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Discussion Starter · #1 · (Edited)
I have a 2010 Mazda3 Touring with 250miles. I noticed that the 5th gear grinds on high gear.

Heres what happens; going 80mph, i take it out of 5th gear and put it in neutral,wait till the RPM goes back to 1k , I then step on the clutch all the way and shift into 5th gear -this is when i get the grind.

I have had this problem on old cars where the syncros failed, but i find it hard to believe that that is the case on this brand new car.

Anyone other Mazda3 owner experience this problem?

Can you test the same scenario i provided above and post back your finding
 

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Couple of diagnostic questions for you:

1) Just driving and shifting normally, getting onto a freeway, when you shift 4th to 5th and then cruise, is there any noise from the tranny?

2) Just double checking, you have the 2,0L and 5-speed manual, right?

3) I'm not sure why you would take it out gear and then put it back in, but whatever, when you do that, are you first matching the revs? Meaning you note what the rpms in 5th (let's just say it's 2,500 rpm), put it into neutral, let clutch out, push clutch in, bring engine rpm back up to 2,500 (matching revs) and then engage 5th again?

4) You're saying "Grind". You mean the actual grinding sound of gear teeth not engaging? Like the sound it makes when you try to start a car with the engine already running--that horrible gnashing grinding of the starter teeth grinding on the flywheel. That kind of grinding sound?
 

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Let me explain something about manual transmissions if I may. I'm old enough that when I started racing back in the 70's racing trans usually didn't have synchros. So you had to double clutch and rev match or the box wouldn't go into gear. Because of that training, I'm very easy on trannys and don't put much wear on the synchros--I automatically do their work for them.

Synchros are designed to spin gears up or down in speed to match revs and save the gear teeth/dogs. When you upshift, the engine drops in revs and you will engage the next gear at a lower speed then the one you shifted up from. The synchros compensate for this by changing the gear sets speed.

When you downshift, you will engage the next gear at a higher rpm then you when you shifted out of gear. Here, the synchros really work hard as they spin the next gear set up in rpm in just a second or so.

This is why "speed shifting" or slamming the gear shift through the gears as fast as you can (with or without the clutch) is so hard on trannys--you're forcing the synchros past their long term design duty cycle. It's fine to make fast shifts when you're playing--now and then. Do it all the time, and you'll be rebuilding the trans much earlier than you want to.

Assuming you've got a 5-speed, the transmission is designed to synchronize the upshifts from 1-2, 2-3, 3-4, and 4-5. It's also designed to synch on downshifts from 5-4, 4-3, 3-2, and 2-1. Note that there is no UPSHIFT into first, and there is no DOWNSHIFT into 5th--this never occurs.

However, if you are shifting from 5th into neutral (thus dropping the engine revs), and then back into 5th without rev matching (with the engine revving higher than the state you're leaving), you are essentially DOWNSHIFTING into 5th gear. And of course in a 5-speed, that's impossible, there's no higher gear to down shift into 5th from of course.

If this is the case, you are asking the transmission to do something it was never designed to do, and then it could very well make noise and damage itself.
 

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Discussion Starter · #4 · (Edited)
Couple of diagnostic questions for you:

1) Just driving and shifting normally, getting onto a freeway, when you shift 4th to 5th and then cruise, is there any noise from the tranny?

2) Just double checking, you have the 2,0L and 5-speed manual, right?

3) I'm not sure why you would take it out gear and then put it back in, but whatever, when you do that, are you first matching the revs? Meaning you note what the rpms in 5th (let's just say it's 2,500 rpm), put it into neutral, let clutch out, push clutch in, bring engine rpm back up to 2,500 (matching revs) and then engage 5th again?

4) You're saying "Grind". You mean the actual grinding sound of gear teeth not engaging? Like the sound it makes when you try to start a car with the engine already running--that horrible gnashing grinding of the starter teeth grinding on the flywheel. That kind of grinding sound?

1. No

2. Yes

3. Sample: on long downhill freeway, i take it out of gear to 'glide'. No, i do not match the rev. I dont think thats normal in driving a stick -especially going at high speed. If so, does that mean i would have to do the same on all the other gears when shifting out of it.

If you have'nt shifted out of 5th gear on high speed before, the rpm usually picks up as you release the clutch -therefore no need to "rev match"

4. Yes the 'Grind' is the actual grinding sound of gear teeth not engaging. So i shift trough the grind to get into 5th while pressing on the clutch.
 

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Don't shift into neutral from 5th while coasting at speed. The owners manual should even warn you against coasting in neutral. I don't know of any transmission that is designed to downshift into its highest gear. You will destroy the tranny rather quickly doing this.
 

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Discussion Starter · #6 ·
Don't shift into neutral from 5th while coasting at speed. The owners manual should even warn you against coasting in neutral. I don't know of any transmission that is designed to downshift into its highest gear. You will destroy the tranny rather quickly doing this.
nothing in the 2010 Mazda3 manual mentions anything about coasting in neutral -i think its because this is the sole reason why modern gearboxes are also called Synchronized transmission. The synchro will correctly match the speed of the shaft rotation to that of the speed of the gears prior to the "teeth" locking into place.

At least thats what i got from doing a Wiki on "Manual transmission" or "Synchronized transmission"

From what i gather, any "Transmission Grinding" while you have the clutch engaged is not the norm -regardless of the speed.
 

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Neutral Situation!

OK, First the manual does not say anything about going into neutral on a downhill, actually its quite ok do so. It keeps your RPMs down and there is no problem with resyncing the transmision. Although I have done it a couple of times with a couple of my cars I dont really like to because sometimes you have to find the right gear for the right speed as you slow down, thats the only real problem. Second the Manual says, quote, unquote.. Never turn your engine off as your coasting because this can cause damage to your engine and transmission. See theres a difference between going into neutral and shutting your engine off! :eek:hsnap 1:
 

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edangs

Hey I tried your scenario with my 3s at 80 and 85 mph and looks like theres no problem with mine?
 

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I said the manual should say, not that it did say.

If you are coasting downhill at 60 mph, the output shaft of the transmission is spinning at high rpm--this shaft is mechanically connected to the rear axle, and it's rpm is exactly proportionate to the vehicle speed. The output shaft is spinning at high rpm, which means the output shaft's fixed gears are also spinning at high rpm.

If you shift the engine into neutral, the engine rpm drops off toward idle and the transmission input shaft drops to low rpm. So you now have have the input shaft spinning slowly, and the output shaft spinning quickly.

If you now drop the trans back into 5th gear, the synchro cones have to engage and rapidly spin the input shaft up to match the output shaft's speed--exactly what happens when you are downshifting. So you are literally downshifting into top gear, which is not a normal operating parameter.

It's your car, do what you want to do. I'm just telling you that my experience, which includes re-building and modifying dozens and dozens of street and racing transmissions (both synchro and non-synchro as well as motorcycle dog cog transmissions) over the years, this is not something I would recommend doing.

Two other points to consider. JadeButterfly is technically correct, under some circumstances, you can actually burn more fuel in neutral then you would if you left it in gear. That's because your ECU is programmed to shut the fuel flow off to the engine when it senses parameters (such as high intake manifold vacuum, closed throttle, and vehicle speed). This means you are burning zero fuel, and your engine is helping to brake your car.

If you shift to neutral, your ECU has to continue to inject fuel into the engine to keep it running, literally burning more fuel than leaving it in gear. You also have no engine braking, meaning you have to use the brakes more, increasing brake wear.
 

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Well if one 2010 is making this noise and another isn't then something isn't quite right with one of them, so it's worth having the dealer look at it just to make sure everything is ok. Jade and ntechnic are also correct, you will burn more fuel than if you were to leave it in gear. Either way its not something one should practice regularly, as transmissions aren't really designed to be taken out of one gear and then put back in that same gear (see ntechnics through explanation). Besides that it is actually illegal to do as you don't have full control over your vehicle (if you were to do this during a drivers license test you would automatically fail).
 

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Master of the 6th Spd
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True

Ntechnic, after reading your discussion, I do agree about some of the stuff. Newer cars do seem to use the ECU to gather data of the car in motion and therefore try to adjust to all parameters. Technology has changed alot since I have started driving. I was taught to coast down hills in cars.. since my parents taught me and that they said it saves fuel. In that day, and I am wondering, did the cars back then use the same settings in their ECU's? Just Curious. Yes your point is very valid as I noticed that my MZ3 when in Gear tried to maintain a certain speed while in a certain gear. If your car is in gear it is easier to engine brake, which I am big fan of using or believing in. The Newer ECU's in cars I believe are programmed to control the cars system more than they were before. :mellow 1:
 

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Mazda Knight3:

The changes in ECU's over the last ten years are unbelievable! Basically, the ECU of a 2010 car compared to a model year 2000 is like comparing a quad-core 3 ghz computer to an old Pentium III. The processing power and speed of current ECU's allows the engineers to do things that were unthinkable 10 years ago.

The primary areas of change are in fuel control and ignition timing. Every possible BTU is wrung out of every droplet of fuel, with timing much closer to the ragged edge than was ever possible.

One of the things most ECU's (including ours) do, is actually cut off all fuel under certain conditions, like coasting down a hill.

The most exciting thing that modern ECU's help bring about is direct injection. Injecting fuel at extremely high pressure directly into the combustion chamber creates very large increases in horsepower AND improved fuel mileage. When Mazda moves our non-turbo cars to direct injection (and they will in the next few years), you will see 2.5L Mazdas putting out 200 hp AND get a couple of more mpg. Now that's exciting to me!
 

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Master of the 6th Spd
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I can hardly wait! Which reminds me, I had a thought, is the 6 spd tranny the same from the Mzspd3? IF it is, does that mean the turbo engine can be dropped into our 2010's if we wanted to?
 

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According to the salesman who sold me my mazda: Yes. BUT I dont know if he was serious or just saying that? But i'd imagine it would seeing its pretty much the same engine just stroked up to a 2.5. Thats just IMO! (Id totally do that BTW)
 

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I have learned that since I did the car salesperson job before, that alot of salespeople dont really know that much about the car. Only the few and very rare do! Usually its the ones who are more interested in cars or the product really know about it. So alot of times I found that I couldnt rely on the salesperson. But logic would dictate that if they were using the 6spd tranny, wouldnt it be easier to install the one they already made from the MZSPD3? Now if only I could find that turbo engine for cheap, lol! :shuriken:
 

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Discussion Starter · #19 ·
Im glad this thread has excellent contributors.


But I just came back from the dealer.

apparently, there is something wrong with the car. the dealer tested the same scenario with another similar car and could not replacate the problem.

I then test drove my car with the service director to confirm the problem.

He will file the report to mazdausa as this is a 2010 model and mechanics arent yet certified to open the transmission and considering the car only has 600miles.

So I will see what MazdaUSA will say, i'll post an update.
 

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sux bro... hopefully it works out yea? But how the hell are they not certified to open the tranny? shyyt... just give you a new one dammit! Cheap bastards!
 
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