‘Leave it alone’: Expert explains why doing a ‘transmission service’ after 100K miles could ruin your car

Auto tech and TikToker Chris Craig (@chris_mf_craig) says you might be ruining a good thing if you service your transmission too late. According to the mechanic, automatic car transmissions 100,000 miles and more that have never been serviced, should stay that way.

According to him, folks could be opening up a whole new can of worms with their vehicles. He explains why in a TikTok that's accrued over 87,000 views as of Saturday.

Too little too late?

"If you have a customer that comes in and says, 'Hey I want a transmission service.' And it's out of the blue, they're usually trying to fix something," the TikToker says at the beginning of their video.

Next, he launches into a skit between a service tech and a service sales rep. The tech tells the salesperson they're not performing a transmission service. That's because the car has over 100,000 miles clocked on the odometer. This, according to the tech, just means that they're going to set themselves up for a world of issues.

He says that the transmission is going to start "slipping" and "jerking around." This is because it hasn't been serviced for the entirety of the vehicle's life.

"Your customer's gonna be upset," he says. "I'm telling you, my advice as a technician is to not touch this transmission."

Why better not to service?

After the skit, Craig explains why these procedures are so tricky.

"Now, there's two different things," he says. "You have a transmission flush and you have a transmission service."

He says folks have always debated which of these two procedures are better. Craig says he's "always leaned towards service because we're gonna drop the pan and actually replace that filter." Flushes, on the other hand, have techs flush the fluid "through an old filter" which may or may not be "OK."

But he says that performing the service on a vehicle that's never had it done before is problematic.

"You really don't wanna service the fluid in most cases. Because you don't know what you're going to find," he says. Next, he anticipates a response folks may have to that: If there's a problem, tell the customer, right?

@chris_mf_craig The transmission service on a high mileage vehicle… here is a little of my 2 cents along with some technical information! #chrismfcraig #serviceadvisor #weowebetter #technician #dealershiplife ♬ original sound - Chris_MF_Craig

A transmission service could cause new issues

It's not that simple.

"You might also start a new problem," he explains. "You see, if a transmission is at 100,000 miles and has never been serviced, the damage is already done."

Craig explains there are "clutch packs" inside the transmission and some plates called "frictions and steels." According to him, these have been eroding because of a lack of lubrication from good fluid since it's 100,000 miles old.

Due to the transmission's components marinating in that fluid for so long, Craig says they "start to erode."

"And all the stuff that peels off in there, think about brake dust, only its clutch dust, in between those frictions and steels," he continues. "That's what's helping to get it to grip and adhere while you try to drive down the roadway."

He says if you flush that fluid out and replace it with new fluid, you're "also taking that debris from that clutch material out of the system."

Removing this debris, he says, while that may seem like a good idea, is actually hurting the damaged transmission.

"When they try to grip now, they're gonna slip," he explains. "Now sure, you have brand new fluid in there. And you have a brand new filter. But you don't have that debris in there anymore."

Despite the debris not belonging in there, he says the damage is done.

"And you're gonna start to make that transmission show its age by doing that service," he says. "That's why a lot of technicians, myself included, don't really recommend doing a transmission service on a transmission that has not had it done in over 100,000 miles."

Diagnostic time

To close out his clip, Craig says customers requesting transmission services are probably trying to fix a problem. So instead of immediately performing that task, asking them about their vehicle is a better solution. Instead of jumping right to a service, performing a "diagnostic" is a more appropriate course of action, he recommends.

The high mileage transmission service debate on vehicles that have never had their transmissions serviced is a prevalent one. Folks in a Car Talk community post cautioned one car owner to forego the service on a 2000 Toyota Camry wagon that's running great. Although the vehicle has never had the service completed and its transmission fluid is dark (a sign of debris). Doing so, one person warned with logic similar to Craig's, could dislodge the debris and cause new issues.

Someone else in this Bimmer Post forum also addressed this debate. One car owner was told by the previous owner not to touch the transmission fluid. Several folks who responded to their query referenced Craig's transmission service hypothesis. One user said if the car has a manual transmission then fluid should always be changed. And that the flush/service quandary only exists with automatic units.

Others say always change that fluid

According to this Motor Trend article, transmissions can only benefit from having their transmission fluid changed. The outlet states that "changing the fluid on a regularly driven vehicle can only help revitalize the clutch material.

TikTokers who responded to Craig's video also stated that they thought transmission services would only be helpful in these situations.

"High mileage fluid and no cleaner. It's not difficult," one commenter wrote.

Another replied, "Just did a 2007 jeep Cherokee transmission service with 128k miles shifted great before and even better after."

While someone else penned, "Perform the service, I have seen this fix the problem more than hurt it, plus if it starts to slip again then just as some anti-slip additive and I’ve seen this add years to the trans."

However, some agreed with Craig's argument. "Do your schedule service or don't do it at all," one wrote.

The Daily Dot has reached out to Craig via email for further information.

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