4wd 4-speed upgrade to 5-speed?

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moroza
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Isuzu vehicle(s): 1984 diesel longbed 4wd P'up

4wd 4-speed upgrade to 5-speed?

Post by moroza »

Saw a few excellent posts regarding upgrading 2wd transmissions, but other than reports that no 2wd trans will bolt to a transfer case, haven't found much info on what I'd like to accomplish: upgrading my 11/83 4wd diesel longbed 4-speed to a 5-speed. My understanding is that 86-87 turbo Pups and Troopers had a 5-speed behind their C223T, but those appear to be hen's teeth (car-part.com shows one, in Alaska). I assume that with a bellhousing swap, an 88-95 2.3 4wd trans/case will bolt up, just like the 2wd, but what about at the back - will it fit the stock mounts, frame, shifter location, and driveshafts? Any other options?
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JoeIsuzu
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Re: 4wd 4-speed upgrade to 5-speed?

Post by JoeIsuzu »

The turbo isn't relevant, all '86-'87 4wd transmissions were 5-speed. That might broaden your search a bit, but it's still a rare transmission, even if you include gas models. I'm pretty certain the 4wd MSG-5 was not offered after 1987, because (if I recall correctly), all 4wd Pickups and Troopers had the 2.6L 4ZE1 engine (or a V6) from 1988 on, and they used the MUA-5 transmission.

Some 4-speed 4wd bell housings will not mate up to the newer transmissions. If the input bearing cover has only four bolts, it is not compatible. Compatible transmissions have six (?) bolts on the bearing cover (maybe more, but definitely not four). You can get a look if you have a bore scope -- through the clutch fork opening.

As for rear mount and overall length -- I don't know. Someone else will.

Output shaft and slip yokes are the same size and spline count on all 4wd transmissions.

Jack
moroza
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Re: 4wd 4-speed upgrade to 5-speed?

Post by moroza »

Ah, thanks, there are quite a bit more 86-87 2.3 gasser 4wd transmissions out there. However, the photos I'm seeing show a bellhousing integrated with the front/main transmission case. [url=https://imageappoh.car-part.com/image?seller=3033&partsourceid=3033&partGUID=3033-1-428271&vehicleGUID=3033-1-V15161&display=1986 Isuzu Truck Mini Pickup Transmission Assembly-Stock%23 25829]This, for example[/url], described as "2.3,5SPD,8-85".

EDIT: [url] is ON, BBCode is ON, the formatting looks right... why won't the link compile correctly?

I'll stick a borescope in there and see what's up with the bearing cover.
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JoeIsuzu
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Re: 4wd 4-speed upgrade to 5-speed?

Post by JoeIsuzu »

Yes, we're having an issue with URL encoding. I hate that, but I have not found a "quick fix" for it yet, and have not had the time to devote to fixing it myself.

But yes, what we call the "bell housing" or "bellhousing" is the front case half. There are two halves, joined in the middle by an iron (or steel) plate that holds the shafts. The entire front cases interchange between gas and diesel, provided they're both cast for the same bearing cover. See the third and fourth photos here (I can cheat and make the internal links work).

When using your bore scope, you will have to peek behind the clutch fork. The old four-bolt style has the pivot ball mounted separately from the cover, I think.

Jack
moroza
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Re: 4wd 4-speed upgrade to 5-speed?

Post by moroza »

Are there gearing differences between the gasser and diesel 5-speeds?

Will the gasser 5-speed trans bolt to the diesel 4-speed transfer case, or do I need the whole deal and then driveshaft modifications?
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JoeIsuzu
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Re: 4wd 4-speed upgrade to 5-speed?

Post by JoeIsuzu »

moroza wrote:
Fri Jun 11, 2021 4:32 pm
Are there gearing differences between the gasser and diesel 5-speeds?

Will the gasser 5-speed trans bolt to the diesel 4-speed transfer case, or do I need the whole deal and then driveshaft modifications?
I'm not personally familiar with the 4x4 transmissions, but with the 4x2, there are slight differences in gearing in 1, 2, & 3.

And based on what I've read here, the transfer case goes with the transmission.

Jack
moroza
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Re: 4wd 4-speed upgrade to 5-speed?

Post by moroza »

Wasted a bunch of time with a crappy borescope, got a good look at the side of the bearing retainer but not enough to count the bolts or see the pivot pin. I've got several good photos of what the 6-bolt retainer looks like; does anyone have an image of the 4-bolt one?
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JoeIsuzu
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Re: 4wd 4-speed upgrade to 5-speed?

Post by JoeIsuzu »

I searched and found plenty of 6-bolt pics. Just no 4-bolt ones.

Jack
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