Transmission Flush Safe? Harryface + Ian

I was reading the cadillac forums and an individual by the name of bbobynski was posting the dangers of transmission flushes. He supposedly is a GM powertrain engineer for 32 years and he is against the
transmission flush. The pitfalls he mentions are: The last vehicle that was hooked up to that flushing machine was probably on its last leg and was generating tons of debris. Most owners, when the transmission starts to act up, rush to get a "flush" in the hope that it will cure the problem. So...flush machines, by definition, see the worst of the worst. If the lines aren't cleaned, hooked up improperly, oil is re-used or recycled, etc.. then you are screwed as your transmission gets the dose of debris from the last transmission. He says that no matter how good the intentions of the shop, one simple mistake and your transmission gets the debris. He then mentions that Transmission Flushes are money makers for shops and dealerships because they are quick and easy and they can actually charge more money for it under the guise of it being better for the trans.
Harryface, has your bonneville with close to 300K miles had flushes or just fluid and filter changes? I know you have had a transmission rebuild but you seem to have good luck with the number of miles your parts last.
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Vince,
I probably shouldn't tell you what I do, but what the heck, its worked for years with no problems. We'll let the boys in here chew on this routine for awhile.
Before I remove the trans pan & filter I remove the trans line going into the side of the case and then start the car up to pump the oil out. I got a clear tupperware storage container I let the fluid run into. I got a line on the side of the container which is the 2 gallon mark, then I shut the car off. Other guys I know would shut the car off when the oil stops spurting out, but then the trans may get to hot.
Afterwards , I drop the pan & filter.
Depending how much oil is around the house I may pull the line of a day later and pump out another gallon or so, then refill.
Of course since my transmission was rebuilt it runs 5 more quarts than originally intended, 15 instead of 9. The trans man said this trans should run with more oil than what GM originally specified. He said that there were independent tests done and it was determined 15 quarts of oil was better for this trans. Of course nobody at the Chevy dealer I deal with has ever heard of this, nor anybody else I've mentioned it to. But, our trans man has been in business since the early 70's and he does alot of speed work, shift kits & race cars, so I trust his work.
108,000 miles on the rebuild trans.
So, 15 quarts have been in it since 2001 and it don't foam up and works just fine. Now I change it every 30,000 miles. or once a year say.
This is the old style hydraulic trans, not the all electric style like 92 & up.
Good Luck.
========Harryface ======== 1991 Pontiac Bonneville LE 3800 V6 ( C ), Black/Slate Grey _~_~_~298,614 miles_~_~_
~_~_~_~_U.S.A._~_~_~_~_~_
~~~The Former Fleet ~~~ 89 Cavalier Z 24 convertible 78 Holiday 88 coupe 68 LeSabre convertible 73 Impala sedan
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I want to fully understand your transmission flushing procedure. By remove the line come into tranny, (there are two lines, is it the top one?) running the engine to empty the fluid from lock-up converter. One empty, immediately shut the engine off that should take no more than few minutes. This procedure should empty entire transmission fuild? Drop the tranny oil pan and clean the pan/magnet and install new filter Add new tranny oil. Start the engine then check for oil level
Questions: 1/ Any concern with air entrapment? (another word is there a bleeding procedure?) 2/ Is ther an oil pump in tranny? any concern about oil pump damage due to oil starvation? 3/ Generally, I drop the tranny oil pan to drain the oil. Clean the pan and top it up with new oil. If one is corner about the oil lubrication quality, should we change the oil often or doing the job twice.
Sorry for asking many questions!

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vince wrote:

Yeah, I've read numerous posts of his, and have both argued for and against whatever he believes in. He is very knowledgeable, but has this very "corporate" attitude, ie: GM can do no wrong, most problems with their vehicles are the customers fault. Which a bunch of BS...but he does seem to spout the corporate line.

In our dealership, the above is almost totally untrue. And if we have a transmission that is "that" bad....we can decide how much fluid we flush through it....and can simply flush more thru until the fluid is coming out clean. I'd say that 99% of the flushes that we do are regularly maintained vehicles that are regular customers. And I've yet to see any trans failure that could be even remotely attributed to using this "flushing" machine.

This all depends on the machine and it's design. Our machines are auto sensing when it comes to hooking up the lines...you can't hook it up backwards....the oil used is brand new...etc. Our machines are actually "approved" by GM.

Scare tactics.....and it's funny too.....he's a Cadillac engineer and guess where they decided to put the filter in their big 4 speed transmissions that come in the full size Caddies? Under the side cover, where you can't get at it without either removing the trans, or at least dropping the drivers side of the subframe "way" down. So in other words, you can't do the typical "trans service" on those trannies anyway. At least with the flush, you are able to get "all" the old fluid out. It would take you 3-4 "services" to do that normally. Cadillac thinks their transmissions don't need any maintenance, but what I see in the shop says otherwise.

Yeah...so what? What does he think that repair shops and mechanics are working for? Just so we can work for nothing and provide a service with no profit? Of course these machines are money makers....but they perform a service that you could not do easily without the machine. Brake lathes make machining rotors and drums "quick and easy". I wonder whether he thinks we ought to have to just manually file them to get them straight and true?

Having said all this....our shop provides both types of transmission services. The choice is up to the customer, we often simply alternate the two services at the mileages that have been set up in the maintenance schedule. We probably do as many or more old style "transmission services" as we do the flushes.
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Thanks for the quick replies. I appreciate the information. Vince

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vince wrote:

flushing the trans that seemed to be safe and thorough. It said to remove the transmission cooler return line from the radiator (I think it was the top line, for GM anyway) and connect a length of hose to it and put the other end into a 5 gal. bucket of clean fluid. Take an appropriate size nipple and thread it into the radiator where you took off the cooler return line and connect a piece of hose to that going into an empty container (big enough to hold a few gallons). The return line will always be sucking fresh fluid.. Start it up, and (with the parking and service brakes applied) and put it into reverse, drive, 2nd, 1st, and back into park. It helps if you have someone else do it, so you can watch the fluid coming out. Let the car run until the fluid is coming out clean. This way even the valve body and cooler in the radiator are flushed. Filter change could probably be done first, to lessen the amount of time to flush and fluid wasted.
--
Happy Trails,
Paul
a.k.a. Commander Bushkisser
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Thanks for the info. I like this procedure.

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What does this do about the dirty filter? It is my theory that transmission problems are caused by restricted filters that reduce fluid flow and damaging things.
Harry, just to clarify: You did regular filter and fluid change before you needed a rebuild at about 180,000 miles?

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Scott Buchanan wrote:

Of course the filter needs to be changed. That's a given. But when you change the filter on an auto trans, you only retrieve approx 1/3 to 1/2 of the fluid. So the idea of a "flush" is to completely change all the fluid in the transmission, along with changing the filter and cleaning the oil pan.
Ian
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Scott
Trans oil & filter have been changed every 50,000 before the rebuild.
========Harryface ======== 1991 Pontiac Bonneville LE 3800 V6 ( C ), Black/Slate Grey _~_~_~298,984 miles_~_~_
~_~_~_~_U.S.A._~_~_~_~_~_
~~~The Former Fleet ~~~ 89 Cavalier Z 24 convertible 78 Holiday 88 coupe 68 LeSabre convertible 73 Impala sedan
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