B.C.

Daniel:

A few basic MT questions for you:

1) I've been experimenting with trying to improve my shifting. Going down the road today I was shifting into 2nd very slowly. About midway into the full throw maybe I paused too long because it seemed to growl every so slightly at me even though the clutch was fully depressed the entire time. Why did this happen?

2) I was reading in the owner's manual about putting the MT in first or R gear when parking on hills. Should this be done with the clutch depressed before shutting engine, shut off engine, then release clutch or can I simply shut off the car and then put it in gear? In other words, can the MT be put in gear without clutch depressed?

3) Along the lines of (2) I noticed a Nissan mechanic "cycle" through the gears for some reason without depressing the clutch before he started the car so that leads me to believe putting the MT into gear with engine off can be done even without using clutch. I don't know why he did this though since the clutch must be depressed anyway for the engine to start but perhaps this is his habit from old cable, non-electronic interfaced clutch systems.

4) You have said our clutches are hydraulic, will they still engage or disengage with the engine off by depressing the pedal?

5) I know that the clutch is the interface between the engine and MT but with the engine on and in N or with clutch depressed, what keeps the transmission moving? The reason I ask is how does the transmission know not to let you into 1st gear above a certain speed etc? I know there are "synchronizers" but what keeps them in motion to be able to sense this if they are not engaged by the clutch to the engine?

Thanks in advance for the education.

Daniel B. Martin

When the clutch is engaged (pedal released) many of the rotating components inside the transaxle are in motion. This is true when the transaxle is in any gear, even neutral. When the clutch is disengaged (pedal down to the floor) the rotating components slow down and eventually stop. The synchronizers inside the transaxle are speed-matching mechanisms which work by friction. When the two transaxle components which you are seeking to couple are rotating at almost the same speed, the synchronizers have no trouble doing their job. If you hold the clutch pedal down and shift slowly the rotating components start to slow down, but they don't all slow down at the same rate. Remember that the differential is connected to the wheels, and as long as the vehicle is moving some of the transaxle components are also moving. A slow shift increases the burden on the synchronizers. The "best" shift (in terms of transmission wear) is CLICK-CLICK... rapid but not forced.

Either way, it doesn't matter.

Yes, certainly. You may find that it shifts more easily when the clutch is disengaged (pedal on the floor).

Perhaps he did this for diagnostic reasons, to feel if there was any binding or excessive looseness in the linkage.

Yes. The hydraulic actuator does not use electricity or engine power. This is also true of the hydraulic brakes. Some cars use cable-actuated or linkage-actuated clutches. These mechanisms also work with or without the engine running. In all three design variations the clutch is the same. The actuator is the apparatus between the driver's foot and the clutch itself.

" ... in N or with clutch depressed..." may seem equivalent to the driver, but they are two different conditions to the transmission internals!

When the engine is running and the transmission is in neutral, most of the gears are rotating. The car does not move because the gears are not engaged with each other, but they are spinning.

When the engine is running and the clutch is depressed, then all components of the transaxle will be motionless, provided...
- the vehicle is not moving, and
- there is complete disengagement of the clutch, and
- there is no friction in the pilot bearing.

The transmission doesn't "know" anything. Unlike the automatic transmission, a 5-speed has no sensors and no electronic controls. It won't "let you into 1st gear above a certain speed" simply because that is beyond the capability of the synchronizer mechanism. You can shift into 1st gear at a relatively high speed if you help the synchronizer by pressing the gas pedal to raise engine speed while you are making the gear change.

B.C.

Daniel:

Thanks for your help. Your answers really make sense.

In regards to my first question on the "slow shift", you mentioned that during this event the components do not slow down at the same rate. Indeed, I was trying to get a tactile feel for the actual gear engagement process. As I recall, once I heard the noise I completed the gear engagement. I read about "dogteeth" on the internet. Was the muffled growl (not really a hard grinding) I heard the "dogteeth" trying to engage? Can any of them snap off in such a situation or are they fairly robust.

I will definitely take your advice on the rapid but not forced click-click method.

Daniel B. Martin

I've not heard the word "dogteeth" but I imagine it was used as a descriptive term for the "teeth" on a synchronizer ring. Go to http://users.erols.com/elans4/Transmission.htm and scroll down to Figure 14, Synchronizing Mechanism. This photo depicts part of an ancient Chevrolet 3-speed manual transmission but the basic elements of a gear synchronizer are the same. Note the Synchronizer Ring (item 7) has a plurality of small teeth (item 4) arranged around its periphery. Those teeth rarely break but they do wear with normal use, and wear quickly when subjected to abuse. When you hear that ugly sound we call "gears grinding" it is actually a cry of pain from synchronizer ring teeth (item 4) and their corresponding gear synchronizer teeth as they are being worn and chipped. The gear synchronizer teeth are not item-numbered, but you can see them as part of the gear (item 5). The gear sychronizer teeth are clearly pictured in Figure 17, Synchronizer Operation.