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
Thanks for any input.
Cheers - Jonathan
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.
There is NO OIL COOLERS at all on this TRUCK !
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
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
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!!!
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
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.
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.
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
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.
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
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