Transmission Flush

Greetings,
Sorry to re-open this can of worms but I'm looking for some information. There are several threads in various newsgroups concerning the effectiveness
and safety of a transmission flush. Some folks (myself included) prefer dropping the pan, cleaning it out and changing the filter while others believe properly flushing the tranny is OK.
Now here's my question -
Since I have an '04 with the Allison tranny (which has an external filter) wouldn't it be essentially the same if I had the tranny flushed at the dealer then changed the spin-on filter afterwards as compared to dropping the pan to change the fluid then changing the spin-on filter? In fact, I wouldn't even have to drop the pan since the Allison's pan already has a drain plug in it from the factory.
I'm looking for two things: Whichever would be the best and least expensive for my tranny. I understand that just by draining the fluid from the pan thru the plug doesn't get all the fluid out. Does a flush exchange all of the fluid?
Thanks for any input.
Cheers - Jonathan
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just drain the pan, change the filter, and re-fill

effectiveness
expensive
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Jonathan wrote:

There is also a filter inside the pan. And you need special fittings to be able to use a trans flush machine to hook up to the Allison.
Ian
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"shiden_kai" wrote:

Help him possible damage his tranny with unneeded maintainance. Again there is no need to do this if everything is normal and tranny has not been cooked.
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SnoMan wrote:

Ah yes....more automotive wisdom from "the" autoforumz windbag!
Ian
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Jonathan wrote:

Waste of MONEY
I have a 89 s10 with 250,000 miles on it and this truck is used to PLOW SNOW since 1994 ( Driveways , Commercial parking lots.) I have plowed 14 inchs Snow falls with this truck !
It Has The SAME TRANNY FLUID in it that was in it when I bought the truck NEW with 8 miles on it.
PS.
There is NO OIL COOLERS at all on this TRUCK !
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no one wrote:

    First off any Automatic S-10 has a Transmission Oil Cooler built in to the radiator, with 2 lines ran to it from the passengers side of the transmission case.
    Second, you better call a transmission shop and order a TH700R4 for a 4x4 S-truck. Order some corvette servo's and a oil cooler flush kit. Your only a few miles away from the transmission filter snapping the plastic tube that goes in to the valve body. When that happens your TH700R4 will burn up faster then a Albino in Florida at noon.
    Filter Replacement for a TH700R4 is 80,000 miles, Rough Service is 40,000 Miles. Charles
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My Dad had his '02 Allison drained and internal filter changed at the prescribed 50K mile mark. If I recall correctly, back flushing the Allison has the potential to screw it up. The dealer mechanic, due to it being under an extended warranty etc., said that was what he would do and my Dad asked about it twice. Upon returning to pick it up later that day, the mechanic said he learned it could not be back flushed and it was not. Been going strong since the refill and is now up over 70K miles.
My '02 w/ Allison, on the other hand, is only at 30K miles so won't be needing any extra care for a while . . . hopefully! The high pressure power steering line from the master cylinder to the steering box just blew last week at only 30K miles!!! A $75 hose (discounted price) and some frustration getting that fitting lined up on the gear box..... GREAT concept making you lose power brakes over a bad power steering component!!! Glad I only had the fifth-wheel hooked up and not on the road when I noticed the fluid on the driveway....... Sure would have sucked having to STAND on the brakes to bring all of that to a quick stop!!!

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Per K:

Once I tested my 98 Burb once by killing the engine in neutral just to see what happened with no PS or power brakes. Another time the alternator had failed but I hadn't noticed and all systems suddenly went dead just as I was rolling into a red light.
Maybe there could be a graceful outcome on a divided highway, but on a secondary road with bends and/or the need to stop quickly I'd guess there would be a crash.
--
PeteCresswell

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power
frustration
you
the
There three options to provide enough braking power for heavy loads, air over hydraulic, requires air compressor and a hydra-vac unit in the brake lines, viet nam era trucks used the set up, the m35 series(2 1/2 ton trucks) and the M50 series (5 ton trucks). There were lots of booster failures. The next option is a full air brake system. Very effective braking system, the modern ones are split systems just like our hydraulic systems are today. Real good when loaded, very touchy empty, and expensive, I would guess another 2,500 to 5,000 to a trucks price, and your corner garage isn't going to be able to work on it. The third option is what you have, a hydraulic boost system. They provide excellent braking, way more boost than a standard vacuum booster can provide. There is a fourth option, Iveco used a "heavy duty" vacuum assist system on their early cab overs(like the Isuzu tilt master trucks) they sold that required a hefty vacuum pump belt driven, and a device that looked like the hydra-vac system I worked on while in the service. I knew a few hot shotters in the 80s that while they loved the trucks because they had a six cylinder instead of Isuzu's four banger, had lots of problems with the brakes. Anyways, there is an accumulator in the system you have that should provide 3-6 brake applications after a failure such as a line failure in the boost circuit, or a belt failure etc, compare that to the one, maybe two brake applications you get with the vacuum system if the engine dies. The secret if you have a failure is not to pump the brakes but steady pressure till the vehicle is stopped. You got a bad hose, they are not prone to failure, any more than any other power steering hose, or the brake hoses between the frame and the caliper or rear axle for that matter.
Whitelightning
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Per Whitelightning:

Does the reserve get used up over time? i.e. During that single steady pressure application, should one stop ASAP or will it permit a more gradual stop as long as foot pressure is maintained?
--
PeteCresswell

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gradual stop

As long as steady foot pressure is maintained, it will only use the initial amount of boost pressure. If you fluctuate the pedal pressure, each time you apply more pressure will use some of the accumulators reserve pressure. There is usually enough "reserve" for 3-6 applications, but each application will have less boost. Think of the accumulator as an air tank on an air compressor. Turn the compressor off and it holds pressure, each time you open the valve, the pressure drops.
Whitelightning
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It's good to know there is a bit of reserve in the system. Of course I figured the hose was a freak incident as it is only the second power steering hose I've ever had go bad on any vehicle and I generally run 'em a longgg time. Just very frustrating to have it let loose as you are hooking up a fifth-wheel to go camping! :-) As noted, at least it went then and not later....
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K wrote:

    Good Old Hydra-Boost brakes. On my older Trucks that is the first thing I change. I even saw Hydra-Boost on a 86 Monte Carlo once. So engeeners at GM like that system, I think they need to *ahem* retire. Charles
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On Thu, 11 Aug 2005 08:16:08 GMT, Charles Bendig

I guess the ones at Ford should all retire too since they used the same system on the 99+ Mustang GTs. And it works great.
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Ashton Crusher wrote:

    If you like Hydra-Boost your in a minority. Wait ford... Now I remember. The same people that for a few years made a 100% power steering rack. The one where if the pump was not turning, you couldn't steer the wheels. Those units worked "great" as long as the engine was running. Charles
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On Tue, 16 Aug 2005 13:16:34 GMT, Charles Bendig

How odd, I've followed the mustang group for almost 5 years (since I got my 99) and one thing I have never seen anyone complain about was the hydraboost system. Yeah, I'm a real minority.....
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Ashton Crusher wrote:

    So Mustang people like them, that has nothing to do GM cars and trucks with Hydra-boost. Mustang people are a Minority in the Hot Rod World. Charles
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