Torque Converter Won't Unlock

[Bloomy]

Howdy all. Friend of mine has an 05 3500 SRW QC 4x4 with 50k on it. In park and neutral it idles fine. When you put it in gear, you have to have your foot firmly on the brake or the truck will launch. If you remain stopped with it in gear the engine is definitely bogging down. Just like coming to a stop with a standard and not pushing in the clutch. It won't stall itself. So I am thinking the Torque Converter is not unlocking. Any ideas as to why this would happen. I don't know the maintenance record, but will probably bet the oil has never been checked nor the filter. Is it possible that it could be mechanical or electronic? I don't know much about auto's so thanks for the help.



Thomas

 

[WCounts]

It would be throwing codes if it was something electrical like a grounded wire going to the lock up solenoid. I believe something in the torque converter has got it hung up. You could try unpluging the plug going to the transmission and see if it still does it.

If the truck has been modded it may be time for a transmission over haul.

 

[cerberusiam]

If the TC was not unlocking it would kill the motor in gear. More than likely the TC has destroyed itself and starting to seize the stator. Trans will probably need a rebuild as there is probably junk all thru it now.

 

[PGreenleaf]

Must remember also that on the 05s you cant lock out overdrive. So if under the right cercumstances if the trans was going in and out of overdrive and lockup when in fact you should have had overdrive locked out , it would ruin the torque converter lockup .

04s and previous models and 06 on all have OD lockout. 05 is the only year with NO OD lockout.

 

[DBraunig]

If the TC was not unlocking it would kill the motor in gear. More than likely the TC has destroyed itself and starting to seize the stator. Trans will probably need a rebuild as there is probably junk all thru it now.

Agreed, I've seen this two or three times. Stator defect in the converter.



Dave

 

[Bloomy]

Thanks for the info guys. I agree that the engine would stall if it was not unlocking. That is the closest description I could give it. I guess it is time to get it to a transmission shop. Thanks.

 

[raychem]

Before going crazy, I would suggest that you do one thing first. Lock-up as well as overdrive is controlled by a pair of soleniods. If the soleniod for the TCC lock-up will not disengage, it will cause the symptom above. You will have to drop the Valve body to replace the soleniods BC in this case, even if the VB connector for the eletronics is removed the symptom will be still be present. Replace the overdrive TCC solenoids first before rebuilding the whole transmission. It will be much cheaper. Also try not to drive the truck to prevent damage.



Richard

 

[DBraunig]

Before going crazy, I would suggest that you do one thing first. Lock-up as well as overdrive is controlled by a pair of soleniods. If the soleniod for the TCC lock-up will not disengage, it will cause the symptom above. You will have to drop the Valve body to replace the soleniods BC in this case, even if the VB connector for the eletronics is removed the symptom will be still be present. Replace the overdrive TCC solenoids first before rebuilding the whole transmission. It will be much cheaper. Also try not to drive the truck to prevent damage.



Richard

Richard,



Couldn't they force lock up with the scan tool to test the solenoid? they are taking it to a trans shop anyway. If the engine actually stalls when they force lock up, wouldn't that verify the solenoids?



Bloomy,



Does the truck act like it has no power when taking off from a stop? but at highway speeds feels normal again? (no torque multiplication)?



Dave

 

[raychem]

Richard,



Couldn't they force lock up with the scan tool to test the solenoid? they are taking it to a trans shop anyway. If the engine actually stalls when they force lock up, wouldn't that verify the solenoids?



Bloomy,



Does the truck act like it has no power when taking off from a stop? but at highway speeds feels normal again? (no torque multiplication)?



Dave

Yeah they could BUT both the 3-4 solenoid and the TCC solenoid are normally open. This means that while the solenoids are not energized, they bleed off the pressure suppied by the VB. When the solenoid is energized,the check ball in the solenoid closes and the pressure builds up before the solenoid to activate the shift valve. Hence, if the solenoid is clogged or there is debris in the solenoid which I have seen before it will not allow the pressure to bleed off and lock the TC clutch. It can happen with 3-4 also. So yes the scan tool can test the solenoid, you could do it manually too but if it is cloged, the test will only confirm that the solenoids will energize and de-energize.



Also Bloomy stated is shudders and stalls in any gear that is not neutral or park. Same thing that happens when the TCC wont unlock.



Richard

 

[AH64ID]

04s and previous models and 06 on all have OD lockout. 05 is the only year with NO OD lockout.

A buddy is shopping for a truck... do 04. 5 fall under 04 or 05??? Trying to tell him to get a manual, but just incase...





Sorry for the hijack.

 

[DBraunig]

If you remain stopped with it in gear the engine is definitely bogging down. Just like coming to a stop with a standard and not pushing in the clutch. It won't stall itself.

Thomas

His 1st post said it would bogg down, but would not stall. that's what had me thinking stator instead of tcc.



Bloomy let us know what you find out,



Hope some of this helped anyway,



Dave

 

[Bloomy]

I forgot that his 05 has the 7/70 so its sitting at the dealer. We will see what they come up with. Thanks for all of the info. I will let you know what they find.



Thomas

 

[Bloomy]

The truck came back from the dealer. They put a new TC in it. I didn't get a chance to talk with them to see what actually happened, but the truck works now. They also went and did a recall to activate the park/reverse horn alarm that my friend did not want! But, they did it anyway. Thanks for all of the help. I would have been curious to see how much crap is swimming in the transmission now though.



Thomas