Another way to fix OD.
Adminstrator-ess
Joined: Mar 2003
Posts: 22,594
Likes: 19
From: New Holland, PA
My father-in-law put a 1947 international KB-6 cab on my 1992 dodge chassis with a cummins engine and automatic trans. in the proccess we lost the overdrive. changed all the instrament cluster for individule gauges including speedometer. Not sure where to start looking for the problem.
Sent from my Paranoid Android HD2 using Tapatalk 2.
Registered User
Joined: Feb 2017
Posts: 43
Likes: 0
From: MexMo
Fixing my OD problem was a no brainer!
I used an $8 A/C low pressure switch for old Chrysler K-cars, 1/8 NPT extension, cheapie rocker switch, 18 gauge wire, and some spade connectors.
Here's the pressure switch:
Napa #207616 or ACDELCO Part #1550078
Here's the rocker switch:
Here's the 1/8 National Pipe Thread extension:
Here's the 3rd gear pressure test port on the passenger side of the tranny. It's number 4 (highest plug marked) :
I removed the 3rd gear presure test port plug on the tranny and screwed in the 1/8 NPT extension. Be sure to use thread tape or other form of thread sealer so it does not leak. Then, I screwed the switch into the extension. Without the extension, the pressure switch hit the side of the tranny and would not screw in all the way.
I tapped into the ground wire for the OD solenoid and connected it to the pressure switch. I then hit the other side of the switch and ran it up beside some other wires and in through the large round grommet in the firewall. It poked though the middle where the other wires pass through.
The rocker switch has a 1/2" shaft so I popped a hole in the metal bracket that holds the hood and brake release handles. I plugged the wire from the pressure switch into the rocker and grounded the rocker using the screw for the parking brake handle. The switch is hidden from view when sitting in the driver's seat.
The tranny automatically kicks into OD close to 40 mph in my truck (3.54 gears and 265/75-16 tires) and drops out of OD at 35 mph.
Using this on a 4.10 ratio would turn on OD around 35 mph and would drop out of OD around 30 mph.
The pressure switch is nice because the turn-on pressure is higher than the turn-off pressure. That way it won't bounce on and off if you're driving close to the cycle speed.
If these shift points are too high or low for your taste, find a switch that activates at different pressures. Your local parts house should let you dig through the catalogs without any complaints. This one turns on at 38 psi and off at 34 psi. Higher pressure means higher shift points.
The toggle switch is optional and will disable the OD when thrown.
If you use one of the cheapie 3 pole lighted switches like the one shown above, you can't use the light. The switch connects the positive terminal to the load terminal. You've got to use that terminal to control the ground on the solenoid. You won't use the ground terminal on the switch. It remains unconnected.
Putting power to the switch is now a bad thing.
In all, it took me about 20 minutes to slide under the truck and put everything together. Unless you're large or the truck is low, you won't even need to jack it up.
I used an $8 A/C low pressure switch for old Chrysler K-cars, 1/8 NPT extension, cheapie rocker switch, 18 gauge wire, and some spade connectors.
Here's the pressure switch:
Napa #207616 or ACDELCO Part #1550078
Here's the rocker switch:
Here's the 1/8 National Pipe Thread extension:
Here's the 3rd gear pressure test port on the passenger side of the tranny. It's number 4 (highest plug marked) :
I removed the 3rd gear presure test port plug on the tranny and screwed in the 1/8 NPT extension. Be sure to use thread tape or other form of thread sealer so it does not leak. Then, I screwed the switch into the extension. Without the extension, the pressure switch hit the side of the tranny and would not screw in all the way.
I tapped into the ground wire for the OD solenoid and connected it to the pressure switch. I then hit the other side of the switch and ran it up beside some other wires and in through the large round grommet in the firewall. It poked though the middle where the other wires pass through.
The rocker switch has a 1/2" shaft so I popped a hole in the metal bracket that holds the hood and brake release handles. I plugged the wire from the pressure switch into the rocker and grounded the rocker using the screw for the parking brake handle. The switch is hidden from view when sitting in the driver's seat.
The tranny automatically kicks into OD close to 40 mph in my truck (3.54 gears and 265/75-16 tires) and drops out of OD at 35 mph.
Using this on a 4.10 ratio would turn on OD around 35 mph and would drop out of OD around 30 mph.
The pressure switch is nice because the turn-on pressure is higher than the turn-off pressure. That way it won't bounce on and off if you're driving close to the cycle speed.
If these shift points are too high or low for your taste, find a switch that activates at different pressures. Your local parts house should let you dig through the catalogs without any complaints. This one turns on at 38 psi and off at 34 psi. Higher pressure means higher shift points.
The toggle switch is optional and will disable the OD when thrown.
If you use one of the cheapie 3 pole lighted switches like the one shown above, you can't use the light. The switch connects the positive terminal to the load terminal. You've got to use that terminal to control the ground on the solenoid. You won't use the ground terminal on the switch. It remains unconnected.
Putting power to the switch is now a bad thing.
In all, it took me about 20 minutes to slide under the truck and put everything together. Unless you're large or the truck is low, you won't even need to jack it up.
Registered User
Joined: Dec 2007
Posts: 939
Likes: 264
From: Looneyville, West Virginia
I would suggest using Hobbs switches. You need to check the pressures your transmission has at the governor port at various speeds. Mine has a lot more (it's modified) than 1 PSI per MPH. Also that A/C pressure switch doesn't have a NPT thread, it's a straight thread that seals with an o ring.
I thought I posted on here how I controlled the lock up on my 92. I'll see if I can find the schematic on my home computer.
It uses two Hobbs switches, one low PSI and one high PSI with a relay. The two differing pressures on the switches keep it from "hunting" or chattering at the set pressure. But you need to know what your pressure readings are before you order the switches. They are adjustable but only so much.
I thought I posted on here how I controlled the lock up on my 92. I'll see if I can find the schematic on my home computer.
It uses two Hobbs switches, one low PSI and one high PSI with a relay. The two differing pressures on the switches keep it from "hunting" or chattering at the set pressure. But you need to know what your pressure readings are before you order the switches. They are adjustable but only so much.
Registered User
Joined: Dec 2007
Posts: 939
Likes: 264
From: Looneyville, West Virginia
Registered User
Joined: Feb 2017
Posts: 43
Likes: 0
From: MexMo
Registered User
Joined: Nov 2005
Posts: 1,391
Likes: 509
From: BFE, Pennsyltucky
I agree, I was going to do this mod on my RamCharger. I put a gauge in the test port and its way over 1 psi per mph, I think I had about 75 psi @ 50mph. I couldn't find Hobbs that would work, even tried the adjustable ones and no luck, that is why there is a dimmer switch on the floor for OD.
Last edited by BHD; Apr 13, 2017 at 06:23 AM. Reason: typo
Registered User
Joined: Dec 2007
Posts: 939
Likes: 264
From: Looneyville, West Virginia
Hey BHD, I had a hard time finding switches as well. There is a page on the Honeywell site that gives you part numbers and specs for switches. I took those numbers and google searched them to find a place to buy them online. Still it wasn't easy and I had to call Honeywell tech support to find out how the part numbers worked because the part numbers on the spec page are just basic numbers. You still need to add the rest of the numbers for the initial pressure setting and such. So it can be done. I didn't save the sites though so I would have to search for them again.
Registered User
Joined: Apr 2009
Posts: 182
Likes: 28
From: Banning, ca same house 73yrs
I agree, I was going to do this mod on my RamCharger. I put a gauge in the test port and its way over 1 psi per mph, I think I had about 75 psi @ 50mph. I couldn't find Hobbs that would work, even tried the adjustable ones and no luck, that is why there is a dimmer switch on the floor for OD.
Registered User
Joined: Jan 2005
Posts: 75
Likes: 4
From: Rockwell NC
Help please... my overdrive recently went south. I have a lighted switch, but no overdrive. CPS is OK. TPS is OK. Pins 10, 37 & 55 from PCM all show continuity. Following factory service manual, all other connections ring out OK. I considered hot wiring (direct) to the OD solenoid to see if I could hear a click or some indication that it may be working, but unsure whether or not that is a good idea. I would prefer to put an ohm meter on it but can't find any reference values. At this point I don't know what to do next. I am considering the modification described in this thread. I see the last post in this thread is over 6 years old. Has anyone come to a conclusion as to a best pressure switch? Is this still a good option? Is there something better? If I do it I would like to put a 60s-70s floor mounted dimmer switch on it. Any feedback will be greatly appreciated.
Registered User
Joined: Dec 2007
Posts: 939
Likes: 264
From: Looneyville, West Virginia
Help please... my overdrive recently went south. I have a lighted switch, but no overdrive. CPS is OK. TPS is OK. Pins 10, 37 & 55 from PCM all show continuity. Following factory service manual, all other connections ring out OK. I considered hot wiring (direct) to the OD solenoid to see if I could hear a click or some indication that it may be working, but unsure whether or not that is a good idea. I would prefer to put an ohm meter on it but can't find any reference values. At this point I don't know what to do next. I am considering the modification described in this thread. I see the last post in this thread is over 6 years old. Has anyone come to a conclusion as to a best pressure switch? Is this still a good option? Is there something better? If I do it I would like to put a 60s-70s floor mounted dimmer switch on it. Any feedback will be greatly appreciated.
Registered User
Joined: Apr 2009
Posts: 3,317
Likes: 485
From: alaska
The TPS is the most common failure point besides the wiring. "Dead spots" in the TPS makes it useless and is very hard to detect with an ohm meter and is the main control input for OD control. The CPS controls other systems such as charging and air conditioning as well in an ON/OFF fashion. So, if those other systems aren't working, then it is the CPS. I finally solved my OD problem by doing the 47RH conversion and a standalone controller. Smartest thing I ever did to that truck.
Registered User
Joined: Dec 2007
Posts: 939
Likes: 264
From: Looneyville, West Virginia
The TPS is the most common failure point besides the wiring. "Dead spots" in the TPS makes it useless and is very hard to detect with an ohm meter and is the main control input for OD control. The CPS controls other systems such as charging and air conditioning as well in an ON/OFF fashion. So, if those other systems aren't working, then it is the CPS. I finally solved my OD problem by doing the 47RH conversion and a standalone controller. Smartest thing I ever did to that truck.
Registered User
Joined: Dec 2004
Posts: 4,312
Likes: 1,063
From: Commerce, OK
From what I understand the TPS is a potentiometer meaning it is a resistor with a wiper that gives a varying voltage depending on the throttle position. You would need to put the ohmmeter on one end of the pot and the wiper and run it through its range to find the dead spot. If these things are not well sealed then dirt can coat the resistor and prevent the wiper from making good contact. We used to have a cleaner spray to use on "noisy" pots in the old radios back in the day. Don't use WD-40 or the like since that has a lubricant which will just attract more dirt. Use alcohol or carbon-tet.
Edwin
Edwin
Registered User
Joined: Nov 2020
Posts: 669
Likes: 128
From: Pertnear Nashville, TN
From what I understand the TPS is a potentiometer meaning it is a resistor with a wiper that gives a varying voltage depending on the throttle position. You would need to put the ohmmeter on one end of the pot and the wiper and run it through its range to find the dead spot. If these things are not well sealed then dirt can coat the resistor and prevent the wiper from making good contact. We used to have a cleaner spray to use on "noisy" pots in the old radios back in the day. Don't use WD-40 or the like since that has a lubricant which will just attract more dirt. Use alcohol or carbon-tet.
Edwin
Edwin