Changing the transmission oil.

[Yamero]

Ok, so for the longest time I have that if you change the transmission oil on a vehicle with high mileages the transmission is going ti fail. Is this true to the d21 5 speed transmission? I want to change it because I don’t know when es the last time that it got changed and I know for sure that it has at least 5-6 that was sparked.

[SBJ]

Nope, you're good. You'll need to use a GL-4 specific oil such as Redline MT90, though. Sta-Lube also makes one that's a lot more affordable. You probably want to keep an eye on your clutch hydraulics. After several years of not being used I wouldn't be surprised if they leak once you start driving it again.

It's an old wives' tale that changing the transmission fluid will cause it to fail, and refers to automatic transmissions. If a transmission is in good shape to begin with changing the fluid won't hurt anything (assuming it's the correct type of fluid). On the flip side, once a transmission starts acting up the damage is usually already done and changing the fluid won't fix it.

[Cusser]

Originally Posted by SBJ

It's an old wives' tale that changing the transmission fluid will cause it to fail, and refers to automatic transmissions. If a transmission is in good shape to begin with changing the fluid won't hurt anything (assuming it's the correct type of fluid).

Local radio show master mechanic discussed exactly this on last week's show. He said that was a scare tactic used by disreputable transmissions shops to scare folks into getting their transmission rebuilt.

We experienced this in 1995 on Mrs. Cusser's newly-acquired 1988 Suburban, wanted the ATF changed, so she took it to a transmission shop. They showed me the pan, had a few particles in it, but looked pretty good for 100K and previous owner had towed with it. Shop said fluid was black, and putting in new ATF would cause immediate failure, so all they could do was replace the old ATF (which was likely in an R2D2-looking waste container mixed with everyone else's) or offer $150 towards an inspection/teardown, which "of course" would apply to a rebuilt transmission. I told them a unit with 100K miles would NEVER meet original specifications, to put the "old fluid" back in, and she took it home. 50 miles later I decided to check the ATF level, and not only was the level OK - but the ATF was PINK !!! So I called the shop to ask how "black" ATF could turn pink, and they promised to have the shop foreman call me. 27 years later, haven't been called.

I'd never even driven automatic before this, but I changed the ATF myself a couple of weeks later. No "lock up".

Originally Posted by SBJ

On the flip side, once a transmission starts acting up the damage is usually already done and changing the fluid won't fix it.

True

[ahardb0dy]

I used Amsoil GL-4 in my manual, worked good.

[Deerhurst]

Manual tranny you won't have a problem with tranny flushes.





There is more risk with an auto. Fresh ATF can dislodge junk and clog things up. I've known folks that had this happen. Tranny flush then a chunk of crap broke free and clogged a solenoid or filter mesh. Caused some issues with drivability.





I've also seen that with really nasty engines too. Fresh oil with a touch of ATF in it blowing all sorts of nasty stuff out!



ATF is a great detergent.

[LugNut1990]

Originally Posted by Cusser

He said that was a scare tactic used by disreputable transmissions shops to scare folks into getting their transmission rebuilt.

I used to work at an independent transmission shop long ago. No, not always a "scare tactic" -- often a burnt-up trans could still limp along for a while longer with the ancient, gritty fluid providing a little grip in the clutch-packs. When new fluid and filter were installed, it would slip much worse.

When we pulled the pans on failed/failing transmissions (due to clutches, etc.), they were often caked with friction material. In consulting with the customers, it was our honest advice that it was time to rebuild.

[ahardb0dy]

Changed the ATF in my former 94 Pathfinder when it was at 199K miles, no idea when it was replaced last, used Valvoline maxlife, no longer have the truck but new owner hasn't said anything about having any problems with it.

[cadillacdude1975]

People treat the automatic transmission with the no problem, no service/maintenance response. All oils are supposed to be changed at some point. If an auto trans starts having problems, the damage started a long time before the problem arose.

[street_rulerr]

Originally Posted by Cusser

Local radio show master mechanic discussed exactly this on last week's show. He said that was a scare tactic used by disreputable transmissions shops to scare folks into getting their transmission rebuilt.

We experienced this in 1995 on Mrs. Cusser's newly-acquired 1988 Suburban, wanted the ATF changed, so she took it to a transmission shop. They showed me the pan, had a few particles in it, but looked pretty good for 100K and previous owner had towed with it. Shop said fluid was black, and putting in new ATF would cause immediate failure, so all they could do was replace the old ATF (which was likely in an R2D2-looking waste container mixed with everyone else's) or offer $150 towards an inspection/teardown, which "of course" would apply to a rebuilt transmission. I told them a unit with 100K miles would NEVER meet original specifications, to put the "old fluid" back in, and she took it home. 50 miles later I decided to check the ATF level, and not only was the level OK - but the ATF was PINK !!! So I called the shop to ask how "black" ATF could turn pink, and they promised to have the shop foreman call me. 27 years later, haven't been called.

I'd never even driven automatic before this, but I changed the ATF myself a couple of weeks later. No "lock up".




True

isnt this whole thing because theres little bits of clutch floating around and once you drain them theyre gone causing a little more clearance than there was before?



note: i had a honda that had 190k on the original transmission fluid/ every time it shifted it felt like i was getting rear ended by a freight train

[cadillacdude1975]

That clutch dust problem would only be in a filterless automatic…….like a honda. Most other automatic transmissions have a removable pan and a serviceable fluid strainer.