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Author Topic:   Trailering: Transmission Fluid Flush
jimh posted 10-25-2001 09:59 PM ET (US)   Profile for jimh   Send Email to jimh  
I took my trailer-towing vehicle to the local Valvoline Oil Change shop this morning, not for an oil change (which I usually do myself) but to get the transmission fluid flushed and replaced.

The maintenance interval for transmission fluid is often listed at "Every 35,000" miles, but this has to be one of the most overlooked items of car engine maintenance. Most people do not do anything about their transmission fluid, but that is a big mistake, particularly when you are using the transmission for towing.

The Valvoline shop (and others) offers a transmission fluid replacement technique which does not require the removal of the transmission oil pan under the car. Instead they splice into the transmission fluid line where it enters the radiator for cooling.

The process is performed like this:

The fluid line from the transmission to the radiator is removed and patched to a hose going to the flush device. A hose returning from the flush device is patched into the radiator inlet. The flusher is loaded with about two gallons of new fluid.

An additive is poured into your transmission case via the dipstick, and the transmission and engine run in "Park" for five minutes. Next the transmission is worked repeated through the various gears to insure circulation of the treated fluid through the transmission for another five minutes.

The flusher mode is then changed to pump-out/replace, and your old fluid is diverted to a resevoir in the flusher, while the new fluid is pumped into the radiator and then back to the transmission.

As this flushing mode is run, flow gauges are monitored so the rate of pumping out is slightly greater than the replacement rate. The old fluid fills the resevoir in the flusher, while the new fluid begins to fill the radiator and works its way back to the transmission.

When the old fluid is entirely evacuated, the process is stopped and the hose patches removed. The tranmission line is reconnected to the radiator.

A new additive is poured into the transmission via the dipstick. I think this neutralizes any of the first additive (which was probably a solvent to help remove gunk in the transmission.) Your fluid level is checked. Your transmission is running on new fluid!

This technique can replace more of the fluid than a traditional draining and refill of the oil pan on the transmission, as much of the fluid remains hidden in the transmission and torque converter in that method.

I have used this service twice, and so far I have been very pleased with the results.

The cost is about $75 and it takes almost an hour to perform.

Dick posted 10-25-2001 10:29 PM ET (US)     Profile for Dick  Send Email to Dick     
I haven't addressed this in several years but automatic transmisions used to have a filter. The only way to replace the filter was to drop the pan. If there is no filter this procedure sounds good but if there is a filter I would think it needs changed.
grizzly posted 10-25-2001 10:53 PM ET (US)     Profile for grizzly    
I did this procedure to my Suburban about 10 months ago. The correct technique is actually to drop the transmission pan and change the filter first. Then refill the tranmission (this replaces only about 40% of the transmission fluid in my Sub).

Next, do the flush procedure as jimh describes. Thus, all new tranny fluid and a fresh filter.

I also used the occasion to change my tranmission fluid to synthetic (Mobil 1) at this flush. The whole process was expensive, but I tow a heavy trailer and want long transmission life.

It probably isn't necessary to follow this procedure each time. For example, every other tranmission service could be a flush only.

noswah posted 10-26-2001 06:01 AM ET (US)     Profile for noswah  Send Email to noswah     

There are garages that have the equipment to pump out the converter and change all the fluid, but the equipment is very expensive and even the Chrysler dealership where I bought my vehicle doesn't have it.

I to concurr that the right way to do it would be to drop the pan and change the fluid and filter, then pump out the converter thus changing all the fluid.

Anything less is kind of like washing your feet with your socks on.

llewellyn posted 10-26-2001 08:48 AM ET (US)     Profile for llewellyn  Send Email to llewellyn     
Melbourne, FL Ford dealer does the flush along with filter change for $129. It's definitely worth it if towing a lot.
bigz posted 10-26-2001 09:01 AM ET (US)     Profile for bigz    

How about your front transfer and rear differential gear case oil change? You are talking about your Chev Sub 4x4 aren't you? The Ford sedan?

These under towing conditions are the most overlooked area in my mind.

I have always been leery of the lubrication shops and their mumbo jumbo to sell more product and service --- even the 4x4 shop I use doesn't push this trans stuff (yes they can do it) ---

Also if I may ask--- what do you mean with satisfied results, in other words what is your comparison, a previously failed transmission on your tow vehicle without this $75 service?

Anyway as they say about "chicken soup" can't hurt --- Z

JFM posted 10-26-2001 02:59 PM ET (US)     Profile for JFM  Send Email to JFM     
Local trany shop does not recomend the "pump flush" method because it puts to much pressure in the transmission pushing and pulling the fluid. They claim this will cause more problems with blown seals, gaskets and small parts inside. They still drop the pan clean or replace filter. They then drive the vehicle a few miles drain the pan and refill. I make them do it 1 more time just to feel that I have diluted the fluid to be as fresh as posible. Regards, Jay
RWM posted 10-26-2001 09:52 PM ET (US)     Profile for RWM  Send Email to RWM     
If you change your own oil you can do your transmission too. I've been doing mine every 30,000 miles or so for a few years now. I drop the pan and change the filter each time. About 60% of the fluid can be changed. Cost is maybe $30, and it takes about 1 1/2 hours. As Jim says...the big thing is just to change it frequently. For me, I can do it pretty much as fast as if I drove to a shop and waited. Get yourself a big drain pan and go to it...Bob M.
jimh posted 10-27-2001 12:13 AM ET (US)     Profile for jimh  Send Email to jimh     
The ground clearance is a bit of a problem for me to work on the transmission drain pan. It is easier to just reach in and open the oil pan drain. To work on the transmission you really have to get under the car. Maybe I will give it a try next time. I would like to install a drain plug and a temperature transducer if I could get the pan off.

I have a Ford Crown Vic (bought it used with about 60K miles). The transmission had a funny shift from 2nd to 3rd. Changed the fluid at the flush place and that was cured.

I don't know if they put any extra pressure on the transmission. The transmission itself pumps the old oil out, the flusher pumps the new oil into the radiator where it has to fall to the bottom and flow back to the transmission under gravity. Unless there is something else happening that I don't see, I don't think there is any unusual pressures put on the fluid path.

The machine is made by Wynns, I think.


jimh posted 10-27-2001 12:32 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is an interesting article on this subject:

Eric posted 10-27-2001 02:06 PM ET (US)     Profile for Eric  Send Email to Eric     
I'm on my third Crown Vic. If you change the fluid and filter in the conventional manner, but add in the step of draining the torque converter (Fords have a drain plug on the converter), you'll get 12 quarts of fluid out of it. That's a pretty complete fluid change. On my current Crown, a 95 Police Interceptor, that took care of the shifting problems.
triblet posted 11-04-2001 03:56 PM ET (US)     Profile for triblet  Send Email to triblet     
On at least some automatomatic transmissions
('68 Pontiac Firebird 400), the fluid level
is above the level of the pan gasket, so
dropping the pan can be messy. You can
siphon the fluid out through the dipstick
hole before you drop the pan to prevent this.
Allow lots of time (about an hour) as it's a
long ways through a small tube.


JFM posted 11-05-2001 01:50 PM ET (US)     Profile for JFM  Send Email to JFM     
Jimh, Your last post makes me think the local tranny shop can't get the payback on a new machine. Regards, Jay
Hank posted 11-05-2001 10:08 PM ET (US)     Profile for Hank  Send Email to Hank     
Just had my transmission pan dropped and the filter unit and gaskets replaced. The interior of the pan was ugly. It was coated with thick, dirty oil almost the consitency of molasses. The gaskets mounting the filter were crumbly. This is after the recommended 30000 mile interval! The mechanics cleaned the pan, replaced the filter unit,replaced the drained oil with clean oil and installed a new set of gaskets. However,the volume in the pan on my '89 Volvo wagon is only about 38% of the total volume.

This job was done at a local Castrol quick lube franchise.
They do have a machine which will remove all the oil and replace it. Nevertheless,I elected to go for just the filter and gasket replacement and will alternate every 12000 miles or less with the complete transmission oil removal.

Based on the appearance of my transmission pan and filter I think 30000 miles may be too long an interval.


jimh posted 11-06-2001 01:27 AM ET (US)     Profile for jimh  Send Email to jimh     
Based on your observation and other comments, I intend to drop the pan on my tow vehicle's transmission and see what's going on myself.

On a corollary topic, while having some brake work done on the K1500 Suburban, my mechanic noticed the rear axle seals were leaking! I am having them replaced, too. Good catch.

I guess the strain of about 4,000 of towing this summer (on top of 52,000 miles of non-towing) was too much.

I believe that the differential fluid should also be checked and replaced at more frequent intervals when towing. The normal interval is typically "never" so perhaps this is also a canditate for regular inspection and service.

jimh posted 11-10-2001 06:04 PM ET (US)     Profile for jimh  Send Email to jimh     
Following up on the transmission fluid change:

I discovered that a garage I use for tires/brakes/suspension work (and one that I trust) could do the transmission fluid filter change. I had them drop the pan and replace the filter and fluid.

This seems to have cured even more little transmission noises and idiosyncracies! A very good investment!

They charged 1.5 Hours labor (they had to remove a frame cross member to clear the pan), and to total bill (including filter, gasket and fluid) was ~ $150.

They also noticed the rear axle seals were leaking, so these were replaced, too. The Differential fluid was drained and refilled in the process. (Another ~ $150)

Four wheel brake overhaul, repack the front wheel bearings ($200), and the truck is ready for another season of towing!


noswah posted 11-11-2001 07:36 AM ET (US)     Profile for noswah  Send Email to noswah     
jimh, you mentioned brakes and wheel bearings pack. I have found over the years that my brakes are usually 75% used up at 30,000 miles so I just have the pads and shoes replaced at that time. You can usually get a few more miles out of them but by waiting sometimes you will score the rotor to a point where it is beyond turning.

The other reason I replace them then is I don't want my rotors turned unless they are scored. The new rotors they're using on these new vehicles are much thinner than they used to be, and you can usually only turn them once or twice, then you have to replace them. We all know they love to sell you high cost parts.

As for wheel bearings I have a 2000 Chrysler Van and the front wheel bearings are sealed and can't be repacked, I'm just wondering why these boat trailer mfgs. can't do the same thing.

DJS posted 11-11-2001 10:37 AM ET (US)     Profile for DJS  Send Email to DJS     
I own a 1994 Chevrolet Suburban, 4 wheel drive, and it also has sealed bearings. I took it to the dealership where purchased and told them I wanted the front wheel bearing repacked. They said there was nothing to repack because the bearings are a sealed unit. It took them a lot of talking to convince me.
triblet posted 11-11-2001 09:13 PM ET (US)     Profile for triblet  Send Email to triblet     
Most if not all modern disk bracks have a
little metal finger on the pad that will
make a squeaky noise when the pad is mostly
(90%) worn out. You have a few thousand
miles after that to replace the pads. And
you will -- the noise will drive you nuts.


jimh posted 11-12-2001 08:43 AM ET (US)     Profile for jimh  Send Email to jimh     
One more step in the truck maintenance:
Since we won't be driving it much (if at all) in the winter, I also add stabilizer and top off the fuel tank (42-gals!) for the winter layup.

We also store the truck in the in-law's garage (they're in Florida) for the winter. This really marks the end of boating season when we put the Suburban to bed for five months.

GAwhale posted 04-24-2007 09:46 PM ET (US)     Profile for GAwhale  Send Email to GAwhale     
My 2005 Ford Explorer needed to go in for the first 30,000 mile service. I found this very interesting. It has a sealed transmision. Ford does not recommend changing transmission fluid on my model until it hits 100,000 miles.

It certainly saves me money. I'll see how it holds up for the life of my vehicle.

seasled posted 04-25-2007 05:37 PM ET (US)     Profile for seasled  Send Email to seasled     
We have a trans fluid exchanger at are AAMCO in east hartford ct. It has a nice feature that lets you drain the pan first so you can drop it to do the filter change. Nice peice of equipment. SEASLED
lurkynot posted 04-25-2007 06:37 PM ET (US)     Profile for lurkynot  Send Email to lurkynot     
I had an S-10 10 years ago automatic
w/4.3 litre. Used it to pull a heavy salmon rig North in Michigan on weekends. The rig was a little on the heavy side not so much on the engine more so the tranny in my opinion. In an attempt to avoid a rebuild I had a shop braze-in a drain plug and simply drained it after a weekend of trailering. Never had a problem.
Buckda posted 04-25-2007 06:53 PM ET (US)     Profile for Buckda  Send Email to Buckda     
My 2002 Ford Explorer has had the transmission fluid flushed two times (70,000 miles and 135,000 miles) and so far no problems. The transmission has no dipstick, which is a bad thing in my mind, because you cannot check to see if you've burned the fluid in towing applications. Then again, I don't think that most soccer moms who own Ford Explorers worry about that too much.

I'm on a slightly agressive changing schedule due to the heavy towing I do (max capacity) and the number of miles I tow (many).

fisherman posted 04-25-2007 07:04 PM ET (US)     Profile for fisherman  Send Email to fisherman     
Hey Jimh:
What on earth has this topic got to do with "Repair, restore or modify your Boston Whaler". Gothcha!!
seasled posted 04-28-2007 02:12 PM ET (US)     Profile for seasled  Send Email to seasled     
almost all of the new automatics have no filler tube or stick. Filling these new tranys can be tricky after a rebuild. Most have two fill plugs on them. Like a lower unit.with The car (or truck) up on the lift with a person inside to start the engine,you start filling from the bottom plug,start the engine and continue filling till fluid comes out the top plug. SEASLED
towboater posted 04-29-2007 10:51 AM ET (US)     Profile for towboater  Send Email to towboater     
03 F-350 30k mile tranny + oil change at the local Ford Dealer last Feb.

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