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Transmission Limp Mode??

Discussion in 'Engine & Performance' started by Jeff Martin, Nov 21, 2020 at 3:31 PM.

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  1. Jeff Martin

    Jeff Martin Junior Member

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    Hi all, I recently replaced the 5.9 cummins in my son's 2007 Ram 2500. It has the 48RE Trans.
    The truck will shift into drive and rev fine for several minutes then nothing. No funny sound, no vibration, just like its stuck in neutral. If I shut it down and restart it does same thing again. Shifts fine then nothing after several minutes. Fluid level is good. Not throwing any codes. No check engine light. Engine runs smooth and has power when first started. Revs like in neutral when in gear after few minutes. Is something causing it to go into limp mode? I have read that when in LM the truck acts like its in 2nd or 3rd gear with no upshift into OD and revs high. This truck will not move at all after it acts up. I am using an Autel MaxiDiagElite code reader. Trans ran fine before swapping engine which is a reman long block. Any ideas? Thanks.
     
  2. Snake15eyes1998

    Snake15eyes1998 Senior Member

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    My guess would be, something like a wire or connecter got pinched or something didn't get hooked up right. Maybe a wire somewhere didn't get grounded correctly. I would start back from A and work my way to Z again, slowly. Double, triple checking everything you put back.
     
  3. Fast69Mopar

    Fast69Mopar Senior Member

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    Your transmission, the 48RE, does not have a Limp-In Mode. 1st, 2nd and 3rd gears are all hydraulic and 4th gear uses a solenoid and a transducer to engage the clutch along with the Torque Converter Clutch.

    I'm guessing that with a 2007 model your 48RE has some miles on it. When was the last time the pan was off. Have you ever adjusted the front and rear bands?

    When you were swapping motors did you have the torque converter out?
     
  4. Jeff Martin

    Jeff Martin Junior Member

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    I did have the torque converter out and pan off. Replaced filter and put in new fluid. Did not adjust anything as was working just fine before the engine swap. Old fluid looked ok. Not quite brownish yet. Not original trans either. Was swapped a few years back as I understand it. Son only had the truck 2 weeks or so before engine seized on him. Low on oil and engine was full of sludge. Bearings all froze on crank. The torque converter came out with the engine since it was seized and could not rotate to remove the TC bolts. No shavings or anything in the pan at that time. I'm guessing like Snake said, its a wiring connection issue. I'm gonna get some contact cleaner and start at the trans and work my way to the ECM cleaning etc. and see what happens.
     
  5. Fast69Mopar

    Fast69Mopar Senior Member

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    If the trans is acting like it's is neutral and won't shift into 1st gear then it has nothing to do with wiring. The first three gears are all hydraulic. Only 4th is electronically controlled.

    Even if the governor pressure was incorrect it would still shift in to first gear. I would get a 100psi gauge and a 300psi gauge and connect them to the pressure taps on the side of the transmission and see what my pressures were at idle in park and at idle in gear. The pressure gauges will help in diagnosis.
     
  6. Jeff Martin

    Jeff Martin Junior Member

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    If it was hydraulic issue, why would it work when truck is first started and then stop a several minutes later. There may not be a transmission Limp mode but sure seems like a Limp mode situation. I can drive up and down the driveway 20 feet or so, forward and reverse for half a dozen times then at a point when I shift from drive to reverse or the other way it will just sit there and rev but no movement. I shut the truck off and restart immediately and it will do the same thing over and over. Move fine then not. No codes that would cause this as far as I can tell. Codes are P0532,P0533,P1274 which are A/C related because haven't recharged the system yet due to bad compressor. C2100 ABS, U0184 No radio com...not installed. New trans filter. New fluid full. I will try and find some hydraulic gauges as you suggest Fast. Can I get those at parts store or need to order? Thanks.
     
  7. Fast69Mopar

    Fast69Mopar Senior Member

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    You can rent or buy a set of pressure gauges from most local auto parts stores.

    Now, for the reason this is a hydraulic/mechanical issue. Transmissions can do things that will drive a tech crazy. When seals are cold they are hard. When the trans fluid warms up the seals get softer. When they get softer they allow fluid to bypass the seal and when this happens there is not enough fluid pressure on the clutch to keep it applied. Since you are having trouble with the trans not going into first gear my bet is on the seals and clutches in the forward clutch retainer and that the forward/kickdown band is probably very loose and worn.

    Remove the pan and see how much slack there is on the forward/kickdown apply lever. I'll bet you can move it over a half inch. You should only have about ¼" of a gap between the tip of the apply lever and the detent ball.

    The forward/kickdown band may be so loose that is cannot squeeze the front clutch retainer. Give it a try.
     

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