The Stovebolt Site Forums The Shop Area Driveline 55 3100 drivetrain upgrade

I have a 1955.1 Chevy 3100, and I am looking for feedback/thoughts on drivetrain upgrade. I believe the current drivetrain is stock with a 235ci engine and 3 speed transmission. I think it was a three on the tree at one point, but now on the floor. The shifter is into my thigh when driving. Is there a fix for that? Considering a drivetrain upgrade, starting from the rear, working my way forward. I'm looking for better performance ad ability to cruise. I don't need an LS swap but is the 235 fine with a different transmission and rear? What's the relatively cheapest way to go?

Thanks,
BH

The shifter is easily bent to fit with a torch.

Ed

You lucked out in having the only AD with an open driveshaft. If like the 55.2 open rear end you can get a set off 3.38 gears from our host or from Mother Trucker. This makes 60-65 mph cruising possible. With higher speed would recommend a brake upgrade.

I just did a power disc brake upgrade. See page 720 (I think). For pictures in thread what have you done lately. She stops, now I'm working on the go

If you can find a T5 with the proper gear ratios, you'll be all synchronized and you can use either a 3.07, 3.08 or 3.24 rear end very well. Here's how & why: OEM rear end ratio was 4.11 and first gear was 2.94. That gave you an overall ratio of 12.08 and for a pickup which will actually be used to haul things, that is in my opinion a perfect ratio with the 235. Second gear in the OEM transmission was 1.68 and that multiplied by 4.11 equals 6.90. And third gear was 1 to 1 so the overall ratio was 4.11 (1 x 4.11). If your T5 has the 4.03 first gear and you use a 3.07 rear end, you have an overall ratio of 12.37 (very very close to the OEM), second gear will be 2.37 (which multiplied by 3.07 will give you an overall ratio of 7.27 (again very close to original...actually will give you a smidge more second gear power), third gear will be 1.49 (which multiplied by 3.07 will give you an overall ratio of 4.57 (very close to OEM and will again give you a bit more power in third), fourth gear in the T5 will be 1 to 1, so your fourth gear will be ~25% less than 4.11 (at 3.07) and your fifth gear will be .86 which will give you a fifth gear overall ratio of 2.64...and on flat to gently rolling roads without strong winds will work fine. 3.24 will work fine, too...your fifth gear will be better but you'll have a stronger first 3 gears: 13.06, 7.68 and 4.82. Fourth will be 3.24 and fifth will be 2.79. All of which will be good. With the first example, driving your truck will feel exactly like it did when it was new, then 4th will drop your rpms by 25% and fifth will drop them by another 14%. Looks like you're running wider wheels/tires (5 lug), so somebody did some conversion there. Make sure your front end and suspension are in good nick before you speed it up. Good luck.

I think the first thing to do is identify the rear end currently installed. Jon noticed the 5 bolt pattern; the rear end is probably not stock. Post a picture of the rear end - someone may be able to ID it.

If it was the stock rear end, wouldn't it have a 3.90 ratio like the 54 3100's?
Samantha

I agree with Gord, identify and then pull the cover for a gear oil change and count your gears or raise a wheel and count revolutions and do the math. Then do a T5 and fight with modifying that shift lever to work better for your thigh!

Jon, in your scenario which t5 are you using? I read an opinion that the s-10 4 cylinder t-5 had better lower gear ratio spreads for our low power 216's and 235's. Any truth there?

With gear ratios of 3.07, 3.08, or 3.24, when would one ever be able to use 5th gear?
From what I am gathering from your post, 1st, 2nd, and 3rd gear with the T-5 with the 3.08/3.08/3.24 rear end would be very similar to the stock 3 speed transmission's 1st, 2nd, and 3rd gear. To me, that seems like a less than optimal idea. Seems like it would suffer from the same lugging/screaming/lugging/screaming/lugging/screaming scenario of driving a stock truck.
To me, the beauty of a T-5 with a 3.73 or 3.90 is the close together ratios in the transmission, allowing one to be in the optimal power range of the 235 upon every shift without any hesitation and without having to redline the engine prior to the next gear shift to avoid as much lugging right after one makes the shift.
What am I missing?

Wow, I rally appreciate the feedback. I will take some pictures tomorrow during the day and post them. If I go with a T-5, will the driveshaft need to be modified?

If you need to change out, or mod the drive shaft, its not that big of a deal to have one made. Well if there is a driveline shop nearby. Ive had 1 made, included ujoints, painted and balanced ready to install behind a t5 and all i had was the output shaft and it was $200. Might be an option if needed.? I know some places will shorten also, depending on the diameter and condition of the donor shaft. Just food for thought.

A T5 works best with a 3.73 rear axle IMO. The 3.42 and 3.90 gears are also good.

For a good driver, car or truck, use this rule of thumb as a guide.

First gear X rear axle should give a number between 9 and 12, and the OD gear X the rear axle should be between 2.8 and 3.

Example: A 1965 factory C10 three speed tranny had a 2.94 first gear and 3.73 was common for the rear axle. (2.94 X 3.73 = 10.96) As a work truck it could haul stuff with that 10.96 number. A lighter vehicle does fine with a number closer to 9.

An OD gear X rear axle should be a number between 2.8 and 3.0. If the vehicle is very heavy, or doesn’t make much horsepower in the 1800 to 2000 RPM range, then it’s more desirable if the number is closer to 3 than 2.8. A SBC with good HP can handle 2.8 and sometimes lower.

Example: My 1963 230ci doesn’t make much HP even though it runs great. Good compression too. A 230 just doesn’t make much HP.
I have a 0.76 OD in the T5 and a 3.73 rear. It does fine on the highway without lugging. So 0.76 X 3.73 = 2.83

I can echo Lugnutz. A 1352-222 T5 replaced the SM420 in my 3600. The 57,000 mile original 216 with a 4.11 rear gear and a .72 OD does fine in 5th gear in fairly level country running 55. It's happy in flat land up to 70 or so. Now introduce Any headwind or hills and it's back to 4th gear. I've no problem with that. I do have a .83 overdrive T5 I've considered mounting up just to try it out. So far that hasn't happened. I should probably just let it go.

On 1'st gear the T5's 3.97 1st gear is also fine for normal driving or work. Now, that said I do sometimes miss the 7.02 gear in the original SM420 transmission. Places I miss the granny crawl gear, when loading hay in the hayfield, starting off with a loaded trailer or trying to creep along on a old rutted up two track road. But 90% of the time the T5 and its higher 1st is just fine.

RonR

I really appreciate all the feedback. For those who asked I finally took pictures of the rear, my apologies for taking so long.

Reviewing this guide, it looks like a GM 55 passenger car rear end to me. There are other here who will know for sure.

https://www.differentials.com/technical-help-2/differential-identification/

1955 to 57 passenger had no removable differential cover.
Possible ratios:
https://www.trifive.com/threads/rear-axle-ratio.38505/

If this is a trifive rear axle it may not be a good candidate for today's hotrod.
It will not last long with a performance 350 engine and 28" tires for example.
It's about 66 years old and probably still running on the same bearings.

Truck rear axle info:
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=656825

My plan was to replace the entire driveline, starting from the rear working forward. Rearend > transmission > engine. I would like to do it in a way where I can drive my truck between each project. I do not want the truck sitting until I can finish it all before driving. I see all these frame swaps, is it really necessary? Rear axle bearings replaced back in August

I was referring to carrier and pinion bearings in the differential. That's assuming the ring & pinion gear as well as spider gears are decent.

Parts availability:
It can cost more to rebuild a 235 I6 than a 350 V8.
Parts stores make more profit off of commonly used parts than stocking new/refurbished classic and antiques parts.
Most likely your current drivetrain is made up of classic parts and may cost more to rebuild.

Function:
The AD truck was designed for work. Stiff straight axle with leaf springs suspension for pot holes and rough roads as well as working in the field on the farm.
The torquey 6 cylinder engine was made to haul loads. You frequently changed gears back in the 50's road system.
You have "armstong" steering so the original skinny tires do better that today's wide tires.

You have to decide what type of truck you want.
1.) Original
2.) Cruiser (creature comforts)
3.) Hotrod (chrome, more speed, harsh ride)
4.) Ratrod (rust is beautiful but in your case X this one out)
5.) Straddle The Fence (mostly wreck yard or donor vehicle parts...person on a tight budget)

I would say mostly 3, mix In 2 for interior, and a sprinkle of 4 exterior. Hopefully that's not too confusing

That's a "Tri-5" rear end, 55-57 passenger car. The bolt-in center carrier assembly was used through 1964, with the 58-64 housing using coil spring suspension. Those rear ends managed to survive behind torquey 348 and 409 engines, so ignore the "They're too weak" comments. They did have a tendency to turn axle shafts into corkscrews during full throttle "Kamikaze" shifts on the drag strip with cheater slicks on the Super Stock cars. There should still be a good selection of aftermarket gears for those rear ends and limited slip carriers available from places like JEGS or Summit racing.
Jerry

Outstanding! Recommended gear ratio? More cruising than hotrod

Most people these days tend to go too high on the rear axle gear ratio. If you're planning to run a small block V8, I'd recommend somewhere in the 3.50 to 3.90 gear Ratio with a 1:1 top gear in the transmission or a 3.90 or 4.10 rear end if you use an OD trans. Total height of the tires will have a pretty noticeable influence on cruise RPM. The most common standard shift rear axle in those years was a 3.70, and most of the automatics ran a 3.36. I believe aftermarket gears are available in 3.55 and 3.73, and drag race gears down to 4.56 or so.
Jerry

Thanks, Jerry. Last question for all. Is it necessary to do a frame swap if I go small block V8?

No, your ‘55.1 frame is probably already ready to accept the V8. It was an option for ‘55.2 series.

There's a possibility of an interference problem between the steering column and the driver's side exhaust manifold if you use the rams' horn style of manifold. If you use a manifold from a 1955-57 passenger car on the driver's side the outlet is far enough forward to clear the steering gear. Don't get conned into using headers instead of manifolds- - - -there's virtually no difference in exhaust flow until the RPM gets far above anything that's appropriate for street use. I had years' worth of dyno test results to support that claim until an over-zealous assistant principal at the high school where I was teaching auto mechanics had the brilliant idea to discard a file cabinet full of "obsolete" paperwork and a bookshelf full of service manuals from the 1950's and 60's! He dropped off my "favorites" list in a hurry!
Jerry

Thanks, gents!

Sorry I missed all the discussion. This subject always seems to bring out interesting opinions in a forum like this. Before you do anything, I think it is a good starting point to look at the torque and horsepower curves for your particular engine and then to sit with a cup of tea and ponder just what exactly you hope to achieve. Transmission and rear end mistakes can be expensive and once a mistake is made, it can be constantly frustrating. I've seen people turn an okay pickup into a wall to wall un-driveable mess...and never have an understanding how or why all the work and money went to snot on them. I've seen people spend gobs of money converting a closed driveshaft pickup into an open driveshaft style with a common Saginaw 4 speed thinking they were somehow going to get an overdrive gear and wind up with a pickup that can't even start on a hill.

I frequently get told my pickup won't work with a 3.07 rear end. But let's look: My transmission has a first gear ratio of 4.03 and that is instructive and important in this case. Chevrolet engineers have proven an ideal first gear overall ratio for a 1/2 ton pickup should be around 12 using an inline 6 (or any similarly powered/designed engine) and tires with a diameter between 27 and 28 inches. This turned out to be such a solid plan they repeated it in thousands of pickups GM made. The OEM transmission (the 3 speed) had a 2.94 first and the rear end was 4.11...making the first gear overall ratio 12.08 for the AD truck. In my case, 4.03 x 3.07 equals 12.37, which is very close to the OEM 1st gear overall ratio. 2nd and 3rd gear follow suit with the OEM overall ratios. 4th drops engine rpms by 25% and 5th drops rpms by another 14%. All works well with 15 inch wheels/tires. At 60, rpms are around 2000~2100. The torque on the 1959 and later 235 maxes out at 2000 rpm.

Now if I were to use a 3.90 rear end with the transmission I have (which some folks here have earnestly suggested is what I need), let's see what happens. My first gear overall ratio becomes 15.7. That's ok for pulling down barns, but a real bad choice for driving in town because somewhere around 14~15 mph you'll need to shift to second. In terms of distance, that's about halfway across a city intersection. For a cement mixer, garbage truck or shorty school bus full of kids, that may be ok, but for a 1/2 ton pickup...even one with 1000 pounds of "stuff" in the bed that's a real irritation. With the 12 to 1 ratio the GM engineers settled on, I'm shifting from 1st to 2nd around 20~21 mph and I'm completely through the intersection and heading off down the street. To me, shift point with a 235 should be around 2800~3000 rpm and since the 235 is anything but a high rpm engine, getting to 3000 rpm ideally should be slower and smoother than the Ferrari approach.

Would a different rear end have been just as good for me? A 3.24 rear might have been ok...it would have produced an overall 1st gear ratio of 13.05 (which would not have been unworkable if I was using 16 inch wheels with taller than OEM tires), but what about beyond that ratio? How about a 3.55? Some think that ratio is really special, but once again look at the transmission ratios. In my case a 3.55 rear produces an overall first gear ratio of about 14.5 and we're we're only a small fraction better than the 3.90 with that. 3.55 with a first gear ratio of 3.4~3.5 would be good, and while that ratio was used in some T5s for GM products (a few minivans), it isn't what I have. The point I'm trying to make in any of these discussions? Just think about what you have and what you want to accomplish. I've got friends who just ran out and bought the first T5 they found and an unknown rear end with no idea at all what they had. One of them is the proud owner of a T5 with a 4.03 first and a 4.88 posi rear. You can do the math on that one...

Good luck!

Thanks, Jon. Let me start off with my 235 is solid and doesn't even leak. However I really want to be able to run with modern vehicles on the road. On my road to make that happen, I started with a disc brake conversion and now I'm looking at the driveline. I am also leaning toward going to an automatic transmission a th350. I have a Lokar shifter for a th350 that I would use.

My plan was start with the rear and work my way forward. Ending up with a mild no more than 350hp small block. But that's wear the question of the frame came in, as it is not fully boxed. I'm trying to figure out the best path forward

No need to box the frame unless you plan on drag racing the truck. I have a mild 350 in my '56 3100 and have never worried about twisting the frame, but I never launch it from a dead stop either.

Mike B

BigHog, "I really want to be able to run with modern vehicles on the road". Ultimately this means front to rear drivetrain changeout. Let me see if I can draw a mental picture.

1) AD trucks:
Stiff leaf springs, straight axle, flexible frame and the cab on pads (with humans inside) that move or sway with it. This is the way GM designed it to work. Not designed for high speeds in a curve or a quick-agile (thread-the-needle) lane change, on a crowded expressway, at 80 mph. On a modern expressway near a city you have to concentrate harder and think-ahead. It's tiring. I try to avoid congested areas by taking the backroads.

2) Modern trucks/cars:
Stiff frame. The front and rear suspensions takes, or tries to take, all of the movement away from the humans inside and negotiates everyday modern traffic.

To make 1) into 2) requires $$,$$$ unless you are good at safely fabricating parts/material into what you desire. Add to that the time and shop equipment. Maybe it would help if you first determine the amount you are willing to spend on your project then work backwards to see what you can afford to do.

I wish I had the video of a stock Model A "50's hotrod", modified with a "hopped-up" flat head V8, trying to take a sharp turn in a vacant parking lot. They did it, but with only two wheels on the road.

Not enough application of the "loud pedal"- - - - -short turns with a hotrod require the rear wheels to be spinning! That's "dirt track racing 101"! (just kidding!)
Jerry

BigHog, please listen to buoymaker. He made excellent points succinctly. I'm going to add some grim detail from personal experience. If you get the right T5 and rear end ratio, you can make your 235 powered pickup go as fast as you want and a whole lot faster than is safe. With the setup I have, at 80 mph my 235 will be running about 2800 rpm. At 85 I still wouldn't be at 3000 rpm yet. But having owned these trucks for 50+ years I can tell you even traveling in a straight line and going 75~80 mph in an AD truck can put you, everybody in the truck and other drivers on the road in grave danger. Absolutely nothing at all about the stock AD trucks was designed for 75~80 mph driving. No matter what anybody tells you.

In the 60s, 70s and early to mid 80s when scads of these trucks were still being driven around Texas (before the days of T5 transmissions) I came upon a handful of serious accidents involving what were basically stock AD trucks into which small block v8s/automatic transmissions had been installed...with the sole purpose of making them go faster. There was even one man in South Dallas who advertised he'd turn your 1950s Chevy pickup into a "V8 powered freeway monster" for $1100. And he would, but he always left the front axle alone. What he was doing was about as irresponsible as putting that SBC engine into a 3 wheeled golf cart. After doing this about 3 years, the guy disappeared.

Two of the accidents (one in 1978 and one around 1981) were single-vehicle wrecks where the drivers had simply been going too fast on a straight stretch of highway and something happened so that control was lost. Both were fatalities and I doubt the driver in either accident lived more than 15 seconds after the truck started flipping. One had so much blood inside it looked like a human had exploded in there. The other had caught fire from the gas tank which of course sits right behind you. One had flipped to the left and had stopped on the other side of a freeway. Fortunately no other car was hit when it happened. The trucks both looked like they had been forced through some bizarre garbage disposer and I have no idea how many times they rolled over before stopping. Very little about them could be salvaged.

You have a solid front axle with a very tiny caster angle (2~2.5 degrees or so) that was designed for a maximum speed of around 60 or 65 if everything is all Jake in your entire front end. That's not to say you can't drive 70...you can, but at that speed you're flirting with the outer limits of safety from many different standpoints. I know...people here will show up and say "oh baloney...I drive 70 all the time." My suggestion? Take your pickup out and drive at 70 with a stock front end. See how precise and accurate it feels to you and then let's talk about it. This tiny caster angle and unforgiving suspension means at speed your pickup can become VERY unstable given the slightest variation in roadway, a rock, a gust of wind, a shake of the steering wheel, roadkill, some driver distraction...nearly anything. And only God is going to let you regain control at high speed in an AD truck. It is one step better than the old WWII Jeep. And yes...I know...Jeeps today have solid front axles and they all drive at freeway speeds. They all also have power steering, a caster angle between 5 and 7 degrees and camber and other front end settings specifically set to keep the Jeep as stable as possible. If you put 5 to 7 degrees of caster in your stock AD front end you better be a HugeHog. With that much caster you won't be able to drive it anywhere unless you have arms like Bluto...but it will not wander or wobble around on the road at higher speeds.

If you want to drive at the speed some people today are driving pickup trucks, please go ahead and buy a new or newish one. Something made since around 2008 or so, but do your homework. See how professional drivers have rated the handling characteristics of various makes/models. Check the IIHS, also.

Might be time to sell or trade her