Tranny going out, or TPS??

Cummins Driver

Cummins Driver

THE Cummins Driver
Joined
May 16, 2007
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I have been thinking my tranny is going out for a good month or so now. Im starting to think it is just the TPS though. Symptoms

-Doesent like to lock the TC on its own when it gets to overdrive
-Also doesent like to lock itself in 3rd if OD off is selected
-Many times it will downgear to 3rd out of 4th, even at 70mph if i let off the throttle completely

Does this sound like a TPS problem? If it doesent lock itself up, when I hit the lockup switch manually, it will lock right up. So it seems to me as if it isnt getting the correct signal from the TPS. With 215k miles on the TPS I could see it being worn out.

I have been saving for a tranny, but if I can fix it with a TPS that would be great. I plan to go by radioshack tomorrow after class, and pick up a Potentiometer, and maybe some pins to plug into the stock connector, and do the Potentiometer mod in place of buying a new TPS. At least this way i will know for sure since i will be getting rid of the TPS.

So does this sound like a TPS issue, or something internal? Tranny still bangs shifts, and doesent slip, and the fluid still smells good, and is nice and red, so I am starting to convince myself it is only the TPS. Thanks

Eric
 
Well I went to Radio Shack, and bought me a potentiometer today after class, wired it up, got it adjusted and the tranny works great now. I also did me a little 8psi 4wd launch, and it never missed a beat. I love it so far. If anyone wants to try this, let me know, and ill explain how to hook one up.

Eric
 
Ok, the TPS is basically a potentiometer that is encased and bolted to the throttle linkage with a fancy connector on it. There are 3 wires going into it. All you have to do is go to Radio shack and buy a 5k OHM Linear potentiometer for $3.17. Then all you need are some basic soldering skills. Just solder 3 wires onto the potentiometer terminals, and then you will need to find a way to connect the 3 wires to the connector that normally plugs into your factory TPS. The only thing you need to do is make sure the center wire on the potentiometer runs to the center pin on the TPS connector. The two outside wires can be swapped, and it will only control which way you turn the pot's knob to change the speed of overdrive.

This thread on DTR is where I got my info. It shows it being done on a 1st gen, but it works the exact same on our trucks.

http://www.dieseltruckresource.com/dev/showthread.php?t=142641

There are a couple of downfalls. One being that it wont downgear from 4th to 3rd on its own under heavy throttle. But as soon as you push the O/D off button it will kick right down. Also, mine now hold lockup in 4th all the way down to about 1100rpm before it will drop out of lockup and downgear. Once again though, push the O/D off button and problem solved. Those are the only real downfalls.

Some things i like better is the shift from 3rd to overdrive. It used to shift to 4th at 35mph, and then lockup at 45mph, which brought my RPM's down to 1200. Way too low for much power and good for being smokey. I now have my 3rd to 4th shift dialed in at 45mph, and it locks the TC at about 52mph or so under moderate throttle(normal take off) on flat ground. Which only puts my RPM's at 1500, which is perfect in my opinion. No more lugging. Also, everyone who has a 47rh 12 valve know under any kind of hard throttle in 3rd without a lockup switch the TC unlocks. Like pulling a load, or just kicking it, the TC will come right out of lockup. Now with this installed, once it locks, it doesent come out of lockup until you slow down enough. Throttle input doesent matter. Also, if i lock out overdrive, and do a hard launch it will now lockup itself right after it hits 3rd gear. About 60mph or so. It never would lock itself up before under hard throttle except in overdrive.

Overall I really like how the truck drives with this mod, and it was well worth the time to do it. let me know how you like it if you end up trying it. And also, I would set the potentiometer right in the middle for the first drive, and then adjust from there, because with the knob all the way to the left, or all the way to the right i didnt have overdrive or lockup at all. Let me know if ya need anything explained better. I just have my POT mounted under the hood for now. I may put it in the cab, but i have it set about where i want it, so im not real worried about it for now.

Eric
 
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