Automobile Transmissions

[ajstoner21]

Just curious about how transmissions are built.


I used to have a 1998 Ford Ranger. It was a stick and ran great for the most part. I could pull up to a parking spot, put it in reverse with still plenty of forward speed (with the clutch pedal pressed) and have no problem at all. Once stopped, clutch out, i go backwards. Simple enough. No "whine" when in reverse at a higher speed either.

I traded that truck in for a 2011 Mazda 3, also a stick. Now, this car MUST be at a COMPLETE stop before I can put it in reverse or it doesnt sound good (even with clutch pedal pressed lol). This does "whine" at a higher reverse speed.

So, my question. Whats so different here? Why can one be put in reverse with wheels moving, and one cant? Why does one whine, and not the other?

 

[MSPAviator]

The whine is from straight cut gears.

Most manual cars have a reverse lockout so you don't accidently put it in R instead of 1 or something like that.

 

[denverpilot]

Don't some of the newer transmissions also use plastic gears for the reverse to save money? I thought I'd heard that somewhere before... but don't know for sure.

They couple that with a brake-pedal actuated reverse-lockout gate as mentioned above, I believe, on some vehicles.

 

[Ted]

It also will have to do with the synchros (or lack thereof), the size of the gears, the helix on the gears, etc.

Reverse will more typically whine because you have an idler gear in between the input and output shafts that reverses the direction of the output shaft. So not only are your gears more straight cut (which will impact how easily you can get into gear, plus increase noise), you've got this extra little gear spinning faster.

Your Mazda probably has some tiny straight cut gear for reverse, whereas your Ranger probably had a larger gear with a bigger helix on it. Maybe a reverse lockout switch, but if it's a straight cut gear without a synchro, it won't want to go into gear unless the input shaft and output shaft are at the same rotational speed. For the purposes of reverse, that would be zero.

 

[Mike Smith]

Ironically, the Ranger P/U has a Mazda transmission. Mazda B series trucks and Rangers were built on the same platform. My useless knowledge of the day.

 

[AggieMike88]

Ford Rangers do very well for me!

 

[jesse]

Danielle's Scion TC is a manual and it must be at an absolute complete stop for you to put it in reverse with the clutch down 100% of the way. Otherwise it'll grind.

 

[zaitcev]

Danielle's Scion TC is a manual and it must be at an absolute complete stop for you to put it in reverse with the clutch down 100% of the way. Otherwise it'll grind.

For some reason it's rather common. The A-576 that was used in Neon and Cobalt was the same way, for instance. One of the documents I saw even said "_instead_ of syncho, the reverse has a brake".