6 Speed Auto conversion Transit Gearbox

**Rick Fischer** · 28th May 2016, 01:07 PM

Just a thought, diff ratios. Way back with the D1, tdi when LR introduced the auto they reduced the ratio in the diffs so as to use the torque, and the converter, gave a good cruise. Deffie diffs are for manual box. Don't know how the auto vs manual box ratios would line up with rev and torque band?????

One needs to remember that diesels even with computer injection are RPM limited by Cetane number. See https://en.wikipedia.org/wiki/Cetane_number

Cetane number similar for this purpose to Octane in petrol but is much lower "octane" = 15-25RON. Hence the amount of advance available at higher revs limits to around 4500, computer injection and timing will give a bit more.

It was lead, and now other additives in petrol that slow the "flame rate" and allow the ign point to be advanced to compensate for increasing revs. No such stuff for diesel fuel.

Hence with say 4500 upper rev limit, gearing using a stock auto with 1:1 out, or over driven a bit, will probably need lower ratio diff to be tractable.

Cheers

RF

**pando** · 28th May 2016, 01:31 PM

Hi,

Is the gearbox the ford 6R80?

1st and 6th both taller than MT82 and is a double overdrive as opposed to granny 1st and single OD of the MT82.

What transfer case you going to run?

Tombie · 28th May 2016, 01:47 PM

Rick, all diff ratios in D1, D2, RRC, Defender are all 3.54:1. No change for Auto or Manual.

The key reason for Diesel rpm to be lower is a combination of:
- Abrupt combustion requires heavier gear
- The nature of its calorific output means torque is produced at lower revs
- Design criteria is usually torque, and long stroke engines have higher reciprocating mass/inertia reducing rpm capability..

Tombie · 28th May 2016, 01:48 PM

Babs... What is your primary intent/use for this creature you're building?

**JDNSW** · 28th May 2016, 02:42 PM

Originally Posted by Tombie

Rick, all diff ratios in D1, D2, RRC, Defender are all 3.54:1. No change for Auto or Manual.
..........

What was changed was the transfer case high range ratio, which had the same effect. And in this proposed conversion, it would probably make sense to use the T/C or even just the gear set out of a Disco. Actually, I think there are quite a range of different gear sets available.

John

**Disco Muppet** · 28th May 2016, 02:45 PM

Originally Posted by JDNSW

What was changed was the transfer case high range ratio, which had the same effect. And in this proposed conversion, it would probably make sense to use the T/C or even just the gear set out of a Disco. Actually, I think there are quite a range of different gear sets available.

John

Puma Defenders already run 1.2 high range set iirc

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**MR LR** · 28th May 2016, 04:46 PM

What.

A Discovery 1 runs the same diff ratio, and low and high range ratio no matter what engine/box combination is in it.

Same can be said for the D2 range.

Same can be said for the Defender range up until the high range in the Puma changed.

We have an auto 2.2 ranger at work. It is not up to the task of pushing a Defender, I'd rather a Td5.

**PAT303** · 28th May 2016, 05:58 PM

How are you going to get a Transit auto to work,they don't run a transfer?.You need to do your homework,BT50/Ranger etc don't run English/German Getrags and ZF's,they run the cheaper made Chinese units,the same as Mustangs that need a rebuild after every tank of fuel. Pat

**PAT303** · 28th May 2016, 06:01 PM

Originally Posted by justinc

My honest opinion is that picking the right transmission and setting up the controller / shift mapping is king. Pay the $ to get it done right. If it can end up like the trans/engine relationship found in the 2012 on dmax you will be very happy. I'm still yet to find better, they equal the sdv6 3.0l disco4 for driveability ( not torque output obviously&#128558

Jc

Yet Toyota and Mitsubishi who have been around for longer still mange to get it so wrong.The D4D hilux and current Triton are simply awful. Pat

**pop058** · 28th May 2016, 06:14 PM

Originally Posted by JDNSW

What was changed was the transfer case high range ratio, which had the same effect. And in this proposed conversion, it would probably make sense to use the T/C or even just the gear set out of a Disco. Actually, I think there are quite a range of different gear sets available.

John

I used a spare transfer case out of a 3.9V8/R380 combo in my TDi300/auto and have not noticed any difference.

Originally Posted by PAT303

Yet Toyota and Mitsubishi who have been around for longer still mange to get it so wrong.The D4D hilux and current Triton are simply awful. Pat

Happy 44th Pat

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