Need some advice. I'm building a 1956 Chevy 1/2 ton, and I'm trying to decide on a transmission. The motor will be a 350 with 4 bolt mains, stock heads, a mild cam, and TPI intake. There was an old Saginaw 4 speed in the truck but, that will most likely be a bit weak for the later 350. The truck is currently running a 12 bolt rear at 3.90. I'm leaning towards a 5 speed Muncie, Tremec, or NV. Some guys say the automatics are just as good but, I have no experience with auto transmissions in higher performance motors. Since I'm approaching 75, the auto trans does sound like it would make the truck easier to drive. Just wondering if anyone has some advice or experience concerning the selection of a good trans for this build? Would prefer to not do a lot of heavy mods to the cab floor and firewall. Any input will be appreciated. Tom
You might edit this and drop the “95 LT”, that’s an off topic here. I think the bellhousings are the same, but you’ll get more responses and not get locked.
As @miker98038 suggested, edit your post to get rid of any reference to post '65 components. Trans selection will depend on your needs and intended purpose. At 74 years old, a manual trans does not appeal to me, so I'd be looking at a TH350 (no overdrive but a good trans), TH400 (same attributes as a TH350 but hell-for-stout), 700R4 or R200 (I'm not sure of the correct nomenclature, so hopefully someone will correct me), both of which are overdrive. The R200 is physically smaller which might be an easier installation. Good luck
If you want to do a reasonable amount of highway driving, I highly suggest you put an overdrive transmission in your truck - you'll be glad you did. I have a built 700R4 in one of my hotrods - it is a very good transmission and the overdrive makes it much less stressful on the driver and the engine to be driving at 75 mph to stay up with traffic. The key is getting a quality performance build and a torque converter that matches your application and requirements.
I'd get a bit more info on what transmission is in the truck now, and how it's mounted. The original design used a bellhousing that mounts on a crossmember that's riveted into the frame, and it takes some effort to remove it and install a new crossmember under the rear of the transmission, and install side mounts on the engine. But we can only guess at what's there, since you didn't provide much description. Also, if it's a Saginaw 4 speed then it's a car transmission...if it's the original 4 speed truck transmission (granny box) then it's a Muncie SM420. The original rear in the truck has a 10 bolt rear cover, plus a removeable center section, and they were usually 3.90 ratio. It's a pretty common swap to put in a later 6 lug truck 12 bolt, but they did not have 3.90 gears available. So knowing for sure what rear is in it, might also be a good move. You can get other ratios for the 12 bolt rears, but you do need to know which one it is, as car and truck 12 bolts use different gears. There's not much available for the original 56 rear. If you are that old, you might faintly remember before everything had overdrive, and engines used to sing to you when you drove on the highway. Seems a lot of youngsters these days can't deal with that, and have to put overdrive in everything. It's not necessary.
My driving will be mostly local roads but, here in South Jersey, ya kinda gotta use the Parkway (interstate) to get most anywhere up and down the coast. My objective will be to simply keep up with traffic and not cause delays. I'll be doing some research to get caught up on the 700R4. Thanks. Tom
Jim The truck is basically bone stock at this point, except for the 1960s drivetrain that was in it when I got it. The bell housing is the OE type, along with the post type front motor mounts. Those will be changed out for side mounts. Yeah, I figured I'm gonna need a trans cross member if I go with anything other than an early Muncie. The Saginaw 4 speed that was in the truck was OK with the early 350 but, I did not push it very hard. The 12 bolt rear is 1968, from the numbers I got off of it. Not sure of the gear ratio. I'll try to figure that out. It is 6 lug, but that could have been an earlier change someone did. Since I intend to put in an IFS crossmember up front, I'll need to get the correct trans crossmember, and remove the OE trans mount as well. The cutting and welding does not present a major issue as my son is one of those Boilermakers folks. I realize this means serious mods to the OE frame, and some of the purists would object to that. I have never minded an engine that "sings" to me. I've owned a couple of cars and trucks that were a joy to have that discussion with. Over the years since HS, I've proudly driven several Model A Fords, a 190SL Mercedes, a 1939 Chevy, and two 60s Porsches. I also currently also own a 1942 Chevy 3/4 ton. Of course none of those would "sing" to me as beautifully as the Lycoming, Allison, and Pratt & Whitney turboshaft helicopter engines, that I flew with the Army. Those were engines that communicated like a part of your sole. Thanks for the insights. I'll follow up when I have more detained info concerning the 12 bolt rear. Tom
Saginaw 4 speeds are not all way’s weak. What first gear ratio was the one it has/had? Why would the new 350 hurt it now?
When I put the 4 bolt main 350 SBC together for my '39 Chev coupe I planned on using the 3.73 geared Ford 8.8 axle I already had, and I wanted to cruise the freeway without being at 3000 rpm's as my other car is with a TH350. So I chose a 700R4 to use. Only modification outside a typical engine swap was to install a hydraulic lockup switch for the converter which was simply putting a toggle on my dash (just to have a separate switch for 12 v. power, removing an existing plug in the trans, and threading in the hydraulic pressure switch in the kit. My 350 with a large .530" lift full roller engine, and Dart aluminum heads is well over 400 hp, and the trans works great. It also gets 17 mpg on the freeway cruising at 70 mph, at 2000 rpm's. Nothing about this setup is a deficit to an engine trans swap, and if I had room in my tiny old Austin g***er I'd pull the TH350 out, and put a 700R4 in it too. But it's only got about 16" of driveline now, and tight foot space, and I'd need to redo my trans tunnel for the swap. My '39 had a flat floor, and still does, so you wont need to alter your floors at all. My buddy did the same engine/trans swap in his /57 Chev pickup, and plenty of room under it.
The Saginaw 4 speed will hold up to a 350 if it's not driven abusively. I guess you need to decide if it's worth it to go with overdrive of some sort. If you're not going to spend a lot of time on the highway, you'll be fine without it, a 350 can run at 3500 rpm all day and not complain. But if you want a nice quiet ride, you're probably fixing up the wrong vehicle....no matter what gearing it has. I've spent a lot of time behind the wheel in these trucks, they just are not designed to be comfortable as we expect modern cars to be. IFS is ok, but it sure ****s the soul out of an old truck.
Be careful. The extra 2 bolts on the mains for those engines create a ton of HP but for “NV” transmissions. The 3500 is better suited for cruising over the 4500. The 4500 is a big granny geared towing trans. The 3500 has better ratios but not considered performance ratios either. The bell is cast on to the nv3500. If $$$ isn’t an issue the tremec is my choice for street fun
TKX is the best manual transmission. Bolts to the same bell housing as those Muncie and Saginaw manuals. Rear cross member will need move rearward some, drive shaft will need shortening and need a TH400 yoke. Set up with a hydraulic throw out bearing and it is easy to drive. Minimal, if any floor mods. TH350/TH400 are good options. Neither will have overdrive. A TH350 will bolt in place of a M2# Muncie or similar vintage Saginaw. GM 4 speed autos will have overdrive 4th gear but will need some electronics to run them.
That's no kidding... I had one in a slightly OT Malibu ('68) that I beat the hell out of and never had any problem. A lot of trans swaps are done because something is the current "in" thing, not because of a basic flaw.
Ha! Last time I was on the "Parkway" the average speed was in the 80's and dam near bumper to bumper. Better go with an OD
I may not be the smartest guy here, but suspect that Saginaw can live just fine with the engine you mention. I drove a late 60’s C10 with a better 327 than what you mention and a Saginaw for years driving it fairly hard and had no major issues with the Saginaw. I’m sure if I would have put slicks on the truck and launched it at 4000 rpm or so regularly, I would have broken it. But, I mainly just drove it and tires were sort of the fuse to keep from breaking driveline parts. The only reason I would worry about side mounts or a different transmission is if you needed an OD to keep up on the freeway. And, I agree with Jim on losing the soul of the pu putting an IFS under it. I would’t say there are many “purists” here, but a dropped axle and maybe some different front springs is a way cooler setup to me on an old pickup than putting a Pinto suspension under it.
I knew a guy that bought a pickup with a 350/TH350 combo. Chasing mileage, he had someone put in a 700R4. We figured it out afterwards that based on the cost of the upgrade, fuel mileage increase, and average yearly mileage that it would take about 30 years to pay off that transmission on fuel mileage savings. I hear a lot of guys tout mileage as one of the reasons for an overdrive, but in the big picture it's not always worth it. I run 3-speeds in all my stuff and they all happily cruise at freeway speeds. With the 3.90 gear the OP has, I'd be inclined to change the gear and stick with a 3-speed automatic for simplicity.
Well, it’s gone from an edited engine, and a ( hopefully) edited front suspension. But just maybe focus on the intent about what the OP wants and the reason why. Let’s face it, an auto trans is easier to drive. So GM choices with the engine the OP originally wanted, do limit his choices to an E on the end of it, but a non E OD auto can still be used. FWIW, my daily 4wd, closing in on 200K miles has the E version of a 700R4. I don’t abuse the truck, but do pull a large 4 horse trailer with it from time to time. It has a newer version of the OPs engine in the edited post. Since I think he won’t be running a TH350/400 with an add on OD, he’ll need to look a bit elsewhere for what’s available for what he has, things that the HAMB doesn’t discuss. My only real offering to this post, is there are two different transmission covers for TF trucks. One has a hump that was for the 4 speed, other is flat for the 3 speed. The flat one is easier to lay a carpet in, but the hump allows a inch + more room to mount the engine and transmission higher, sometimes an inch is nice when bent over the fender changing plugs
Not to be an a-hole but a 350 with stock heads, mild cam and that tbi thingy isn’t a high performance application. A fun set up, but not top fuel either. Put whatever slush box or stick you feel like/fits the budget Build what ya like, if it fits the forum, post pics.
I’d say it all comes down to what he wants to spend. Turbo 350 and 400 are great transmissions, but getting harder to find used, the later OD ones are more plentiful, but if he is buying one already newly rebuilt then it’s just a matter of how deep are the pockets. I used an AOD in my car because I already had it, if I would have had a C4 or even a C6 I would have used it. Used suppliers are few and far between around here anymore, might be different where the OP lives….
Guthriesmith Thanks for the advice. I know the TPI setup is not really a Hi Perf install. It is what I have available and it will be an improvement over the 60s motor, which was damaged by a disintegrated AC plug in cyl number 7. I'll research the Saginaw's gear ratios to see what came with this truck. I also have another Sag 4 speed out in my garage, which I can check out. The other trans I have is a Sag 3 speed w/OD. The input shaft on the 3 speed looks like its far too light to handle any real torque. The IFS is just a thought right now. It does provide several improvements that enhance safety, drivability, comfort, and steering/braking. It's a thought mostly because I now have the truck stripped to the firewall. So ... if its gonna be done, now is the time. But no, I am not trying to build a dragster or street racer. My 1942 Chevy 3/4 ton is my "purist" truck. This 56 1/2 ton is just for fun. Tom
Guys Thanks to all of you for your advice and expertise. I'll try to figure out the gear rations for the Saginaw 4 speed. It was most likely out of a 60s Camero, cause that's where the rest of the driveline seems to have been sourced. I'll follow up again when I've completed that research. really appreciate the help. Tom
Hmmm....if it's really a Saginaw 3 speed with OD, it should have a full size input shaft. If it's a Muncie 3 speed with no synchro on first, and only has 4 bolts holding on the side cover, then it might be sketchy to use behind a 350. But it would be the most fun overdrive to have, after you get it all working (if indeed it's in good enough condition to work) Good luck with your decision, it's not a simple choice, and personal preference plays a big part.
Checked the Saginaw input shaft groves for the trans that was in the truck. There were no grooves, so that would make the gear ratios as follows: First 2.84, second 2.01, third 1.34, fourth 1.0. Provided there are no other issues with this trans, it will be usable for the present. After driving the truck a bit, if I should decide that a trans swap is needed, I can do that somewere in the future. I will also most likely forgo the IFS swap for the time being. But I will look into modifying or upgrading the front suspension in some way, to improve ride, steering, and brakes. If anyone has a recommendation concerning front end mods, I'm open to any advice. Thanks to all for your help. Tom Jim Yeah, I sorta thought the Sag 3 speed with OD would be a fun drive. It does have the electric solenoid, it is in working condition. I just think it might be a bit too light for the torque produced by the TPI 350. Doubtful anyone has any experience with that combination. Tom
The saginaw 3 speed with OD would be fine, if indeed it is a Saginaw. But if it's a Muncie 319, then it's a bit weak. I can't see which it is from here.
Attached is a pic of the Sag 4 speed case. Took a hellofa lot of pressure washing to clean it up. This comes back as 68 Camero. Probably had every bit of the gunk going back to 1968 caked on it. There are no grooves on the input shaft. Not sure what the code stamped onto the polished surface translates to. The side plate carries number GM 42 3952647. Below that appears to be J128, but its a bit hard to tell for certain. Condition wise it looks pretty good. The seals are seeping a bit. Have not opened it up yet. I will throw the rebuild/seal kit on it before any installation. It was operating smoothly, with maybe a little issue with wear on the 2nd gear synchro. Now is the time to correct that of course. I'll try to get to opening the case tomorrow.
The Jalopy Journal
