HELP! Strange reverse problem, 5HP24

[dshealey]

I have a 5hp24 transmission, which I rebuilt about a year ago. I have a sudden loss of reverse, with no warning. Drives perfectly in forward.

I have used INPA and DIS to monitor everything, and there are no error codes in the car anywhere.

The strange thing is that the the three shift solenoid signals from the EGS controller are wrong only in reverse, solenoid 2 should be on, 1 and 3 off, but only solenoid 1 is on. I put LEDs on the three solenoid lines to be sure, and they prove that this is the case. I drove the car with the LEDs and the solenoids are switched on/off properly in all gears except reverse.

I tried a second EGS controller from the same model and year car, same results.

INPA also shows that the shift switch lines 1 through 4 are correct for all positions of the shifter, so that seems to be working perfectly.

When I select Reverse, shift switch line 1 only is on, correct, but the controller is only turning on solenoid 1, when it should be solenoid 2!

I am feeling that this is a control problem, not something in the transmission, and want to get the electrical issue resolved first before thinking something inside the transmission has failed.

I have spent many hours searching the internet, on multiple forums of cars that use this transmission, and so far seem to have the only instance of this issue ever.

Does anyone have any input as to why two different EGS controllers would have the same problem (correct shift switch inputs, incorrect solenoid outputs)?

[PsYcHe]

I'm not a G/B expert ,but these boxes tend to lose the 'F' seal if I remember rightly in the Audis, which results in a loss of reverse, but with everything still good in D. It's a recon of the box to fix it..

[upallnight]

Could it be the neutral safety switch aka the shift control switch or multi-function switch? Had the one on my Audi which is a 4HP18 go bad on me. The plastic over time had tiny cracks in it which was enough to prevent the contact from completing the circuit.

Switch looks like this

[dshealey]

Originally Posted by PsYcHe

I'm not a G/B expert ,but these boxes tend to lose the 'F' seal if I remember rightly in the Audis, which results in a loss of reverse, but with everything still good in D. It's a recon of the box to fix it..

I have the box out now, will get into it in the morning. I will pressure test the clutch'brakes first (C clutch and F brake) to see if one of them has failed.

My biggest concern is that the three solenoid charts I have been able to find (ZF,ATSG,and Range Rover) all show solenoid 2 on for reverse, but two different ones for the E38, the original and a second used one I purchased, all turn on only solenoid 1 for reverse.

Even if I find something to repair in the box, I am concerned that if I don't get the EGS controller issue sorted out it will just fail again.

I would love to find something that says on the E38 solenoid 1 is on for reverse, instead of solenoid 2.

[dshealey]

Originally Posted by upallnight

Could it be the neutral safety switch aka the shift control switch or multi-function switch? Had the one on my Audi which is a 4HP18 go bad on me. The plastic over time had tiny cracks in it which was enough to prevent the contact from completing the circuit.

Switch looks like this

INPA shows all the switch inputs as being correct, and I also checked them with a multimeter.

I have the transmission out now, will open it up in the morning. However my big concern is the solenoid actuation on two different EGS controller differs from the charts I can find. Solenoid 1 actuated in Reverse instead of solenoid 2.

[HEISING]

Have you tried to "jerry rig" #2 on, just to see if that engages reverse? May want to try that before you get to deep as #1 may be right for that tranny.

[HEISING]

Weird, dont know where my last post went?? Anyways, have you tried to "jerry rig" #2 on to see if you get reverse? I hope you have dropping resistors in line with your LED's (330 ohm in series) or you will take the drivers out of the tranny control module. "be careful"

Good Luck

[dshealey]

Originally Posted by HEISING

Weird, dont know where my last post went?? Anyways, have you tried to "jerry rig" #2 on to see if you get reverse? I hope you have dropping resistors in line with your LED's (330 ohm in series) or you will take the drivers out of the tranny control module. "be careful"

Good Luck

Yes, I did put a DPDT switch in to fool Solenoid 1 and 2, but that just put the transmission in failsafe mode. When in failsafe, reverse would drive at just above idle, but would slip if much more throttle applied. I have the transmission out now checking clutch C and brake F.

Yes I did have dropping resistors, actually 820 ohm for about 15 Ma current. I put the LEDs on the controller side of the circuit, so they are on with the solenoids off, they go off when the controller sinks the circuit to turn the solenoid on.

[HEISING]

Sounds like you are on the right track. Clutches, Band, or Valve body. The terrible three! Im not sure weather they use open collector or open source for the drivers, but you obviously have it handled. Nice to see somebody that knows to use resistors with LED's.

[dshealey]

Originally Posted by HEISING

Sounds like you are on the right track. Clutches, Band, or Valve body. The terrible three! Im not sure weather they use open collector or open source for the drivers, but you obviously have it handled. Nice to see somebody that knows to use resistors with LED's.

I am a recently retired Design Engineer, spent a few decades designing factory automation systems and machines, including control systems.

No bands in these transmissions, all disk clutches and brakes. The EGS uses open collector "sinking" for the solenoid drives.