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JohnnoK

4HP24 Gearbox Failure

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After dropping the brats at school, I stopped in front of my gate to open it, left the car idling in Neutral, and when I got in and selected Drive it made a weird "grumbling" noise and didn't go into gear.
Reverse was brief and then any selection after that was a no-go. Revving it in Drive got a short hop, enough to get it moving, and then back to nothing.
The oil level is good and the GEARBOX FAULT message comes up, but not every time I tried to work through diagnosis.

To add insult to injury, my Nanocom won't come on when plugged in. It works on my Disco, not the P38.

Any ideas, please?

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Could it be a snapped chain in the transfer box?  It'd explain the loss of drive and the noise.

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Transfer box is definitely a suspect. Also check the fuse for the OBD port for the Nanocom issue.

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Cheers for the replies, folks.

Considered opinions all seem to point to the flex plate as the likely culprit. Apparently they either break and lose drive to the TC or they warp under load and disconnect the torque converter from the lugs of the pump drive causing pressure loss.

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Very plausible.  You should be able to see it through the lower housing cover.

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Posted (edited)

If you do remove the gearbox be aware that the torque converter is only pushed onto the input shaft & will happily fall off if not locked into position by some external means. I'd suggest making a 'T' shaped piece of metal with the arms of the 'T' drilled to match up with two of the small bolts that hold the small round cover onto the bottom of the bellhousing & the shaft of the 'T' bent so it goes up inside the bellhousing & presses against the torque converter. Use a piece of 3mm plus steel as the weight of the torque converter will bend thin sheet & then it falls off. (Guess how I know - albeit a 4HP22)

When refitting, the tc MUST be on the gearbox and seated to the appropriate depth which is measured from a straightedge across the bellhousing mouth to the front of the 4 bosses on its front. If not it will fit but will break the pump & you get to take it all off again. Distances given on Ashcroft's site if you don't have the LR manual. Although the manuals show it being fitted with the box horizontal it's MUCH easier to seat if the gearbox is vertical. Once seated use your 'T' tool to keep it in place.

I also recommend making up the LR jack to gearbox mounting plate as these are big heavy unbalanced units. 

Edited by paintman

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5 hours ago, paintman said:

I also recommend making up the LR jack to gearbox mounting plate as these are big heavy unbalanced units.

Thanks for the tips regarding the tool, will definitely do that.

Can you point me at a drawing for this plate, please?

This is going to be a slow "as funds permit" job, so don't be surprised if it goes quite for a while...

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Posted (edited)

Apologies for not getting back sooner.

Mine is the RRC which has the 4HP22 & the diagram for that is in the factory workshop manual.

I've had a look & all I can find for the P38 is reference to a LR Special Tool LRT-99-007 with some pics in the online manual but no dimensional drawing. 

http://www.landroverweb.com/Pdf-files/Manuals/Workshop-Manual-P38-Range-Rover.pdf Page 651

 

Edited by paintman

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Paintman,

Thank you, sir!

The boxes are essentially the same, barring the electronic control and some internal differences, so that will serve as a starting point for a project.

Edited by JohnnoK

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Don't know if this will work for you but I've done a few bits & pieces to the internals of mine & used this UK company for the parts. They were very quick on delivery & very good on prices too. I replaced the steel sealing rings on the input shaft with the Teflon ones which would have cost a fortune from ebay (USA only) but were pennies from them.

Has very good exploded diagrams of the boxes.

https://jpat.co.uk/zf.html

https://jpat.co.uk/uploads/1/0/3/5/103549764/89__zf_1_4hp22-24.pdf

This might be of interest:

http://bmwe32.masscom.net/moswald/zf4hp22_rebuild/zf4hp22_rebuild.html

http://www.cowdery.org.uk/zf.php

Edited by paintman

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Thanks again, paintman.

Right now, it's at the saving up to do it stage, but I am bookmarking this thread to refer back to when I pull the trigger on the job.

 

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