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Discussion Starter · #1 ·
Greeting folks,
I've been reading posts here, learning a lot, while trying to help my brother solve a tranny issue. Long story short, the transmission will engage a forward gear when the shifter is placed in D, 3, 2,or 1, but approximately 1-2 seconds after engagement, it will let go and go back into what feels like neutral. When placing in reverse, it will engage, and stay engaged. So we have reverse, but it won't stay in forward gears, even though it will for a second or two. This transmission has been rebuilt before, approximately 2+ years ago, with parts to hold up to 1000hp. Unfortunately, he had a single disk billet torque converter in it, which we thought was the weak link. It's in a detuned twin turbo set up, at approximately 500 hp. He pulls a big 5th wheel trailer, and an enclosed trailer behind that. This occurred about 3 weeks ago when using a lighter flat bed trailer to help a son move a car. Apparently, the tranny would go into limp mode, he would reset it, and it would go fine for a bit, then go in limp mode again. Apparently, he had shuttering between shift 1-2, and 2-3, and at times would feel as though the tranny wouldn't engage into drive, but if given a little throttle, it would bang into gear, and hold for a bit. Eventually, by the time he got home, there were no more forward gears, but reverse was normal. We have no transmission codes currently, but have only been able to run the truck to test gear engagement on the lift. Initially, he had the P0700 code. Here is what we've done so far:

1] Replaced torque converter with a triple disk billet converter, stock stall
2] Replaced the NSBU switch
3] Checked ohms on all solenoids (at external tranny plug, which were within spec
4] Checked ohms on transmission temp sensor - no reading (open), so replaced the pressure switch manifold (which has the temp sensor in it) - now have normal ohm readings
5] Checked all wiring visually - can't see anything obvious out of the ordinary
6] Tried the TCM out of a brother in laws 2002 Duramax, where it would hold in forward gear a second longer, but would then pop out again
7] Replaced the ignition switch wiring harness
8] Replaced tranny fluid, twice. It doesn't smell burnt, can't see any chunks of metal, or glitter, but there is a very slight darkness (blackish?) on top of the pan filter that wipes off easily.
9] Checked constant and switched power to TCM, all checks ok, @13V

Of note, since the rebuild, twice the pan filter pipe slid out and caused some erratic shifts and engagement until an OEM filter was used, and that solved that problem. One time for sure, the tranny got quite hot pulling a big grade, and he pulled over to let it cool down. When he got home from that trip, he changed the tranny fluid. It was operating normally at that time. and thereafter. He may have gotten it hot a couple of times, but the transmission still worked normally during and after the heating up event.

Questions:
1] Can a trim solenoid test normal with an ohms test, but still not work properly, and not throw a code? We have a new A & B solenoid, but after testing the existing ones, with in spec ohms, we decided not to change them.
2] If the torque converter failed, could it cause other damage internally that would cause this type of behavior?
3] What else should we do before pulling the trans out and tearing it apart?

We're not sure what to do next, so am looking for input from you experienced people here, if you have any advice or further questions.

Thank you in advance.....
 

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Discussion Starter · #2 ·
No takers??

So, we have decided that it's cheaper to replace all of the solenoids than to buy the solenoid test kit, so they have been ordered. This Saturday, we'll replace all of the solenoids, and try again. I'm not sure what the failure rate of having normal ohms readings and yet still not open/close or hold pressure completely, but apparently it happens often enough........... We'll see.
 

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I would start by taking the valve body apart and making sure there's no clutch material or other junk causing problems. But '1000 hp trans',single disc converter,and wrong pan filter says a lot about the trans builder. Don't take offense if you did it yourself, I'm just saying

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Also where the trans fluid line hot flushed before installing the new rebuilt Alison
 

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Discussion Starter · #5 ·
I would start by taking the valve body apart and making sure there's no clutch material or other junk causing problems. But '1000 hp trans',single disc converter,and wrong pan filter says a lot about the trans builder. Don't take offense if you did it yourself, I'm just saying

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No offense buddy, we weren't the trans builder, and even requested a triple disc converter from a shop, but they installed a single disc because they thought " It will shift too hard" which was not discovered until much later..... BS.... thats why we dont go there anymore..... We've been using OEM filters since we discovered the filter issue, and havent had any more trouble..... when we inspected the external valve body saturday, it was sparkly clean, but we disnt remove it..... good advice....
 

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Discussion Starter · #7 ·
So, putting in all new solenoids didnt change anything...... still pops out of forward gears after a second or so.... we'll be pulling the tranny next saturday.
 

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Discussion Starter · #8 ·
We pulled the transmission apart today, and found C1 clutches smoked..... One of the plates got so hot, it warped.....And, as we inspected the pump, we found the main pressure regulator stop broken.... We think the tranny must have burned up after loosing pump pressure. My brother thinks he remembers finding a small chunk of steel in the oil pan over a year ago, and as he thinks back, remembers that the tranny started overheating after he found that piece of metal. At the time, he couldnt figure out where it came from, but now we know.
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Discussion Starter · #11 ·
So, after meticulously rebuilding the transmission, with all of the modified clutch packs, valve body, and pump mods, we re-installed the tranny last Friday. It works excellent, with smooth shifts, excellent holding power, and solid TC lockup. We are still working with the new cooling set up, removing all of the stock cooling, and running lines to the rear of the truck where a Derale cooler with fan is wired up, using a thermistor to control fan activation between 160-180 deg temps. We have a manual switch over ride in order turn the fan on manually if desired. Tranny runs around 180 deg, sometime s a little lower, sometimes a little higher. We still want to get the temps down further for pulling big loads in the summer. As far as the tranny goes, it is working excellent now.
 
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