The Stovebolt Site Forums The Shop Area Driveline Swapping AD to open drive

Is it possible to replace the guts from a later 50's rear into a '52, converting it to open drive and a better selection of gear ratios?
I've been told that it is a boltin upgrade.
I found it hard to believe and thought I'd ask.

Yup If you're referring to a 1/2 ton, you can use the center section from a '55-'62. I just did this swap this summer with a '61 3.90 rear. You will have to weld up the apring perches where they pivot at the axle. I also had to grind a little of the axle housing opening so the ring gear would clear for installation.

Yes, '55 through '62, center section only. You use your '50 housing and axles, you can also switch out to Bendix brakes if desired. Axle perches will be burned off and then an axle saddle is substituted. Better selection, short ans. NO, you will go from your 4.11 to a 3.90, that will provide an open driveshaft so that you can use an overdrive trans., like a T-5 if highway speeds are your goal.

You will also need to change the tranny from a closed to open driveline.
I switched out my tranny to a SM420, open drive, 1955.1 rear gears, and axle housing (ne need to mess with welding up the pivot type perches

I'm dense guys, is there a tech article I can see pics? I get lost when you mention replacing the center section and grinding/welding spring perches.

You are 'lost' and you list yourself as:

Occupation: automotive fabrication shop
Hobbies: Fishing, traditional hotrods ????

Use the search function. We don't have a Tech Article for this procedure yet, there are 'traditionalists' who want to put the truck back to as close as possible to 65 years ago, 'period hop-up guys' who heat it up a bit and change drivetrain, transmission, and 'people who want to put a v-ate in there' power windows IFS, AC, etc.

What's YOUR objective? Time to go back to the guy who said it was "a...bolt-in up-grade" and ask him to be specific. The above posts by myself and others have pointed you in the right direction.

The center section... the pumpkin, third member, etc (whatever YOU call it in your region). If you need to... google image "third member"... but if you need to do that, I'm not sure you should be doing this project yourself...

In regards to the spring perches needing welding. With the torque tube driveline, the spring perches (connecting part between axle housing and springs) are made to pivot for when the suspension traveled. In modern drivelines, we have u-joints and slip joints, etc. (those with more experience can correct me)

Ahh, got it. The springperch work is needed because of the torque tube replacement and not because of the centersection. Thats what confused me.
There is a huge difference between a 'center section' and a 3rd member and the early 12bolt has a 3rd member, the truck does not.

Cosmo, go to my website: www.clarkecountyspeed.com
I am good enough to admit I don't know everything.

OJ, you don't know everything but, you know a TON OF STUFF!!! Welcome to the site!

Thank you Sir, I tip my hat to you.

I am not as smart as some of you, so I just got a 1955 1st series rear end. It fits our trucks like it belongs there. 3.90 gear set means about 65-75 on the road, I can live with that.

I then got a Borg R10 unit behind my 3 speed sag which bolts right to the bell housing without worry, then a driveshaft out of a 62 suburban.

The only thing I havent told you yet is that you need to make an adapter plate to move the stock leaf spring perch to center.

We REALLY need a How-To article on this subject. I would love to get some of you guys together to THINK TANK this one out.

Deve

RE: Center section swap, perch welding and adding bendix: What does all this gain over just putting in a later rear end? 55.1, 55.2-66 and up.

It keeps the stock axle housing, which is the correct width for the truck.

No later WMS-WMS is the same or within 1", 1/2" per side?

I'm sure that there are, but none with the correct 6 x 5.5 bolt pattern. If you're not doing a 5 lug conversion on the front, and want to maintain a reasonably stock look, the 3rd member swap is the best viable alternative, other than perhaps swapping the entire rear end from a '55-'59 truck.

Another bolt-in "upgrade" is the 3.55 Ring & Pinion conversion in the original 47-55 GM 1/2 ton enclosed drive-shaft rear end.

I went from Deve's 3.90 rear-end (which was standard in my 54) to the 3.55. I have never regretted this conversion, especially because I also replaced all bearings and seals. My Suburban is remarkably quiet at 60-65mph (I attribute this to good new bearings and a tight differential). The only reason I do not normally go faster is that my MPG reduces dramatically after 65mpg (wind resistance, I assume). I impress my friends (and win bets) by taking it up to 90mph for a few seconds a few times every year.

That is my tact when answering questions from generic people who I dont know the expertise level, knowledge, anything about them. No offense to them, I was YOU once. But if you start with the idea of a 55-59 rear end, which just bolts right up, you can then later if you wish, change the gearset as Tim stated.

But if you do that, you have done the heavy lifting already, since you now have open driveline (upgradeable) putting you in the ballpark of your goal.

There is NO right answer. The minute you think there is, someone wants to put a positrac, T5, LS package in their truck. Just saying what I did. Im good to go.

Tim

Next time we see each other, which I hope is soon, I 'd like a ride shotgun at 90 mph please....

There is just something about a 261 at speed that just makes me smile.

I'll let you drive it, Sweet
ATHS 2015 at York, PA

You can pay the fine if we get stopped. The 261 now has a GMC Holley AA-1 carburetor with adjustable jets (à la Bill Miles' impressive 302).

I have a mid to late 60s six lug 12 bolt from a half ton truck which visually meets your description of pretty danged close looking to stock width. With the skinny tires, it looks stock to me, if you don't look at the rear differential cover. Then when you see the 12 bolts you'll say, "Cool! A 12 bolt!"

I think in all fairness a rough cost comparison of the basic mph/decreased rpm's are in order.

From Patricks site the 3.55 conversion is about $1000, shipping included, you will be doing all the work. This method can pretty much be done in a weekend. I expect some feedback here.

For my 3.90 conversion, the center section was $125 from a boneyard, another $200 for the bearings for the axles and differential, crush sleeve, etc., $100 for the open driveshaft, $125 for my Borg-Warner 3sp+od, $75 for it's rebuild kit, $25 for axle saddles and another $25 for the spring relocation kit, for a grand total of $675. I wasn't by far the first to do this but acquired my knowledge from an incredible source...Jack Halton, past president of Inliner's International who made bi-yearly trips from FLA to VA-PA in his beloved GMC with a 302 ci and the aforementioned drivetrain combination. I was lucky enough to call this man friend.

The extended 3.90 method with overdrive will take much more time and without hunting down the scarce getting scarcer by the day Borg-Warner 3sp+od one can now go to a T-5 which is stout enough for our trucks.

With the above combination .70 overdrive and 3.90 rear my rear end is at 2.73 in 3rd overdrive, 70-75 mph is at 21-22 hundred rpms, a delight to drive on long trips and economical as well.

Yup, Cosmo, thats my setup. I am good with it. These trucks were meant to drive 45-50mph. If I can do 50% better, Im just fine. You cant drive too fast, otherwise you would be taking away from other peoples enjoyment looking at the old truck!

Thanks for all the input, this is an interesting subject. It seems like theres' lots of ways to get there, and they're all the right way.
I'm going to go check out this patricks' conversion Cosmo, thanks for the detailed explanation of you did yours'

You are welcome. I am a dd/only vehicle guy so in the planning there was a long term thinking to go to the open drive with od. I think the 3.55 makes a lot of sense, especially if you're not going to be putting 5k/year on the truck. If you were you can foresee how an overdrive would be much more economical over the long run.

Early on when I first got my truck it had bias plys and I thought I was going to wreck every ten seconds as it 'tracked' linear splits/breaks in the road and I had to fight it off. Got my radials on stock rims no tubes for 18 years now, one week after taking ownership. My torque tube differential imploded and having a second vehicle at the time I then went with Jack Halton's advice for the open conversion. He actually sold me my first '62 3sp+od that lasted 14 years, had a catastrophic failure of second gear and then installed 'THE HOLY GRAIL' (at least MY HG)., a '69 all-synchro Saginaw/Borg-Warner 3 sp+od, now two happy years after the rebuild.

Cheers,

Hello and welcome to "Stovebolt." I did the swap on my 1949 1/2 ton and it was not hard at all. Most important is either weld up the spring perches or change to new spring perches. Either way you've got to do some welding. My ratio is now a 3.90.1 the new drive shaft cost a little over $200.00. I'm pleased with the swap but would rather have like a 3.55.1 ratio, or somewhere around that. Good luck. Steven

I made an adapter plate for my first restoration. Its just a 1/4 inch by 1-1/2"x 6" plate with a hole in the center, and a pin on the other side to move it to center. On my second restoration, I went ahead and just had new springs made with the 1955 spec.

An alternative might be a swap to a 55-57 Chevy passenger car rear end housing. The center section is interchangeable from 55-64, and gearsets are readily available that include ratios like 3.70, 3.55, 3.36 and even 3.08 if you want to give up any hauling capacity or trailer towing ability. It's possible to get axles made with 6-lug flanges, or convert the front to 5 lugs with early 1950's Chevy passenger car hubs. Disc brake conversion kits are also available for the tri-5 rear end housings.
Jerry