When i bought the truck, the OD worked great... Few months later when i would be on the highway i noticed it would only work 3/4 the time and when it did work i noticed that the RPM's would rise above 2500 for a second then drop again below 2000. My guess now was it was working, then didn't, then did again..

Now i can't get it to work ever! My first thought was it needed a service so, this past weekend i drained, adjusted bands (even thou it shifted fine in all other gears, and refilled with Vavoline Full Synthetic ATF+4. and still nada...

So my question is where should i start in the process of elimination?

i read online that a bad TPS can cause it.. mine was replaced last june with one from Autozone... i also read that a bad brake light switch can do it too. any truth to this?

 

so by following this formula i found this....

with 65 MPH, multiply by 3.92 and then again with 336, dividing all by 31 gives you the before RPM of 2761



Does that seem right?? seems a bit high to me??

 

somethings not right with that formula. At 65mph I'm right at 2000rpm with 3.55 gears and 235 (29.5") tires and according to that formula I'm at 2862rpm which isn't right.

 

you right, the 336 should be 235 and that puts me at 1931 rpm's with 3.92's

 

thats still not right tho your arent taking the transmission gear ratio into account

maybe instead of using the 3.92 or 3.55 if you used the overall drive ratio it would work.

 

Just above the rear cooling line you will find a 1/8 npt fitting...This is the OD clutch pressure test port......If you attach a pressure gauge and find pressure at the time trans should be in 4th, then the problem is mechanical....if no pressure, then there is not a command to shift or there is an massive hydraulic leak, but that will generally show as low pressure..

Goodluck
Brian

 

Here's a thread that hydra made will all kinds of transmission troubleshooting steps, maybe it'll help.

https://dodgeforum.com/forum/1st-gen...agnostics.html

 

HYDRAULIC PRESSURE TEST
Hydraulic test pressures range from a low of one psi (6.895 kPa) governor pressure, to 300 psi (2068 kPa) at the rear servo pressure port in reverse.

An accurate tachometer and pressure test gauges are required. Test Gauge C-3292 has a 100 psi range and is used at the accumulator, governor, and front servo ports. Test Gauge C-3293-SP has a 300 psi range and is used at the rear servo and overdrive ports where pressures exceed 100 psi.

Pressure Test Port Locations
Test ports are located at both sides of the transmission case

Line pressure is checked at the accumulator port on the right side of the case. The front servo pressure port is at the right side of the case just behind the filler tube opening.

The rear servo and governor pressure ports are at the right rear of the transmission case. The overdrive clutch pressure port is at the left rear of the case
Pressure Test Port Locations

Test One - Transmission In Manual Low
NOTE: This test checks pump output, pressure regulation, and condition of the rear clutch and servo circuit. Both test gauges are required for this test.

Connect tachometer to engine. Position tachometer so it can be observed from driver seat if helper will be operating engine. Raise vehicle on hoist that will allow rear wheels to rotate freely.
Connect 100 psi Gauge C-3292 to accumulator port. Then connect 300 psi Gauge C-3293-SP to rear servo port.
Disconnect throttle and gearshift cables from levers on transmission valve body manual shaft.
Have helper start and run engine at 1000 rpm.
Move transmission shift lever fully forward into 1 range.
Gradually move transmission throttle lever from full forward to full rearward position and note pressures on both gauges:
Line pressure at accumulator port should be 54-60 psi (372-414 kPa) with throttle lever forward and gradually increase to 90-96 psi (621-662 kPa) as throttle lever is moved rearward.
Rear servo pressure should be same as line pressure within 3 psi (20.68 kPa)
Test Two - Transmission In 2 Range
NOTE: This test checks pump output, line pressure and pressure regulation. Use 100 psi Test Gauge C-3292 for this test.

Leave vehicle in place on hoist and leave Test Gauge C-3292 connected to accumulator port.
Have helper start and run engine at 1000 rpm.
Move transmission shift lever one detent rearward from full forward position. This is 2 range.
Move transmission throttle lever from full forward to full rearward position and read pressure on gauge.
Line pressure should be 54-60 psi (372-414 kPa) with throttle lever forward and gradually increase to 90-96 psi (621-662 kPa) as lever is moved rearward.
Test Three - Transmission In D Range Third Gear
NOTE: This test checks pressure regulation and condition of the clutch circuits. Both test gauges are required for this test.

Turn OD switch off.
Leave vehicle on hoist and leave Gauge C-3292 in place at accumulator port.
Move Gauge C-3293-SP over to front servo port for this test.
Have helper start and run engine at 1600 rpm for this test.
Move transmission shift lever two detents rearward from full forward position. This is D range.
Read pressures on both gauges as transmission throttle lever is gradually moved from full forward to full rearward position:
Line pressure at accumulator in D range third gear, should be 54-60 psi (372-414 kPa) with throttle lever forward and increase as lever is moved rearward.
Front servo pressure in D range third gear, should be within 3 psi (21 kPa) of line pressure up to kickdown point.
Test Four - Transmission In Reverse
NOTE: This test checks pump output, pressure regulation and the front clutch and rear servo circuits. Use 300 psi Test Gauge C-3293-SP for this test.

Leave vehicle on hoist and leave gauge C3292 in place at accumulator port.
Move 300 psi Gauge C-3293-SP back to rear servo port.
Have helper start and run engine at 1600 rpm for test.
Move transmission shift lever four detents rearward from full forward position. This is Reverse range.
Move transmission throttle lever fully forward then fully rearward and note reading at Gauge C-3293-SP.
Pressure should be 145 - 175 psi (1000-1207 kPa) with throttle lever forward and increase to 230 - 280 psi (1586-1931 kPa) as lever is gradually moved rearward.
Test Five - Governor Pressure
NOTE: This test checks governor operation by measuring governor pressure response to changes in vehicle speed. It is usually not necessary to check governor operation unless shift speeds are incorrect or if the transmission will not downshift. The test should be performed on the road or on a hoist that will allow the rear wheels to rotate freely.

Move 100 psi Test Gauge C-3292 to governor pressure port.
Move transmission shift lever two detents rearward from full forward position. This is D range.
Have helper start and run engine at curb idle speed. Then firmly apply service brakes so wheels will not rotate.
Note governor pressure:
Governor pressure should be no more than 20.6 kPa (3 psi) at curb idle speed and wheels not rotating.
If pressure exceeds 20.6 kPa (3 psi), a fault exists in governor pressure control system.
Release brakes, slowly increase engine speed, and observe speedometer and pressure test gauge (do not exceed 30 mph on speedometer) Governor pressure should increase in proportion to vehicle speed. Or approximately 6.89 kPa (1 psi) for every 1 mph.
Governor pressure rise should be smooth and drop back to no more than 20.6 kPa (3 psi), after engine returns to curb idle and brakes are applied to prevent wheels from rotating.
Compare results of pressure test with analysis chart.
Test Six - Transmission In Overdrive Fourth Gear
NOTE: This test checks line pressure at the overdrive clutch in fourth gear range. Use 300 psi Test Gauge C-3292 for this test. The test should be performed on the road or on a chassis dyno.

Remove tachometer; it is not needed for this test.
Move 300 psi Gauge to overdrive clutch pressure test port. Then remove other gauge and reinstall test port plug.
Lower vehicle.
Turn OD switch on.
Secure test gauge so it can be viewed from drivers seat.
Start engine and shift into D range.
Increase vehicle speed gradually until 3-4 shift occurs and note gauge pressure.
Pressure should be 469-496 kPa (68-72 psi) with closed throttle and increase to 620-827 kPa (90-120 psi) at 1/2 to 3/4 throttle. Note that pressure can increase to around 896 kPa (130 psi) at full throttle.
Return to shop or move vehicle off chassis dyno

 

If the transmission slips in fourth gear but not in third gear, the overdrive clutch is slipping. By selecting another gear which does not use these clutches, the slipping unit can be determined. For example, if the transmission also slips in Reverse, the front clutch is slipping. If the transmission does not slip in Reverse, the rear clutch is slipping.

If slippage occurs during the 3-4 shift or only in fourth gear, the overdrive clutch is slipping. Similarly, if the direct clutch were to fail, the transmission would lose both reverse gear and overrun braking in 2 position (manual second gear)

If the transmission will not shift to fourth gear, the control switch, overdrive solenoid or related wiring may also be the problem cause.

This process of elimination can be used to identify a slipping unit and check operation. Proper use of the Clutch and Band Application Chart is the key.

Although road test analysis will help determine the slipping unit, the actual cause of a malfunction usually cannot be determined until hydraulic and air pressure tests are performed. Practically any condition can be caused by leaking hydraulic circuits or sticking valves.

Unless a malfunction is obvious, such as no drive in D range first gear, do not disassemble the transmission. Perform the hydraulic and air pressure tests to help determine the probable cause.

 

Seen most of these issues fixed with replacing the transmission output speed sensor, and/or TPS sensor. Here is a diagnosis that might help: http://www.dodgeforum.com/forum/1st-...-problems.html