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Power loss at 4th gear and 6000+ RPMS

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Old 08-29-2008 | 12:30 PM
  #1  
juanjux's Avatar
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From: Madrid, Spain
Power loss at 4th gear and 6000+ RPMS

Hi,

Today I've just noticed that my car can't go past 6500 RPMs in 4th gear. In all the other gears it goes smoothly until the engine cut at 9000 but in 4th gear it goes well until these RPMS and then it starts to do an ugly noise, like when the chain of a bicicle is going bad.

What could be the problem? If this was some engine, clutch or cat problem it should happen on all gears (I think.)

Last edited by juanjux; 08-29-2008 at 12:33 PM.
Old 08-29-2008 | 01:10 PM
  #2  
rotary.enthusiast's Avatar
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This really doesn't make too much sense to me. This is the only theory I can come up with at the moment, and it's not a very good one I don't think: If the clutch is on the way out, then it might start slipping at high load. The renesis torque peak is right around 6500 RPM, and in 4th gear there is more internal load on the transmission than in lower gears, so maybe this is when it first starts exhibiting the behavior.

To test it you could try putting the car on stands and see if it behaves in the same fashion (with no load on the wheels it shouldn't slip). Another thing you could do is floor it at highway speed in 6th gear... I would think you'd see clutch slipping even at lower RPM in 6th.

Answering these questions might be helpful in receiving an answer: How many miles on the clutch? When was the last time you checked/changed the transmission fluid? When was the last time you checked/change the brake/clutch fluid? What type of fluid was used in both cases? What year is your car? Any previous problems with the transmission before this?
Old 08-29-2008 | 01:24 PM
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I don't think is the clutch. Is doesn't slip (the revs doesn't go up without accelerating) and I don't detect any funny smell like the last time I changed it.

The asnswer to your questions:

It's a 2004 RX-8 with 40K miles.

The clutch has 10.000K miles.

The transmission fluid was changed one year ago (see below the last answer.)

No idea when the last time Mazda changed the brake/clutch fluid. I do the mainteinance on my Mazda dealer, on monday when I call them about the problem I'll ask. The type if problably what Mazda usually use.

I had problems with the transmission just a year ago. The fifth gear was broken and it was replace along with a lot other related transmission parts (under warranty). The sintoms were totally different too, I could not engage the fifth gear at high revs, but if I engaged it at low revs and accelerated it worked; in this case I don't have any problem changing to 4th gear from high revs but I can't go up from 6500RPMS.
Old 08-29-2008 | 01:50 PM
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rotary.enthusiast's Avatar
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From: Big D, Texas
Interesting. Well I hope it's still under warranty

I really can't think of anything that would cause what you're describing... sorry
Old 08-29-2008 | 04:23 PM
  #5  
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From: Planet Earth
This tranny suck, I wouldn't be surprise if they have to replace your tranny.
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