What kind of transmission service?

Roger · May 13, 2002

What are the pros and cons of the various automatic transmission services?

You have the flush method that takes all of the old fluid away (I've heard it can damage the transmission and seals) and you have the old drain method which does leave some of the old fluid in.

Which method is the best? I know dealerships that will swear that the method that they use is the best one (but then I've wondered if the old method dealerships are just too cheap to buy the flush equipment).

I'm coming up to my first servicing with my 01 Silverado (getting it done at around 10K-12K)

May 13, 2002

I've had mine flushed each time. I've never heard of flushing damaging anything and frankly, I don't see how it could damage it.

From what I understand, the transmission is flushed with tranny fluid at a low pressure(normal pump pressure).

Just swapping out the filter leaves an awful lot of old, dirty, broken down fluid in the system.

carguru · May 13, 2002

Flushing is the way to go. I haven't heard anything bad about that process if done correctly.

racer0175 · May 15, 2002

i've just bought a 99 silverado with 37000 miles on it. i dont think that the fluid was ever changed, although the truck is mint and appears to have been maintained well. i want to change the fluid and filter will this be fine or should i get it flushed professionally??

gilbo · May 15, 2002

i would agree flushing is d way 2 go

Suburbanite · May 15, 2002

If you don't mind paying the money, flushing is definitely the way to go. I'm too cheap, so just install a drain-plug at the 1st change & then drain the tranny fluid and refill after a few hundred miles.

Specs below will perhaps help in your decision:

4L60-E -- Drain & refill ------------- 5 qts

--------- After complete overhaul -- 11 qts

4L80-E -- Drain & refill -------------- 7.7qts

----------After complete overhaul -- 13.5 qts

So, for both of these trannies roughly 1/2 the fluid remains unchanged with just a drain & refill.

Bulldog · May 16, 2002

Hmmm, someone on another board told me that completely changing the fluid is a bad thing to do because the fluid mends with the parts over time. They stated that it is not like an oil change where the oil actually burns and gets dirty, the tranny fluid should only be changed when there is trouble. At most they said to change whats in the pan when you change the filter. Now I'm wondering, flush or just change whats in the pan.............

carguru · May 16, 2002

Hmmm, someone on another board told me that completely changing the fluid is a bad thing to do because the fluid mends with the parts over time. They stated that it is not like an oil change where the oil actually burns and gets dirty, the tranny fluid should only be changed when there is trouble. At most they said to change whats in the pan when you change the filter. Now I'm wondering, flush or just change whats in the pan.............

Old think was that it was fine to replace the fluid in the pan and filter. Replacing just the fluid in the pan still leaves a lot of dirty fluid within the tranny. Since the tranny is not as often serviced item, it is hard to tell whether the filter is clogged during service. For this reason, flushing is well worth the effort. Early equipment (if available--really expensive so many shops did not have them) that flushed used higher pressures and would sometimes blow seals within the tranny. The latest equipment uses much lower pressure (about the same as the internal pumps in the tranny). Tranny fluid also tends to glaze parts over as the fluids break down. This also is not a good thing. Typically the manufacturers recommends changes at regular intervals (more often if you tow, drive much in stop-go traffic, etc.). Tranny fluid does get dirty. It collects all of the wear particles from the tranny. I guess that it is sort true that you can change fluid only when there is trouble. It is not PM then, it becomes repair work. I'd recommend flushing.

May 17, 2002

I agree with carguru 100%.

I think transmissions in general and especially automatics are largely ignored as far as periodic maintenance. I guess this is because with a light or normal workload, most of them are pretty maintenance-free. However in a vehicle that does a lot of heavy work, I can't afford to take a chance on mine.

I've had to change too many of them in the old beater trucks that I've driven over the years. Now the autos are way too expensive to swap out.

Shoot, ten years ago you could have a TH-350 for $75.00 with a converter.

A TH-400 was $250.00

Try to find a 4L80E...