Honda/Acura tranny failures explained ?

Having read through many of your posts regarding Honda's AT failures, I felt a little on the skinny behind the failures was in order.

FYI, these failures are not limited to the 6 cylinder models, many of the 4 cyls fall victim to the same malaise: Honda's unashamed attempt at wooing the a different type of customer- the cushion/pillow drive craving, the captain's-chair-in-a-buick (with supersize cup-capable cupholders), the should be driven and not driving consumer.

See, fundamentally for those who do not know, Honda's transmissions (and engines for that matter) are closely related to the race motors they are derived from. Being race-bred this technology spills over into the marketplace were everyone from your average Jane to Joe Rocket can sample and love or lump it.

That said, let me formally introduce you to Honda's AT's. They are hydraulically actuated manual transmissions!

What does this mean? Well simply in means there's a little man in the gear box whose selecting gears for the driver, this so those who would rather not don't have to. However for those who want a more descriptive intro, read on.

In a syncromesh manual trans (which is what cars marketed today are equipped with) all you ratios are in constant mesh fixed on one shaft while freewheeling on the other. Gear selection is accomplished by locking the freewheeling gear of the desired ratio to the shaft it’s spinning on and voila! Your output is served. The make the transition between ratios smoother (as the different ratio gears are obviously turning at different speeds for a given shaft speed) clutch-like devices, known as "syncros" accel &/or decel gears in adjacent ratio pairs before the locks (dog clutches) engage.

Compared to your conventional epicyclical/planetary gear set automatic transmission, ratio selection is far easier, selection more positive and transmission design less complex for ratio addition. In view of this (and the fact that this conclusion had already been arrived at in racing circles, Honda devised and implemented a means of automating gear selection of their manual transmissions instead of lamely following convention. Their efforts yielded the hydraulically actuated manual transmission found in all their AT equipped vehicles.

"How did they achieve automation?" you may ask. Simple. By replacing the brass syncros with wet clutches, all they had to worry about was the ratio itself because clutch pack actuation was already a mastered technology.

The quirk to this transmission was that it had very positive shifts a consequence of wet clutches. Considered more of a boon than a nuisance to race teams, commuters found the shift quality rather alienating, especially since their previous exposure to AT's was limited to the forever-slipping-into-this-ratio-or-that conventional AT.

So the A[lmighty]HM charged to the rescue with soft shifting (read: longer slipping pre-engagement) transmissions. Of course slipping is not good for any clutch and a wet clutch is so not excluded. So in '96.5, Honda introduced phased clutch engagement. This allowed for partial engagement of your 'to' gear before your 'from' gear was fully disengaged. This allowed for dramatically smoother shifts than previous models. The ugly side to this advance was not to reel its ugly head for a couple of years. In late '97. DTC P0740- torque converter circuit failure- was discovered lurking somewhere in between the super-gizmo-wizardry of the PCM and the technologically advanced tranny.

Now early investigation found internal leaks &/or clogged valves to be the culprits.

OK. We thought.

But the shift quality still wasn't smooth enough. But before I get to what engineer's @ AHM decided to do, let me ask you all a question.

How many of you have ever wondered why Honda has always (not now in the advent of flattering emulation by other marques) had 2 drive selections: D3 and D4?

Hold that thought as we return to Honda's tranny refinery.

Realizing that pressure modulation was the to shift shock reduction and that clutches would only stand for so much abuse, Honda looked to a formerly overlooked resource for addition shock dampening: the torque converter clutch. Formerly only used to positively lock the crank to the input shaft, Honda decided to phase its engagement in further efforts to make the AT's operation transparent. It worked for a while. But while existing problems brewed, a whole new batch was thrown in. 740's were jumping all so acrobatically out of the wood work and the more powerful powertrains fell first but their less endowed siblings were soon to follow suit.

While driving, the softer shifts were aggressively wearing away clutch material sometimes in particles that were trapped in screens and filters other times in smaller ones that made it through these lines of defense. In the former situation, the filters (which by the way, are not serviceable) were clogged. This led to pressure loss, which exacerbated the transition duty of the clutches, affected essentially fuelling the vicious cycle's inferno of destruction. In the latter case, accumulation of deposits could occur in the fine passages of the valve body, in/on valve seats etc. Essentially depositing sh!t where it don't belong. Now add to this the fact that you average commuter drives in D4 at speeds that equate to the threshold of TCC engagement, the mapped criteria of engagement coupled with the advanced partial engagement modes of the TCC you have a recipe for ATF & Clutch stew. That's an artery clogger if I ever saw one! (No pun intended!).

In so much as these tranny failures seemed to come out of the woodwork all at once, it was actually the accumulation of un-addressed undesirable operational consequences that all came to a head.

Now the newer 5-spd transmissions have the ignominy of having a third working geared shaft. Unfortunately, prolonged torture testing for reliability of this set wasn’t long enough and internal lubrication and cooling weren't discovered until many owned vehicles with these ill-fated trannies in them. The fix: add point of correction cooling+lubrication by plumbing ATF to the problem. Hence the latest trans recall in a seemingly endless stream of tranny woes.

I must say one thing at this juncture. Redesign has rid the 5-spd transmissions of their heating problem and as for the earlier models, "Oh-oh, better get MAACO!" ;-)))

Sorry to take up so much of your time but I thought you might want to know.

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princess said:

On the Honda site it LOOKS like there's a 4 cyl, MT with leather & Nav. Probably hard to find, but the chart makes look like it's offered.....

http://automobiles.honda.com/models/specifications_full_specs.asp?ModelName=Accord+Sedan

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