1996 4 Speed Transmission Problems

I just bought a 1996 Ram 3500 Cummins. Truck has just over 100,000. The original window sticker says the truck has the HD 4speed option but the sticker on the hood says std so not sure about that. The truck
goes in forward and reverse smooth and shifts smooth. The problem I noticed is that right around 55 to 60mph (which also happens to be regulated commercial truck speed) the truck seems to hunt or slip in and out of what I think is OD with about a 300rpm change. I turned od off to see if it would stop in it drops about 700rpm but is steady but if you continue to slow down to say 30 or 40mph with the OD off it hunts and slips the same so that is why I don't know if its actually OD or not. But like I said at around 55 60mph with OD on it feels like the OD is slipping in and out. Any speed above that it doesn't seem to have a problem.
I checked the fluid level which was good but fluid smelt little burnt so I changed it. That leads into a whole world that I have never experienced. I have always had Fords and this is my first Dodge so I don't know anything about the fluids. The dipstick says ATF 3 or Dexron II. Everybody I talk to says never to use Dexron. The manual says ATF 3 for 2000 and older and 4 for newer. So I went to Napa and they told me to use the Valvoline ATF 4. Right on the bottle it says it replaces ATF 3, so thats what I bought and a filter. So I really don't know if that is the right fluid or not. Some websites say that ATF 4 in older trans causes seal leaks but is better fluid. I changed the filter and fluid (most fluid, just pulled pan) and did the recommended band adjustment which was quite interesting. They put that nice square adjuster on there so I had to make a tool to fit so I could use my torque wrench. I followed the service manual and did the 72 inch pounds then back off 2 7/8 turns for forward and 2 turns for reverse. So checked level and took truck for drive and it did the exact same thing, no change.
I'm sure my next step will have to be take to a shop but was wondering if this sounds familiar to anyone. It would be nice that by some slim chance it was something simple to fix but I know with most trans problems there usually not. Thanks for your time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Could be the TPS or a brake light switch. The switch is the cheapest and easiest to fix.

You should me okay with the 4 imo.

thoughts.
Roy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

What you're experiencing is the torque converter clutch engaging and disengaging - not the transmission slipping or hunting between gears. This is almost always an electrical problem. As Roy said, your Throttle Position Sensor could be going bad, sending a false signal to the PCM that thinks you've floored the accelerator pedal, causing the PCM to unlock the converter clutch. A shop manual or even a Haynes manual, and an analog multimeter can determine whether or not the TPS is at fault.
However, there may be a simpler fix. As posted on the Turbo Diesel Register:
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
Lock Up Complaint: Issue 52, page 39, offered an in-depth look at torque converter lock-up. Although the author was specifically talking about the '98.5 and newer trucks, this tip applies to torque converter lock-up on Turbo Diesels '94 and later. As documented, many people have replaced the TPS or APPS, transmission temperature sensor and numerous other parts trying to correct the ongoing converter clutch problem with varying degrees of success.
Well, for all of the shadetree mechanics in Turbo Diesel land, before replacing any parts or wasting time connecting a scan tool or voltmeter to the electrical circuit, start with the easiest step first.
I have found the cause of the lock-unlock problem to be a frequency-induced electrical noise into the ground circuit of the battery which causes a fluctuating voltage signal from the TPS to the PCM.
The Solution: Locate the 10-gauge ground wire that runs from the negative post of the passenger battery to the back of the alternator. This wire is often tan with a black stripe.
Starting at the back of the alternator loom where the tan/black striped wire heads for the battery, wrap the wire with a piece of tin foil about 4" - 6" in length. Wrap the tin foil with black electrical tape to secure it in place.
Road test the vehicle. If the problem is corrected, smile.
Tony Garcin Dunrite Converters Vancouver, WA (360) 693-3200
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tom Lawrence wrote:

Thanks, this is good info. I cleaned all my electrical connections and did the aluminum foil trick but that didn't help. I found an article on-line with the specs for diagnosing the TPS so I checked mine and it was way out of spec. I tried adjusting it and cleaning it but nothing helped so I replaced it. After replacing the TPS I checked the idle voltage and it was still out of spec so not sure what the problem is yet. My reference voltage is 5.11 so that is good and I used the ground wire going to the TPS to check the reference so I assume the ground is good. I am still searching for the answer. Thanks for your help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Please let us know what you come up with.
Roy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roy wrote:

Finally fixed my overdrive/ converter issue. I have been on the TPS warpath througout this problem because mine was out of spec. TPS voltage should be around 1 volt at idle position plus or minus .2 volts. My old one was .33. I cleaned and adjusted and the best I could get out of it was .59 so I bought a new one. I rechecked the idle postition voltage which was still only .66 on the new TPS. I drilled out the mounting holes a little and got it in spec with .81. Thinking it should be fixed I test drove it and to my suprise absolutely no change, still same problem. You can only imagine the veins in my head. So after alot of thinking the one thing that I had forgotten about was the fact that the cruise control didn't work anymore. The power light would come on but would not operate. It was at that point something clicked and I relized the trans and cruise both have the brake switch in common. I replaced it and fixed the problem. I blew alot of money on the TPS but like I said it was out of spec so I got stuck in that rut and didn't think of anything else other than the TPS and circuit being the cause. I will do alittle more diagnosis next time even if something is questionable. Thanks for everyones help. What a relief to have this fixed without replacing the trans. Thanks again.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good deal glad, it worked out for ya.
Roy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.