Trick for P&G On an automatic.. Hint, you need Cruise Control - Page 5 - Fuelly Forums

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Old 06-26-2008, 10:27 AM   #41
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Lucas Tranny fix stuff
Watch out about additives, there's a lot of debunking on those. i think amsoil, BITOG or somebody has an experiment showing that those turn everything to foam in a trany.

BTW, my other car IS a stick , and it's easier to control P&G even though there's a pedal, because I feel in control, though I'm sure I wear my clutch more, since I don't always revmatch.

I feel better about N-D shifts now that I've actually read how an AT trany works...

I think now the issue is to experiment with those cruise buttons.
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Old 06-26-2008, 10:57 AM   #42
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Was trying to pull up anything on BITOG, nothing... Specifically "Lucas Transmission Fix" not anything else, is good in my book, and google can't find anybody who has actually used it saying anything substantially bad against it. It's supposed to have antifoaming agents in and be new car warranty safe. I know there's a lot of bad things that other types of additives can do, and tell people to avoid them, but this is damn good stuff. It held a slipping ATX with 220,000 miles on it together for another 2 years and 40,000 miles in a '94 Ford Tempo, it worked wonders in my Escort for shift quality, I had it in Marvin before I shiftkitted it and switched to UTF and don't need it any more, though if it starts to feel like anything is sticking, it's getting it in straight away.

So if you can find anyone with anything bad to say about it, other than "It didn't work in my obviously badly broken transmission" or "all additives are baaaaad mmmkay" I'd like to see it.
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Old 06-26-2008, 11:10 AM   #43
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So you are trying to tell me that coasting down the freeway going N->D from 800 rpm to 2750 rpm is going to tear up the transmission more than my car being revved to the red line and going from 6700 to 4000 in the same amount of time with an engine that's wide open?

Additionally, your saying I'll tear up the transmission by taking it out of overdrive on the freeway with the gas let up all the way. That's about a 1600 rpm increase in rpm as opposed to a 1900 rpm N->D increase.
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Old 06-26-2008, 12:05 PM   #44
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Originally Posted by sonyhome View Post
When in "N" coasting, the driveshaft rotates fast, and the torque converter rotates at idle RPMs.
When engaging to "D", the torque converter shaft is jolted suddenly from 800RPM to say 3000RPMs.
The torque converter in that case is counter productive because it will oppose a force, increasing the stress on the torque converter shaft.
Once in gear, the torque shaft turns at 3000RPMs, and the torque converter handles the decoupling with the engine flywheel which before that was rotating the torque converter shaft.

So I see that you could prematurely wear the tranny's brake bands and clutches that way, because the "N" to "D" shift is not really protected by the torque converter so those take the force by slipping... Unless indeed you rev-match the engine before engaging to "D".
That's my answer, and I'm sticking to it, I will rev match before I shift back in drive and in turn saving my automatic transmission. Even if I didn't notice a real "bump" in the first place when I did it without..
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Old 06-27-2008, 01:50 AM   #45
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Hey, don't just take my word, I learned trannies last nite.

Let's talk about how AT trannies break... Maybe we can infer if N-D shifts cause wear or can break trannies.

Failure 1 - Ford pickup
I've been in a Ford truck that broke a tranny while going uphill. It was towing a boat, and the AT decided to downshift, causing a big jolt. We made it home with the tranny kinda stuck (luckily not in N). What happened? Ford trannies are notorious for being weak OK, but 3->2 was a matter of tigtherning or releasing some parts so I suspect a clutch or a band broke or got stuck.

Explanation 1?
The downshift caused a sudden change in the torque converter shaft speed suddenly going faster, and its speed delta WRT the flywheel absorbed by the torque converter. That shaft suddenly saw lots of torque from the torque converter trying to adjust engine RPMs to drive axle RPMs.

Explanation 2?
More likely everything is sync'ed, and the trany downshifts, but there's so much load on the drive axle and the engine that the pistons or bands can't take the stress of shifting gear, and break.

This scenario uses a heavy load, but breakage happened from shifting (down not up).

=> Can we construct such a worst case failure mode in N-D shifting?

Failure 2
(Your example)
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Old 06-27-2008, 06:09 AM   #46
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You acknowledge the heavy load but I think you don't give it enough credit, however...

Explanation 3:
Not only was it under heavy load, but both sides of the tranny were heavily loaded in opposite directions. The back side was loaded with the truck and trailer slowing badly (trying to pull backwards), and the front side was loaded with the engine's maximum output pushing forwards. When it shifted, that steady-state load (already at the tranny's maximum) had a moment of disconnect in which to wind up like the backswing of a hammer, and became a major shock.

In a P&G style N->D shift, there's a moderate load on the back side from the momentum of the car continuing forward, and almost zero load on the front side from the engine also going forward and not strongly resisting being turned even faster by the transmission. That's minor load, both in the same direction.

Again, a very easy rev-match reduces even that load.
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Old 06-27-2008, 08:22 AM   #47
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And manually shifting it sooner would have saved the tranny Though not for much longer if abused for a while.

Explanation 4: Due to trying to pull up the hill in too high a gear, the TC was slipping a lot, putting lots of shear force into the the ATF, this got it close to burning/boiling and something melted.
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Old 06-28-2008, 03:10 AM   #48
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So what breaks in a Ford tranny, they're known to overheat, so what stops working? Do you melt the aluminum?

Also a friend who drag raced his autos says the torque converter would break often. What? The fins tear?

BTW, I'm not saying N-D is bad... nor good... for the tranny, just trying to see the difference with known failure cases, see if we can find correlations that would yield something to worry about.
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Old 06-28-2008, 03:13 AM   #49
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BTW,

Tried cruise, then "Decel" button, RPMs just go down smoothly. No DFCO, not even idle.

Tried cruise, then P&G, in the G mode, RPMs drop to 2000. Again, "N" is better.

So on my CR-V, the cruise control is no savior for P&G.
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Old 06-28-2008, 05:14 AM   #50
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That reminds me...

Not an automatic, but I tried "Decel" button while hooked up to my fuel rate meter in my VW yesterday. It lets of the throttle smoothly, instead of just closing it right off, so it takes ~5 seconds before it can DFCO.
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