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Trying to figure out what transmission goes in my 91 GMC Sierra 4x4 manual

679 views 7 replies 4 participants last post by  cerial 
#1 ·
Does anyone know what transmission will fit in my 91 GMC Sierra 4x4 manual? Or like what other years will fit in without making change? And another thing I've heard people say you could keep your manual transmission in and switch it to automatic!! Is that true? Or do I HAVE to go and pop an automatic trans in? any advice would help thanks guys
 
#5 ·
With a 91 you have many options. You can stuff any automatic 200r4/700r4/th350/th400/4l80/4l80e in there all you need to do is shorten and lengthen the driveshafts a bit.
You can also mount a sm465, NV4500, NV3500 or many others.

The only issue is the correct splines for the adapter to the transfer case. Most of these will have a married transmission. If you can going divorced makes things so much easier. You could have many diffrent transfer cases back behind your current transmission right now. My guess is that you have a 241 and if so it is good news because there is tons of support letting you easily find adapters for it to mount any transmission up.


When choosing a transmission you need to ask yourself what your going to be doing with it. A sm465 is a great transmission for offroad use with it's granny gear but worthless on the highway(unless your running like a 3.08 rear). A NV4500 on the other hand has overdrive but is less forgiving then the sm465.
Things like gear ratios, percentage drop between gear ratios, rear axle ratios, intended use, replacement/upkeep cost, power ratings, available torque multiplication ratios in the transfer case, transfer case activation process(button or lever), front axle disconnect or not, and working with the engine all come into play in proper transmission selection.


First thing you need to do is figure out what you want to do with the truck. Once you know that get a creeper and measure the distance from the front of bell to the front of the transfer case. This is the amount of room you have to work with(give or take an inch) without changing the length of the driveshafts. You should check id tags as well as bolt pattern and general shape of the transmission/transfer case to have some information to find the exact drive train you have. Look for differences in color of the aluminum between the transmission and transfer case that may hint that an adapter has been used.
Now you can go to novaks website and compare the transmissions/transfer cases finding out what you have. That will show you what you can do. If you do not mind changing driveshaft length there are adapters to mount practically any transmission to any transfer case out.

Novak Conversions Transmission Knowledge Gateway
Novak Conversions Transfer Case Knowledge Gateway
https://www.novak-adapt.com/catalog/adapters/transmission-to-transfer-case/
 
#7 ·
Thanks yeah I'll be doing very little of mudding mainly pulling or just turning it into a show truck. I will have the transmission with married transfer case off tomorrow then iv gota find another transmission lol just need something to get it moving don't care if it stays manual. Bc I heard dropping an auto in it is more work than just dropping it in putting an auto stick to it adding a cooler and driving lol. But thanks guys if yal know anyone with a trans for sale please let me know looking to spend no more than 400$ for a good used one
 
#8 ·
The easy answer is stuff another 3500 in there(if that's what you have).
But for $400 I would search for part outs in your local craigslist. You can do something like find a entire truck the same wheelbase as yours(important) with a blown engine(same cylinder count as yours) or one with a deer hit etc for $600 and have the trans/transfer case and driveshaft making it a true bolt up deal.
You are rolling the dice a bit here and if you can get the thing to drive through the gears on Jack stands that is better then buying A pile of parts. If you can take the thing safely down the road and put a load on it testing do it.
Later you can scrap the truck for $150 or so keeping tires or such to make up the other 50.

With those years you should be plug and play with the harness. The good thing about having a partout is if you do need parts to swap in a automatic you have them. You also get tons of spares of used accessories. Those little parts that a swap takes (center council, seats, bolts, brackets, crossmember, etc) all add up. Having them ready to pull next to what your swaping them into saves time and money making the swap faster.
If you have the room for another truck using a partout may be a good option to reduce the overall cost and get this thing moving.
 
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