MYY Gearbox?

**Dougal** · 15th April 2013, 04:33 PM

Has anyone seriously looked at these? I can't shake this idea.

6 speed, 1st comparable to the MSA, but closer spaced in the middle and a slightly higher 6th gear. Sounds like just what the doctor ordered.

5 speed front on.

6 speed. side on.

Bellhousing bolts on from the back, should be no problem to adapt a 4BD1T bellhousing in.

I need to physically find one and measure it to confirm yes/no.

**rick130** · 15th April 2013, 05:16 PM

I wonder what needs to be hooked up for the AMT setup ?

I'm guessing it works through the engine ECU ?

**Ancient Mariner** · 15th April 2013, 05:47 PM

Dougal Just be careful if you get one of these boxes There is a recall on some

Seems a wire to the reverse switch fatigues

and de light don`t work

**C H T** · 15th April 2013, 06:01 PM

Dougal

Basically an R380 on steroids - the internal ratios 2-6 are very close to an R380 1-5. First in the MYY6- is of course lower. The MYY6S is geared slightly higher in 6ththan 5th in an R380. The MYY6P is slightly lower in 6th than an R380 in 5th.

If I could make one fit in my 4BD1T powered Defender I would.

FWIW

C H T

**Dougal** · 15th April 2013, 06:11 PM

Originally Posted by rick130

I wonder what needs to be hooked up for the AMT setup ?

I'm guessing it works through the engine ECU ?

I found a research paper on the Isuzu AMT shift schedule once. Must have been really bored that day.
AM, looks like the typical Isuzu reliability problems then. Try to keep everything else around it running.

I've been measuring up my spare LT230 and I think I can get away with up to 110mm gearbox protrusion from the centreline and that clearance isn't needed for much length either.
Bulk around the top and fitting it under a rangie centre console might be a concern. But I have a body swap planned anyway so some slightly thicker body mount rubbers could be snuck in.

**flagg** · 15th April 2013, 07:27 PM

Can they be run without AMT? I imagine the ECU connections and programming would be complicated..

**Dougal** · 15th April 2013, 07:44 PM

Originally Posted by flagg

Can they be run without AMT? I imagine the ECU connections and programming would be complicated..

Amt is an option. Most seem to be manual. The automated ones I've found pics of look like it all just unbolt.

**Bush65** · 16th April 2013, 07:16 AM

Originally Posted by Dougal

...

I've been measuring up my spare LT230 and I think I can get away with up to 110mm gearbox protrusion from the centreline and that clearance isn't needed for much length either.
...

It's possible they may be narrower than my MXA-6R, which is a good 120mm from centreline over the extension housing where 6th gear lives. I think this may be because it was based on a 5 speed MXA, with 6th added - 5th and 6th are both overdrive and so the gearwheel on the layshaft for 6th is so much larger.

In a dedicated 6 speed on the same shaft centres, or even a little larger centres, with only one overdrive ratio, they could make the gearwheels for 1st and 6th close to the same diameter and reduce the case width.

**Dougal** · 16th April 2013, 08:52 AM

I had another measure on my spare LT230. The pinch point of 110mm from the centreline extends for ~170mm from the mount flange.

My current MSA gearbox has 193mm of adapters before the LT230, meaning the back of the gearbox doesn't actually reach the pinch-point and my LT230 is in the stock mounting position.
The MYY6 pictures do show a bulge on the back corner where we don't want it. Whether it's a problem or not depends mostly on overall length of the MYY.

This is a 5 speed showing that bulge.

The 6 speed showing the same bulge but longer:

SheldonA · 16th April 2013, 09:27 AM

Originally Posted by Dougal

Has anyone seriously looked at these? I can't shake this idea.
<SNIP>

Define serious.

I've looked and measured them up in trucks. Can't remember measurements, however it appeared they would fit.

I've also looked at a 6 speed box that was behind a latest model cummins engine (can't remember which truck).

My main reason for looking at 6 speeds was for the length. Instead of having to fabricate up an extension housing to put the transfer case in the correct location, the extra length would only require a thick plate - making it simpler.

When it came to more gears, extra length in the gearbox, price and simplicity, the MSA's with the splitter on the back I thought were the best way to go.

As we speak I have a MSA-5S with the splitter on the back getting pulled out of the truck I have. The splitter is very narrow where the front output of the LT230 would end up - so no clearance issues what so ever. From driving it, the main 5 gears of this box appear to be the same as the 5G and the splitter seems to be about a ratio of 20% over drive. This gives 10 forward ratios of;

5.788
4.630
2.998
2.398
1.594
1.275
1
0.8
0.776
0.621

Obviously the splitter adds length, and a little too much pushing the transfer case back if left alone. I am looking at trimming the extension housing down of the splitter to keep it all at stock length. If not, they would still fit with the transfer case moved rearward.

Given these boxes go for not much more than a standard MSA, or the same price if your buying the whole truck for the engine as well, they bolt straight up to a 4BD1 (and are found behind the 4BD1's). 10 is better than 6 right

That's been my serious look into more gears.

My thought personally is that behind a well intercooled and turboed 4BD1, a wide spread of 5 gears is more than adequate. The bucket loads of torque compensates for any slight ratio advantage. I get over changing gears so quickly when driving my 110, 6 would make it even worse

In a N/A may be a different story and more is always better... just comes down to time and cost like everything else... I've even bee struggling to find time to do 5 speed conversions

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