Transmission Filter Change - Vintage Mustang Forums
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post #1 of 11 (permalink) Old 03-22-2019, 12:35 PM Thread Starter
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Transmission Filter Change

I've been told (I am a rookie) not to change transmission fluid if there are not problems with the operation. The reason being new fluid will clean the transmission and create gunk and crap inside that will cause ultimate failure- and a rebuild. However I have had the car on ramps tending to rust issues so it's been sitting for about 2 weeks. I have noticed a transmission fluid leak on the ground below the pan and drips on the pan bolts. My thought is the pan gasket is bad because the car has not moved. Also the car sat for about 5 years, but has been running (I should say moving because it did not run well b4 I got) for past 999 miles b4 I got it. So my question is the pan gasket a good suspect? Since I've got the pan off i'm going to change out transmission filter too. And 2nd question- What transmission fluid is the best to put back in?
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post #2 of 11 (permalink) Old 03-22-2019, 12:45 PM
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It's not that new fluid "creates" anything, it may swell old hardened seals and could cause friction material on the clutches and bands to degrade. You "could" capture and filter the old fluid for re-use, but a couple quarts of fresh ATF most likely won't do any harm. I definitely would not recommend any of the tranny flush service.

If you have an FMX, C-4 or C-6, use TYPE F ATF only.

You leak could also be the shift shaft seal and kickdown o-ring. Both can be replaced while you have the pan off.



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post #3 of 11 (permalink) Old 03-22-2019, 01:23 PM
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Originally Posted by rvahomes View Post
I've been told (I am a rookie) not to change transmission fluid if there are not problems with the operation. The reason being new fluid will clean the transmission and create gunk and crap inside that will cause ultimate failure- and a rebuild.
I used to hear that when I was a lad back in the '70s. I'm not a transmission expert, but that philosophy has all the markings of an Urban Legend. Personally, I'd put it the same category as, "If you bore a block more than .030, the engine will overheat". People will insist things are true, but it doesn't make it so.

If it was my car, I would change the fluid, the filter and the pan gasket. If it failed shortly thereafter, I would chock it up to high miles and lack of proper maintenance from previous owners and not because I did the maintenance.

That's my take, FWIW.

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post #4 of 11 (permalink) Old 03-22-2019, 02:00 PM
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When I put a shift kit in mine I saw all the small passages and springs in the transmission, doesn't make sense that would run better with gunk running through it not allowing the fluid to flow unimpeded. Knowing that an automatic works on hydraulics just doesn't make sense to me either that old fluid is better. Just my opinion.

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post #5 of 11 (permalink) Old 03-22-2019, 02:26 PM
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Any transmission shop that's been in business many years can verify it is NOT an urban legend and does happen. To the point that they will refuse to change fluid on some vehicles. Knowing full well it would mean the customer coming back a week later saying their transmission worked fine until the shop worked on it and now it won't even move.

It's not that hard to avoid that though. Very brown and "soured" fluid are indicators. Also fluid that is "lacquered", IE it smells like paint remover. Transmission fluid has a buttload of detergents in it, which wear out over time. Fresh ATF sort of takes new scrub brush to the inside of a transmission and does what can be destructive stuff to a transmission's insides. BUT, generally speaking if the fluid still has some red color to it and doesn't stink it will probably be OK. If the fluid has been changed just once or twice in its life it's also very likely fine to change. None of that stuff really happens to vehicles that just sit for years and it's generally fine to change the fluid in those. The fluid does get old and contaminated by moisture (I've seen spider nests!) and stuff. Does such a transmission nothing but good to change the fluid. And get after leaks.

Also Ford stopped producing the weird metallic automatic transmission clutch plates that absolutely required Type F fluid like fifty years ago and no one else ever made those as replacements. So rule of thumb is that if the transmission has been rebuilt or "freshened up" in the last fifty five years or so it will work just fine with Dexron III/Mercon fluid. Because the replacement clutches made by everyone who makes them are of the same material as used by 1970's Fords and GM's. But is you have any doubts at all, Type F is a safe bet to use either way. Some people even prefer it with modern clutch lining material because it makes the shifts feel a bit sharper, like a very modest shift kit. DO NOT use any modern full synthetic fluid like Mercon V or LV. There's a bulletin from Ford even out there warning not to. So "best" would be F. If it's hard to find, Dexron is OK.
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post #6 of 11 (permalink) Old 03-22-2019, 03:43 PM
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I actually had that problem with my own car ages ago.

I didn't change the fluid when I bought the car because it worked, so why touch it? Eventually I figured that since it's supposed to be red, not the nasty brown color it was that I should be nice to the car and change it. And that's where I messed up.

Within days the car stopped going into forward gear until it was good and warmed up. Eventually it stopped liking reverse too till it was warm. I ended up getting the whole thing rebuilt to fix it.

Once the fluid stops looking like transmission fluid and starts looking like gunk some seals or something inside get to the point where they don't work once you flush that gunk out.

As long as it still looks like transmission fluid you're probably fine to change it. If it looks and smells nasty and brown though I'd leave it alone unless you're ready to rebuild the whole thing.
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post #7 of 11 (permalink) Old 03-22-2019, 04:45 PM
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I even drain the converter on c4/c6 fords when i do the filter, i'm a rebel.

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post #8 of 11 (permalink) Old 03-26-2019, 09:42 AM
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I dropped my '67 off to have the C4 rebuilt yesterday and asked the builder this same question, after his long laugh "because everyone asks that question" he started his explanation. According to him, if you change your fluids like you should, changing your transmission fluid WILL NOT cause any harm, the problems that do appear after changing fluid are due to lack of maintenance. He said he sees it all the time, an owner will run 100K to over 200K and never change fluid, but when the tranny starts to shift funny or slip, they decide it's about time to change the fluid. Well. the problem is already there and not introduced by the new fluid, it is aggravated by new fluid. So I ask, "why does new fluid aggravate the problem"? His response was the detergent level in tranny fluid is very high, he suggested I try cleaning my greasy hands with tranny fluid once and see how good of a detergent it really is, this high level of detergent will dislodge the years and miles of crud and plug up little holes and filters quickly, making it seem like the new fluid was the problem, but the true problem is always lack of maintenance on the vehicle.
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post #9 of 11 (permalink) Old 03-26-2019, 09:59 AM
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I worked in a tranny shop for a few summers back in the early 80s as a clean up kid and helper.

I an agree with most of what was posted.

for fluid changes we turned away the work more often than not. If the car had signs of neglect and the fluid was burned or the car was never service with us
and he /she had no prior proof it was ever serviced anyplace else we walked.

if we touched it we owned it. back then a $55 flush would cause a $400 argument over a rebuild "because my car is not shifting right after you touched it"

shops have no defense over those arguments to keep peace and save face with the community

first thing that guy is going to do is tell every one knows how bad the shop is and how they dont gaurentee their work and how they messed up his car

bad news travels faster and further than good news.

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post #10 of 11 (permalink) Old 03-28-2019, 09:11 AM
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Originally Posted by Houdini View Post
I dropped my '67 off to have the C4 rebuilt yesterday and asked the builder this same question, after his long laugh "because everyone asks that question" he started his explanation. According to him, if you change your fluids like you should, changing your transmission fluid WILL NOT cause any harm, the problems that do appear after changing fluid are due to lack of maintenance. He said he sees it all the time, an owner will run 100K to over 200K and never change fluid, but when the tranny starts to shift funny or slip, they decide it's about time to change the fluid. Well. the problem is already there and not introduced by the new fluid, it is aggravated by new fluid. So I ask, "why does new fluid aggravate the problem"? His response was the detergent level in tranny fluid is very high, he suggested I try cleaning my greasy hands with tranny fluid once and see how good of a detergent it really is, this high level of detergent will dislodge the years and miles of crud and plug up little holes and filters quickly, making it seem like the new fluid was the problem, but the true problem is always lack of maintenance on the vehicle.
It's not just the idiot owners that cause the "never change it until there's a problem" issue.

A couple of times when I was younger and dumber I had transmission issues come up and when taking it to the garage, THEY RECOMMENDED replacing the fluid and filter. In both cases the cost was over $100 and in both cases it didn't help at all and I was installing a rebuilt transmission within a week.

What I "learned" right or wrong is that every transmission problem can be easily solved by installing a quality rebuilt transmission and all other "fixes" are futile.

I'm sure that's not 100% right....but it's been my experience.

Ohh...and on my stuff, I try to get the fluid changed at about 75,000 miles and sell it before it gets to 150,000. That has worked for me on the late model stuff. When you do have an older late model vehicle, a bad transmission can essentially "total" the car. When these new 10 speeds Ford and Chevy are using need rebuilt, can you imagine what that will cost? OMG!

Phil

Last edited by HoosierBuddy; 03-28-2019 at 09:14 AM.
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post #11 of 11 (permalink) Old 03-28-2019, 11:56 AM
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Sounds like you went to a transmission shop that didn't know (or care) what they were doing. But you still make a point. Most often a total rebuild is the way go. If the failure was caused by an internal seal getting old and giving way, you can bet every other seal in there is lined up to fail next.
Mechanical failures sometimes can be "fixed". A broken band on a C4 is prime example. They have an ill-designed stress point that commonly fractures. It was such a common issues years ago that someone designed a replacement that you didn't have to disassemble the transmission to install. All often as not, that's all they needed. Later on the early AOD's would "cook" the reverse servo seal. Drop the valve body, swap in a new servo and all would be good again. Some other failures are different. A low sprag gives way but to replace it you have to pull the transmission out and tear it ALL the way down to get to that sprag. And since you already have every bit of it apart it only makes sense to freshen it all up with a rebuild.

The newer transmission aren't as impressive as they sound on the face of it. There's a Dodge three speed you can jigger mechanically and have nine gears. They won't work very well but with a simple multiplier you would technically have that many ratios in one fell swoop. We know this becasue actually did so when they went from a four speed 42TE to a six speed 62TE. They chose only to enable and use six of the potentially available ratios at the time. Many of the newer multi speeds don't even use all those gears either. The newest Ford 8 speed FWD's don't ever use second unless you manually command them to. From a repair point of view, there are more drums and shells but the valve bodies are much less complex. A new 4R140 has a conglomeration of drums that fit together like Russian nesting dolls and weighs as much as a whole T5 but also has like only five control valves. Bunch of solenoids. Leaky valves from wear has been a plague on automatic transmission repairs since ever. Solenoids are MUCH easier to deal with and diagnose. So it's a pretty fair trade off, somewhat more (easily inspectable) mechanical complexity for less complex control systems. More control is being passed off onto the computer.

Rebuild costs drop as soon as Taiwan tools up to make repro parts so rebuilders have choices outside OEM. They do that in Taiwan just like they do with old Mustang parts. Most available new parts for T5 five speeds come from Taiwan these days fro example. I think mainly because Tremec quit making them and there is still a market
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