Hello all. Hope I can find someone to guide me though this problem. I have read lots of issues like this but none has given me a north.
I was driving normally, never an issue or error codes for anything. When standing at a traffic light, when came the green light pushed the accelerator normally (not hard) and heard a pop, not too loud but very noticeable and then no more drive… only reverse.

We have done many many tests and everything looks good with transmission, TCM, valve body, switch selector, solenoids, wire harness, torque converter, transfer box… but the car Wont go in drive.
We have fully rebuilt the transmission changing all clutches, seals, gaskets and performed a very detailed revision of every gear inside the transmission using magnifiers. Nothing is broken or slightly damaged than could have caused the pop. We tested the wire harness performing continuity and impedance and everything is fine… tested from TCM down to selector switch and also from TCM to solenoids and speed sensor.

Also tested all solenoids and speed sensor for ohms reading and everything fine as it should be. ( assembly of everything we followed lots of manuals available out there)
There is absolutely no error codes and the display shows the gear selected on the dash display, P, N, R, D, 3, 2 so we can assume selector switch is working as it is supposed to do, but still we tested signals coming from it and reaching the TCM inside end at the circuit board…and are all right.
Transfer box is switching 2WD to 4WD correctly… tested only in reverse as no Drive right now.
oil level is where it should be, brand new. Torque converter should be fine as we do have normal reverse. When in reverse, no noises coming from torque converter.
Tested the pump using a manometer and reads fine both on main line and torque converter port… 150 psi continuous in torque converter port no matter the gear selected.
Main line port shows 150 psi when in drive or any other forward gear and 0 for reverse, N and P
Solenoids were taken out and bench tested applying 12 vac and verifying flow direction… all MV1 MV2 and MV3 good. MV5 ( regulator) was bench tested using a PWM generator to see its movement used to regulate pressure… everything fine.
Opened TCM and tested for correct energization of valves depending on gear selected and TCM is sending the right signals to all of the valves as it should.
Speed sensor is working right, measured for continuity with an external magnet and works as it should.
I am done of ideas… even replacing the full transmission I am not sure if this will solve the problem because we are pretty sure that transmission is in great shape as every part of it has been fully chalked and all rebuild kit has been used. Solenoids ok, valve body is fine as well… cannot think on replacing the TCM as it looks to be working as it is supposed to… the last thing we would plan to do is to bench test the transmission, applying pressure to the main line and activating the solenoids to see if we have movement when in drive…of course applying movement to input transmission main shaft ( not using the torque converter) with an electric motor variable speed… but that’s lots of work.
One another reason not to change transmission: my car is in South America where I cannot find a transmission for this car or any other like BMW that uses this 4HP24… and shipping a rebuilt one from overseas costs more than the car itself.
Anyone could think just go ahead and junk the car… but I am car collector and want this car working to add it to my collection. Also Range Rover lover for years.

This forum is my last hope to see what are we missing

Thanks to any one for shooting me any idea.

It sounds like you have done everything to check it and found nothing. When you say it works in reverse does it work normally? I had a gearbox fail on me and that wouldn't work in reverse either. The only thing I can suggest is you phone Ashcroft Transmissions (https://ashcroft-transmissions.co.uk/) and speak to Dave Ashcroft, he should be able to point you in the right direction.

cant find it on their current site, but their old site had an FAQ and one of the first questions was loss of forward drive:

https://web.archive.org/web/20120411155405/http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=221

Failed A clutch, seems a common failure point.

Theres also the possibility of an inverted sprag clutch, in which case it'll pull away in "1" but not D.

will it go if you put it in gear manually , if so you have most likely inverted the sprag clutch and that's a gearbox removal job.

Gilbertd wrote:

It sounds like you have done everything to check it and found nothing. When you say it works in reverse does it work normally? I had a gearbox fail on me and that wouldn't work in reverse either. The only thing I can suggest is you phone Ashcroft Transmissions (https://ashcroft-transmissions.co.uk/) and speak to Dave Ashcroft, he should be able to point you in the right direction.

Thanks Gilbert’s. I will do so Thanks!!
Reverse is absolutely normal

Aragorn wrote:

cant find it on their current site, but their old site had an FAQ and one of the first questions was loss of forward drive:

https://web.archive.org/web/20120411155405/http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=221

Failed A clutch, seems a common failure point.

Theres also the possibility of an inverted sprag clutch, in which case it'll pull away in "1" but not D.

Thanks Aragorn. We will take the tranny down again no problem and send some pics and confirm once again for A clutch. As reverse and Drive share clutch E but reverse is OK, we will concentrate on clutch A and not in clutch E. Same with sprag K, it is shared by Drive and reverse so We will concentrate again on sprag J. Will post some pics. This will be the third time we take apart for verification

mad-as wrote:

will it go if you put it in gear manually , if so you have most likely inverted the sprag clutch and that's a gearbox removal job.

Thanks mad-as. We will do that today… take down tranny and check clutch A and sprag J again posting some pics or/and videos

UPDATE. Checked all sprags, clutch A and in general everything again and all fine.... still no reverse. So next step is test bench of transmission from torque converter to output shaft. We will adapt a variable speed electric motor to torque converter, and activate solenoids according to rpms, etc as well as acting the regulating valve for soft gear change... will post results

Thanks for keeping us updated. It sounds like a very strange one.

i do know of a person that rebuilt a transmission and used the wrong rags when cleaning and wiping everything down . the rags left lint in major parts of the transmission and it all balled up and blocked of major capillaries in the valve body and blocked up the valves so the transmission failed within hours of the rebuild. maybe this is a similar issue where something has blocked off the small capillaries in the valve body . even thou the solenoids are operating the oil flow is not flowing by the sounds of it , could be a piece of clutch plate or rubbish that is lodged in the wrong place or similar giving an open flow of the oil . something to think about .