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Old 02-19-2017, 06:06 PM   #1
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How to diagnose bad Torque Convertor vs. bad transmission?

How can I tell if the problems I'm experiencing is related to a bad TQ convertor or a bad transmission?

Vehicle is a 1996 Dodge ram, 2wd, 5.9L I6 12valve Cummins turbo diesel. 77k miles. (Trans was already rebuilt at 30k miles) (Less than 5k miles in past 5 years)

Several months ago, maybe even going back to last winter, when I'd drive the truck maybe 4-5 times a month, the first thing I noticed was that when I started it up and put it in reverse, it would not move. I'd then have to lightly rev it up a few times and then the trans would seem to engage and it would reverse out of the driveway. After that it would drive fine, forward and reverse. It only did that if it sat for a period of time, which was usually 1-2 weeks.

Then back around September or so, while driving it seemed to occasionally have issues with overdrive. At speeds between 45-55, it would almost feel like it would upshift and downshift randomly. When I would accelerate around those speeds, sometimes it would shift up normally, other times it would hang in a lower gear until I let of the throttle, then it would upshift fine on its own.

Now this morning, I had to sightly feather the throttle to reverse, even though I drove it just yesterday with no issues. So then I went to the store and stopped at a stop sign in the parking lot. When I tried to move again, it felt like the truck was in neutral. Nothing at all. But 2-3 seconds later the trans engaged again and I was able to drive fine. I parked, got breakfast, and the truck acted normal backing up and leaving the parking lot. However, once again at speeds 45-55 it seemed to get confused about overdrive again. I got to where I was going and checked the fluid, it was actually overfilled by a decent amount. I know it was at the proper level(hot, running in idle) back over the summer and no one else had touched it since.

I'm wondering if the transmission itself is shot, just the torque convertor or maybe its the valve body. Any idea how to diagnose it a little better?

The issues were never really consistent so taking it to a trans shop would be hit or miss, plus I no longer know of any good trans shops. All the ones now just seem to say you need a full trans rebuild no matter what. Perhaps taking it to a diesel specific shop would be the best idea. I've read that bad grounds or a faulty TPS could possibly cause trans issues on these Rams. If I do need any new parts, I will not go with stock since I do plan to increase my HP level eventually and I know the stock trans wouldn't survive that anyway.
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Old 02-19-2017, 06:20 PM   #2
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Get a trans pressure gauge, run the line into the cab and start recording numbers for PRNDL etc. IDK what that trans calls for in each gear but you should be able to get a baseline somewhere online.

That will get you more specific direction.
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Old 02-19-2017, 09:14 PM   #3
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I could be wrong, but I believe the Converters were weak on those specific trucks. My buddy had a dually that had trans issues but after swapping the converter out for another it seemed to fix the issue.
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Old 02-19-2017, 09:44 PM   #4
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my blazer is doing everything u have described lol. i had the filter and fluid changed and it got a little better. i have about 35k on its rebuild also.

i was thinking its about time to remove and clean the throttle body and related sensors, its been quite a few years since that was last done, and has 178k miles now
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Old 02-22-2017, 01:07 PM   #5
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Well on monday and tuesday it drove basically like normal. I did experience a high rpm(~2600) 1-2 shift at full throttle off a light but not sure if that is normal or not. Also seems the convertor lockup speed happens to be around 50 mph so thats part of the issue I think im seeing driving on this one road where I vary between 45 and 55. I do still feel there is some real issue still going on, but I dont feel its really major or possibly even mechanical at this point. I almost have to drive it just until it fails completely and then I'll know better whats wrong.

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Old 04-01-2017, 02:38 AM   #6
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unknown if related, but i had my fuel pump replaced, and the battery was disconnected at this time, since getting it back ive only had this occur once and it was very minor.
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Old 04-01-2017, 09:10 AM   #7
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Well, one thing that I've read online that could be a cause is a dirty ground. I have yet to do anything about my issue yet. It seems to be ok most of the time. Hasn't free-reved since that one time and reverses like normal too now. Still gets confused around 45-50 with down shifting and upshifting. I may try a fluid/filter change and see if that helps. But yes, i also want to disconnect the batteries and clean the terminals/chassis grounds. I start a new job Monday and will be working at least 6 days a week so time to do anything will be limited.

Last edited by V; 04-01-2017 at 09:12 AM.
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Old 04-01-2017, 11:31 PM   #8
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Well, one thing that I've read online that could be a cause is a dirty ground. I have yet to do anything about my issue yet. It seems to be ok most of the time. Hasn't free-reved since that one time and reverses like normal too now. Still gets confused around 45-50 with down shifting and upshifting. I may try a fluid/filter change and see if that helps. But yes, i also want to disconnect the batteries and clean the terminals/chassis grounds. I start a new job Monday and will be working at least 6 days a week so time to do anything will be limited.
Ha i know the feeling. i have 3 days off in all of april.
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Old 04-02-2017, 02:22 PM   #9
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I know those trans' for those trucks suck. Had a couple friends blow them up in that body style.
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Old 04-02-2017, 03:12 PM   #10
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I know those trans' for those trucks suck. Had a couple friends blow them up in that body style.
Yes they do suck, lol. Basically all dodge transmissions in general too.
That's why when it blew with just 30k miles, we had a private shop rebuild it instead of going back to Dodge for warranty. The shop did some upgrades as far as I can remember, but the guys were getting old and they closed for business many years ago.
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Old 08-17-2019, 01:00 PM   #11
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So here's somewhat of an update:


I have not done any work or diagnostics of the truck yet but a few weeks back, I was watching some automotive tv show, possibly "Truck U", and they were discussing the vacuum system on diesel trucks. They were saying how diesel motors don't create vacuum like gas engine and require a vacuum pump to operate the brakes and other components. I also do believe they mentioned something in regards to the transmission in Dodges about being somewhat vacuum controlled. The more I thought about it, I realized it takes a little bit after I start the truck in order to get the power brakes working right since there's no vacuum apparently after sitting for extended periods of time. So today when I took the truck out, it would not engage reverse right away and instead of revving it a few times like i usually do, I just let it idle for maybe 10 seconds. When I let off the brake then, it started reversing like normal. So its seems my issue is most likely related to a slow vacuum leak that is only seen when the truck sits for a week or so. That is easily something I can deal with and accept without worrying about trying to fix it anytime soon. For now, I'm just glad that it doesn't appear to be a mechanical issue.
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