Trans Flush Advice

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AW-71 on a red block volvo - 170k

Trans service at around 75k

What is the story about trans flushes being bad? I have a hard time buying that they will destroy the trans because of dissolved gunk.
 
Depends what kind of flush. The problem is alot of times from the fluid being forced through the transmission it can stir up sediment. The sediment can then clog ports and then cause fluid starvation internally. If they flush it where the transmission sucks I the new and pumps out the old then its probably not going to stir anything up. You could just do a couple drain and refills.
 
I think the accepted method is a fluid exchange. The popular method is to disconnect a cooling line and allow the engine to pump the trans fluid out. Once it cavitates you add more fluid and repeat until new fluid is being pumped out. I find it easier then pan drops. You don't mess with RTV sealant, gaskets or 2 dozen bolts and fluid dripping everywhere.
 
Originally Posted By: BrianF
I think the accepted method is a fluid exchange. The popular method is to disconnect a cooling line and allow the engine to pump the trans fluid out. Once it cavitates you add more fluid and repeat until new fluid is being pumped out. I find it easier then pan drops. You don't mess with RTV sealant, gaskets or 2 dozen bolts and fluid dripping everywhere.


And you get to leave all that sediment on the bottom of the oil pan and a dirty filter.
 
I was hesitant to do an ATF flush in her 150k mile Volvo, but last spring we had to do something when it started slipping. All is good now.

If you arent experiencing any any issues, now is the perfect time to get started.

We did a cooler line flush with a kit from FCP Euro. Sadly with these, the "pan" doesn't come off and the the filter cant be changed. We did pull the drain plug while the engine/ transmission was hot though. Roughly 3.5 quarts come out with this method.
 
Originally Posted By: Local Color
AW-71 on a red block volvo - 170k

Trans service at around 75k

What is the story about trans flushes being bad? I have a hard time buying that they will destroy the trans because of dissolved gunk.


There seems to be no such thing as a forced flush. Not a single auto trans "machine" applies any pressure or "forces" any fluid into your trans. All they do is allow your pump to do the work required. Nothing is flushed or forced, just new fluid is introduced and follows the exact paths within the trans as normal operation does.

Also remember that for a normal auto trans the majority of debris is generated early in its life. Typically these can be fewer as the trans ages...
 
They shouldvcall a "flush" an automated fluid exchange as it just uses the transmission pump to push out old ATF. The machine supplies new ATF to the pan at the same rate old ATF is pushed out. But a machine allows the mechanic to do something else for 20 minutes.

The filter (if there is one) should be changed before the flush. And the pan bottom and magnets wiped clean.

No kind of flush even with a BG chemical will clean the filter. Despite what some service managers may want to tell you.

Consider installing a Magnefine inline filter, you should not need to drop the pan with a Magnefine installed.
 
SteveSRT8 said, "There seems to be no such thing as a forced flush. " I bet to differ.

I've seen machines tied into cooling lines setting in front of cars with their lines jerking and shifting with the force of the fluid's pressure.

That's all I can tell you. AS IF TO SAY: Was that the exception or the rule? Or, was that ever a popular machine? etc. I don't know the industry.
 
Whether you do a pan drop, suction drain through dipstick, or cooler line exchange, Sonnax engineers have found that circulating solid contaminant levels are going to sharply increase.

The key here is to make sure that an external filter of some type is installed that actually has the capability to catch these contaminants. Even something as simple as a Magnefine is a big improvement over the stock transmission filter.

Honestly, I think doing both a pan drop and a cooler line flush is a good idea. When I recently did the Mark VIII's transmission, the pan was completely disgusting, and the magnets absolutely overloaded. I will not be doing a cooler line flush again without doing a pan drop at the same time. The transmission is worth the effort.
 
Originally Posted By: Kira
SteveSRT8 said, "There seems to be no such thing as a forced flush. " I bet to differ.

I've seen machines tied into cooling lines setting in front of cars with their lines jerking and shifting with the force of the fluid's pressure.

That's all I can tell you. AS IF TO SAY: Was that the exception or the rule? Or, was that ever a popular machine? etc. I don't know the industry.


Some vehicle's transmission lines are under serious pressure.

Beyond that, I can't draw any logical path of how forcing fluid into a transmission could possibly damage it, because that's not actually possible.

A transmission's pan is an open reservoir. If the fluid were introduced at necessary pressure and volume to be "forced" into the transmission, it would erupt out of the dipstick tube first.
 
I have a built TH400 that will burst normal rubber lines used for coolers. It generates a ton of pressure!

Transmissions have check valves and such all over to insure correct direction of flow. No machine can force fluid into them.

I own a B&G Trans "machine". All it is is a cabinet with a bladder for new fluid and a can for the old stuff. A small sight glass on the face is there to let you see the fluid coming out. No machinery of any kind. Also a nice tray of adapters to fit almost any car.
 
Originally Posted By: DoubleWasp
Whether you do a pan drop, suction drain through dipstick, or cooler line exchange, Sonnax engineers have found that circulating solid contaminant levels are going to sharply increase.

I don't see how a cooler line exchange would have more turbulence than regular transmission operation.
 
I have done many drain/fills on our 2004 and 2007 Volvo's. Use the correct specification fluid. No issues. I just keep diluting the contaminants and wear particles while refreshing the fluid characteristics.
 
Originally Posted By: Kestas

I don't see how a cooler line exchange would have more turbulence than regular transmission operation.


From what they have stated, it would seem new fluid has the tendency to loosen up solid contaminants in a way that old fluid no longer does.
 
In response to Lubeneer, I do agree that opening up the pan to remove the filter and clean the sump would be beneficial. That's what I do, mind you I have yet to find anything out of the ordinary. My doctrine is on the first fluid exchange to drop the pan, clean it and put in a new filter. Then from there leave it buttoned up and continue with regular exchanges.
 
Originally Posted By: BrianF
In response to Lubeneer, I do agree that opening up the pan to remove the filter and clean the sump would be beneficial. That's what I do, mind you I have yet to find anything out of the ordinary. My doctrine is on the first fluid exchange to drop the pan, clean it and put in a new filter. Then from there leave it buttoned up and continue with regular exchanges.


That is pretty much what I have done over the years with all my vehicles. On my Ford F150 I put a drain pan on with a drain bolt. From here on out it will be a dump and fill procedure for changing my fluid. On my Toyota Tacoma I owned in the past I put a transmission drain plug on. I used that as my satellite install truck. Every other oil change I would also drop the transmission fluid and refill. I was able to keep the fluid freshened up that way and never had a lick of transmission trouble.
 
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