5th Gear Grind on High Speed of 80mph above

[edangs]

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

 

[Antonio DiMarco]

You may have a bad synchro

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 so im cruising at 80mph. 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

Bring it in. Do it now before you get any more miles on it. Just because it's new doesn't mean there isn't a defective part.

 

[xX StitcH]

There is nothing wrong with your car

There is nothing wrong with it. First, I am going to explain some stuff. Then you should read about how manual transmissions work.

That, in essence, is a 5 speed transmission. In reality there is a lot more to it than that, but this gets the point across. The yellow shaft from the differential is permanently attached to the collars (purple gears). The blue gears are on bearings so they can spin independently of the wheels spinning. The red gears and shaft (layshaft) are permanently connected. If your foot is not on the clutch, the layshaft is spinning which means the blue gears are spinning.

Lets assume a 1:1 ratio for 5th gear on the Mazda. So if you foot is not on the clutch and you engine is idling (~800 RPM), the blue gear is spinning at around 800 RPM.

Now lets find out how fast the collars are spinning at 80 mph. The diameter of a P205/50R17 is aroun 25.2". This makes the circumference 79.13". This is equal to around .001249 miles. 80 miles per hour translates to 1.3333 miles per minute. So if we take 1.3333/.001249 we end up with around 1,067 RPM. So your tire is spinning at 1067 RPM at 80 mph. Assume a final drive ratio of around 3.86:1 (the driveshaft spins 3.86 times every time the tire spins once). Therefore, 3.86*1067 = 4119 RPM. That means the yellow shaft in the picture is spinning at 4119 RPM which also means the collar is spinning that fast.

The collars engage with the blue gears by use of "dog teeth". There are "teeth" on the collars, and holes on the blue gears. In order for the teeth to go into the holes, the collar and the blue gear have to be spinning at somewhere around the same speed. Synchros help match the speeds of the two before the teeth engage, but they can only do so much.

In this case, the collar is spinning at 4119 RPM compared to the gear it is trying to match with which is spinning around 800 RPM. See why it is grinding now?

I have no idea why you would want to coast at 80mph, but if you really want to, rev the engine with your foot off the clutch before you try to go back in gear. This will speed up the blue gears which will make it easier for the gear to match up with the collar. Have you ever heard of double clutching? That is basically what it is. You needed to do it before synchros were invented because the gears would not match up with the collars if you didn't double clutch.

Let me know if I explained something poorly and I'll try to make it more clear

 

[edangs]

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.

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

 

[BlueWagon]

Update?

 

[mazdaspeedster3]

Why are you putting it in nuetral at 80 MPH? Also, try revving it when in nuetral to put it back in gear. I hate to say it but you may need a rev match.

 

[mazdadude]

Why are you putting it in nuetral at 80 MPH? Also, try revving it when in nuetral to put it back in gear. I hate to say it but you may need a rev match.

Yes, not sure why the OP would want to be coasting like that. +1 on what the others above said. Before you take it out of neutral, and put it back into 5th gear, you will have to depress the clutch for a moment longer than usual, and then blip the throttle to the appropriate RPM before trying to shift back into 5th. When you blip the throttle, you put a tiny bit of pressure on the shifter in the direction of the gear you want to go into. If the rev match is correct, the gentle pressure on the shifter combined with correct RPMS between engine and transmission will allow the shifter to just fall into the gear you are attempting to shift into.

When you get real good at rev matching, you will be able to drive the car without using the clutch except for when you are starting from a stop. (Not very good for the synchros in the MTX, but still a ton of fun driving like a race car driver!)(poke)

 

[mazdadude]

There is nothing wrong with it. First, I am going to explain some stuff. Then you should read about how manual transmissions work.

That, in essence, is a 5 speed transmission. In reality there is a lot more to it than that, but this gets the point across. The yellow shaft from the differential is permanently attached to the collars (purple gears). The blue gears are on bearings so they can spin independently of the wheels spinning. The red gears and shaft (layshaft) are permanently connected. If your foot is not on the clutch, the layshaft is spinning which means the blue gears are spinning.

Lets assume a 1:1 ratio for 5th gear on the Mazda. So if you foot is not on the clutch and you engine is idling (~800 RPM), the blue gear is spinning at around 800 RPM.

Now lets find out how fast the collars are spinning at 80 mph. The diameter of a P205/50R17 is aroun 25.2". This makes the circumference 79.13". This is equal to around .001249 miles. 80 miles per hour translates to 1.3333 miles per minute. So if we take 1.3333/.001249 we end up with around 1,067 RPM. So your tire is spinning at 1067 RPM at 80 mph. Assume a final drive ratio of around 3.86:1 (the driveshaft spins 3.86 times every time the tire spins once). Therefore, 3.86*1067 = 4119 RPM. That means the yellow shaft in the picture is spinning at 4119 RPM which also means the collar is spinning that fast.

The collars engage with the blue gears by use of "dog teeth". There are "teeth" on the collars, and holes on the blue gears. In order for the teeth to go into the holes, the collar and the blue gear have to be spinning at somewhere around the same speed. Synchros help match the speeds of the two before the teeth engage, but they can only do so much.

In this case, the collar is spinning at 4119 RPM compared to the gear it is trying to match with which is spinning around 800 RPM. See why it is grinding now?

I have no idea why you would want to coast at 80mph, but if you really want to, rev the engine with your foot off the clutch before you try to go back in gear. This will speed up the blue gears which will make it easier for the gear to match up with the collar. Have you ever heard of double clutching? That is basically what it is. You needed to do it before synchros were invented because the gears would not match up with the collars if you didn't double clutch.

Let me know if I explained something poorly and I'll try to make it more clear

BTW, XXstitch, That is a great explanation, and a great first post! Welcome to the forums!

 

[xX StitcH]

Thanks

I'm looking to buy my first new car and I have always liked Mazda 3's. So I figured I would start looking around on forums and see what everyone else thinks about these beautiful machines. I can't wait to sell my motorcycle so I can get a 2010 Hatchback

 

[edangs]

Manufacturer finally looked at the car and confirmed that the 5th gear and the synchros will need to be relpaced.

I would have preferred they replace the car, but that does not seem it will happen.

Anyone have suggestions on how i can insist on the dealer or manufacturer to replace the car?

 

[Kymerik]

you want them to replace an entire car due to a transmission issue?

Let me be the first to call you a lunatic... if everyone demanded a replacement when something went wrong with a new car, manufacturers wouldnt exist.

Just be glad they arent calling it user abuse or something and are actually fixing it for you

 

[edangs]

you want them to replace an entire car due to a transmission issue?

Let me be the first to call you a lunatic... if everyone demanded a replacement when something went wrong with a new car, manufacturers wouldnt exist.

Just be glad they arent calling it user abuse or something and are actually fixing it for you

The car is a 2010 model with 650 miles. im sure anyone would be looney if they are in my position. i just spent 20k and i have to go through this and more importantly, who knows how this tranny is now gonna be down the road.

 

[dmention7]

Asking to replace the entire car might be overkill, but I would certainly press to have the transmission replaced outright. The thought of a brand new car with a transmission that has been disassembled and put back together would give me the heebie-jeebies.

 

[BlueWagon]

As of right now, it wouldn't qualify as a lemon, so they won't replace your car, but I feel for you bro. Hard earned money and an early defect.

 

[Kuro3]

yo xx stitch, that was a fantastic explanation, did you ever do physics in school? if not, you should become a teacher or something, bro, awesome.

yeah, whenever I teach a new friend how to drive stick, I always try to explain the dynamics of how a manual transmission is put together in the first place so they know what is going on when they are stepping on each pedal. I feel this helps a lot.

great job

 

[Antonio DiMarco]

Defects happen

you want them to replace an entire car due to a transmission issue?

Let me be the first to call you a lunatic... if everyone demanded a replacement when something went wrong with a new car, manufacturers wouldnt exist.

Just be glad they arent calling it user abuse or something and are actually fixing it for you

+1

This is why you have the warranty. I had the same thing happen to my 95 Protege with 12,000 miles. They fixed it and the car drove fine until I got rid of it with over 160,000.

 

[twowings]

Let them fix the transmission....ask for a loaner car or rental car assistance.....cooperation with the dealer service department will get you a lot farther than ranting and raving.....remember the dealer didn't BUILD the car....and they only have a limited time to do a pre-sales check and can't possibly duplicate the myriad situations your vehicle might experience....document all conversations with dealer/zone rep/MazdaUSA... if they don't make it right CALMLY inform them you're sending registered letters to Mazda and your state attorney general's office to get your problem solved....
don't lose focus because of anger.

 

[Antonio DiMarco]

+10

Let them fix the transmission....ask for a loaner car or rental car assistance.....cooperation with the dealer service department will get you a lot farther than ranting and raving.....remember the dealer didn't BUILD the car....and they only have a limited time to do a pre-sales check and can't possibly duplicate the myriad situations your vehicle might experience....document all conversations with dealer/zone rep/MazdaUSA... if they don't make it right CALMLY inform them you're sending registered letters to Mazda and your state attorney general's office to get your problem solved....
don't lose focus because of anger.

Great advice. More bees with honey...

 

[edangs]

Dealer finally finished the replacement of the 5th gear and synchros and guess what...... problem is still there.

dealer is awaiting instructions from, now, MAZDAJapan.

It has been 10days and counting. 10 more days and i can file for lemon.

Any transmission specialist out there that can explain why the replacement did not resolve the problem?

 

[mazdaspeedster3]

Manufacturer finally looked at the car and confirmed that the 5th gear and the synchros will need to be relpaced.

I would have preferred they replace the car, but that does not seem it will happen.

Anyone have suggestions on how i can insist on the dealer or manufacturer to replace the car?

I think you are lucky they arent calling it abuse. Did you tell them you were putting it in neutral and then again trying to find the gear at 80 mph? No offense but that would warrant abuse. Going over the speed limit in any state in the US and in 5th when you have 6 gears. Doesnt sound like you are breaking it in much eh? Let us know what happens though, Mazdas typically dont have transmission problems that I have seen, not like Hondas that is for sure.