Engine/Transmission (1994 - 1998) Strange transmission behaviour

[Crowhurst]

I'd appreciate some advice on some transmission behaviour I don't understand. My 47RE transmission is standard, but I have fitted a BD exhaust brake, auto-loc and torque-loc. I am towing a 6500 pound travel trailer at 60 mph on a level section of interstate highway. O. D is locked out, so I am in 3rd gear at about 2400 rpm, with the TC locked. I pull out to overtake a vehicle, and apply wide open throttle. The noise of the transmission suddenly increases, as if the transmission has kicked down to second gear. I assume this is impossible at this speed. I check the rev counter, and the revs have hardly increased, although from the noise, it would seem the revs have increased a lot. The speed stays the same. I have installed an LED in the lock-up signal line to the torque converter clutch. This LED is flashing on and off several times a second. I back off the throttle, and the situation resolves. I suspected that the TC lock-up clutch was slipping, but if this was so, would I not see the revs climbing much higher, and would the LED not just stay illuminated? I do not understand this behaviour, which has occurred several times. Can anyone assist, please? Is there a mechanical or electrical problem, or is it a driving method issue? Thanks.

Nick.

 

[DHawk]

Normal Software For The 47re Is 3rd Tcc Engagement Is Modulated Which

Means The Converter Is Being Locked And Unlocked So It Is Not Completely Locked Down. You Did Not Say Whether Your Torque Locker Was On Or Off At This Point. 4th Gear Is Fully Locked But Third Is A Partial Lock Or Modulated. 3rd Meaning O/d Locked Out.

Dhawk

 

[jtwcummins]

The converter unlocks at WOT. Causes engine rpm to increase and if you have a transmission temp gauge the fluid temp starts up.

 

[Joe G.]

If the LED is flashing then you may have a TPS problem. The wire to lock up the TCC is grounded to cause that lock. It is ungrounded to unlock. If the LED is wired so that one side has 12 volts all the time so that it lights when the TCC lockup wire is grounded then the ground is making and breaking. The PCM will do this if the TPS is dirty or otherwise making a poor connection. I don't know if the auto-loc and torque-loc get involved with this condition or not.

 

[Crowhurst]

I do appreciate the points so far raised. The BD Auto-loc is hard wired "always on" when the exhaust brake is switched on, which it was. On installation of the Auto-loc, I opted for "over-drive off" on start-up, rather than the normal "overdrive enabled" option. The TC was locked before I applied WOT, and I was in 3rd gear, the highest gear enabled at that time, as I had not manually opted for overdrive to be enabled.

I clean the TPS with spray contact cleaner every oil change, but I will check out the grounds with my resistance meter. I wired the LED as Joe described. Thanks again.

Nick.

 

[Crowhurst]

I've been able to produce this fault without towing a load. To reproduce it, I need to be in 3rd gear at about 60 mph, and then floor the accellerator rapidly. The fault will then occur. If the throttle is applied more gradually, the vehicle will accellerate smoothly. The fault occurs with either the exhaust brake enabled or disabled. I cannot reproduce it in 4th gear (o/d). I'll now get back to those grounds. Nick.

 

[tp0d]

Sounds like you just need a method to keep the trans locked manually.



I added a mystery switch on a 30" lead with a momentary pushbutton on the end. I`ll see if i can get a pic up of it. I push the momentary and it activates a relay next to the pcm and grounds the output to the trans lockup (black/orange, I forget which connector) Then I have a disable switch up next to od lockout.



Anyways, it works real nice when you know you`ll need to keep it locked. I`ve gotten pretty used to it.



-j

 

[EBansberg]

Mine does the same thing. 3rd gear locked up, punch it, TC unlocks. 4th locked up, punch it, 35+ lbs of boost and locked up still with no slipping. It annoys me that it unlocks. Are you guys saying you can override this function? I'm assuming this is what's happening with yours too Crowhurst.

 

[Crowhurst]

Mine does the same thing. 3rd gear locked up, punch it, TC unlocks. 4th locked up, punch it, 35+ lbs of boost and locked up still with no slipping. It annoys me that it unlocks. I'm assuming this is what's happening with yours too Crowhurst.

I wouldn't be concerned if the TC simply unlocked. It is the rapid cycling on and off and the lack of any accelleration (just when it is needed) that concerns me. I have cleaned the TPS again, and I'm currently studying the shop manual to establish the location of the relevant grounds.

Nick.

 

[Joe G.]

You may have to take the TPS apart to clean it. Others have had to do that.

 

[Howard Durand]

If you want to test the TPS, connect a sensitive voltmeter between the center wire and ground. Advance the throttle manually and watch the voltmeter. The voltage should increase or decrease smoothly with no blips. If it does that, it is probably OK.

It should read a minimum of 0. 8 volts at rest and increase to 3 volts or more as you advance the throttle.

 

[Crowhurst]

Joe and Howard, many thanks. I'll get the TPS out, clean it, test with my digital voltmeter, and report back.

Nick.

 

[Crowhurst]

I dismantled the TPS, cleaned it out, removed corrosion from the two small flexible contacts, and re-assembled. I checked the voltage with a digital meter by piercing wires in the loom. With closed throttle it was 1. 5v, and at WOT was 4. 0v. The range is correct, according to my shop manual, but the low voltage should be 0. 8v to 1. 2v. I couldn't follow a smooth progression with the engine off, because the throttle break-over point was so sudden. With the engine running, the voltage increase was smooth, although an analogue meter would have been better for this purpose. Although the low voltage is out of spec, I wouldn't suspect this is the cause of my issue, although that's just an ignorant guess. A year ago I asked for ideas about a strange noise from the transmission (still there now), and I wonder if there's any connection. The noise is like an arcing short from within the transmission pan, at its back end, when the ignition key is turned 2 clicks, but the engine starter is not engaged. If I remove the loom connector for the transmission solenoid assembly on the driver's side of the transmission, the noise stops. I am still hoping to trace this noise. In a couple of weeks I'll be back at my base, and, weather permitting, will pull the pan to attempt to isolate the noise, perhaps to a specific solenoid. (I suspect the TC clutch solenoid, but I have no idea what could cause this sound. ) I appreciate the help. The local 5 star Dodge dealer service manager admitted his people did not have the expertise to deal with the diagnostic issues, even if the Auto-loc was disconnected.

Nick

 

[Crowhurst]

The thread about the noise is at https://www.turbodieselregister.com/forums/showthread.php?t=115695&page=2&pp=15

Howard and Joe were extremely helpful on that issue. I did not receive a reply from the BD help desk, although I tried a couple of times.

Nick.

 

[Ridesamule]

Altough I still have a stock valve body, when my TPS went out around 40K ago I bypassed everything and placed a 1. 2K rheostat in my dash and have never missed having a TPS. I marked 1. 8 volts for normal driving and hardly ever touch it. The transmission still locks and unlocks according to the speed sensor, although a higher voltage will delay the 3-4 shift point. If I want stay unlocked I just turn up the voltage with the rheostat.

The TV cable will still force a down shift if needed. When I let off on a hill I stay locked up unless I touch the brake. As a side note I have also noticed that after light pressure on the brakes for a period of time the ECM will actually throw the converter back into lockup.

No TPS and never looking back... .

 

[Howard Durand]

Ridesamule,

With the TPS removed and using a fixed voltage, are the OD and TC shifts more predictable? Mine, when left to it's own devices, tends to shift into OD at different speeds depending on temperature and other unknown reasons.

I have a pot in the ground side of the TPS which allows manipulation of the low end voltage but the TPS still advances the volage above that setting and the shift points vary. If the shifts are more predictable with your setup, I will try it.

 

[Ridesamule]

Howard,

The shifts have been the same and very predictable since I started using this type of setup. With the miles I have on this transmission 220k+, I do not expect it to kick down and beat the other guy. I haul a steel horse trailer with living quarters in the hills a lot tho. and it is helpful to sensibly control the lockup functions from inside the cab with other than the foot. I have a lockup/unlock switch I seldom use since relocating my TPS.

 

[Howard Durand]

Ridesamule,

I am going to try your scheme. I wouldn't be surprised if some of the others on this forum try it too. I have the DTT transmission but it is still an RH so it retains some of the bad habits of the beast.

Howard