Transmission Flush

[One Acre Farm]

Just purchased an 03 silverado that I plan on doing some towing with. It has 100k miles and I want to change the transmission fluid. I have been told by one mechanic that a flush is the best option, I have been told by another mechanic to drop the pan and change the filter, he claims a flush isn't the answer cause you want to leave some fluid in the system. He explained that the clutch additives were helpful. (or something to that effect) Any thoughts?

 

[moship]

Flush is the only way to get a larger % of the old fluid out, however the filter is not typically changed during the process. If planning on keeping for any length of time have the trans flushed and ask them to change out the filter also. Unlike years ago, most filters are screens and not fibrous material.

I am not aware of any reason why it is necessary to keep any fluid in the trans during a pan drop vs. flush. When rebuilding an auto trans the system is fairly dry except for possibly prefilling the torque converter.

Would you only want to change 1/2 the hydraulic fluid in your tractor and call it good?

It is common during the flush to add a cleaner first, drive for 10-15 minutes, flush and install and additive package. Some companies that sell the flushing equipment/fluid will warranty the trans depending on the mileage at time of flush.

Additives in automatic transmission can make a big difference and is how some of the OEM's alter their shift characteristics. It's crazy how they use chemistry to impact symptoms.

 

[timswi]

Have it flushed..I had an 04 that needed this every 40k or so and the performance difference is very noticable.

As was said, there's just a screen, so no filter to replace..Supposedly the flushing process takes care of cleaning it.

You really don't want to leave old fluid in there if it can be avoided.

Costs about $160 at the dealer.

 

[crashz]

I've never flushed them, however all my vehicles have the filter and pan fluid changed yearly and a pan fluid change at each oil change. Saves going to the dealer for a flush and I've never really liked the "bucket" method.

Without know the maintenance history, I recommend a flush as well.

 

[Diamondpilot]

Do the flush. I do it my self by dropping the pan, changing the filter, topping it off, removing the output hose off the tranny cooler and putting it in a bucket, starting it with a helper, pumping out 4 qts, fill, pump out 4 qts more, fill, pump out 4 qts more, fill, pump out 4 qts more, top off and drive.

Cost about $60 to do it yourself. If you are not comfortable doing this take it to the dealer. Either way, flush it. The second guy you talked to is dumb as a box of rocks. Flushing is always better.

Chris

 

[brokenot]

I don't think flushing is a bad thing, but why isn't it recommended in the maintenance schedules of most vehicles? In many cases, I think it's one of those service practices that's offered up by garages because the cash register likes it.

On another forum, I posted that I thought it was mainly a "gimmick-sell" because most maintenance schedules don't include it. They say to change the fluid at recommended intervals, but don't mention flushing at all. One member scanned and posted his entire maintenance manual to "prove" they did recommend it...but he didn't read it real close, because it simply said "change" as well. The only time "flushing" appeared, was in reference to the cooling system. If they recommend flushing anything, it's called out specifically.

I overhauled automatics for years, so I'm not unfamiliar with their inner workings. I just think that had the owners simply dropped the pan and changed the fluid as recommended, most of those transmissions would have never ended up on my bench. (Well that and sticking with recommended towing guidelines and such.)

A vehicle sitting still in park with a cooling line loose will get out more of the old fluid than just dropping the pan, but if you're just sitting there in park idling there's not a whole lot going on. Servos, pistons, clutch packs, valve body ports and pathways, etc. will be sitting there essentially doing nothing.....and as such won't benefit from the flushing. Show me a flushing apparatus that allows the trans to be shifted through the ranges under a light or no load simulating and easy cruise down the road to really flush things out...and that would be another story. That's not how it's done however, and if it were done that way the sign outside the garage wouldn't read "$99 Trans Flush Special".

For a DIY-er, I think sticking to recommended change intervals is more than adequate. Reading the actual owners manual and heeding payload and tow ratings is a good thing too.

 

[Hematite]

Brokenot, I agree completely. A fellow that I worked with had his auto trans damaged at a dealer because they set the pressure too high on the flushing machine. Blew out a spot on the casting. They "fixed" it with a wad of epoxy putty. LOL. Leaked after that.

Drop the pan, change the filter (extremely important), use a parts cleaning brush (new) and solvent and air to clean the debris from the pan and put the pan back and replace the oil. Never "wipe" the interior of any trans with any type of cloth. The tolerances on new transmissions are so close that the tiniest lint will cause a problem. Unless the fluid has been ruined (burned) by abuse, that is all that an auto trans needs to have done.

 

[brokenot]

Unless the fluid has been ruined (burned) by abuse, that is all that an auto trans needs to have done.

Funny you should mention that, because lots of the trans flush questions and answers I've stumbled across on the 'net have originated with a post from a vehicle owner that has burnt fluid and/or a transmission that's acting up. So it seems like a lot of the folks that are curious about it, haven't had their curiosity peaked because they're really all that maintenance-minded. It *sort of* appears to be considered in lots of situations as a "fix" for one thing or another.

I'm still unconvinced, because it's simply not recommended. I think instead of a flush at 100,000+ miles, the normal fluid changes should occur at the recommended 30 or 40K intervals. Doing it the other way kind of sounds to me like ignoring a bearing repack recommended service interval that's around every 40K or so....and then doing it really well at 100K by cleaning the parts in a jewelers ultrasonic cleaner instead of the old parts washer in the corner.



Once again though, I'm not "against" the so-called flushing, I just wonder why the OEMs didn't put a convenient downward-facing tee fitting in one, (or both), of the cooling lines. It could be easily hidden, (if they so desired), so Joe Homeowner couldn't easily access it, but it could be opened up on the hoist at the dealership to make flushing simple without having to muck about with line fittings.

But they don't, so....

 

[Hematite]

The homestyle "flushing" that Chris recommends, above, also can be a problem. Since you are working with a bucket, there is an excellent chance that dirt of some nature is going to be introduced into the transmission. Either from clothes, gust of wind, dust, etc. It doesn't take much to screw up a transmission.
I believe the transmission flushing machine came into use to wholesale remove fluid in a transmission that has been abused. Unfortunately, at that point, changing the fluid is probably a waste of time, the trans is toast. As long as the trans is maintained and not abused, I feel the filter replacement and pan cleaning is more than adequate to ensure reliability and longevity.

 

[Diamondpilot]

When I do a bucket flush the bucket is only used to catch the old fluid. I pour the new fluid in via the dipstick with a funnel from the qt containers it comes in.

Also, many modern trannys have no filters. Same thing with fuel systems. They are sealed units.

Chris