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Last Post 31 Mar 2010 10:59 AM by  Steve Hoelscher
Help me pick a tow vehicle part deaux!
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Steve Hoelscher
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22 Mar 2010 08:30 PM

Hi Dick. That's a dang good question. Converter clutch engagement on 4R70W's has always been quite subtle. Most drivers never notice it. Even a trained tech has to pay close attention to know when the clutch applies. The problem is compounded when you realize that the clutch applies in 3rd (but not always in 3rd) and is released momentarily for the 3-4 shift, 4-5 shift and 5-6 shift. The easiest way to tell a shift from a clutch engagement is by watching the tach and speedo. As the clutch applies in 3rd (or 4th) for the first time, you will see the rpm stabilize as the speedo continues its steady climb. Once the clutch is fully applied, the speedo and tach will track together until the next shift. The clutch will be seamlessly re-applied after the shift and the tach and speedo will track together again. As a general rule of thumb, a normal upshift will take about .7 to 1.0 seconds and the clutch application will take 2 to 3 seconds.

When I had my shops I employed a couple of Aamco Certified Master Technicians. Now despite what you may think of Aamco as a company, an Aamco Master Tech is as good a rebuilder as you will find in the industry. Period. The training and testing required to get that certification is the best in the industry. So one of these guys was very bright and had a bunch of tech bulletins publish in his name. One of the Tech bulletins he wrote was on 4R70W converter lockup. He figured out that drilling a hole in the valve body separator plate to vent the cushion circuit for the torque converter apply would quicken the engagement. So this mod was used when he rebuilt the unit in my van. The problem is, its only slightly quicker engagement as the clutch plate in the torque converter itself is cushioned by the rate at which the charge is vented.

AStocker
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23 Mar 2010 07:47 AM
Steve Hoelscher wrote:
AStocker wrote:

Thanks for the info Steve.

Other than changing the fluid regularly, is there anything I can do proactively on this tranny to avoid ending up on the side of the road?

Well, changing the fluid annually is the very best preventative measure. Also, if you don't have a "big" external transmission cooler, get one. From there learning what the transmission is doing and why then will give you the opportunity to being proactive when driving. To that end, go out and find a nice flat, straight, piece of road to practice on.

With the trans in the normal "OD" position, start of with moderate throttle pressure and let the transmission run through the gears, counting as it shifts. Note the shift sequence: starting off in 1st gear, then 2nd gear, then 3rd gear, then the torque converter clutch applies and then 4th gear. Do this several times until you are accustomed to the feel of the torque converter application and how it differs from a "shift". Next, while driving at cruise speed (say 60-65 mph) in OD, steady state, hold the throttle steady and reach over with your left foot and touch the brake pedal. Not enough to slow the truck, but just enough to turn on the brake lights. While doing this, note the rise in rpm (probably about 100 rpm). This is the torque converter clutch diss-engaging. It will re-engage a few seconds after you release the brake pedal. Try this several times until you are familiar with the action of the torque converter clutch locking and unlocking. The converter clutch will also diss-engage when you lift off the throttle for a moment and re-apply to steady state. Try this as well to learn its action.

Now that you are familiar with the torque converter clutch locking and unlocking, try this: At steady state cruise, again about 65 mph, begin gradually adding throttle pressure. As you do, note the engine rpm rise. At some point, the additional throttle pressure will force the torque converter clutch to dis-engage. Your earlier practice will make this easier to note. Now ease off the throttle and wait for the clutch to re-engage. Try this several times until you are familiar with the opperation. Also, try continually adding throttle pressure until the transmission downshifts to 3rd and note the difference between the torque converter unlocking and a downshift to 3rd.

Now that you are familiar with the torque converter operation, when towing, you never want to run the transmission in OD any more than a few seconds with the torque converter unlocked. When climbing even slight grades, if the torque converter unlocks, immediately downshift to 3rd either by applying additional throttle or my manually shifting to 3rd. Also, when climbing any grade that you know will require a downshift, anticipate the downshift by downshifting manually to avoid lugging the motor in 4th or allowing the torque converter clutch dis-engaging.

Running the transmission with the torque converter dis-engaged builds tremendous heat very fast. In only a few minutes it can build enough heat to boil the transmission fluid. So you are far better off to run the transmission in 3rd with the torque converter clutch applied than in 4th without. In fact, if the torque converter in hunting (in/out of lockup) you should instead downshift to 3rd and stay there until it can run consistently in 4th with the clutch applied.

Also, if you have it rebuilt, the best upgrade you can do is to "pin" the torque converter regulator valve. This is a simple mod that keeps the torque converter regulator valve fully open all the time. This keeps the clutch at 100% apply any time the computer commands "apply". The valve normal operation is to regulate slip so the clutch is never at 100% apply. This builds a lot of heat and wears the clutch. Why GM does this, no one knows.


Great info Steve. Thanks.

One more question: The Avalanche is equipped with a "Tow/Haul" button that I use every time I tow. It dramatically changes the feeling of the tranny and its shifting. How does this fit into the above advice?

Paul

Steve Hoelscher
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23 Mar 2010 08:21 AM
AStocker wrote:

Great info Steve. Thanks.

One more question: The Avalanche is equipped with a "Tow/Haul" button that I use every time I tow. It dramatically changes the feeling of the tranny and its shifting. How does this fit into the above advice?

The tow/haul button simply raises the line pressure inside the transmission. This delays upshifts slightly and slightly raises the "apply" pressure on the clutches and band servo. The idea is to reduce clutch slip and quicken the shifts under load. The thing is, it is my belief that this button is more "marketing" driven than actual functional benefit. Line pressure is managed by the transmission programming based on MAP (vacuum which is an indicator of load) and throttle position (request for load). If this map is properly programmed, the mapping will raise line pressure as necessary without the need for the button. I think GM's marketing department wanted a response to Ford's OD/Cancel button which is actually very useful. (I use mine all the time as it makes downshifting for those big climbs a piece of cake.)

Bottom line. Use the Tow/Haul button but everything previously noted, still applies.

atcovan
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24 Mar 2010 07:15 PM
Valuable information, Steve. Thanks. I'm certain you've saved me a ton of $$ on my 5.7 2001 Express van. I have the monster Hayden cooler and change the fluid at 25k intervals.
Matt93SE
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28 Mar 2010 12:17 PM

Update from my end..

Last week I was able to find an '02 F250 with the 7.3 Power Stroke in Tulsa with just 110k miles. flew up to Tulsa and drove it back to Houston on Wed. averaged 18mpg on the way home at 75mph and spent about two hours in stop & go traffic. not bad, all things considering.

Loaded up the trailer on Friday and drove it 400 miles round trip to Austin. didn't even bother to worry about mileage since I was running behind and all I wanted to do was get there on time. I can say, however that the truck pulled my 24' enclosed just fine at 75, with a bit of room to spare for the uphills and random left-lane parkers. trial by fire, and it passed!

atcovan
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28 Mar 2010 02:05 PM
Matt93SE wrote:

Update from my end..

Last week I was able to find an '02 F250 with the 7.3 Power Stroke in Tulsa with just 110k miles. flew up to Tulsa and drove it back to Houston on Wed. averaged 18mpg on the way home at 75mph and spent about two hours in stop & go traffic. not bad, all things considering.

Loaded up the trailer on Friday and drove it 400 miles round trip to Austin. didn't even bother to worry about mileage since I was running behind and all I wanted to do was get there on time. I can say, however that the truck pulled my 24' enclosed just fine at 75, with a bit of room to spare for the uphills and random left-lane parkers. trial by fire, and it passed!

Hi Matt, sounds like you found a nice truck. If memory serves, the 7.3 injectors are problematic and really sensitive to oil condition/cleanliness, so change it often. At 110k miles, it's only just breaking in!

Matt93SE
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29 Mar 2010 07:29 AM

Thanks for the heads-up! I hadn't heard that about the injectors, so I'll keep an eye on them. I called the Ford dealership's name that was on the keyring (I bought it from a VW/Audi lot strangely enough), and it seems to have been pretty regularly serviced at their dealership, including a regular diet of Rotella.

Joe_914
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30 Mar 2010 04:16 AM

Wise choice on the Super Duty, I have gotten as high as 19.7 cruising empty @ 70-75 but that is rare. 16 towing and that is at the same speed.

I have found nothing to get better mileage other than stay out of boost. (bed covers, 4" exhaust, big air filter). none affected mileage. Mine has 241K and runs great, and tows anything I can hook to it.

wrchas
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30 Mar 2010 08:06 AM

http://www.thedieselstop.com/ is probably the best source for information for Ford diesel trucks.

In regards to mileage, both the '99 F250 that I had and the '01 F250 that I have, have returned mileage figures as high as 20 and as low as 11 with an overall average of about 15.5mpg (that's some commuting, pulling an open trailer, pulling an enclosed trailer, and some long trips not pulling anything). The '01 received a DP-Tuner (with stock, +60hp, and +80hp tunes) which made for a nice power gain but mileage gains are marginal at best. Trying to get good fuel mileage on a long trip recently, the stock tune got me just over 15mpg. The return trip with a +80hp tune got me just under 16mpg. This was pulling a car on an open trailer.

The cost of diesel trucks and maybe even the operating cost may be higher than other vehicles, but the ease and comfort with which they tow is worth the difference. I haven't been around the Rockies so I can't comment on montains but here in the southeast, the truck takes all the hills in stride - going up and coming down. After I wrecked a 1/2 ton gas pickup truck pulling an enclosed 24' trailer, I decided I wanted a 3/4 ton diesel. I've never regretted my choice.

Joe_914
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30 Mar 2010 01:31 PM

Yep, tow kinds of people that tow trailers.

ones that have a diesel

and those that will have a diesel.

Don't personally know anyone that went from 3/4 ton or more Diesel to 1/2 ton gasser.

BigEnos
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30 Mar 2010 02:05 PM
Joe_914 wrote:

Yep, tow kinds of people that tow trailers.

ones that have a diesel

and those that will have a diesel.

Don't personally know anyone that went from 3/4 ton or more Diesel to 1/2 ton gasser.

Then you have the 'tweeners like me who are happy with their 3/4 ton gassers. I just can't make the economics of a diesel work, and I only tow open trailers so I don't really need all that extra power. It would be nice to have the power reserve and in theory the mileage, but the newer trucks seem to not do as well on MPG, though I'm sure the pendulum will swing back to diesels getting great mileage. The $7K-9K price of admission to the diesel party is just too much for me.This is just my opinion, I don't want to start a diesel vs. not thread. Everyone has their reasons.

I can't say I wouldn't go to a 1/2 ton, but I'd prefer not to. I probably would only do that if my truck was going to be my permanent daily driver.

Steve Hoelscher
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31 Mar 2010 08:39 AM
Joe_914 wrote:

Yep, tow kinds of people that tow trailers.

ones that have a diesel

and those that will have a diesel.

Don't personally know anyone that went from 3/4 ton or more Diesel to 1/2 ton gasser.

I have had a diesel and went back to "a half ton gasser". I bought my current van (gas clubwagon) in '98 as a temporary filler while I shopped for a diesel van. I had used a Powerstroke F350 extensively but wanted a van but they were pretty scarce at the time. I liked the gas van so much I kinda quit looking for a diesel. Then I had a chance to buy a '95 F350 Dually with a 460 Gasser at a bargain price. The truck pulled great but the mileage sucked and while it had more power than the van it wasn't as good a tow vehicle. Its a really long and wide truck with far less usable space than the van and is far less comfortable. I used the truck occasionally until I traded it for a '96 F350 Powerstroke. I liked the truck more than the 460 but the higher costs of fuel and maintenance, plus the annoyance of living with such a large vehicle wore thin. I never sold the van and later had a chance to sell the truck at a nice profit so I jumped at it. So I was back in my old van again. The van is nearing 300K miles and is still going strong. But it won't last for ever and I am now shopping for a replacement.

I prefer towing with a van and if I had a diesel van that would likely be the difference for me. I had intended to switch to an enclosed trailer when I switched to a prepared car, that's why I bought the F350 PS. But after using it some, I decided to stick with the van and open trailer. Ultimately, I will probably replace my existing van with a diesel or V10 van and get one of the new style, small, ultralight, aluminum, enclosed trailers.

Joe_914
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31 Mar 2010 09:45 AM

Hey Steve, I guess I have to take that back. Since I officially know you now since Dixie Tour.

BTW Ed and I love the Race Keeper. once we figure out all the other cool things it does (or at least how to use them) we are certain to love it more.

Steve Hoelscher
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31 Mar 2010 10:59 AM
Joe_914 wrote:

Hey Steve, I guess I have to take that back. Since I officially know you now since Dixie Tour.

BTW Ed and I love the Race Keeper. once we figure out all the other cool things it does (or at least how to use them) we are certain to love it more.

Glad you like the system. And we have more, even cooler, stuff coming. [:D]

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