Auto OD

[PPettit]

A freind of mine is looking at a 93 CTD with an automatic transmission with overdrive. I didn't know they made these from the factory in 1st gen trucks. Is this something to avoid? He says when he drove it it dropped out of overdrive with the slightest application of throttle.



Phil

 

[dan brooks]

IIRC, the OD trans came out at the same time as the trucks received an intercooler. It's basically a 727 trans with an overdrive unit bolted on the back.



As long as it's otherwise shifting okay, chances are the TPS is just out of adjustment - easily corrected with an OHM meter and a 10mm wrench.

 

[paccool]

The TPS (throttle position sensor) needs to be adjusted to stop the downshifting. This is located on top of the injection pump and is easy to adjust. This item is also one that gives problems, do a search in the archives for information.



The 518 transmission is basically a 727 with a OD unit added. Was used in the 91. 5-93's. The first gens don't have a lockup converter. (I was told that a few of the later 93's had converter lockup but I cannot confirm this. )

 

[steve m.]

paccool, when did you get your ATS manifold? Iwas on ATS web site and they don't list one for 89 /93 trucks. thanks Jim

 

[paccool]

Steve,

I got it from Piers. I think it is the same as used on 94-98 12 Valve. Be warned though, you will need to do some major porting on the new manifold to get things to match up. The ports match fair but there was a lot of material inside that needs to be removed to make it flow better. I had HDM48 do the manifold for me, I matched the turbo housing myself. Had to take almost a 1/4" off one side to get it to match right. Also, if you get one, I can give you some info on coating that I found and used on mine. It is holding up well so far. Was not cheap though, was about $60 for 12 oz can(not a spray can), only used about a third of it. Sprays on 1-1. 5 mils thick. Any thicker they said it would peel off.

 

[1stgen4evr]

drops out of OD

I have two OD trucks and have not been satisfied at all with the TPS function of either. TPS is an acronym for total piece of (pick your own invective) in my opinion. You can work around that however and if the truck is nice and is otherwise what your friend is looking for, he will like the rest of the truck for sure. The hunting that the OD does is mostly an 'in traffic' problem and isn't a problem at highway speeds.



There is a good bit of info on how to eliminate the TPS and make the OD perform according to one's own instructions rather than the PCM. A recent post on the TPS by a member suggest that a rehostat can be substituted for the TPS and the shift point can be dialed in to match one's specific driving habits. I have not tried this mod but it sounds like the way to go in eliminating the problems. There is also info suggesting that the TPS can be cleaned internally and reused. The new part is available but is pretty expensive and won't last very long either. I bought a new one from the dealer and feel sure I got a used one in a new box. It didn't work either. The TPS isn't the only thing that the PCM uses to reference the shift point and you can chase the problem till you drop.



That said (or vented if you like), the TPS is a rehostat and must be set to certain specs. You may indeed be able to simply set the output voltage and have the OD work correctly for a time.



1stgen4evr

James