Good news, that Phil is a top bloke....  Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Well chaps my gearbox repair from a good few months back has unfortunately hit a hurdle and floundered. As in a similar thread to this I put up some pics to show how I removed and stripped the front of the box down, to find I had the 'O ring of doom' failure. (The common cause of this transmission failure) Meaning I had 1st ok, but changing from 1st to 2nd meant there was now no hydraulic pressure, and box over-revved, and a sensor throws its toys out, and thumps the box into 4th and bongs etc.
By changing the o ring, and filter and sump gasket, and refilling, I was back on the road. (Note no debris entered box, I had whole o ring to remove etc)
Last week I was cruising along, all warmed up and ok, -pulled away from lights and 1-2 tried to change, over revved, and thumped again! Bongs, and I'm in 4th. I drove very slowly home, and parked it up.
Day off today to sort it out. However, started it up, and reversed off drive ok, changed to 1st and had over-revv again and straight into 4th. (Note, car is cold engine on less than a minute.) Not the typical o ring symptom of 1st to 2nd over Rev. Got it back on drive, and decided to check fluid level.
With it warming up, on tick over, I undid the plug, and It did gush out a handful before I quickly refitted it. So it's quite full up. However at that point I burnt my wrist a bit on exhaust, so I'm having a cup of tea, to wonder how to attack this symptom.
Here's hoping Obi-Wan (RRphil) will kindly come to advise me, along with yourselves.
I actually have a spare gearbox from a FFRR on hand, but wondering if I should switch the valve bodies round before I do anything too surgical. I also have a new filter and gasket to hand too.
Just to recap, box over revving from start, fluid appears full, will fully warm up and recheck later, car was driving perfect no snatching gurgling or silliness before incident. The history is, it's a fully recon box, with new mini rad and pipes, that went out of garuantee 2years ago, (20k)previous owner had this work done....(£2250 receipts) company can't do anything unless it's booked in. -(so forget that idea)
My burnt wrist is on ice, and the tools are ready...
Thanks in advance.

Trans level check should be done around 30c fluid temp??

To update this issue.. (5hp24 2002 4.4)
I did some fluid chicks all seemingly ok, so decided to drop the gearbox out, assuming the a-b clutch pack o ring seal had failed. Got it down...Got it apart and it's ok, no failure, not even hardened or nicked. So I'm left wondering where to look next.
Maybe I should have just changed the fluid and filter first. I have these to hand. -but these were new only 2000miles ago.(see above post)
The only issue I have noticed on removal, is that the top breather pipe rubber boot, had become twisted. Perhaps from previous reassembly, and had then split, and some fluid was present on the side of gearbox. If a significant amount had gushed out, I would be looking at a drenched underbody, which I don't have. (Its position is at top of bell housing to gearbox join, and vent appears around the rear heater hoses.)
To recap, I had no 1-2 gear change, from a traffic light start. And when tried from cold next day, no 1st, and bongs and straight to 4th. Drove it back onto drive.
I will possibly remove sump when it stops raining, and check filter is not blocked. Also maybe measure the resistance of solenoids , in case I have a failed one.
Possibly I have a failed solenoid or valve sticking.
I have all day watching it raining, to decide wether to replace box or further inspect.

Could be the valve block, RRPhil has the ability to test them...

Did you get my text on Thursday?? Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

I did, I should have asked who it was... I may give you a reply in a while...
P.s. Thanks.
Still scratching my head!