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One more gear
Published: 10/22/1999  
Author: Rick Metcalf AKA Tweek
Where is that gas station? Where? The sign said 2 miles......... Yeah, I know, it's stupid to expect something that says '454SS' on the rear fenders to get good gas mileage, but please.... On a good day, the 25 gallon fuel tank will get you abo

Yeah, I know, it's stupid to expect something that says '454SS' on the rear fenders to get good gas mileage, but please....

On a good day, the 25 gallon fuel tank will get you about 200 miles down the road. Then it is time to do the gas station search again. Even more important to me is the fact that this big-block is really screaming just to try to keep up with traffic. In 1990, 55 MPH was the rule, remember? Now that the states here in the south have finally gotten some sense, the typical speed limit is 65, 70 in Georgia and West Virginia. (I gotta admit going to West Virginia from time to time. Beautiful scenery and the roads are like glass there. This is the state where the houses have wheels, and the cars don't!)

Those of you that are frequent web site visitors are already probably used to my normal upgrade path. I try to look to the factory for what would be the next logical step in the evolution of a certain vehicle. In this particular case, the factory, for 1991, changed from the venerable TurboHydramatic 400 to the much more advanced 4L80E. This unit is an electronically controlled overdrive four speed transmission. Problem solved, right? (Insert sound of wrong buzzer here!)

How is it that one of the world's largest automobile manufacturers can as often get things wrong as right? The original drivetrain in the '90 454SS is almost anvil-like. Spare me the comments about certain common problems, most arising from revving the hell out of these things on the highway. Now, for 91, the factory puts this overdrive transmission into the truck, and undoes this upgrade by also installing a 4.11:1 gearset in the differential. As a side benefit, the 4L80E proves to be very fragile, with multiple recalls, weak torque converter clutches (TCC), solenoids that get stopped up with TCC lining, and warranty extensions offered to original owners for the inconvenience of having the truck lay down at an inopportune moment. (Next to a Mustang GT at a red light with all the local street gang watching, for example)

Some simple math here. The 90 model was geared 3.73:1. The 91 and up model was geared 4.11:1 and had an overdrive ratio of approximately .7:1, yielding an actual working ratio of 2.88:1. This is some help, but not exactly what I had in mind. Now let's put the same .7:1 overdrive ratio into the '90 model with the 3.73:1 gearset. 2.61:1 working ratio. 9.25% difference between the 90 model and the 91 with the same overdrive ratio. How does this translate into the real world? How 'bout turning about 2100 RPM to go 70? How 'bout pegging the speedo and still having a few revs left? Better MPG? Yep. Lower oil consumption? Yep. Way less wear and tear? Oh yeah. This sounds like a good place to go.

overdrive.BMP (444514 bytes)
Here is a view of the installed unit, left of the pic is to the front of the truck.
This view shows the relocated speedo pick-up and fluid lines clearly.

Do you remember those Frito-Lay trailers that you used to see around all of the time in the late '80's? They were all that awful Frito color. These were Chevy Duallys with those long trailers on a goose neck. Those power units, as they were called, had the same drivetrain in them that the 454SS had. They, too, were geared 3.73:1 and ate gas and engines for lunch instead of Fritos. This was not a good thing. It probably did not help that the engines were ungoverned and the drivers seem to really delight in spinning the hell out of the right rear dually pair every right turn they made. Tire smoke x2!

Along comes American Eagle Overdrive. These guys designed and built an electrically operated hydraulic overdrive unit that will bolt on in place of the TH-400's tailshaft housing. U. S. built, this unit uses commonly available automatic transmission parts internally. Rated 30,000 pounds GVW, and beautifully built. They also have units that bolt up to the TH-350 and for some....ahh....Fords, too. Sorry, excuse the bad word there.

So let's cut to the chase. What does it take to get this in your '90 model 454? Read along and see.

Here is where the 454SS web site puts our usual demand that you read and understand our Disclaimers. Working on vehicles is a dangerous activity. The 454SS is Heavy! It will break cinder blocks and Chinese jacks and jack stands. Your body will NOT support the truck when the jack breaks. Please be careful!

1. Out with the old...

Remove the driveshaft and the electronic pick up assembly from the factory tailshaft housing.

2. Support the transmission under the pan with a jack and remove the transmission mount and the tailshaft housing. Remove the bolts....all of them....and lightly tap on the housing to loosen it from the back of the transmission casing. You did get all of the bolts out didn't you?

3. There is a small boss cast into the electronic pick-up. For the pick-up to mount correctly, you must trim the boss away, leaving a level surface for the hold down bracket to press against.

4. Install 1 15/16 inch plug into the transmission case where the pick-up used to be mounted.

5. Install the bearing supplied in the kit to the end of the output shaft and tighten the allen screw securely. A small drop of lock-tite on the allen screw is a good idea.

6. Position the transmission gasket to the flange using silicone sealant. Let me add a tip here. Everyone seems to feel that if some silicone sealant is good, then a whole lot of sealant is better. I have taken apart engines and transmissions that have failed solely because excess silicone sealant breaks away from the seal area, and is then carried away to the oil pump pick-up, clogging it up totally. Of course, this clogged pick-up screen starves the engine or transmission pump and toasts the unit.

Here is the trick to using silicone sealant in correct amounts and having a leak proof seal:

A. Squirt a small amount of silicone sealant between your thumb and index finger, then take the gasket and gently rub the silicone onto both sides of the gasket simultaneously. Hurry! When you apply the silicone this way, the layer is thin and dries quickly.

B. Normal clear and white silicone will not stand up to the oil and heat. Forget the left-over caulking silicone in your caulking gun. Fel-pro Ultra-Blue. Enough said?

C. Where was I? Oh, yeah.

7. Install the overdrive unit to the transmission case, re-using the original bolts. Torque the bolts to 30 ft.-lbs.

8. Install the u-joint yoke fully into the overdrive and then pull it out 1/2 inch.

9. Install your original transmission mount to the overdrive unit, using the original bolts. Check the condition of the mount, and replace now if there is any question as to the condition.

10. Measure the distance from the center of the front yoke cup to the center of the rear yoke cup. This is the length the driveshaft should be. The truck absolutely MUST be resting on all 4 wheels, on level ground, with a normal fuel amount in it. NO ramps. You should bounce the truck to settle the suspension before taking this measurement. Want to be really correct? Have someone sit in the driver's seat to simulate normal operating loading, and roll the truck forward and back to unload any suspension tension. This dimension is critical. Do not screw this up!

11. Have a competent shop shorten and re-balance your drive shaft. Replace the u-joints if there is any question as to their condition. The shop that shortened my driveshaft told me that the rear u-joint was shot. At that time, my truck had about 6600 miles on it. Right. Turns out that they had put too much pressure on the press removing the yoke and crunched the u-joint. Well, they were right, the u-joint WAS shot after they were done with it!

12. Install your shortened driveshaft and torque the bolts to manufacturers specifications

13. Remove the plug on the side of the transmission between the shift lever and the electrical kick-down connector. Install the oil supply line from the transmission to the overdrive unit.

14. The overdrive comes with a switch that is installed by cutting off the end of the tilt wand, and replacing it with the switch. Nope. I don't think so. I bought a switch from Radio Shack, and installed it into an empty switch position under the heater controls. Your choice here.

15. Wiring time. The wiring chart supplied is well thought out, and should give you all the information you need to hook up the unit. Use plenty of tie-wraps to keep the wires off the exhaust system. You will have to extend the wires leading to the speed sensor.

16. There is a special switch that is used to insure the overdrive is locked when the truck is in park. If the overdrive isn't locked, the truck will roll freely when you select park, because the park awl locks the transmission output shaft, but the overdrive unit is still free to turn. Again, there are complete illustrations for this step.

17. Start the truck and check the fluid level. You shouldn't have lost much at all during this installation. Switch the overdrive on. You should feel a definite gear-change when you activate the switch. Do not drive the truck if the overdrive will not shift. Correct any problem before driving. Checking fluid level: Leave the fill level a bit low. There are nearly 11 quarts of fluid in a typical transmission, and when you get this much fluid hot, it expands quite a bit. Always check the fluid level when the transmission is hot and has been driven some distance. Does your 90 model have the recall dipstick? (It has a red locking handle that must be flipped down after checking level, etc.) The original dipstick has been known to push out under heavy loads expelling trans. fluid on the hot manifolds. You can forget trying to find a gas station, and instead, look for a fire extinguisher!

18. You're done! As always, I have a couple of pointers on the operation of this unit.

A. Pop quiz: When is the highest torque being applied to the driveline? At launch with out wheelspin. Torque converter multiplication, remember? And, unexpectedly, at the bottom of each gear. Remember, the torque peak on the 454 is at a low 1700 RPM. This overdrive can be used to split gears, and in fact will even overdrive reverse, if desired. But this is not recommended. The best profile for the overdrive unit, is to use it like a fourth gear only. No driving around town leaving it engaged, as this is when the torque curve is really beating up the unit. Just let the transmission go through the gears normally, and when you have reached cruising speed, hit the switch. Instantly loose 900 RPM from your cruising revs, and gain about 4 MPG. Forget about the 454SS normal oil burning problems, they are history!

B. Also not recommended, but fun, is the street race that you can tell will be short. Like less than an 1/8 mile or so. Do what ever you have to do get a good launch, and then let it turn toward the red-line. As you approach the red, hit the overdrive switch. The overdrive splits the difference between 1st and 2nd, keeping the engine in it's power band. The problem is that the next step is for the transmission to change to 2nd, and this bogs the engine down, because it is already in the overdrive gear. If you are really quick, you might be able to turn off the overdrive when the transmission gets ready to make 2nd gear. Not recommended, like I said, but if you get used to the timing required, the extra 2 gears will really shock you with the extra acceleration. 2 gears? Yeah, 1st, then overdrive 1st, 2nd, then overdrive 2nd. This will kinda freak out the Mustang driver who thinks he just been driven away from by a six-speed 454SS!

19. You might want to confirm your speedometer hasn't been corrupted in the change over. See the article here on the web site about 90 to 91 dashboard conversion to find out how to check your speedometer calibration.

20. While doing all this work to the transmission, now would be a good time to service the trans, or even do a shift kit if you haven't previously done so. The American Overdrive folks really like shift kits, because they typically raise the line pressure inside the transmission. This makes the overdrive unit shift more positively, and will also make it last longer. I suggest the B&M 20227. Remember, theTurboHydramatic 400 in the 454SS is a bit odd. This is the kit for the one in the 90 model only. This shift kit allows several levels of performance. This is one time where I council going for the max. The kit offers heavy duty (towing), street, and strip settings. Guess which one I chose? Can you say: Bang, Screech? Sure you can! Actually, after you get used to the new shift points, you can modulate the throttle to reduce the harshness of the shifts when you are just easing around town. However, full throttle shifts will knock the ashtray partially open when they hit!

21. Wanna hit even harder? Mix half and half Ford (I know, I know...) and Dexron/Mercon Transmission fluid. The Type F fluid actually is less slippery than the Dexron juice. Long term problems? The seals are not exactly formulated for the Type F fluid and you might end up with a leaking transmission. Bummer.

22. Forget most of the aftermarket transmission filters. Go for the AC/Delco replacements. Pay the price at the dealership, etc. They are well worth it, especially when you get a FLAT pan gasket, instead of one that has been wadded up inside a little box for about a year! You can tell that the folks who make those products don't ever use them. Small rant there, sorry.

23. Transmission coolers: Tough subject here. For what it is worth, here is my rule about this. The factory fluid to fluid cooler (contained within the radiator) is very efficient. Adding a fluid to air cooler is not that big of a help, despite what the aftermarket manufacturers want you to believe. I think a cooler thermostat is of more benefit. Run your final set-up for a while, monitoring the fluid color and condition. If the fluid is anything other than cherry red after a several thousand miles, start thinking about a cooler. This does not apply to older trucks that already had dark fluid before any changes. It is really hard to get a good fluid change, because there is really no effective way to empty out the torque converter. Messy, but you can start the engine with the lines disconnected from the factory cooler on the radiator, and use the trans. pump to purge some of the fluid from the torque converter. Don't run the engine long or rev it up while doing this. You are warned!

What did I miss? I am sure there is something. Well, if you have any comments about this article, or any additions, feel free to e-mail these to me. It is not uncommon to find your responses added to an existing article if they are pertinent.

Late addition to the article:

As this article "went to press", I attempted to find out current pricing and availability of the American Overdrive unit. It appears that they have gone out of business. I understand the tooling for these units is still around. The last contact information I had for American is:

American Overdrive, Inc.
4155 Oasis Rd.
Redding, CA 96003
(916) 244-4465

If anyone finds American, please let me know, so I can add this information to the article. I apologise for the sudden demise of the feature item in the article, but I feel it still has worthwhile information contained within, so it has been posted as written.





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