No overdrive???

95cummins4x4 · 10-23-2011, 05:44 PM

I have a 1995 dodge cummins 2500. the OD on/off button has never worked and the light is always lit. Got a new button for it didnt help at all. the truck was going into od even with the light lit. but the truck never wanted to downshift when you got on it. so i took it to a shop they said they adjusted the cable but it didn't help. when i picked it up from the shop it was going the same then all the sudden it downshifted into third and ever since then it wont go back into OD. do you think its whatever the shop did when they adjusted it? because it never had problems before just that the button never worked on the dash. Also my dash lights don't work and when i turn my lights on my radio and outside temp gauge will dim. do you think a bad ground could be causing this? i think the gauge lights and OD button are the same circuit? any help would be greatly appreciated i need this truck and its hard to find time to take it to the shop.

RPegram · 10-24-2011, 06:10 AM

The lights that dim when you turn on the headlights are doing like they are supposed to. For the OD problem, I would recommend a factory service manual. Cheapest I've seen is from Geno's Garage online. You've got a lot of testing ahead of you to fine this issue and the manual covers all the tests. The manual also give a complete wiring diagram so you can trace out the wires going to the OD button on the dash.

95cummins4x4 · 10-24-2011, 05:52 PM

my radio will dim so much i cant even see it. no gauge lights no heater control lights? and thanks ill have to look into the manual. so does it sound electrical to you though? absolutely nothing happens when you push the button no noise. doesnt even feel like theres a click or anything

RPegram · 10-24-2011, 06:55 PM

In the daytime my radio and overhead will dim so low with headlights on i can barely see them, but they are plenty bright at night. I believe you need to get the issues taken care of with the OD button and then you can move on to diagnosing the OD issue. What you are feeling as OD, could it possibly be converter lockup and not OD? Easy test is to get to highway speed, keep right foot on go pedal and keep speed steady, touch brake pedal with left foot just enough to turn on brake lights and see if RPM's change. They should go up a few hundred and drop back down a few seconds after letting off the brake. IIRC correctly, the OD button simply grounds out a wire when you push it and does nothing while not being pushed. It grounds wire again when you push it and light toggles off or resets when you turn ignition off. The converter should lock no matter if your in 3rd or OD. One other thing to check is the TPS. Here are instructions to do so:

Click > TPS testing and adjustment

95cummins4x4 · 10-24-2011, 07:54 PM

yeah see mine go completely out at night but during the daytime with no headlights on they work just fine. pull back on the light switch and they go out i cant even change my radio station and i can barely read my outside temp gauge. almost like the power is not making a full pass through the circuit(bad ground) but getting enough juice just give off a weak light. also when i turn my dimmer dial. nothing happens. is there anywhere online that i can just get a wiring diagram for free? i haven't been able to find one.. what does lock up feel like? when im cruising at 50 im running about 1750 rpms. ill let off the throttle and it will idle all the way down to about 800-900 rpms. get back on the gas and it will go up a little bit in rpms but feel like nothing is grabbing then give it some more gas and it will finally feel like it catches again almost like driving a standard and holding the clutch in. should it do that? this is my first diesel so im new to this all my other gas trucks would not drop that kind of rpms when letting off the throttle. and with that brake check test. what does it mean if my rpms do change? whats that telling me? i appreciate you actually responding to me by the way everyone says search but ive been searching for a week and couldn't find my exact problem. so thanks

RPegram · 10-25-2011, 07:31 AM

When you touch the brake pedal, whether on the go pedal or not, the converter should unlock. The converter has clutches inside and these clutches lock and actually give you a direct connection between the engine and rear end, just as in a manual truck. When the converter locks there should be a 200-300 RPM drop and vice versa when it unlocks.

The OD button on the dash has nothing to do with converter lockup and unlocking. In a stock trans, the converter should lock in either 3rd or OD (4th). Under light throttle the converter should lock around 35ish in 3rd and around 50ish in 4th (OD).

Something else that can cause loss of OD in a '95 is the trans temp sender. This sender is located in the steel cooler line coming off the trans. Most with these years trucks will unhook the wire from the sender, solder in a 1,000 ohm resistor between the two terminals on the wire (not the sender itself) and tape the connector up real good and leave it unhooked. This sender is what tells the PCM the trans is running hot and to disengage OD. IIRC the light on the OD button will also illuminate along with a trans temp light on the gauge cluster.

I've not seen any links to wiring diagrams online for this year of truck. Each year is different so you really need the proper year manual.

95cummins4x4 · 10-25-2011, 10:07 PM

huh illl have to check out the trans temp sender! i tried the brake thing i could not get it to do anything i was doing it at a speed of around 55mph. also i counted the shifts and i can only hear it shift from 1-2 then 2-3. when the truck use to go into overdrive when it shifted it almost felt like someone was pushing the truck it would kind of lunge forward when it shifted in. but now that you mention it back when i thought my truck was going into OD it would do it at 35-40 under light throttle, and ive always thought my truck runs high rpms. at 55 im at 2000 rpms is that high? under the hood it says gear ratio 3.5. and ive never been able to get my truck to do much over 70 mph! maybe fourth gear has never worked? whats it mean if my rpms didnt change on the brake test? bad solenoid or something?

DirtMerchant · 10-26-2011, 05:57 AM

Quote:

Originally Posted by 95cummins4x4

huh illl have to check out the trans temp sender! i tried the brake thing i could not get it to do anything i was doing it at a speed of around 55mph. also i counted the shifts and i can only hear it shift from 1-2 then 2-3. when the truck use to go into overdrive when it shifted it almost felt like someone was pushing the truck it would kind of lunge forward when it shifted in. but now that you mention it back when i thought my truck was going into OD it would do it at 35-40 under light throttle, and ive always thought my truck runs high rpms. at 55 im at 2000 rpms is that high? under the hood it says gear ratio 3.5. and ive never been able to get my truck to do much over 70 mph! maybe fourth gear has never worked? whats it mean if my rpms didnt change on the brake test? bad solenoid or something?

I have 3.55 gears on mine, with the stock tire size (245-75-16) mine was pulling 1800rpm at 70mph....and mine definitely goes into OD exactly at 47mph...sounds like you had lockup in 3rd gear and never had OD.

RPegram · 10-26-2011, 06:45 AM

I'll second no OD. Sounds like you had lockup, but have now lost that. RPM's should be a lot lower at 55mph. You've got a good chance no OD and the OD button light staying on are all related.

95cummins4x4 · 10-26-2011, 07:37 AM

yup i thought the rpms seem way to high. so where do i start now? just bring it to a shop? its all starting to seem more complicated haha

95cummins4x4 · 10-26-2011, 06:39 PM

i have 315-75-16s but wouldnt that make my rpms lower not higher with a bigger tire?

illflem · 10-26-2011, 08:15 PM

Quote:

yeah see mine go completely out at night but during the daytime with no headlights on they work just fine. pull back on the light switch and they go out i cant even change my radio station and i can barely read my outside temp gauge.

This may be stupid but you know that by twisting the headlight knob you brighten or dim the dash lights right?
Maybe the dimmer portion of your switch is fried.
Pretty common as the switch gets smokin' hot if a person runs the lights dimmed way low for extended periods.