BG Trans Flush Procedure?

[Skibane]

Just had my transmission flushed at an independent garage, after replacing the filter myself. The tech added BG transmission flush and then ran the engine for perhaps 15 minutes. I ran through all the gears several times while the old fluid and flush chemicals were circulating, and then he used a BG flush machine to replace the old fluid with fresh Mobil 1 synthetic ATF and a can of BG transmission conditioner.

However, while he was replacing the fluid, he told me that it isn't advisable to run through all the gears again, due to the way the flush machine is "teed into the cooler lines and uses the transmission's oil pump" (his words).

This doesn't make sense to me - How is the new fluid supposed to displace all the old fluid and transmission flush chemicals, if it doesn't get a chance to circulate through all the valve body passages?

Am I missing something, or am I still driving around with several quarts of old ATF and solvent circulating through my transmission?

[elwesso]

I think hes right... The idea with the flush chemical is that you want it to go ALL through the valve body and clean the valves and passages.... The valve body only holds a TINY bit of fluid (its hard to say how much, but its not very much AT ALL), so even if some of the fluid with the cleaner is still up in there, its not enough to matter..... It certainly most likely holds MUCH less than 1/2 pint (1/4 quart)... This is why its impossible to get a 100% fluid exchange, its only like 90-95% at best.... Still better than most other methods, which are like 80-90% at best.

You dont want to shift gears while doing the flush because then you redirect fluid into other parts of the trans, and it mixes more of the fluid.

Technically there is still some stuff moving around in there, but its probably less than 5% of the total fliud anyway, PLUS the cleaner has evaporated away already.

[Q451990]

Sounds like you got a good flush...

Heath

[maxnix]

This is why its impossible to get a 100% fluid exchange, its only like 90-95% at best.... Still better than most other methods, which are like 80-90% at best.

You dont want to shift gears while doing the flush because then you redirect fluid into other parts of the trans, and it mixes more of the fluid.

BG distributor told me it is in excess of 98% exchange of old fluid.

Seems like I remember Q45tech recommending going through the gears with the BG machine as it used the transmission pump. Sun machine has its own pump.