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Doubler for the MSG5?

Tue Jul 28, 2020 10:31 pm

Lets not worry too much about the "why", looking to see if anyone has any experience with it....

In my 87, Ive got a freshened up 2.6l running a weber and a jerry cam, larger 2.6 clutch, through the MSG5 and 8/10 bolt axle combo (Soon to be 10/12, saving up for my front Lokka) on 33s. The 1.87 Low range just isnt low enough. My first thought was swap an MUA5 in, and go for the revo gears, but thats alot of money for not so much reduction. Certainly better, but id like more. Basing off my dads 2.8 trooper on 31s with the 2.26 low range, I feel that needs more too. Also, MUA trannies are scarce and expensive in Canada (Been quoted $400 and $450 on the 2 Ive found) and with covid border closures, no crossing the line for one. Which has led me to the doubler option.......

I see on the MUAs you can run a T case from an auto behind the MUA case, can you do that with the MSG as well? I see the MSG is slip yoke and all of the doublers I see use fixed yoke cases. But the casing on the MSG is steel/cast iron or something, which could be easier to attach the mounting plate for the auto case and close up the MSG case after lobbing off the front output. Although welding cast iron doesnt always go well either....

Just going through my options i suppose, I have one last line for an MUA I have to check out, an older fellow has a trooper on the side of his barn that he has let me pull parts from before. Havent been by in a few years, but I plan soon to take a drive and see if he still has it...


Re: Doubler for the MSG5?

Tue Jul 28, 2020 10:48 pm

Why not use a divorced t case after the trans?

Re: Doubler for the MSG5?

Tue Jul 28, 2020 11:46 pm

Thats also an option, however I havent had any luck tracking one down yet. Theres lots of 205s around but no divorced ones...

Do you think a divorced unit would make the rear driveshaft too short? I guess as long as i dont go further back than the driveshaft center bearing, it shouldnt be much different that stock. This rig is staying IFS, has roughly 3-4 inches of lift on it. Not planning on any more except maybe a 1 inch body lift.

Re: Doubler for the MSG5?

Wed Jul 29, 2020 2:59 pm

I think the turbo diesel MSG's had a removable front output! That would make it easier.

Doing a doubler on a slip vs fixed case is pretty much no different, just more or less output shaft to work with (I think, heck it might be the same).

If you wanted to go divorced, the nissan t100 case is a good option. They were in 80s Datsun and Nissan pickups. It's gear driven, 2.09:1 low, and can be clocked to any position. The outputs are aligned, so you end up with a bit of a compound angle to the rear end if you clock it over very far. But, it's a pretty compact unit, and you can see that with a very short intermediate shaft, you could probably get away with only losing a foot or so of rear driveshaft length, and maybe add the same up front. Might get you to equal length.

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Re: Doubler for the MSG5?

Wed Jul 29, 2020 4:41 pm

Very interesting, another option for a divorced unit. Looks a little more compact than the 205. I'll have to keep my eyes open for one.

I heard the diesel MSGs also had the removable front output. But those are even harder to find than MUAs

Re: Doubler for the MSG5?

Wed Jul 29, 2020 8:08 pm

With a doubler, do you add the reduction, or multiply it? If you have Revo 3:1 in your original transfer case, then add another factory T-case that is only 2:1; with both in low, is your final ratio 5:1, or 6:1?

Re: Doubler for the MSG5?

Wed Jul 29, 2020 11:11 pm

Ive been calculating it as overall crawl ratio, which is 1st gear x low range x diff ratio.

In my case, stock is 3.76x1.87x4.56 which gives me a crawl ratio of 32.06:1. Adding a doubler would make it 3.76x1.87x2.26x4.56 which would be 72.5:1 crawl ratio

Atleast i think im doing that right....

Re: Doubler for the MSG5?

Thu Jul 30, 2020 12:48 am

I think you are calculating that correctly. I think I'm either asking a different question, or the answer you provided is just a more complex, and correct, way of answering my question.

Re: Doubler for the MSG5?

Thu Jul 30, 2020 9:15 am

You multiply each. 1st gear x tcase1 x tcase2 x diff.
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