1995 3500 auto tranny going in and out of lockup, why?

MrClortho · 12-17-2009, 08:36 AM

I have a Dodge 3500 diesel truck with an automatic transmission. When I get up to highway speeds, sometimes it will shift in and out of lockup on a flat surface at a constant speed. It will lockup for a couple of seconds, then unlock for a second and then lockup again and the cycle will repeat until I either increase or decease the throttle.

What would cause this?

I have been having a 'sticky throttle' sometimes and the parts stores say it does not have a throttle cable. Could the throttle position be the factor in the transmission getting confused on the throttle position and shifting in and out of lockup?

Joe G. · 12-17-2009, 09:41 AM

That is a classic symptom of a bad throttle position sensor. Are you using cruise control?

MrClortho · 12-17-2009, 09:43 AM

Hmm, it does appear to be worse when the cruise is set. And, it only seems to happen when I have the throttle in a static position.

I suspected that was the cause but this is my first diesel and wasn't completely sure how the throttle worked yet. It almost feels like a worn throttle cable even though it does not have one.

Thank you very much for your help.

Joe G. · 12-17-2009, 09:48 AM

What happens is that when the TC clutch unlocks RPM goes up a little bit so the throttle moves to reduce RPM. Then when it locks up again the opposite happens. If you have a bad place in the TPS then it will do that.

MrClortho · 12-17-2009, 09:50 AM

Yup, that sounds exactly like what is going on.

Again, thanks for your help.

Racer9 · 12-17-2009, 10:00 AM

You DO have a throttle cable. There is even a TSB on them. Recall #970 - throttle cable
But your problem sounds more like the TPS.

MrClortho · 12-17-2009, 11:30 AM

OK, I got it figured out now after taking a look at how it works under there. Looks like I can get the TPS for about $225 and will slap it on there myself.

I will hit up the local dealership for the recall while I am at it.

Thanks for all of the help.

illflem · 12-17-2009, 11:51 AM

$150 for a TPS from Napa but first try this TPS testing and adjustment

Also read this 47RH Tranny Troubleshooting

reason95 · 01-28-2010, 03:29 PM

are your mpg's suffering?

12-17-2009, 08:36 AM	#1 (permalink)
MrClortho Newbie Join Date: Aug 2009 Posts: 14 Thanks: 0 Thanked 1 Time in 1 Post iTrader Score: 0 reviews MrClortho's Truck Pics	1995 3500 auto tranny going in and out of lockup, why? I have a Dodge 3500 diesel truck with an automatic transmission. When I get up to highway speeds, sometimes it will shift in and out of lockup on a flat surface at a constant speed. It will lockup for a couple of seconds, then unlock for a second and then lockup again and the cycle will repeat until I either increase or decease the throttle. What would cause this? I have been having a 'sticky throttle' sometimes and the parts stores say it does not have a throttle cable. Could the throttle position be the factor in the transmission getting confused on the throttle position and shifting in and out of lockup? __________________ '95 Ram 3500 Dual, Auto, exhaust brake, gauges - Audio system (Pioneer Premier, Fosgate digital, 10" MB Quart sub) - Veggie Oil Powered

12-17-2009, 09:41 AM	#2 (permalink)
Joe G. Diesel Head Join Date: Apr 2007 Location: Eureka, CA Posts: 1,799 Thanks: 2 Thanked 53 Times in 50 Posts iTrader Score: 0 reviews Joe G.'s Truck Pics	That is a classic symptom of a bad throttle position sensor. Are you using cruise control? __________________ KDP tab fix info and fuel system article jgeorge1@suddenlink.net '95 2500 CC auto 4X4, 3.54, EGT, boost, fuel pressure, trans temp guages, PacBrake, TST #5, DTT VB, DTT triple disk TC, DTT billet flex plate, Cummins chrome kit.

12-17-2009, 09:43 AM	#3 (permalink)
MrClortho Newbie Join Date: Aug 2009 Posts: 14 Thanks: 0 Thanked 1 Time in 1 Post iTrader Score: 0 reviews MrClortho's Truck Pics	Hmm, it does appear to be worse when the cruise is set. And, it only seems to happen when I have the throttle in a static position. I suspected that was the cause but this is my first diesel and wasn't completely sure how the throttle worked yet. It almost feels like a worn throttle cable even though it does not have one. Thank you very much for your help. __________________ '95 Ram 3500 Dual, Auto, exhaust brake, gauges - Audio system (Pioneer Premier, Fosgate digital, 10" MB Quart sub) - Veggie Oil Powered

12-17-2009, 09:48 AM	#4 (permalink)
Joe G. Diesel Head Join Date: Apr 2007 Location: Eureka, CA Posts: 1,799 Thanks: 2 Thanked 53 Times in 50 Posts iTrader Score: 0 reviews Joe G.'s Truck Pics	What happens is that when the TC clutch unlocks RPM goes up a little bit so the throttle moves to reduce RPM. Then when it locks up again the opposite happens. If you have a bad place in the TPS then it will do that. __________________ KDP tab fix info and fuel system article jgeorge1@suddenlink.net '95 2500 CC auto 4X4, 3.54, EGT, boost, fuel pressure, trans temp guages, PacBrake, TST #5, DTT VB, DTT triple disk TC, DTT billet flex plate, Cummins chrome kit.

12-17-2009, 09:50 AM	#5 (permalink)
MrClortho Newbie Join Date: Aug 2009 Posts: 14 Thanks: 0 Thanked 1 Time in 1 Post iTrader Score: 0 reviews MrClortho's Truck Pics	Yup, that sounds exactly like what is going on. Again, thanks for your help. __________________ '95 Ram 3500 Dual, Auto, exhaust brake, gauges - Audio system (Pioneer Premier, Fosgate digital, 10" MB Quart sub) - Veggie Oil Powered

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12-17-2009, 10:00 AM	#6 (permalink)
Racer9 AlGores worst nightmare Join Date: Dec 2006 Location: Erie Pa Posts: 2,053 Thanks: 0 Thanked 23 Times in 19 Posts iTrader Score: 0 reviews Racer9's Truck Pics	You DO have a throttle cable. There is even a TSB on them. Recall #970 - throttle cable But your problem sounds more like the TPS. __________________ '96 2500, CTD, 4X4 flatbed, Isspro gauges, Skyjacker D-25's, ThurenFab track bar, DSS, HD steering. Motor; BHAF, #100 fuel plate, Shimmed gov springs, Loose starwheel. 306hp/743tq Exhaust; Schwitzer S300G, 4" downpipe, 5" turnout stacks. Trans; Dunrite VB/TC, Intelligent Engineering billet input shaft, Burt Brown rebuild/upgrade.

12-17-2009, 11:30 AM	#7 (permalink)
MrClortho Newbie Join Date: Aug 2009 Posts: 14 Thanks: 0 Thanked 1 Time in 1 Post iTrader Score: 0 reviews MrClortho's Truck Pics	OK, I got it figured out now after taking a look at how it works under there. Looks like I can get the TPS for about $225 and will slap it on there myself. I will hit up the local dealership for the recall while I am at it. Thanks for all of the help. __________________ '95 Ram 3500 Dual, Auto, exhaust brake, gauges - Audio system (Pioneer Premier, Fosgate digital, 10" MB Quart sub) - Veggie Oil Powered

12-17-2009, 11:51 AM	#8 (permalink)
illflem Super Moderator Join Date: Nov 2005 Location: Montana Posts: 7,453 Thanks: 6 Thanked 424 Times in 359 Posts iTrader Score: 0 reviews illflem's Truck Pics	$150 for a TPS from Napa but first try this TPS testing and adjustment Also read this 47RH Tranny Troubleshooting __________________ Bill '95 2500 4wd auto '95 3500 5 speed heavy hauler Stock for one day

01-28-2010, 03:29 PM	#9 (permalink)
reason95 Cummins Fan Join Date: Dec 2009 Posts: 59 Thanks: 4 Thanked 0 Times in 0 Posts iTrader Score: 0 reviews reason95's Truck Pics	are your mpg's suffering? __________________ 2nd gen 12v; 4x4; 3.53 rear; afe stage 2 cold air intake; 4 inch exhaust; recent rebuilt auto trans w/ low stall tq converter; 95,000 miles

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