it bump forwards when in gear with clutch depressed? Mine did this before clutch slave failed. Felt like someone tapping my bumper gently with their car when I was stopped.
Yes it bumped forward but I have been unable to reproduce it. It's only happened once.
 


Quisp

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#6
Mine failed a couple thousand miles after engine replacement. Started out with not disengaging fully than failed completely while in traffic. A bitch getting it through 2 miles of traffic.
 




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