m5od grinding going into 3rd sometimes

[inferno94]

The truck has about 12000mi and has started this about 6 months ago, is this a common thing?

 

[AllanD]

On an '07?

Ok, this is an "issue" and it's often more related to shift technique than an actual mechanical problem.

On most '98-up transmissions the "dog teeth" on 2nd and 3rd gear are not symetrical basically the transmission was redesigned so that the synchros don't actually function on upshifts, basically the correction is to be more "agressive" on upshifts.
(Trust me this is better but you NEED to understand what is going on to take advantage of it)

IF you understand that a synchro functions sorta like a clutch (or a brake) to make two pieces that are moving at different speeds match speeds before they engage half the explanation is not necissary.

On the assymetrically cut dog teeth if you shift QUICKLY into that gear the synchro "slider" will slide between the dog teeth and start transmitting power to the "new" gear before the brass ring is engaged against the "cone" on the gear.

The rub is that less than ideal shift technique will eventually result in dammage to the teeth on the synchro slider (collar)

Essentially the late boxes don't like being "granny shifted"
IF you get a little mad at them they work perfectly...


a "chunk" or "buzz" on upshifts is siply part of the price you pay
or having a transmission that CAN be shifted quickly, the other part of the price is that you MUST shift it quickly to get it to shift well.

FWIW I'm running a late gearbox in my truck and I find it difficult to shift at times. usually when I'm either tired or in a layed-back mood.. If I'm angry, in a "sporty mood" or in a hurry the late boxes are a "joy", because you CAN speed shift them.

A poor shift in my truck (which only I drive) is regarded as a need to refill the caffein reservoir in the driver

I'm not saying that your problem isn't mechanical
But of all the transmissions I've test driven that people complained about
(including quite a few that I tested "on the sly" for the used car manager
at the dealer where my brother worked) most had nothing wrong with them
that couldn't be fixed by telling the owner that shoulda bought an auto.

Again, not saying that it's the case here....

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[inferno94]

I didn't realize the box had dog gears (that would explain the whine in 2nd and 3rd when it was breaking in). Makes sense if that's how it works cause it is often when I'm driving slow that it does it.

That said I'm mostly shifting it quickly as I'm coming off a b2200 which has a miata tranny (awesome trans). After noticing this I asked at the local dealer and they had no clue. If thats how the 2nd and 3rd work than it makes semse why its grinding.

I don't shift the truck anywhere near as fast as my car (mazda 323) as it (the truck) feels way too notchey to shift it like a race car.

 

[AllanD]

No, I didn't say "dog gears" I said "dog teeth"

The "secondary" teeth that the syncronizer collars engage.

all the gears in the tranmission are helically cut.

IF you are familiar with the normal "bidirectional" synchro teeth
(which look kinda like monopoly houses) the "assymetrically cut teeth"
are vaguely D-shaped (kinda like an orange wedge) to that as you
shift quickly the collar teeth are intended to "miss" the first tooth
and engage on the "flat" of the next tooth...

The effectiveness of this design is variable with user understanding of the setup
and dependent on the user upshifting quickly.

BTW, another factor with those assymetrically cut synchro teeth
is that they ALWAYS use synchro RINGS that are lined with a carbon fiber friction material that tends to be really "Grippy" against the cone of the gear, so they tend to be rather "positive" on downshifting.


The carbon lined synchro rings just feed weird when you are handling them and engaging them to a gear cone.

They are almost Sticky in their engagement.




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