I have a 1993 dodge 350 cummins dually 4x4. Its got about 200k on it with some heavy trailer towes under its belt. Its got the automatic 4speed overdrive transmission with electronic manual 4th gear lockout and an aftermarket transmission cooler mounted behind the driver's side duels. The transmission has started slipping when changing from 3rd into overdrive. 4th does engage fully after a few seconds of slipping even if the drive line is under load. The fluid level is ok and the fluid is not discolored or burnt. The transmission seems to shift good and strong 1st-3rd. The lockout control works ok.

Anyone know what I'm up against here? If its a tranny rebuild on the auto I'd like to consider a swap to a manual. I have owned a 5speed 1993 same midel and liked that setup better. Advice on going for the swap? If its hands down for the auto rebuild does anyone have experience with gear vendors aftermarket auxiliary unit. The stock tranny seems geared a bit tall for towing. I been told the stock torque converter is partly to blame for a loss of power so added suggestions there also helpful.
I guess the bottom line is does the current automatic have a problem that's associated with something repairable from the outside(or by dropping the pan) like a sensor or filter or is it just a matter of time before I'm gonna need a tow off the road due to a complete trans failure. Thanks..

 

Not towing in Overdrive are you? That is a sure way to smoke the trans.

Common failure in these is the snap-ring that holds the O/D unit together breaks. You lose engagement pressure on the clutches in the o/d unit, and... it slips..... Might be able to get away with just rebuilding the O/D unit, but, if it goes too long, you will have debris throughout the trans, and a full rebuild will be the only sure fix.

Manual swap would solve a lot of issues..... and probably cost about the same. (provided you do most of the work yourself.) PATC (transmissioncenter.net) makes some bulletproof autos though..... north of 2 grand though.

 

I do let overdrive engage when I'm running on the flat or down grade. I disable the unit when I start to pull any grade worth mentioning. Thanks for the advice do you have any references why could go to learn about the potential fix you recommended? Some talk about band adjustment for the automatic is that in the cards for a repair or not something that's done with this trans? Also has some talk about fluid and filter change to make sure the pump isn't starved for fluids and losing pressure during the shift. Finally I know I had a throttle l positioning sensor that went out years ago and then the transmission could not decide between 3rd and overdrive. Is the condition I have potentially caused by a failing sensor? By the way that's the best price I've heard on a bulletproof rebuild automatic thanks for that recommendation. Any advice on aftermarket converters. I've heard they are a weak link in the driveway.

 

The overdrive seal maybe too hard from the high mileage and heat. Causing the fluid to leak pass the seal. It happens to all transmissions. You can try a aftermarket torque converter, But you may need to replace the flex plate/flywheel. I would recommend what HeyYou had said, remove the overdrive unit and check the overdrive clutches and maybe inspect the direct clutches and steels too. Just so you know, You don't need to remove the transmission to remove the O/D unit. Just don't tear the gasket. I also have a button to take the transmission out of overdrive and drop the transmission into 3rd gear. I do this all the time.