Has anyone had this issue? When driving I occasionally have a situation when the transmission finds a false neutral when at speed in drive ( street speeds of about 40 to 45 mph suddenly little or no engagement). If I coast down then shift into 3rd manually it seems to be engaged. Transmission was recently rebuild, but I now have little confidence in the shop. I will bring it back in, but want to know if there is any history out there as to whether this might be a mechanical or electrical issue. New neutral safety switch that has been working fine. Could this be a connector issue? This whole transmission is a transplant, so I don’t have a history with it.
Thanks!

 

Probably not a solenoid issue since both shift solenoids are off in 4th gear or NSS. Fluid level good? Throttle-body to trans cable adjusted properly? Wiring-wire, damage to the wire for the rear output speed sensor might cause it to downshift into 1st if it thinks you're not moving, but you'd likely have symptoms at all speeds and not upshifting out of 1st when you takeoff. Possibly, the shifter cable just needs adjusted since you said shifting into (3) helps.

 

Thanks for the quick reply. I’ll see if I can make it happen by how I position the shifter cable. I would think the detents in the transmission guide it into position in drive?
I pulled over and hooked up the renix reader, but then it was back to normal. The only thing changed in that process was the shifter cable. Is it actually adjustable? Mine is a column shift now and there’s no detents at the shift lever itself. Maybe due to the routing it’s not always solidly in drive.
thanks for the tips. I’ll let you know what I find out.

 

I did some more thinking on this - from about midnight until 3AM!! :-). There is a thread on another site where a lady is having a very similar issue with a grand Cherokee. Jumps into neutral then when she pulls over and starts out again it seems fine for another couple hundred miles. No real answer on what her result was. However, this is what happens with mine. When it happened the other day I pulled over to connect the reader and of course it back to normal. Today it seemed fine too - though on the reader I never seem to see the TC lock up either - what speed should that happen? My brake switch to power that circuit is working fine according to the reader. Could they be related? Not sure why they would.
Anyhow, the shift cable seems to be well engaged in the drive detent too. Looks like it is back to the shop and the supposed professional - I wish I could make it happen consistently though. Thanks again!

 

Hi all - its been a while since I last updated this thread and mostly because I have not determined the exact cause of my issue. However, I may have another thing going on and I am hoping Mr. Lawson or someone can shed some light on it. While trying to diagnose what is happening with the neutral thing, I noticed that my TCU is not sending a TC Lockup signal. Here is what I know of my brake/torque converter lockup system and I am thinking I have an improper switch at the pedal.

Switch is positioned correctly and works when the pedal is pushed - but maybe not as it should. When the pedal is in the rest position, brakes off, the switch reads open and when the pedal is pushed, the switch makes contact. This falls in line with what Cruiser 54 posted somewhere else on another thread.

From REM reader, When pedal is in rest position 'Brake" reading is "on", then goes to "off" when the pedal is pressed.

Also from REM: While driving in fourth gear Solenoid 3 reads "off" at all times until I press the brake pedal just a little bit and then it reads "on" and I see the RPM drop.

So, I'm thinking that the switch I have needs to be a normally open switch so that when the pedal is at rest its actually making contact and not the other way round??

Can anyone verify this and maybe provide a specific part number for that switch? I thought I had purchased the correct one, but who really knows at this point!!

Just for kickers, what I am thinking might be happening with the false neutral is solenoid wiring related and I am going to build a cable and LED box that tells me when voltage is being applied to the solenoid wires as close to the location the cable enters the transmission as possible. Will add a switch to remove the fuse connection too so I can see if by reverting to a manual mode it mechanically goes into fourth gear. I am wondering if the "False Neutral" I am feeling is actually the trans going back into first gear... more on that later.

Thanks everyone for your attention to these wonderfully frustrating at times vehicles!!

Mark

 

That's backwards. The white tcu/cruise switch closes when the plunger is pressed in, and grounds the wire from the TCU. The black wire is ground, light-blue/yellow is from the TCU. There is a resistor wrapped up in the wiring harness about a foot or so from the TCU, that "pulls" pin C10 to +12-volts when the pedal is down and the switch is not grounding the wire. Later years just wired directly to the brake lights, and skipped the extra switch and pull-up resistor nonsense (which in hindsight, I could have done too when I did my manual->auto swap).

It's been a while since I touched that on my 89, and just walked outside with a meter to check my memory. I don't actually have the white switch, but rather a relay wired off the brake switch that opens when the brake is pressed.

Also confirming my memory: https://atsgmembers.com/memarea/bull...s/98/98-03.pdf
"Terminal C10 should have battery voltage only when the brake is depressed. When the brake is released C10 should drop to 0 volt"

 

Ah, Thanks so much for the quick reply and confirmation. What an incredibly convoluted way of applying battery voltage to a pin! I'll look to see if I have the brake light switch that has two sets of contacts. Otherwise I'll find a way to supply voltage to pin C10. This pdf is very useful too for diagnosing other issues. I'll need to save it for certain.

Cheers!
Mark

 

Today I cut some wires and spliced in a feed from the regular brake light. I removed the resistor completely and tied into the splice that directly feeds C10 and what do you know - it works like it should!! Although it does seem to lock up the tc almost simultaneous with shifting into fourth when I am moving right along. If I am driving a reasonable rate and it happens to hit fourth gear it does not lock. I'll do some testing to see at what speed this occurs. I do know that the REM speed readout thinks I am going much faster than I really am - likely due to gearing and tires - (I'm only running 3.54s and 30 inch tires). I can only hope that this is also somehow connected to my false neutral issue - maybe with things trying to work backwards before things may have become confused.. Only time will tell - until then I can hope. Thank you very much for the links and info on the brake light/switch feed. I looked everywhere and could not find the proper TCC switch - beside, this is so much more simple! If the TCC stops working properly, I'll check the brake lights first...

Thanks again!
More to come when/if the other issue continues.

Mark

 

The TCU doesn't know how fast you're going. It's just reading the output speed of the trans. Is the REM showing reasonable numbers for throttle position? Mine locks up the t/c pretty quick when I hit 4th with light throttle, takes a little longer if the switch is set for power versus comfort or I'm on the gas.

 

I have not looked at what the throttle position is when it locks. I did notice this morning it shifts into fourth at about 40 mph if I am not hard on the gas. Then the TC locks at about 45. It unlocks if I take my foot off the gas pedal - is that normal? Seems like it should be, but I have not had a ton of experience with it working "properly" now. I have mine permanently set to power mode - the switch did not come with the wiring harness I bought, and I figured I would pretty much always have it in power mode anyhow.