Your transmission came off the production line at Saarbrücken on 30th November 2000 so it is fitted with the old F-brake piston design (unless, of course, your transmission has since been rebuilt and updated).

We really need the fault codes from the diagnostics test to be able to help determine if you have an electrical or electronic fault.

Temporarily removing the 16-pin connector will force the transmission into failsafe mode and the transmission will select 4th gear when you engage Drive, and Reverse should operate as normal. Because the pressure isn’t modulated in failsafe mode it will engage with a ‘clunk’. If Reverse works perfectly without the plug connected but then doesn’t work once the plug is reconnected, then my opinion would be that you have an internal clutch leak and the transmission will require a rebuild. This isn’t cheap (for example, I charge £1650 incl. VAT) so it is worth considering a replacement transmission, providing you know its history. Clearly, though, this isn’t without risk.

I assume that the transmission you’ve been offered is from a 4.4 V8 M62 E53? The reason I ask is that there are 24 variants of the 5HP24 transmission, and only one of them – the ‘029’ model – will fit your X5. Actually, I lied. The ‘034’ model from the 4.6iS would also fit in your car but it has extra clutch plates, a different torque converter, and revised hydraulics to suit the higher torque engine so it isn’t really suitable.

Out of the 335,000 5HP24s that ZF manufactured for BMW just over 85,000 of them were ‘029’ models for the 4.4 E53, so they’re fairly easy to come across (only 11,000 were ‘034’ models for the 4.6iS).

Phil