transmission fluid changes

[caddydude1]

I have a 1987 Fleetwood Sixty Special and the mechanic I take the car to is recommending that I have the transmission fluid changed. The car has 122k miles on it. I was reading online where its sometimes not a good idea to change the fluid after 100k miles because it can cause the transmission to slip. Does anyone know if this is true? Should I have it changed or not? Any advice would be appreciated. Thanks.

[dplotkin]

My rule is that in your situation; if the fluid looks and smells next to new (clear, red and smells oily) AND the transmission otherwise operates as designed, leave it alone. If however the fluid is dark, gritty and/or smells burned...and/or the transmission is acting up, change it.

Dan

[russ austin]

If your mechanic is recommending it be changed, then I would follow the advise of a mechanic.    Have not heard that one about not changing the fluid before.

[dplotkin]

  Have not heard that one about not changing the fluid before.

The thinking here is that fluid that appears to be in good condition but has not been documented to have been changed for an extended period of years, in an old transmission that otherwise operates satisfactorily, should be left alone because sedement and debris can be stirred up in the draining & refill that could lodge in the tiny orifices or hang up valves in the valve body.

In a transmission with nasty looking and smelling fluid, and/or if the unit is malfunctioning, a flush and refill can only improve things, there is nothing to lose.

Dan

[Alan Harris CLC#1513]

I have heard the one about not changing fluid in an older transmission. I have never believed it.

I owned a 1986 DeVille back in the day. My recollection is that the fluid and strainer were supposed to be changed at 100K for the first time. I am sure that by now, your strainer is not at peak efficiency and your fluid's additives are depleted. I would change it.

[EAM 17806]

Just review your owner's and/or shop manual for recommendations. I would agree to change the fluid after 100 thousand miles for continued good transmission operation.  EAM

[Glen]

Is it possible there is confusion with draining and flushing?  I’ve never heard of not changing the fluid.  I have heard where someone got a flush and the transmission never work right since.  The flush would stir up a lot more sediment and could damage seals. 

I would do a change and change the filter too. 

[Big Fins]

GM's problem is no drain plug in the converter. Pulling the pan and filter will only get you a 4-5 quart fluid exchange. It is noted that the best way is to drop the pan, replace the filter, clean the sediment out of the pan and put it all back.

Then remove the return line from the cooler and run the car while adding new fluid through the dipstick, you are flushing the old fluid out. It's messy and time consuming. But unless you pull the unit out, it's the best way to assure all of the fluid is changed.

Don't ever let one of these oil change places use one of those flush machines. Most people never service the transmission until there is trouble. And all of their trouble gets trapped in the machine and run through your transmission.

[Scot Minesinger]

I have heard that changing transmission fluid has caused failures, but I don't believe that was the real cause of the failure.  Generally a transmission acting up is sent in for service and the fluid is changed without curing the problem, and then of course failure is blamed on the fluid change.  The other issue is that unskilled and careless mechanics are often assigned the simplest tasks such as this, and the pan debris is not cleaned out, the pan bolts are over tightened, the filter is not changed, or done so incorrectly and etc. 

You should change the fluid, I would do it myself to be able to be sure it is done correctly and to inspect when pan is off.  Read the shop manual on this procedure.  Often the dip stick tube O-ring requires replacement at this time and it is never done.  Before replacing dip stick tube O-ring, clean all debris off surrounding area where dip stick tube penetrates the body of transmission.  Otherwise use a very trusted mechanic.  If your transmission is working well, then a fluid change properly done will be an asset.  If the transmission is not operating perfectly, best to get it fixed correctly now in addition to fluid change to avoid more costly repairs and major inconvenience later.

Good luck,

Scot

[TJ Hopland]

I have heard that changing transmission fluid has caused failures, but I don't believe that was the real cause of the failure.  Generally a transmission acting up is sent in for service and the fluid is changed without curing the problem, and then of course failure is blamed on the fluid change.  The other issue is that unskilled and careless mechanics are often assigned the simplest tasks such as this, and the pan debris is not cleaned out, the pan bolts are over tightened, the filter is not changed, or done so incorrectly and etc. 

Scot

I think this pretty much sums up about 90% of all the horror stories we have heard about.   Everyone leaves out the little bit about how it was acting up before they took it in or that they have not done the previously factory recommended services.

What I have started doing on my stuff is when I do oil changes I suck the fluid out of the PS reservoir and transmission and refill.  I know that does not change it all or get any crap that has settled out but it does get what ever stuff is suspended in the fluid out and introduces a fresh additive package.    My 80 would not shift when it was below zero F out and by 96 truck had strange up shifts, just changing a little of the fluid during oil changes has kept both of them acting normal for almost 2 years now.  I'm sure they both have a lot of wear and issues but I can't complain, they both have a lot of miles by previous owners so I'm am just happy they are working.   

[76eldo]

I did a drain and refill of the Trans on my 76 Eldo
A few years ago and immediately noticed a smoother shift.

The fluid looked ok, no burned smell and it was replaced with the filter as a preventative measure.

I would stay away from the flush machine for the reasons stated above.

Leaving in old nasty fluid is not wise and its a myth.

Brian

[TJ Hopland]

The flush machines I have seen have a big clear cylinder in them that has a piston in it and 4 hoses.   When you are ready to do a flush you stick hose A into a jug of new fluid or its connected to a drum of new fluid.   You push the fill button and it pumps the new fluid in which pushes the old fluid out hose B.  Cylinder is now full of new fluid.  Hose C and D are connected to the car's cooler lines.  You flip the switch to flush mode and old fluid pushes into the cylinder which pushes the piston up which pushes the new fluid into the system.  This leaves the machine full of old fluid that will get spit out next time its filled with new fluid.    Its not like there is a single tank that keeps getting new and old fluid cycled through it.  I'm thinking piston moving in the cylinder does a pretty good job of keeping the walls of the cylinder clean.    So other than the cylinder wall itself the fluid is not getting mixed anywhere that I can see. 

Maybe all machines are not like this one?

[Big Fins]

Or maybe they've updated the machines.
I asked once about them. I was told that the fluid was run through a series of filters, then returned to the car. It didn't sound right to me. I looked the machine over, inside and out. All I saw was a canister that held new fluid that appeared to be for looks only.

That alone tells me that something is below board. At least when I'm laying on my back, I know it's being done properly. New fluid, new filter, new pan gasket, and the bolt holes in the pan are returned to the original pan pressing to insure a good seal when it's put back.

[TJ Hopland]

I would imagine there are several types of machines and the service shop gets what they pay for which may not be at all related to what they charge or claim they do for a service. 

The one I worked with also had a light behind the cylinder so you could see the color of the fluid that was coming out.   I remember thinking it was pretty neat that it seemed to stay layered.   You knew you had it pretty well flushed when it got red again.

I just looked at photos online of the machines and I see some like the one I used with the one big cylinder.  The majority appear to have 2 cylinders or at least sight glasses.  There are also some that you cant see anything like that looking at them. 

[russ austin]

Has a 20005 Buick, and had the trans fluid flushed by the local garage. Soon after, the trans started to slip.  Talked to a transmission shop, and was told that that specific GM trans needed to be flushed a specific way.

Side note; there were no problems with the trans, prior to the fluid flush.

[wbdeford]

I stay away from flushes....I would just change the fluid multiple times if it has been neglected.

[wbdeford]

Another valuable thing to keep you from neglecting the fluid is adding a drain plug if your car doesn't have one.  SO much easier to drain from a plug!  I added one to my '93 Dodge Intrepid, which needed frequent fluid changes....transmission lasted the entire 306K miles I had the car.  Just don't use the plug as an excuse to never change/clean the filter.  Another thing to do is add a magnet to your pan if your car doesn't have a magnetic drain plug or magnet in the bottom.

Also, be sure to drain the torus cover/torque converter if practical, as a large amount remains in there after draining the pan.

[TonyZappone #2624]

I have done flushes on my 56 Eldo (sold), my 58 convert, and my 2002 DTS.  I have changed the fluid on my 47 convert.  In all cases, there were no problems, and all continued to work properly except for the 56, which was never worth a damn, for all the reasons we are aware of.