The Stovebolt Site Forums The Shop Area Driveline AD rear end options

Starting to think about a swap. The 55-62 HO30/ 55T in my 51 3100 is at least half worn worn out. I’d like to keep my stock 16 inch 6 lug wheels.

Parts to rebuild this particular rear are expensive and the expertise to do so is probably scarce, although I think I’ve found the right guy that could do it.

Actually the old timer that could do this work was the one who recommended looking for a more modern rear.

* I’ve seen the early Chevy Colorado rear recommended.

* Somewhere I’ve seen Coilover recommend a Ford Explorer rear and use steel adapter to get back to 6 lug.

* I’ve heard of of Camaro/firebird rears being about the right width, but then again you’re looking at adapters

What else should be be looking out for?

What transmission are you running?

SM420 open driveshaft. But have a t5 waiting in the wings.

I would make the decision on which transmission you plan on ending up with before i would select a rear end with emphasis on the gear ratio.
A SM420 will need highway gears in the rear end. A T-5 will benefit greatly from a rearend ratio between 3.73 and 4.64, depending on the the overdrive ratio that comes in the T-5.
If the 5th gear ratio .86, a 3.73 rearend would likely be optimal.
It the 5th gear ratio .73, a ratio as high as 4.64 would be recommendable.
Keep in mind that you can dial in the setup by selecting a specific tire diameter.
I have a T-5 with a 2001 Nissan Xterra six lug (Chevy pattern) limited slip axle with a ratio of 4.64. I tweaked it into perfection by changing to 30.5" diameter tires.
With this set up, I can pull a tree stump, and drag it down the road at 80 MPH.

My tires are 215/85r16. Need to go look up the OD ratio on the t5. I had it at one time and forgot.

Did you have to have the Nissan hubs drilled for different studs? That’s an interesting option. Never knew they were 6 lug.

I think they came that way, Toyota LC, etc., also.

Ed

The Xterra/Frontier rear seems like a really good option from a width and lug pattern standpoint. I think they’d be easy to find as well.

Curious how folks have done the wheel stud conversion (or not).

The Toyota 2wd are 5 lug. A plastic wheel lug pattern gauge and a tape measure plus a visit to a junkyard are an option. The Explorer solid axle rears are getting a bit harder to find but not scarce yet. Most in yards now have the swing axle rear. Used a Trailblazer rear in a recent swap and would NOT recommend it.

Evan, just curious as to why you would not recommend the Trailblazer set up.

Don’t they have an odd bolt pattern?

Ed

I’m under the understanding that the Colorado and Trailblazer have a 6 by 5.5 pattern. It’s expressed in metric terms sometimes.

Yep, later trucks and cars (newer than 1999 as my F250 is metric) use metric patterns. 6 on 139mm is close to 6 on 5.5 inches. But not really close enough that the wheels for earlier vehicles will fit right. Someone is going thru an issue like that on a disc brake swap right now.

Okay, for another opinion (slanted toward being able to still use your pickup as a pickup, enjoy all 5 of those gears usefully and also have nice economy on the highway): Find a rear end from a late 1960s 1/2 ton truck. It will be a 12 bolt and made very well. The width will be almost perfect---within 3/4 inch or so. If you're lucky, you can find a 3.07 ratio. And on another note if you had bought a brand new pickup in 1967, you could have had the 230 six coupled with the 3.07 rear end...it was an option along with 3.73 or 4.11. You could also have gotten the 3.07 in the El Camino...along with the overdrive transmission if you got the 3.73 rear end (and please keep this in mind as I'll hark back in a moment). I've had some people tell me "oh, well matching the 3.07 to an automatic transmission changes everything." Yes, but not in a good way. The automatic had 2 speeds and a 1 to 1 final gear ratio, so if anything it made it worse.

If you have the T5 with the ratio chain that begins with the first gear as 4.03 and ends with fifth gear being .86, you are good to go with a 12 bolt rear of 3.07 and you'll have the 6 bolt hubs. Really? Yes, I've explained this before...maybe 20 times here and equally as many times on other forums. It is a way to make the 5 speed mate with the 235 as if it was designed for it. With your OEM gearing (with the 235) your overall first gear ratio was 12.08 (2.94 x 4.11). This is just perfect if you want to load 800 to 1000 pounds of "stuff" in your bed and drive without problems. And it is likewise ok if you just want to carry a dozen 2 x 4s over to your friend's house. The GM engineers didn't choose this ratio because they were dummies, by the way. If you want an engineer's viewpoint on this from a man who was there at the time, please call Tom Langdon. Please tell him I said "howdy from Texas." He and I have discussed this many times over the years. With T5 first gear of 4.03 and a rear of 3.07, you get a first gear overall of 12.37...two and a half percent off OEM...which is as close as you can get using a T5. Second and third will follow along this same OEM pattern with only fractional differences and when I hit 4th gear I am enjoying a 25% reduction from that annoying and gas guzzling 4.11. And then if I'm on a mildly hilly to flat highway with no headwind problems I pick up another 14% reduction by going to fifth. You do need a 235 made from 1959 forward or at least the camshaft GM designed for those years. And that is because the 1959 through 1962 235 produced higher torque at lower rpm. GM tells why and how they did this in their corporate data and you can read this on their Heritage Pages. Take a look at the torque curve of the 235 from those years while you're at it. At 1800 rpm, you're in spitting distance of making as much torque as you're going to produce and that line stays flat until you almost reach 2700 rpm. It is a beautiful and not very common thing to have a max torque line running flat for nearly 1000 rpm. In fifth, at 65 mph my engine is loping along at about 21~2200 rpm. You mentioned a 3.73. Let's consider a 3.73 rear and a 4.03 first. This gives you an overall first gear ratio of 15.03. That is way more than I like and a factor of 2.66 higher than your truck was designed to have. Which is very notable. Honestly even if you live in a very mountainous area it will tire you rapidly and remind you of a cement mixer. Unless of course you plan to haul a heavy trailer around frequently. You'll be wanting to shift from first to second about halfway through a city intersection. By the way, why did everyone start in 2nd gear with the SM420? Because it had a second gear ratio of 3.57 to 1. 3.57 x 4.11 = 14.67 overall. Even that is more "oomph" than you need for overall first gear unless you're hauling something heavier than a 1/2 ton pickup was designed to do. The difference of a factor of 1+ in your overall first gear ratio matters more than you might think. A factor of 2+ and greater than that is fine if you're wanting to pull barns down or carry 2000 pounds. Not good for driving around in a 1/2 ton pickup, however. Study what GM engineers used in 1/2 ton pickups. As I mentioned, these engineers didn't choose those ratios because they were stupid and they stuck to them for many years when the words "light pickup and inline six" were in the same sentence.

Now, I mentioned the 3 speed overdrive you could have had in 1967. It was a 30% reduction. So let's see what that does for us. Let's say you had the 230 six with a 3.73 rear (a friend of mine had this in an El Camino he bought new) with a 3 speed overdrive. 3.73 x .7 equals a final rear end ratio of 2.61. With mine, I have .86 x 3.07 or a final rear end ratio of 2.64. As for weight the 1967 El Camino weighed 3200 pounds. My 1952 Chevy truck? The same...3200 pounds (actually a bit less because the T5 weighs only 75 pounds). Anyway that's the homework I did on all this...and it works no matter which gear I'm using. The neat thing is if I get into a very hilly to mountainous area, I simply shift back to 4th and I still have the benefit of a 3.07 rear end. Now if I have 1000 pounds in the bed and I find driving on the highway to be taxing on the engine...I simply shift back to 3rd gear and I have an overall ratio of 4.57 (and truthfully closer to 4.11 because I'm using 15 inch wheels). Remember, please with the OEM 3 speed, I would have had 4.11. Literally all bases are covered with this approach and the OEM light truck scheme is preserved as close as it possibly can be. Friends of mine have gone out, bought a T5 without checking the ratio chain at all and a rear end without having any idea whatsoever what it was. Almost every one of them has told me the T5 just didn't work for them. One of them admitted he had a 5 speed with only 3 marginally useful gears.

Now I should add this important gas mileage fact: 55mph is an ideal speed for the AD truck. At any speed over 55, wind drag gets exponentially cuckoo. And it isn't just the AD truck, although the AD isn't exactly heralded for aerodynamic superiority. If I drive our Subaru Forester (which is more efficient than the 1952 Chevy pickup will ever be) at 57 mph on flat to mildly hilly roads without strong headwind, I'll get 40 mpg. If I increase the speed to 65 mph, gas mileage drops to between 30 summer and a max of 32 winter.

My two cents worth. Hope it helps.

The Xterra swap was the easiest swap ever. The width is correct, the wheels are Chevy 6 lug pattern , and the single cable operated parking brakes just needed to have the cable attached to one of the original parking brake levers on the passenger side of the parking brake cross bar. I ground the original leaf spring perches off of the axle, cut them lengthwise and narrowed them to 1 3/4" and welded the halves back together, and welded them to the axles in the correct locations for the Chevrolet truck springs.

Did you just go ahead and use the Nissan metric studs?

Why not the Trailblazer rear? I'm contemplating using the rear out of my 04 and re-drilling to 6x5.5 vs. the factory 6x5. I know redrilling to a 5 lug pattern is near impossible.

Good reading.

How much would my taller tires (215/85r16) change your calculus on an ideal rear end?

Quick answer: it will help notably if you use a 3.73 rear end with the tall tires you have. Basically the 215/85r16 should have a diameter of apx 30.5". The tires I'm using (205/75r15) have a diameter of apx 27" (all tires will vary a bit, but we can use those numbers). Your original 6.00-16 tires were 28 to 28.5 inches in diameter. I've always used 28" because it was easy to remember...16" + 6" + 6" = 28", but as I recall 28.5" is the amount the tire industry used. But the key is to compare your tire height to mine and the 3.73 to 3.07. That's where it gets interesting.

Going through the rpm/mph calculations, using 30.5" diameter tires and a 3.73 rear end with the same transmission gear chain I have (4.03, 2.37, 1.49, 1.00, .86), you will be just fine. The best news is you'll be able to stay in first gear until around 15~16 mph. And after you're through 4 gears and go in 5th, your rpms will fall back to 2100~2200 at 60 mph...which is right where I am. For contrast, however if you had my wheels/tires/transmission and the 3.73 rear end and wanted to shift at 2500 rpm, you'd be going from 1st to 2nd at 12 to 13 mph. The extra 3 mph may not seem like much, but at that speed it will make the difference between needing to shift too soon or wind your engine up another 500 rpm. But I should add I drive in city traffic...which is monumentally different than traffic in a small town or village.

I don't recall what I used for lug nuts. I believe that axle from an Xterra is actually a Dana which is probably why the bolt pattern is right for old Chevy rims.

I have a 79 nova but again, adapters. I also have a 79-pacer front end. and I use 6-hole multi-lug hole wheels.

I need to do Lugnutz’s suggested procedure to verify gearing of my t5.

I have a 52 with a 216 engine. Will this discussion apply to my engine as well? I currently still have the Granny 4 speed and closed driveshaft.

Mike, the 216 will produce less torque (and horsepower) and the engine has lower compression, so it sort of depends on what you're hoping to accomplish and how healthy your engine is. Are you thinking of making changes?

Jon, I’ve located a 6 lug 71 gmc. Would that be the same width as the late 60s rear of which you spoke?

The T-5 swap will do the same thing to a 216 as it does to a 235. Improve the overall performance of the truck by giving you more gears which keeps your engine's RPM at the optimum powerband of the engine every time you shift gears.
No more lugging right after a swift followed by making the engine scream before the next shift to prevent the engine from lugging right after that shift. It is remarkable what that T-5 does to a stovebolt engine.