Do I need to change my transmission fluid in my 1990 f150?
Posted by PublicLlama@reddit | askcarguys | View on Reddit | 25 comments
I asked my mechanic, but he's got a mixed reputation. He said not to because it would ruin my transmission. My truck wasn't well maintained before it was loaned to me. It's at a little under 500,000 miles, and I don't know if it's turned over. No one knows the last time the transmission fluid was changed.
Heavy_Performer1007@reddit
If you do change it, do not use inexpensive fluid that might say "comparable". Get the best fluid you can get and use that. Also get an inline filter
faroutman7246@reddit
Give it back.
Blu_yello_husky@reddit
500,000 MILES??? and its still running and driving?? Jesus christ, you found a unicorn. Anyway, if its not shifting funny (VERY unlikely, the AOD tranny ford used in this era was a massive turd) then I probably wouldnt touch it. If you do decide to do it though, use only the recommended fluid from the disptick, do NOT use the "universal" full synthetic or the full synthetic replacement for the original fluid. Synthetic oils are fine in rebuild engines and trannies, but in original drivetrains, the synthetic additives can actually break down old seals and gaskets and cause premature failure. Only use synthetic fluids if you've had the thing rebuilt in the last 10 years.
Oh, and if you pull the pan off and theres a little white knob floating in the pan, that means that the tranny has never been serviced since that plug is meant to be thrown away after the first tranny service. Again though, theres no way a 2nd gen ford AOD has made it to 500k on the original filter and fluid without severe shifting problems, so I wouldn't worry about it if I were you.
PublicLlama@reddit (OP)
The most it does is make a loud clank when I shift into drive.
Blu_yello_husky@reddit
Thats not even transmission related. Check your U-joints
crookedledder@reddit
Yes, you should change it. No, new ATF will not damage an old transmission.
Blu_yello_husky@reddit
Thats not entirely true. If you use full synthetic fluids in old transmissions, even if the bottle says its compatible, the additives in the synthetic fluid can actually break down internal seals and gaskets, whuch will cause internal pressure loss and shifting problems. The old rubber and gasket materials from the 80s and 90s is not compatible with modern day synthetic fluids. Youll be doing more harm than good if youre nit rebuilding the whole tranny.
Illustrious_Tea5569@reddit
It calls for mercron v which is a synthetic blend so the seals are infact compatible with synthetics.
Blu_yello_husky@reddit
Ford AOD transmissions take mercon M2C185-A, otherwise just known as regular mercon. Merc 5 is the REPLACEMENT for regular mercon, as mercon was phased out in the late 2000s. Merc 5 didnt exist in 1990 when this truck was new. You want Dex/Merc regular non synthetic tranny fluid for old AOD transmissions, not merc 5.
If you read the owners manual for a 1990 ford pickup, the tranny fluid spec will say "use only Ford M2C185-A (Mercon [TM])". I will bet you money. Merc 5 is like Dex 6. Its the synthetic supercedant for regular mercon.
Illustrious_Tea5569@reddit
I run merc 5 in my 91 aod and e4od with no problems
Blu_yello_husky@reddit
Have you ever heard the term 'anecdotal evidence'?
Illustrious_Tea5569@reddit
It did exist in 1996 while they were still producing these same transmissions with the same internals and seals. They switched because it was a better formula for those transmissions not because they changed transmission design.
ThirdSunRising@reddit
Jesus man at half a million miles anything could be the case. May or may not be the original trans.
And the previous owner must have been doing something right to get it here. If that stuff is original, fluids have been changed. There is no way this thing has half a million on its original fluid.
I’m on team go ahead and change it.
Curious_Hawk_8369@reddit
Yeah, I think they’re not aware how to read the odometer on these trucks, it’s a six digit cluster, but the last digit is tenths of a mile. The AOD in my 89 f150 went to 310k, and then overdrive went out.
I drove it for several years with the overdrive locked out, it was just noisy at highway speeds, and got worse fuel economy. I eventually had it rebuilt at like 325k, and the guy that rebuilt it said he couldn’t believe it drove to his shop. It was so worn inside he claimed it had to of only had one gear. It had 1-3, and reverse though, it was definitely shifting. At 500k if original, I’d think there’d be nothing left.
howrunowgoodnyou@reddit
Yes also your friend is an idiot
Jumpy_Childhood7548@reddit
Look at the fluid on the dipstick.
Chainsawsas70@reddit
A "Basic service" will be fine... What you Don't want to do is a Flush because that can cause deposits that have sealed up leaks to be sent through the system and cause damage VS a basic service will replace Some of the fluid and give you a new filter. The only way to really know what's going on is to get the pan off and look which is what happens for a basic service.
sharpshooter999@reddit
I've heard of more guys having issues after doing a flush than not. I always pass on them
LAM678@reddit
i had a mechanic flush the burnt-up fluid in my 1979 mercedes and now it shifts a lot better, YMMV
gmehodler42069741LFG@reddit
Drain and fill. Every 50k every vehicle ever made.
bygoneOne@reddit
500k miles? Do not touch it, lol. Just pray it starts every day.
PublicLlama@reddit (OP)
It's a blessing when it starts and when I get home. I'm broke, but the tires are dry rotted, the coolant needs to be flushed, and God knows what else it vibrates and makes weird noises, but danm, I love that truck. And it's all I got.
OlYeller01@reddit
As others have said: drain & fill only. Drop the pan, clean out any gunk, change the filter & refill with the correct fluid/quantity. DO NOT FLUSH the trans or drain the torque converter. Repeat every oil change or every other oil change until you get the fluid back to nice & red. You don’t have to change the filter every time, I’d probably go 3 cycles or so before changing the filter again.
You can find aftermarket trans pans with a drain plug built in to make drain & fills easier in the future. A 2.5 gal paint mixing/measuring bucket from the hardware store can help you keep the right amount of fluid going in/out.
Informal_Ad4399@reddit
He's probably referring to an issue sometimes when you change old fluid. Sometimes that fluid is acting like duct tape to hold some failing system in the transmission up.
Not changing it is worse. You're only kicking the can down the road and turning something that may be fixable into a complete transmission replacement.
Either way, you won't know until it's changed.
Reasonable_Tax_5351@reddit
You don't mention if it's an automatic or a standard. If it's a standard you should absolutely change it. If it's an automatic that's a more contested issue as changing the old fluid can absolutely lead to it starting to slip due to worn out clutch packs.