LOST JEEPS :: View topic - Tranny oil change, drop pan or flush?

Somehow, years ago, the rumor got going around that by flushing a tranny it would cause catastrophic failure. My theory is that it was started by some transmission repair shops who would rather do a rebuild for $2000, than a flush for $150. All sorts of ridiculous theories have been given as reasons not to do a flush such as that it "washes the "grit" out of the clutches", or gets "chunks" into the valve body. The fact is that most who claim that it is detrimental have no idea what the process of flushing involves. A flush is done in one of two ways. The inferior way is with a machine that recirculates a constant volume of fluid and the old fluid gets diluted with fresh but not 100% gets replaced with new. The better way is with a machine which replaces all of the old fluid with new in one shot. Neither one of these machines can push fluid backwards through the check valves of the transmission. It is not done under any appreciable pressure, so there is no danger of blowing out any seals or damaging valves.

The idea that the Transmission fluid should not be flushed is paramount to saying that changing one quart of engine oil at a time is all the engine needs. Dropping the pan and changing the filter will give you 3-4 quarts of new fluid out of the 14 total quarts of fluid. In my opinion 30K miles is a good interval for a filter change and 60k a good time for a flush but I have nothing to base this on other than how my fluid looks at that time.

Author:	Endurance [ Thu Apr 30, 2009 2:01 pm ]
Post subject:	Tranny oil change, drop pan or flush?
Hi all, Im at 56k miles and due for my 2nd tranny service. The first time I had the shop drop the pan, drain the oil and replace all the filters. They told me the next time I come by it should be flushed. What do you think? Will it be OK to drop the pan again or do I need to do a flush this time?

Author:	danoid [ Thu Apr 30, 2009 2:42 pm ]
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Unless you're towing, off roading, or it smells burnt, my vote is leave it alone. Brown is OK, the dye wears out quickly.

Author:	DGM635csi [ Thu Apr 30, 2009 3:40 pm ]
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IMO, you should never flush an AT. When you flush, you are simply forcing all the crud/debris that has built up in your tranny over the last 30K back through the same dirty transmission filters, so you end up with new fluid but you may also have clogged your filters at the same time. I would drop the pan, let the tranny drain for 4-6 hours or overnight, change the filters, then refill it with a good ATF+4.

Author:	bugnout [ Thu Apr 30, 2009 4:32 pm ]
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x3 for service, don't flush

Author:	nursecosmo [ Thu Apr 30, 2009 6:49 pm ]
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Somehow, years ago, the rumor got going around that by flushing a tranny it would cause catastrophic failure. My theory is that it was started by some transmission repair shops who would rather do a rebuild for $2000, than a flush for $150. All sorts of ridiculous theories have been given as reasons not to do a flush such as that it "washes the "grit" out of the clutches", or gets "chunks" into the valve body. The fact is that most who claim that it is detrimental have no idea what the process of flushing involves. A flush is done in one of two ways. The inferior way is with a machine that recirculates a constant volume of fluid and the old fluid gets diluted with fresh but not 100% gets replaced with new. The better way is with a machine which replaces all of the old fluid with new in one shot. Neither one of these machines can push fluid backwards through the check valves of the transmission. It is not done under any appreciable pressure, so there is no danger of blowing out any seals or damaging valves. The idea that the Transmission fluid should not be flushed is paramount to saying that changing one quart of engine oil at a time is all the engine needs. Dropping the pan and changing the filter will give you 3-4 quarts of new fluid out of the 14 total quarts of fluid. In my opinion 30K miles is a good interval for a filter change and 60k a good time for a flush but I have nothing to base this on other than how my fluid looks at that time.

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Author:	tjkj2002 [ Thu Apr 30, 2009 8:35 pm ]
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nursecosmo wrote: Somehow, years ago, the rumor got going around that by flushing a tranny it would cause catastrophic failure. My theory is that it was started by some transmission repair shops who would rather do a rebuild for $2000, than a flush for $150. All sorts of ridiculous theories have been given as reasons not to do a flush such as that it "washes the "grit" out of the clutches", or gets "chunks" into the valve body. The fact is that most who claim that it is detrimental have no idea what the process of flushing involves. A flush is done in one of two ways. The inferior way is with a machine that recirculates a constant volume of fluid and the old fluid gets diluted with fresh but not 100% gets replaced with new. The better way is with a machine which replaces all of the old fluid with new in one shot. Neither one of these machines can push fluid backwards through the check valves of the transmission. It is not done under any appreciable pressure, so there is no danger of blowing out any seals or damaging valves. The idea that the Transmission fluid should not be flushed is paramount to saying that changing one quart of engine oil at a time is all the engine needs. Dropping the pan and changing the filter will give you 3-4 quarts of new fluid out of the 14 total quarts of fluid. In my opinion 30K miles is a good interval for a filter change and 60k a good time for a flush but I have nothing to base this on other than how my fluid looks at that time. X2................ The key with transmission flushes is to start early and do often.About every 30,000 miles is a good schedule,I personally flush mine every 15,000miles and change the filters every 30,000miles(flush 1st then change the filters).You can not do a "reverse flush" on a auto trans,the pressure required would blow everything including the machine.A place that does a true flush does cost $$$ because you should go through 2X's what the transmission holds at least to make sure you get all the old fluid out.So for a 545RFE or 45RFE that would be about 28qts of ATF+4(which isn't cheap to begin with). Can a flush be harmful? Yes it can if you have 100,000+ miles and never had a trans service before but not always will it hurt.Where I work we use a chemical(BG fluids) 1st to clean the trans then cycle through new fluid,on higher mileage transmissions I for go the chemical and just do the flush after the customer is aware of what might happen. Because of the high cost of the good flush machines this is one job I do not do myself and allow the dealership to do since they use the correct fluid and it comes with a 12month/12,000mile warranty also,well worth the cost in my opinion.

Author:	ATXKJ [ Thu Apr 30, 2009 11:28 pm ]
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^^^ What he said - "flush 1st then change the filters"

Author:	DocB [ Fri May 01, 2009 2:15 am ]
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In the very near future we plan on the following. You fellas see anything wrong with this? 1. Drop pan, new fiters, new oil. 2. Cut return hose just before it enters tranny, install temp sensor fitting. 3. Flush entire system with new oil, letting it drain out at sensor fitting. 4. When it runs clean button it up.

Author:	vtdog [ Fri May 01, 2009 10:22 am ]
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I also had pan drop at 30k by local shop. Shop owner said that only a flush would be needed next time and that I could wait 50k (80k total miles) until next service, but I had it done at 30k anyway as it was only about $130 for the job. He does not normally stock our tranny fluid and has to order it in (10qts?) for the job. He does not use Mopar fluid, but a synthetic that exceeds Jeep specs.

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