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Old 09-24-2008, 02:00 PM   #11
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But if it's lubricated where is the heat coming from? The majority of heat in an automatic transmission comes from the torque converter. Without the torque converter in use(ie engine off in neutral towing) I can't see the transmission getting any hotter than a manual transmission.

It's always been my impression that the bearings lubricate differently in an automatic than a manual transmission. Since there is a hydraulic pump in the transmission they can use sleeve bearings with pressurized hydraulic oil as opposed to roller or ball bearings and gear oil. This keeps manufacturing costs down but without the pump running you are relying on the atf staying in the bearing to keep it from wearing.

A lot like the main and rod bearings in your engine. With a loss of oil pressure it'll be ok for a very short period of time but once that oil is gone the bearings aren't going to last long. The main difference being you are just rotating a shaft in the transmission(you aren't even applying power to the shaft), as opposed to the extreme conditions main and rod bearings see.
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Old 09-24-2008, 02:02 PM   #12
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It's my understanding that, in common automatic transmissions, they still have a high enough oil level when off to stay lubricated but without circulating that oil the heat builds up and fries the oil/transmission.
very interesting...

synthetics claim to lower operating temps(compared to conventional). wonder if it would protect well enough under minimal EOC?
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Old 09-24-2008, 02:38 PM   #13
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I would imagine that synthetic fluid would be better than dino. It certainly isn't worse. At the very least the syntetic will take a lot more heat before it breaks down.

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Old 09-24-2008, 02:43 PM   #14
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I would imagine that synthetic fluid would be better than dino. It certainly isn't worse. At the very least the syntetic will take a lot more heat before it breaks down.

-Jay
i wonder if anyone out ther is willing to experiment with this? naturally they'd have to have an AT, an AT temp gauge, and the willingness to try it.
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Old 09-24-2008, 04:09 PM   #15
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Quote:
Originally Posted by dkjones96 View Post
But if it's lubricated where is the heat coming from? The majority of heat in an automatic transmission comes from the torque converter. Without the torque converter in use(ie engine off in neutral towing) I can't see the transmission getting any hotter than a manual transmission.

It's always been my impression that the bearings lubricate differently in an automatic than a manual transmission. Since there is a hydraulic pump in the transmission they can use sleeve bearings with pressurized hydraulic oil as opposed to roller or ball bearings and gear oil.
That's a much more complete analysis than anything I said. That could very well be right. However, some data and experimentation tell me that it's not the complete story.

I think I've read of experiments with ATF temperature gauges, but I know of one experiment: My wife's 2000 Isuzu Rodeo. It didn't even need the engine off, just idling for engine-on neutral coasting caused the transmission temp light to come on. The only reason I could think of is that, at idle speed, the engine isn't turning the transmission pump fast enough to cool the transmission. Heat was obviously generated in the transmission without the TC, since the TC wasn't carrying any appreciable load -- in Neutral, is the input shaft operating anything more than the pump?

For those wanting to experiment (and confident that temperature is the only issue), check your manual to find out if you have any kind of transmission temperature indicator, and if so, what temperature triggers it. My truck will display a few levels of warning on its dot-matrix display, but I haven't been willing to risk it...I just can't afford to be wrong right now. I have EOC'd it a few times while stopping for a long red light.
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Old 09-24-2008, 04:17 PM   #16
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Scangauge will report trans temp as an xGauge on many cars. I haven't tried it on The Beast though. Still, for a trans temp sensor to read properly the fluid still needs to circulate.

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Old 09-24-2008, 08:21 PM   #17
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i wonder if anyone out ther is willing to experiment with this? naturally they'd have to have an AT, an AT temp gauge, and the willingness to try it.
I didn't have an AT temp gauge, but...I used to do a fair amount of EOC back in the day when I was commuting in my '84 Lincoln Town Car...on the way home from work, there is about a 3-4 mile downhill stretch of two lane road just made for EOC, especially when there is a tailwind (which there is much of the time, all you have to do is look and see which way the wind turbines are pointed!). I spaced all the cautions about towing cars with automatic transmissions.

Well, in time, it happened. Driving home one afternoon, getting on the freeway, the car took off fine in first, second fine, but the engine revved up when I hit third, and fourth was gone. Apparently a clutch pack burnt out. All I had was first, second, and reverse. I made it home, but it was not a fun drive. The car has since sat in my driveway for over a year...looking for some kid to buy it for a project (would probably look pretty cool w/24" rims, 2KW stereo and a new paint job)...don't really want to junk it since it is too nice for that, but the wife is making "get that damned thing outta my driveway!" noises, so I may have to do that...

Don't know if the EOC was the complete cause (car has 165k miles on it), but it probably helped it along...

BTW, most auto transmissions before 1960 or so, and some later, had a rear pump on them. That was how you could push start these cars, even though they had automatics. I remember one time getting a push start for my Corvair from a Pomona cop back in the day...however, even these cars gave strict warnings about towing...I remember our '48 Cadillac being towed by picking up the rear end, and being told it was because you couldn't tow an automatic transmission car with the rear wheels on the ground, or you would ruin the transmission.
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Old 12-23-2008, 03:00 PM   #18
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Towing EOC

From my experience with autos, not since the 1950's have autos had a back oiler, it's what they used to call it, it ran off the drive shaft, so when the car was coasting, the rear bearing got oil. I'll tell you from experience with my 86 Ford Aerostar. It got towed 3 miles, when the ignition module went out one night, to my home. That 3 mile tow created a screaching sound the next day, 3 day's later the rear bearing seized so hard, it cracked the back part of the case of the transmission. $2600 no core replacement tranny, gave the transmission place my van, the van was worth $1200 at the time. Sticks can lubricate themselve, but auto trannies need the engine running to pump oil to the bearings. Now I don't know of any manufacturer that makes a back oiling transmission anymore, it's a simple cost cutting measure that the auto maufacturers did.

Now from what I'v read here, even putting an auto in neutral and coasting with the engine on is risky in some cars. I used to put Ford Type F in all my cars, because it was thicker and would build more pump pressure and make the clutches grab harder extending tranny life. It was a cool old drag race thing of the 80's to do. Now a days, my friend who is a Toyota mechanic said, Ford Type F would over pressure a trans and break parts. So I only use the recommend tranny fluid now. The only thing I do now is put the tranny in neutral at lights, that saves gas.

Now tranny temp is right from the torque converter, once again in the old days and still today in drag racing, you hold you foot on the brake and get the tires spinning or get the engine loaded to take off. Pop the brake pedal and launch. With an engine doing this, transmission fluid will Flash in 30 seconds, meaning in 30 seconds the transmission fluid will go over 300 degrees and break down, meaning the 14 or so quarts of tranmsiion fluid is now junk, change it or again were looking at bye-bye bearings.

I see these giant diesels now-a-days and the 500 plus pounds of torque they put out and all I can think about is the transmssion fluid turning into coffee. I know some models of Honda's didn't use tranny coolers, but they could use them. If you have a factory one, its in the radiator and helps the tranny warm up fast in the cold and keeps the tranny temp around 180-200, giving you a 100 degree safety cushion from going to full temperature flash.

I also understand that it is recommended to change transmission fluid every 15 or 30 thousand. Now another Used-To is that you could take of the tranny cooler lines and hook it up to a machine for $120 and pump out the old and pump in the new. I know this service is done at Jiffy Lube and other garages, but now I'm hearing this can be bad for a transmission due to the pump pressures being different. Again I don't know what models can be effected, but once angain, cooked bearings and a new transmission hang in the balance.

The best you can do is if you have a drain pan or drain bolt on your tranny, drain out the 3 to 5 quarts in the pan with every oil change, eventurally through repetition changing or keeping the tranny fluid fresh. Also if you have an auto tranny, change the filter. My 89 Ford Festiva had an auto tranny and at every 30k if you didn't replace the filter it would start to slip in city traffic. I'd put in a new filter every 30k and the problem would stop.

If you ever get the chance, take apart an auto trans, the old ones you would pull off the front cover and turn the trans upside down and the entire Pan Cake could come out in a stack. The pan cake is a stack of planetary gears and clutches and they are put together in one big stack, it is really neat looking at the clock works of parts moving around in there.
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Old 12-23-2008, 03:02 PM   #19
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Oops

Oh yeah and you could also push start a car with a back oiler, I forgot about that, sorry.
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Old 12-23-2008, 04:50 PM   #20
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There are some rear-oilers. Motorhome forums can tell you which vehicles are so equipped; and they can also tell you where to get a tranmission pump to let you EOC. They like to tow their cars behind their RVs without using a trailer or dolly.

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Now from what I'v read here, even putting an auto in neutral and coasting with the engine on is risky in some cars.
There is lots of FUD that goes around about this. I have yet to see anyone post a technical reason why it's dangerous to try.

You did mention in this or another thread that some automatics don't run their pump in N. Can you cite any examples or data on this?

My wife's 2000 Isuzu isn't ok for neutral coasting. The transmission heats up too much; presumably idle RPM doesn't pump fast enough in that vehicle. I don't think the small amount of neutral coasting she did caused any permanent damage, but it did eventually show the "A/T Temp" light.

My 2002 GMC is quite happy with neutral coasting. I admit I've only been doing a lot of neutral coasting for the last 4,000 miles, but it has had abuse from towing a 6000 pound trailer up mountains and various other such things. It's still going strong at nearly 180,000 miles.

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If you have a factory one, its in the radiator and helps the tranny warm up fast in the cold and keeps the tranny temp around 180-200, giving you a 100 degree safety cushion from going to full temperature flash.
I have a factory auxilliary transmission cooler that came with a HD towing package.

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I also understand that it is recommended to change transmission fluid every 15 or 30 thousand.
I think the maintenance schedule on my GMC says every 50,000 miles, or 25,000 for severe service. I think those recommendations are for the half-assed change you do by dropping the pan.

I happen to have the maintenance schedule for my VW bookmarked and checked what the automatic would need and it only says to check the fluid level every 40,000 miles. The schedule makes it to 100,000 miles without saying to change the fluid at all.

Quote:
Now another Used-To is that you could take of the tranny cooler lines and hook it up to a machine for $120 and pump out the old and pump in the new. I know this service is done at Jiffy Lube and other garages, but now I'm hearing this can be bad for a transmission due to the pump pressures being different.
I haven't heard that the procedure is obsolete. Can you cite anything for it? I was actually thinking of doing it for my GMC next summer.

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The best you can do is if you have a drain pan or drain bolt on your tranny, drain out the 3 to 5 quarts in the pan with every oil change, eventurally through repetition changing or keeping the tranny fluid fresh.
That could be an awful lot of maintenance! I think you're way overthinking it. They are made to be more robust than they used to be, not less, and it shows. For all the abuse and lack of maintenance people practice, automatic transmissions last an awful long time.

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My 89 Ford Festiva had an auto tranny and at every 30k if you didn't replace the filter it would start to slip in city traffic. I'd put in a new filter every 30k and the problem would stop.
Remember, that was also a 1989 Kia Pride. Still, any time you change the fluid, you should change the filter too.
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