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Transmission/transaxle fluid change question


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One thing has always bugged me, and that is why don't they put drain plugs on transmission pans? It would certainly help make a messy maintainence task a bit less tedious. And beyond that, my owners manual tells me that unless I drive under severe conditions (Taxi, High heat, Towing, etc.) I should never have to change the fluid! (I have a good friend that runs a transmission shop and he says he sees more ruined transmissions because of lack of maintainence than anything else. He further suggests that I change the fluid and filter at least every two years to help prevent big repair bills. In his eyes it is the most neglected maintainence procedure by a car owner).

Any thoughts pro or con?

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Your owners manual tells when to change the trans oil.My 67 manual says oil & filter at 24000 miles,I change my 87 Regal about 55000 miles,the Park Ave.says to change it at 100,000 miles.So I guess its up to you.

They dont put a drain on the pan because you have to remove it anyway to get at the filter.Norb B.

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I only meant it would be a heck of a lot neater to drain the fluid out before dropping the pan. 6 quarts dribbling over the edges makes a real mess. I suppose with a lift and proper container to catch it in would be a lot better.

My '96 PA owners manual states on page 6-20 in that there's no need to change the fluid anyway. That still seems hard to believe, considering how long these cars last today. So why did I do it in the first place? Hmmm. I guess I'm just old fashioned.

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I know transmission fluid changes can be messy, so here is what I do to minimize the mess, assuming of course that you don't

have a lift.

1 - Get a couple of lasagna baking pans (the big ones) and put it under the transmission pan.

2 - Jack up the car as high as you can from the front.

3 - Loosen the bolts so the fluid drips into the pan.

4 - Take out all the bolts EXCEPT those at the four corners of the pan.

5 - Let the car down almost to the ground

6 - Get two three ring binders and a small laundry basket.

7 - Slide the laundry basket (upside down) underneath the tranmission pan.

8 - Use the two three ring binders to ELEVATE the laundry basket so it is snug against the tranmission pan.

9 - Take off the four remaining bolts.

10 - Jack the car up high from the front and back if necessary.

11 - Pull the two three ring binders away from the laundry basket which has the tranmission pan on top of it.

12 - Either pull the laundary basket towards you or take the pan off the basket from underneath the car.

This method cut way down on the mess for me.

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Guest scott mich bca # 6619

You don't state what year car or transmission your question pertains to.

My transmission shop also recommends that you change the trans. oil every two also.

Once you have changed your trans. oil, it is very easy to drill a drain hole

in the pan when it is off, and weld a threaded bushing to accept the new drain plug.

Scott Mich BCA #6619, OCA # 3947

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Whenever there is a recommendation for transmission fluid change intervals (i.e., 100,000 miles or similar), there is usually also a "severe usage" maintenance schedule in the mix also that will recommend a change at a much shorter mileage interval. Also, the current DexronIII fluid is better than the fluids of the '60s by a long shot so change intervals can be extended from what was recommended back then.

Considering that many modern fwd vehicles will never be exposed to the uses of their rear wheel drive forefathers, the life of an automatic transmission is somewhat easier. Hence, the trans oil temp will very probably never see the critical 270 degree F temp where ATF starts to break down. But, just as in the "old days", when the fluid starts to change color (turn brown from its normal red color) and the smell changes from it's normal pungent odor, it's time to change it.

The electronic controlled automatics now in use also have a temperature override switch in them. When the transmisision fluid temp gets to a certain level, it will downshift the transmission AND/OR let it freewheel whenever you back out of the throttle so it will try to cool itself. Sort of a fail-safe operational mode (but not good if you are trailer towing!). With that built-in protection mechanism, trans fluid temps should never reach the levels they used to. Of course, in heavy duty towing situations, adding the biggest aftermarket cooler would keep the fluid temps down so the driver would retain full control of the transmission and the vehicle. Depending on the ECM programs, engine compression braking via the trans can be a thing of the past too, even on car applications (notice the tach on your late model car to see how it reacts).

B&M sells a kit to put a drain plug in an automatic trans pan that didn't come with one. Some pans of the '70s still have the flat spot where the plug would go anyway. Some of the current rear wheel drive truck automatics have drain plugs in their pans too.

Before the dacron filters came into vogue, the typical filter screen was just that, a screen of fabric or brass wire. As such, that "filter" would be somewhat self cleaning as the fluid above the screen in the trans would drain back into the pan when the engine and oil pump stop. In those earlier days, there were no massive amounts of clutches to wear and the magnet in the pan would catch the non-alloy metal clutch materials anyway.

In a modern transmission, there are more clutch packs and other friction materials in the main transmission, not to mention the torque converter lockup clutch. Everything's modulated electronically for a controlled amount of slippage for the ultimate smooooooth shift between gears. Some of that smoothness comes from engine computer power modulation during the split second the shift takes place and then there will always be a certain amount of clutch slippage involved too.

Now, the "Trick Deal" is a transmission flush. Remember, when you change the fluid in the pan, there is still fluid in the torque converter (where the drain plugs went away along about 1970). A transmission flush may not include a filter change, though, so be an informed shopper. Also, some of the machines require constant supervision and others work automatically. In some cases, it's a good deal but overkill in many others.

I read an article in the early '70s when people were starting to bemoan the lack of trans pan and torque converter drain plugs. A GM engineer was quoted as saying that when you just changed the trans pan fluid, there was enough new fluid and related additives in the new fluid to keep things up to snuff internally in the trans (i.e., detergent and viscosity additives).

Granted, the trans fluid change can be a messy affair. Other than the baking pans mentioned above, there are now plastic drain containers (usually available at WalMart) that are rectangular and wide enough to contain the bulk of trans fluid that will come out from around the pan. In the case of a trans that is pretty dirty inside, addding a detergent additive prior to the drain might be advisable. In the earlier times, Berryman's B-12 (pour can) was used with good results as it would cut the varnish and such from the valve body passages. Following that with a change of fluid was usually all it took, but a second change might be needed too in some cases. GM also has an Automatic Transmission Conditioner additive that has a little detergent plus seal expander to keep things working well in higher mileage transmissions.

In what might be an "ultimate cost saver", GM deleted the dipstick on the Turbo 125 transaxles several years ago as they were so trouble free. Things have come a long way.

In any event, check the fluid reasonably often for level, color, and smell as those things haven't changed (unless you have something with the T125 in it). That way, you will be checking the condition of the fluid in your own driving conditions. Or, you can go the time and expense of changing it every 24-36,000 miles.

Now, it might also be advisable to consider changes based on your climate conditions and where the vintage car might reside when not in use. Keeping residual moisture from the fluid for a car that sees little use might be a consideration. Just as with engine oil, the transmission fluid needs to get good and warm to let the residual moisture cook out of it each time it's run. This might take 30 miles to happen, too. Therefore, just as with motor oil, short trip uses might need some added consideration in that deal too.



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