Newbie needing help!

[S.R.copper]

Hey yall, hope all is good. Call me Smokey. A friend turn me onto this site so figured I'd join and see what's up. I have a 81' 3/4 4x4 long wheel base camper special. Just pulled the old 350 and put a rebuilt 350 in. She runs good, quite a bit of after market stuff Goin on...but I'm lookin for something to make her run a little more efficient.
Note: 4 inch suspension lift and 35-12.50s.
The transmission in the truck is my topic of concern. Ppl call them different names, but mine is a granny low 3 speed. L,1,2,&3. I'm looking for one with granny low, and gears 1-4. That extra gear on the end would stretch my highway speed out while bringing my RPMs way down. I don't have a tach installed, I think they're tacky. Never the less, running 55mph, I'm Goin to assume I'm somewhere around 2.5-3k rpm. I shouldn't be complaining. Im averageing 15mpg. With 35s, engine bored 40 over with flat top pistons, small RV cam, 1.6 intake rockers and 1.5 on exhaust with poly locks, smaller harmonic ballancer, 15lbs shaved from factory flywheel, hooker headers. Fairly hot MSD distributor, wires and plugs. But a janky old elderbrok carb....taking that into consideration, it gets great gas mileage. Not to mention we put exhaust on it so my foots always in it some to hear the pipes. The boy that helped build it says she's damn near a street stock dirt track truck, if there were such a creature.
So my situation is, I want to keep my lift and tires. As well as my hotrod motor. This truck is my daily driver. And with that being said, granny low is wonderful in town at stoplights and on hills. So i dont want to lose low gear. Downside, I'm late for everything. I'll be late to my own funeral. And being late, I drive balls to the wall. Hammered down. The truck with run upwards around75-85. I generally stay way slower than that, but sometimes I dont. Running 60-65 is the normal. Even though she pulls all the way to the 80 mark on my speed-o-meter, if I had L,1,2,3,&4 instead of just L-3, 4th gear would allow faster hwy speeds as well as improved fuel economy since the motor wouldn't be wound up so tight. So, my underlying questions are; 1. What's the model of the transmission do I currently have, L,1,2,&3? 2. Whats the model of the transmission I am seeking, L,1,2,3,&4? 3. Would it be sensible to swap trannys? Or would it be useless, per say that 4th gear doesn't stretch much farther to make a different. Like if the transmissions performed the same, one not better or more efficient, one just had an extra forward gear with roughly the same top speed. And ? number 4, if the swap was a good idea and I decided to proceed foward with it, will my transfer case fit the new transmission, or would I need a different one? Sorry for the book guys, but that's what I'm looking for. Any and all help is greatly appreciated!

 

[Justin V]

First off, welcome to the site.

From the sounds of things you have a SM465 manual trans now. As for the transfer case, well, there were options, and not knowing how many people had their grubby little fingers into your truck before you, I think that the best advice is to tell you to crawl under the truck and look for the ID tag on the back of the t-case. Depending on the amount of $$$$ you are willing to invest in the trans swap, it may be better to source a particular t-case over what MAY be currently in the truck.

As for the transmission you are looking to swap to, a NV4500 is the obvious choice.

5 total forward gears, the 1st being "granny", and the 5th being overdrive.

Unfortunately, these gearboxes had a few variations over the years, and I am not completely versed on all of these variations.

Some (but maybe not all) variations include:

Internal or external clutch slave cylinder

I believe there was a version with a lower first gear than others

There are differences between GM and Dodge versions (is there a ford version?)




This is something that you'll have to investigate further.

@campfire put a NV4500 gearbox and a SM465 bellhousing together with some fine drill operating skills. He may be able to shed more light on the subject.

I believe that if you are getting an actual 15 MPG already, that you are doing pretty freakin' good, and you may not getting much more efficiency out of this thing. A 5th gear would allow for higher cruising speeds at less RPM though...

 

[campfire]

Your truck came with an SM465 and a mechanical clutch linkage. Probably (definitely measure this) your tranny is short relative to GM's other options. In the mid 80s, GM standardized transmission lengths so they will all swap fairly easily. The granny-gear 5-speed manual transmission you are wanting is the GM NV4500. 4th gear (3rd in your marking scheme) will be the same 1.00:1 drive ratio that you currently have, and O/D will be a 0.73:1 drive ratio (the first 3 gears will be pretty close as well). So if you are correct about cruising at 2500RPM, your new final cruising speed will be 1825RPM (0.73 * 2500). That's pretty anemic for a 350, so I would definitely get an accurate tachometer reading before you start tearing into things. You don't want to tear into your truck and then find that you don't like the final outcome. If you're on the 15MPG end of the spectrum you don't have much to gain by adding O/D. Unless your truck has been regeared you've already added half a gear's worth of adjustment just by increasing your tire size (changing from 31" tires to 35" tires yields a drive ratio of 0.89:1 compared to stock). In stock form granny gear is usually too low to be very useful on the street.

If your tranny isn't the standard length, switching to a newer box (of any type) will require redoing driveshafts. I'm not quite sure if '81 is new enough to have a 6-bolt round-pattern transfer case, but if not you'll need to upgrade that as well. It is possible to fit an SM465 bell housing to an early GM NV4500 (1992-1994), keeping all of your existing clutch linkage, clutch, & flywheel. The block pattern and input retainer are the same, but the bolt pattern on the tranny end is different. The cross member is at a different height. Round-pattern transfer cases have 32-spline input shafts unless you have a TH350/700R4. So all the GM manual transmissions can swap T-cases once you get past the short adapter 10-spline days.

On my TH400/NP208 rig I took a hydraulic clutch SM465 bell housing, attached it to my NV4500, and the rest of it bolted up perfectly once I fabbed up a spacer for the tranny crossmember mount. If it had been a 1985+ square body I would not have even needed the block.

The 96+ NV4500 boxes have a higher 1st gear, internal slave cylinder, and a removable shift tower ('95 boxes got half of these changes). This will also work with your truck, but you will be stuck converting to hydraulic clutch linkage. The input retainer is different, so the bell housings won't swap like the early ones will. This is also why Dodge NV4500 units will not bolt readily to GM bell housings (and also the input shaft is different).


In short, the swap is a bolt-in swap if you have an '85+ truck, but yours would require some mods. Read through my CUCV thread (link below) and look at how I measured the tranny length (27.5" from BH to T-case face, IIRC). Then compare that to what you already have. If it's not the same you will be needing new driveshafts & a relocated cross member.


Let me know if you have any other questions.

 

[campfire]

Oh, a note about the nomenclature. Some GM NV4500s are marked L,1,2,3,4 like your SM465, but others are just marked 1,2,3,4,5. Not sure if there's a rhyme or reason.

Since I didn't have a real NV4500 shifter, I repurposed one from an SM465. So mine just says L,1,2,3.