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What might cause a car with a manual transmission that in 5th gear when given a punch of gas revs to very high rpms – with no power transferred to the wheels (i.e. the tachometer and speed go out of sync).

For illustration (and I'm making these numbers up), at around 2000 rpm on the tachometer, and going 60km/h "punching" the gas causes the tachometer to hit 4500 rpm yet the speed remains at 60km/h.

I would expect the revs to remain at a constant ratio to the speed, so I'm wondering what might be going wrong.

My first suspicion is a problem with the clutch, but I was wondering how I may test this or suggestions as to what else it may be.

The car I'm thinking of in question has only around 27,000 km on it, which seems like a very short lifespan for a clutch!

Thanks for reading, appreciate any insight.

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2 Answers 2

up vote 9 down vote accepted

It sounds like the clutch is worn out... You can usually tell by gradually applying the gas in the top gear, probably around 2,500 RPM, and the car should accelerate a little bit, but at some point as you press the gas further and further down, you will feel it release and the revolutions will shoot way up without road speed increasing.

It basically feels like you have pressed in the clutch while it was accelerating...

Can it happen on a car with only 27,000km on it? Absolutely... The first car I had I destroyed the clutch, put a brand new clutch in, and that one was doing the same thing you describe after another 12,000 miles. It just depends on how the clutch is operated. One of my current cars (it's now 25 years later) we bought new and just turned over 199,000 miles on the original clutch. Obviously, I've learned a thing or two since that first car. :-)

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@Sean: Great answer, what you've described is exactly what's happening. My wife is learning to drive stick shift, and while I'm proud of her for learning it, I wasn't terribly surprised to see the clutch go. ;) I'm glad it's not something more serious, like a diff or gearbox. –  Brian M. Hunt Mar 29 '11 at 2:27
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@BrianMHunt I don't know whether you are a fix-it-yourself type of person, but if you are, I would recommend NOT replacing a clutch yourself. It is a multiday project, you'll want to rip your hair out by the end and you may want to smack you girlfriend's father (who is helping you change it) :-) Oh and also, make sure you get the flywheel turned. –  Patrick Apr 2 '11 at 4:03
    
@SeanReifschneider I had another thought, it might be if this is only happening in 5th gear that it is probably the transmission and not the clutch. My father's car had the 5th gear get 'spun out', where the 5th gear was worn down compared to the rest of the gears causing slippage. He took it to Honda and had just that gear replaced for much less than a new transmission. –  Patrick Apr 21 '11 at 14:13
    
@Patrick, did that grind when it was happening? With the clutch slipping, there's really no unusual noise. –  Sean Reifschneider Apr 26 '11 at 16:48
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@Patrick: Higher gears are more susceptible to clutch slipping because there is more resistance to acceleration. When a clutch slips, you have passed the maximum amount of torque that can be transferred through it. In lower gears, less torque needs to be applied through the clutch to make the car accelerate. –  qes Jun 10 '11 at 23:21

If no power is transfered at all, the gear box is probably broken.

If any some is transfered (and there are no noisy metallic sounds :), it's probably the clutch. There should'n really be anything else that can slide.

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