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AUTO TRANS. fluid & filter change? or fluid flush?


Well-known member
Jan 27, 2001
St. Peters, MO.
1996 LT4 coupe + 2004 Z06 Z16
I was wondering if the transmission fluid flush service that many transmission shops offer for around $100.00 is worth it over the usaual "fluid and filter change" they charge $40.00 for or you do it yourshelf in your garage.

Seems like you leave a lot of fluid in the convertor and other parts when you simply drop the pan and drain it that way.

This should apply to all automatic transmissions, but, mine in question is the 4L60E in a 96 Vette and also in my 94 GMC pick-up!


I'm no C4 buff but I can say pretty confidently that the flushes are far better than just dropping the pan and refilling regardless of what kind of car. Depending on the trans your looking at anywhere from half to two-thirds of the fluid staying in the system. I get my trans flushed once a year on both of our drivers and they both have relatively high miles and I've never had an instance of trans problems. My opinion is that I'd rather spend 75-100 now when I'm planning on it than 500-1000 when I'm not.

If your fluid is old and/or darkened you will probably notice much better response after a flush and as a bonus the trans is going to run cooler.
You should change your fluid (in the pan) and filter about every 25,000 miles.

As for whether or not you need to change the whole load (ie: flush) of fluid, it depends on the overall mileage on the vehicle, the condition of the trans and the condition of the fluid.

If the trans works well, has less than 75,000 miles and the fluid is bright-to-dull red, I'd leave it alone if you are significantly less than 25,000 miles from your last filter change. If you're near your next filter change, do a normal fluid/filter change. Flushing is probably unnecessary.

If the trans. is high mileage and the fluid is redish-brown or brown, flush the trans and change the filter.
Don't flush past 75K

Every car I have ever had ( High milage ) that I have had flushed in a little while has started to slip. The brown material in your tranny is usually shedding from the friction clutches. If you remove this it is typically bad news. A tranny flush typically will not include a filter change. I am of the opinion that every 30K drop the pan and just do it that way, droping the pan will also let you know how bad things are inside, Bronze shavings indicate bearings going, dull grey case metal, brown stuff friction material etc. I have had my fair share of tranny problems..... DONT FLUSH, change filters & inspect! Oh and NO ADDITIVES

71Shark said:
as a bonus the trans is going to run cooler.

By the way how hot is normal for the automatic trans in a c4 specifically a '95?

Trans Flush or Filter and Fluid Change?

When I got the 94 Convertible, I took it to the dealer for a trans flush, it had 63K miles on it. Their records showed the previous owner had the FLUSH done at 25K and 50K miles. So I just had a fluid and filter change done. He said any dealer database can tell you, if your not the orginal owner, what has been done to the car. Is this true? He also told me the same thing in earlier post in this thread, do not flush if over 75K miles!. However he did tell me that you can change the filter and fluid every 10K miles and get the trans clean over a period of time. This allows the fluid to stay at the right viscosity. Flushing is a shock to the system if not done on a regular basis. As mentioned in earlier post in this thread, it can cause the tranny to start slipping and leaking, this is caused due to the increased pressures building up inside the tranny with the amount of NEW fluid that is put in during a flush. He told me 60% of the orginal fluid in a tranny stays in it during a fluid and filter change, is this true? And if so it stands to reason that if your car is over the 75K miles, more frequent filter and fluid changes will keep it running at its present operating condition, and extend its life. Any thoughts on this type preventive maintenance program would be appreciated. I would like to have mine flushed as well, but am afraid to do so.


Re: Don't flush past 75K

vigman said:
Every car I have ever had ( High milage ) that I have had flushed in a little while has started to slip. The brown material in your tranny is usually shedding from the friction clutches.

Ahhhh....be careful in diagnosing the brown material.
When you have automatic transmission fluid that changes from red to brown, the fluid has been overheated. Automatic transmission fluid contains a thermally-sensisitive component in its red dye that turns brown when the fluid has been overheated. ATF that's been overheated begins to oxidize and that oxidation forms solid particles that abrade the metal parts in the transmisison. The dye's change of color is to alert the user that the fluid is oxidized or is oxidizing and needs to be changed.

Now, if you drop the pan and find fragments of brown, gray or black fiberous material stuck to the filter or in the bottom of the pan *that* indicates you have clutch plates that are failing. Also, if you drop the pan and find more than about a dime's worth of fine metal powder, you're probably due for overhaul.

Yes that is correct! ( from the overheating & Dye standpoint) However The brown material is "usually" sheding from the friction material. I did forget to say that I assume ( making an ass out of myself again) that most Vette owners here do not beat their cars.

( having a crow sandwich )

However I still stand on the NO flush past 75K

If they don't drop the pan and change the filter, I would say no way to a flush. Even on a good, not abused tranny, you will find some "gunk" on the bottom of the pan and the magnet. I took my filter apart, and it looked fine. Doing a filter change on the '96 will require only a little over a gallon to refill (less than 5 qts.) so you are certainly not changing all the fluid.
A flush can stir up little particles that can cause any one of the delicate spool valves to stick. Then a shift problem results.

Many newer vehicle have no change systems because of exactly that reason, things get stirred up and bingo, a problem, and this is under the assumption that filter/ATF would have been changed.

Its best to go by the book for proper care.

Additives and flushes have damaged many an engine and transmission. I see it alot.

BTW my '88 has had regular fluid/filter changes, I clean the material off the magnet. It shifts perfectly everytime
Thanks for the input,
Looks like I'll just change the fluid and filter in the pan like always. About every 25,000 to 30,000 miles.
Issues with A/T

HI there,
First, normal temps can hit as high as 245-260, depending on if you race autox or not. Normal driving, 230. This goes for any year and model with a torque converter clutch.
As for the changes, my customers are advised, every 2 year or 24k, without exception. There are many reasons for this, and many opinions, however, I like to stand on facts, so here is what is known.
Transmission fluid does many thing within your units. Transfers power within the torque converter, provides cooling to your transmission, shifts gears within the valvebody, AND LUBRICATES.
With this in mind, you must understand that all fluids breakdown over time, and in that, you can never change your fluid too often. The lubrication properties are critical to friction band, clutches, sprags, and bronze bushings within the transmission.
Remember that fluid does almost 85% of the work in the automatics, so you can see, the life of the fluid is critical to the well being of the trans.
If you drive your vehicle hard, and you know who you are, LIKE ME. I change it every year, or 12000. While you can hold to the 75k theory, I can understand why, as varnish is built up within the transmission, you are washing the varnish away, when you change your fluid. However, the more you change your fluid, the less varnish build up there will be, therefore, less chance that your will experience problems.
A last thought on fluids, DO NOT, under any circumstances, use a generic brand of Dexron 3 ATF. These fluids are just above Dexron 3 standards, and will not have the lubricity, or additive packages to correctly work within your transmission for the life of the interval.
With this, as with most everything else, you will get what you pay for.
Besttoyouall, c4c5

HI Keith,
Personally, I like synthetic Mobil 1 ATF, only because it resists breakdown, and oxidation better than conventional tranmissions fluids.
I have used many different name brands, all with good reliability. Castrol, Quaker State, Mobil, and others all have good fluid. What I was refering to was the generic brands, like a name you never heard of before. Yes, it holds to Dexron 3 barely, but without alot of the additives that normally work to help seal life, and internals.
Besttoyou, c4c5
Hi there,
I will change out the fluid, filter, and then, remove the upper line into the radiator. I add 4 quarts to the trans, and then run it till it stops. I do this 3 times, and that will flush the fluid out of the converter.
besttoyou, c4c5

If you switch to a "synthetic", like Mobil 1, do you have to flush the entire transmission? or can you just change whats in the pan from now on to the synthetic fluid?

Does synthetic mix with conventinal Dextron3 ???


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