V8 auto behind TD5 will it need a tune??

**Tins** · 19th December 2022, 07:54 AM

Originally Posted by Reddirt204

Haha yep, all thanks to a "HD" front drive shaft who's cardan joint seemed like it was taking grease but was actually just spitting it out the side, nice blue heat marks in the joint where it seized up. Once I get everything sorted I'll post a photo of the damage

Cheers

Redd

Ah, the dreaded double cardan failure. Did you get any warnings or did it just let go?

**shack** · 19th December 2022, 08:14 AM

Originally Posted by loanrangie

Yes TCU is in the ECU ie not on the valve body like later ZF boxes, stall speed will only affect take off so I assume the tune slows the upshift to cope with that.

The TCU is under the left hand front seat, it handles all shift points and lockup points etc... It uses some data from the ECU, which is next to the battery, to help it decide what gear to be in and whether to lock the converter.

Not much can be done with the TCU to help remediate the lower stall speed of the V8 converter on pull away.

The ECU however can be tuned for higher output which WILL help pull away with the V8 converter.

The only issue with the V8 converter on a stock TD5 is Probably the lag on pull away.

There are some terminology problems with the abbreviations used above... Depending on where you are from!

TCU always means transmission control unit.

ECU can mean engine control unit or electronic control unit.

So sometimes you will see written: "engine ECU" or "ECU" for the engine controller.

And: "Transmission ECU" or "TCU" for the transmission controller".

Confusing Hey!!

There are a few other confusements as well, but I haven't got time to list them at the moment.

Cheers
James

**Tins** · 19th December 2022, 09:33 AM

Originally Posted by shack

The TCU is under the left hand front seat,

Remarkably clever engineering from LR. It's just a pity they couldn't get the planned drain hole underneath it past the bean counters.

Originally Posted by shack

There are a few other confusements as well, but I haven't got time to list them at the moment.

Variations by continent, and some lapses in language translation, can be a source of merriment... when you're not trying to fix the thing.

**Reddirt204** · 19th December 2022, 06:07 PM

Originally Posted by Tins

Ah, the dreaded double cardan failure. Did you get any warnings or did it just let go?

I had been driving to and from Perth (3.5 hours each way) each week for work (4/3 FIFO roster) for about 4 months and no issues. My young bloke needed the Disco again (it was his car) he was driving from Safety Bay into the CBD each day for work, he rang me saying there was a bad vibration (this was Sunday) we walked through a few things (handbrake shoes etc) I told him I'd be up on the Thursday to check it out. Tuesday arvo I get a call, he's broken down on the freeway

So a little notice but not a lot, the shaft didn't let go (still in one piece but only just) but did smash into the side of the trans snapping the extension housing off and cracking the output shaft.

Climbing under the car and being able to see the insides of the trans was a pretty good indication that there wouldn't be much forward motion in the near future

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