The Stovebolt Site Forums The Shop Area Driveline rear end advise for 1950 3100

I know there is thousand of threads on what to swap on a 1950 3100. What I have available is a 74 nova rear end with 3.08 possible gearing. I don't think it is, more like 2.55. I am going to re-gear to a 3.73. It is also 60" wide. I have the opportunity to acquire a Camaro rear end with 3.73 gears and it is 61" wide. Cost between the 2 and getting what I am after is minimal. I am doing this mainly because the 420 trans is not healthy and I was given a good T5. I may as well swap if I have to take the trans out anyway.

The big question is.... Which one do any of you recommend and why? I am leaning toward the Camaro do to the width allowing a more assortment of wheels available do to a 4" back space to a harder to find 3.5". It also could be I have overthought this.

*Some* of us have been accused of "overthinking" stuff. But it sure doesn't hurt to cover as many bases as you can with some pros and cons. I'm sure you'll get some good insights here.

Just4Fun, It would help to know what the final drive ratio on the T5 is??? They came with several different overdrive ratios and not knowing which one you have makes it a bit hard to give good advice on which rear axle drive ratio may work best. Also would help to know which engine you have and what its operating condition is??? More details please.

If you have the T5 with the gear ratio chain that begins with 4.03 (first) and ends with .86 (fifth) and a 3.07 or 3.08 rear end you will like the combination a lot. The first three speeds will match the OEM overall gear ratios so you can use it as a pickup, fourth gear will be a 25% reduction from the old 4.11 rear end and then fifth will drop that by another 14%. Good luck!

I have a 1962 235 and it runs extremely smooth. Whoever rebuilt it did fantastic job. It has a L.J. Messer Company tag riveted to it that tells me it is 30 over. Lets say hp is about 110-120 being generous. The T5 final drive is .76 and 1st gear is 4.03. If i calculate correctly that puts me at roughly 72 MPH at 2300RPM with 30" tall tires (235/65R18 or 265/65R16 or some where there abouts, undecided). Which seems good for the occasional town hop down the interstate. Mostly an in town runner.

My question has more to do with axle width. When does a replacement get to wide? 61" seems better than 60" and I know that the Nova axle works with a 3.5 back space.

FYI I don't have access to the truck as it is still on the books to be transported. I am just collecting so down time is at a minimum. I would love to be able to actually put tape measure to it. I know the bed width is 50" and the fender wells are 12"

As I am waiting for the truck, I start to overthink and get ahead of myself so a nudge from people here and there keep me centered.

Thank you.

3.73 with 30 inch tires and .76 5th gear will allow you to pull a stump in 1st gear and drag it down the road at 65 MPH in 5th gear.
Every time that you shift gears, you will find yourself in the optimal power range of a 235. no more lugging, and screaming engine between every gear shift.
With either the 2.55 or 3.08 gears, you won't need 5th gear until you reach 65 -70 MPH.

Thank you 52Carl. That is exactly what I was looking for when I was looking at gearing. I also knew tire diameter plays into the equation.

Thank you Peggy M with the edit. You are a peach 😊. I'll watch the paragraph structure in the future. 👍

Just,
I put a 4.64 rear end out of a 2001 Nissan Xterra on my '50 3100. I was worried about it being too steep in 1st gear with 28 inch tires, and it was. I switched to 30.5" radial tires and that dialed it right in. Now 1st gear of my T-5 is usable as first gear instead of granny gear. My overdrive is .73, so my ideal highway speed is 65 MPH at about 2700-2800 RPM. I'll bet I can do 100, but that is probably a bad idea in general

3.73 will work fine. You might want to get a cup of tea...this could take a while as I have a few different scenarios in mind for you. Over the 50+ years I've studied and set up gearing, I've learned two things: most people find 2500 rpm a point at which a gear change "sounds" and "feels" right. For the 1959-1962 235, a shift point of 2500 is about perfect as you've already reached maximum torque at 2000 rpm and at 2500 rpm you have not yet begin the drop-off in torque that will come around 2800 rpm. Torque is after all the important consideration--not horsepower.

The second thing is most people do not enjoy what I've come to call "the cement mixer effect"...meaning it is necessary to shift through three or four gears too quickly because the gear ratio chain is mismatched for the engine and the person is simply trying to get to fifth gear asap. Fortunately you won't have to worry about that, but friends of mine who have simply bought a T5 and a rear end without knowing much about either one have created that problem.

With 30 inch tires, a 3.73 rear end and the T5 you've described and assuming you shift at 2500 rpm, here is what your shift picture will be:
You will shift from first to second at 15 mph.
You will shift from second to third at 25 mph.
You will shift from third to fourth at 40 mph.
You will shift from fourth to fifth at 60 mph. At 65 mph (in fifth gear) you'll drop down to 2100 rpm (which is workable, although I'd be happier with slightly higher)

For the sake of comparison (and because some people for whatever reason don't seem to understand how I can make a T5 with .86 fifth work with a 235 and a 3.07 rear end), if you had a 3.08 rear end, a T5 with a .86 fifth gear, 26.5 inch tires and assuming you shift at 2500 rpm, here is the picture:
You will shift from first to second at 16 mph.
You will shift from second to third at 28 mph.
You will shift from third to fourth at 43 mph.
You will shift from fourth to fifth at 62 mph. At 65 mph (in fifth gear) you'll drop down to 2200 rpm (remember the .86 fifth ratio)

So, is there any difference between what I've got and the 3.73? Not much, as you can see. I drive a bit further before I shift but that's better for city traffic. Very minor difference overall and I really hope it helps folks understand better. In Dallas, we have several long streets with no stop signs or street lights and 40 to 45 mph speed limit. The shift from 3rd to 4th was set specifically for this. I shift to fourth at 43 mph (2500 rpm) and then I can drive along very easily, efficiently and with better economy.

Now for the sake of another point of view let's say you decide to use 28 inch tires and you have the T5 you described plus the 3.73 rear end. Let's see if 2 inches less in tire diameter changes the picture for you a lot or just a bit. Actually if I'm thinking right one factor will be improved...
You will shift from first to second at 14 mph.
You will shift from second to third at 24 mph.
You will shift from third to fourth at 38 mph.
You will shift from fourth to fifth at 56 mph. At 65 mph (in fifth gear) you'll drop down to 2200 rpm (same as me).

In my opinion 28 inch tires will be fine, they will cost you less and they will improve one thing. The shift from first to second and second to third will be almost indistinguishable from the 30 inch diameter option. Shifting to fifth at 56 mph is good and there is the improvement. You increased the cruising speed by 100 rpm. Which believe it or don't will make a difference. I'm fine at 2200 to 2500 rpm and unless I'm in headwinds or very hilly zones all will be Jake. You haven't said where in TN you live so it is not easy to hit the bullseye, but we ought to be able to get you close. Ideally you ought to only do the transmission/rear end/tire size calculation exercise once. Done correctly we should use only the first 4 gears in town and then fifth for the highway. If you're using 5th gear in town, something went very wrong in your calculations or you're about to get a speeding ticket. Hope this is helpful.

And for one more very important note not related to gearing: If you use taller tires on the rear and smaller tires on the front, make absolutely certain to have your caster angle adjusted correctly. Taller in the rear and shorter in the front by definition reduces your caster angle. That makes your truck steer easier but it may cause it to wander. If you fail to have at least 2 to 2.5 degrees of positive caster, even if the rest of your front end is in perfect shape, you'll have unstable steering. 3 degrees is best, but it will increase slightly the effort to steer in a parking lot. I add this because 30 inch tires may not work well for the front of your pickup. It was designed for 6.00 x 16 wheels/tires which are 28 inches tall and skinny by today's standards.

As for a rear end that fits nicely in the AD truck, one option is the 12 bolt rear (late 60s, early 70s) Chevy truck. 15 inch 6 bolt wheels are what it came with. You can even alter the stock 1950s parking brake cables to work with it. Good luck!

I am right below Nashville and in the county not city. I have 4 interstates that I typically have to get on to go anywhere that has distance. They are I24, I65, I840 and I40 and all are 70mph. My commute to the office is about 5 miles on a 55 mph stretch. Not a whole lot of in town and even at that it is typically 40-45 mph. 3rd and 4th gear will be the most used.

Torque is absolute something I have considered. 2500rpm is what I based the calcs off. You align with what I have come up with per the Tremec Gear calculator.

3.73 rear end gear. 30" tire

1st gear 4.03@2500 rpm= 15MPH
2nd gear 2.37@2500 rpm= 25MPH
3rd gear 1.49@2500 rpm= 40MPH
4th gear 1.00@2500 rpm= 59MPH
5th gear .76@2500 rpm=78MPH

You are right a 28" tire doesn't change a great deal. However I was considering a 18' wheel( Dad had 15" with a 225/70 on there) in which a 30" will look good. If I go to a 16" I may end up with a 28" or 29" depending on the aspect ratio. I will not go miss match, so if 30" doesn't work on the front I will go smaller.

On my basicaly stock 54 engine I have a 1979 Chevy Nova rearend and I believe 2.73 gears. It was driven from southern Indiana to the Smokey Mountanins National last weekend. I have made 9 trips to Kansas City, Mo.

Thanks for the Tremec calculator information. Encouraging they and I were at the same place...nice to see, actually.

What I've learned about these is that shallow rubber band type tires are not good. The thinner the tire, the worse it all works and the less you'll enjoy driving it. And the less wide the tire is the better, also. Wide tires tend to not steer very well on these trucks. The suspension in them wasn't made for comfort and the steering works best if all things are like new (kingpins, kingpin bushings, bearings, tie rod ends, drag link ends, all balls, etc...by that I mean no steering play) and if the tires are as close to the original as possible (in terms of diameter and width). Why? Because some things like camber are not adjustable. Well, they are but you won't find many shops today who can do that without screwing it up badly because the axle has to be bent in a cold state (NOT HOT) and once bent it will be out of adjustment for any other tire/wheel except that particular one. There are two adjustments: toe-in/toe-out and caster. 600 x 16 inch tires were used back then and they were crazy common...used on scads of vehicles and may have been the most common size. Now they're essentially gone except for some high dollar repro tires. I use 6 lug 15 inch wheels and P205/75R 15...Hankook Optimo tires I bought on Amazon for something like $55 each a few years ago. Maker claims a diameter of 27.1" but it seems more like 26.5" to me. I expected a pretty horrible tire for that price but they're quiet, have great grip, are all-season, stay balanced and wear very slowly. As I said, thinner tires will steer better and will perform at higher speeds just fine. Plus this size will take bumps really well. A thin tire on an 18" wheel will let you feel even the small bumps. Just something to keep in mind...

Here is an article on low-profile tires which mentions pickups: https://carbuzz.com/features/what-are-low-profile-tires-understanding-the-pros-and-cons/

I have Hancook Optimo tires on the Galaxie, and Mustang. They are excellent tires for the money and handle well.

I have zero interest in low profile tires. I will most likely end up with a 16" rally wheel. It has been what I keep falling back too. However I have been wondering about going to 18" wheels. It should still give me at least 5" of side wall which I don't consider low profile. If I can't get 30" tires to clear at the front then 16" wheels is a given with no more wondering about 18" wheels. I believe everything I have looked at has kept tire with at 8" mostly with 10" on a couple. I would throw a picture of what dad left me on here if knew how, but I am not even sure I can yet.

I have to keep the Hancook in mind. They are missed matched now and at least 2 of them are Firestone Duelers.

Just4Fun, You are well past being moderated and can easily put pictures in your posts and replies. One of the easiest methods is to follow along with the video from Kevin (klhansen) POSTING A PICTURE WITH A CAPTION. If you can get it done that way,check out the post How to add pics to a post for alternate instructions that may work for you.