this is not to one tranny , but why the wifes tale of not changing older transmission fluid because it will cause the tranny to fail. i understand changing the fluid wont help a pulled pin tranny. but it seems it would help a older functioning unit. basic maintenance
Some fellas believe if you change the fluid it will stir up particles on the bottom of the pan and clog passages others believe that it will clog the valve body. I change it if it needs changing. I don't care if its an old tranny or a new one.
I have heard that the clutch fiber friction materials, as they wear, go into suspension in the fluid and the gritty fluid helps make the worn clutches work. Drain that out, and the clutches slip... I cannot guarantee the validity of the statements herein.
It all depends on how bad the fluid is, how old the tranny is, and how or if it was beat. In the 80s trannys (metric stamped on their pans) had nylone clutch material, and as nylon does it become brittle, so grit and grime helped it, but when new fluid and high detergent was flushed in, the clutches slipped chipped ect. Newer trannys are much different, adj line pressure, there isnt as much jolt on shifts with the use of locking tourque converters, so now there is more aluminum stuff. In short, if the fluid is slightly burned, but nothin major you should be fine. Notice the particles at the bottom of the pan, there will be some black fine stuff, and maybe some glitter. All normal. just no chunks of clutches ect.
If the trans is already on the edge of being toast, changing out old burned fluid can cancel whatever few miles the trans had left. Changing the fluid in a good trans, using the right fluid, won't cause it to fail. I do know of some cases where flushes of an old trans or converter has stirred up contamination that caused problems, but that's different than just changing the oil.
The reason i'd heard is that the detergents in new fluid could dislodge crud/varnish built up in the valve body, which could then plug up the smaller passageways. After 25 years of messing with the things, i realize that it's no big deal to pull the pan and undo a few more bolts, to clean the valvebody any way if there's an abundance of gunk. besides- you need to pull that pan anyway to do your filter and take advantage of that time to install a damned drain plug. rick
I have changed the fluid on trans that the fluid was so old it would barely pull the car with success.
My THEORY is that most folks don't change the fluid til the tranny starts acting up or slipping,,,,,,,,,,,, Then they change the fluid.......... Then the tranny fails, not as a result of the new fluid, but in spite of the new fluid... Owner blames the new filter and fluid... Kind of like my little sister, when she was 4 or 5 she ate spaghetti, and then got the stomach flu, blamed the spaghetti, wouldn't eat spaghetti for years...... Sometimes we are so stuck on "one thing leads to another" that we miss what is really going on.
All too often the fluid doesn't get changed untill the transmission quits working properly. Then folks seem surprised that they didn't get a liquid rebuild. Guy I used to work with was typical, his fluid had turned black and stunk so bad you would hate to pull the dip stick. He took it to a friend of mines shop and told them to change the fluid. About two weeks later he's towing his boat and the trans quit pullin. It was all the shop's fault (truck had over 150,000 miles on it). He spent the next six months bad mouthing the shop to any one who would listen. Man claimed that the shop owner should have warned him about changing trans fluid. 39 All Ford types faster than me(hell most everyone does).
I do know that on the 700R4 series trannys that you had better change the fluid every 50,000Miles. It might go a lot more but one day it won't shift into 2nd gear. On some of the Dodge truck trannys a few years ago the manuf. suggested every 20,000 miles but those trannys were nearly junk anyway. I take no chances; change it every 50,000 or sooner. Seems like the fluid in later model vehicles [towing pickups maybe] the fluid seems to get thick and it has clutch and band fibers in it as well.
Contaminated and/or burned fluid isn't as slippery as good fluid. If the trans is on the edge, new fluid can cause it to slip, or slip more. It is a well known fundamental in the auto repair business. Who ever touched the car last is the cause of whatever goes wrong. After all, "it was fine until you worked on it." I have seen several versions of the following happen over the years. It was going to snow so we had a customer bring his car(Jaguar) directly into the shop. I watched the guy drive in, turn the engine off, and get out of the car. A couple days later one of the mechanics was going to work on the car and it wouldn't start. The computer was dead. Hard to explain to a customer that the car was fine and now we are telling him it doesn't run and needs an expensive part. Fortunately he understood. That period was probably the all-time low for Lucas.
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