A couple related questions:
A) We have not been diligent about changing the transmission fluid (on an automatic transmission) after 114,000 miles. The car is just beginning to show hints of a potential issue. Two friends in the know have said if you change the transmission fluid now, it can actually cause more problems. However, I don’t know why this is. (I can only picture the fluid is now akin to a thick glue holding everything together?) Can the SD car wizards please expound upon why this may be, if it is true? And, is it purely a crap shoot if we change the transmission fluid at this point?
B) Along these lines, have you car gurus known of an automatic transmission to hesitate at low speed? It is hard to describe, but to me (one with no knowledge of the what’s happening) , I can only say it feels like the car doesn’t want to go for maybe 1-3 seconds and finally responds with a slight jerk. Perhaps it equates to “slamming the gears” with a stick?
I should add that this “feeling” is not unique to an older cars. I’ve had two new cars that will respond like this for no apparent reason - even with fresh transmission fluid. Under warranty, the dealer will drag their feet claiming they can’t find the problem until it totally fails…which equates to “we can’t be bothered to chase this problem to ground”. Any clue what / why this is happening?
no, it’s largely* a myth. the transmission’s oil pickup draws through a filter, and most suspended particles don’t pass through. There may be some small particles (probably clutch material) which might, but that’s not materially going to affect the fluid’s properties.
If your transmission dies shortly after changing the fluid, it was about to die anyway.
yeah. either there’s a problem with the pump, or the fluid level is low. most automatic transmissions are operated hydraulically, and have one or two internal pumps to generate the hydraulic pressure they need. if the fluid is low, or the filter is completely blocked, or the pump has a problem, it may not generate sufficient pressure at idle. when you try to take off, the increased engine speed drives the pump faster, the pump is able to build pressure, and the clutch/brake for 1st gear slams into engagement.
Improper fluid can cause this. back in the day, pretty much any auto box used Dexron/Mercon fluid. now, different manufacturers have their own fluid requirements which account for things like friction modifier additives. if you use the wrong fluid, you can have shift quality problems.
I say “largely” because there’s a kernel of truth here. When Chrysler released their 4-speed “Ultradrive” transaxle (original model code A604, later 41TE) it was fairly radically different in that it was directly electronically controlled rather than relying on a mechanical/hydraulic valve body. The Transmission Control Module (TCM) directly controlled clutch/brake engagement and relied on the specific friction properties of the intended Chrysler ATF+3/+4 fluid. But they weren’t clear enough that this transaxle needed that specific fluid, so people (and shops) would do a fluid change and put generic Dexron/Mercon in. Lo and behold, the trans would shit the bed shortly thereafter.
The older transmission fluid change in an old mechanics myth.
You’ve changed the transmission fluid in the past, but have you ever changed the transmission filter? On most automatic transmissions, you have to drop the fluid pan to get that the filter. Often the quickie lube places do a flush by connecting to the transmission cooling lines and don’t do anything with the filter. A clogged filter could cause problems.
Are you sure that it’s the transmission? Maybe the engine is hesitating some. Do the engine RPMs go way up yet the car doesn’t move? That could say that the transmission is at fault. If the engine RPMs don’t increase much, the it could be the engine.
Do you have a Check Engine or Service Engine Soon light illuminated on the dash? That could tell you there is something wrong with the engine and/or transmission.
Not totally a myth, but as with many things automotive overstated and exaggerated by people who don’t really know, who take as gospel something they hear from someone who thinks he knows.
Decades ago it was not unknown for a car to be driven into the shop, have its automatic tranny fluid changed, and then not be able to be driven out. These were extreme cases. Typically the fluid was severely burnt, not just dark red, or orange, or even brown, but black – nasty black. The common explanation was that significant varnish deposits (from major fluid deterioration) were inadvertently sealing significantly worn passages (from major mechanical wear), and that the new fluid’s aggressive detergent capabilities dissolved enough varnish to where pressure could no longer build up properly in the valves, and bingo! No gear engagement, no go. “I can only picture the fluid is now akin to a thick glue holding everything together” was a pretty close guess, and the observation that “if your transmission dies shortly after changing the fluid, it was about to die anyway” is true. While not every tranny with black fluid would suffer this fate, tranny shops learned to NOT do fluid service on cars in that shape.
For most modern vehicles that use synthetic trans fluid 114k miles is not a big concern. As others have said, the first thing to do is make sure the fluid level is okay. However, some cars (Honda comes to mind) do tend to develop problems, such as sticking solenoids, which can be avoided and sometimes solved by fluid changes.
As usual, not all cars are the same in certain significant regards, and we can give better advice if we can identify exactly what we’re dealing with. Year, make, model, submodel, and engine size, please.
I had a car that would hesitate and occasionally mimic a transmission slip when taking off quickly.
I went to check the ATF and by chance noticed a belt had grazed a vacuum line when it slipped out of its retainer clip and wore a small hole in the line.
$10 and a short walk later, the hesitation was solved.
Many (most?) modern passenger vehicle transmissions are computer-controlled. This lets them (hopefully) make better decisions on when to change gears, and thus improves mileage. A modern transmission will often have a better EPA MPG rating than the same car / engine with a manual transmission.
The unfortunate side effect of this is that you can now have software bugs in your transmission. There’s a rather famous BMW one called the “Steptronic clunk” where the car will decide to drop down a few gears in certain situations, like when you brake going down a steep hill. Disconnecting the battery for a few minutes would cause it to forget this “bad habit”, but it would pick it up again within a few hundred miles. BMW had a service procedure to be done “upon customer complaint only” to update the transmission software. But you had to know about it to ask for it, and if you waited until the warranty expired, you were SOL.
Other clunks & thunks can be from the differential, due to slop. Normally this will happen when you begin to slow down by coasting, then speed up again within a short time. This seems to happen more often with AWD cars, probably because there’s more gears and shafts involved.