Which rear end to use

[Rob Fisher]

I am trying to decide which route to take with the rear differential on my 1964 GMC long box. It has a mild SBC and will have a 700R4 installed soon.
I currently have the stock Dana 44 with plans to completely rebuild with new lower gear ratio and some brand of posi-trac. Also planned would be a rear disc brake conversion using a kit from www.tsmmfg.com which would include Cadillac Eldorado rear calipers with integral park brake. The other option would be to put a truck 12 bolt in, again completely rebuilt and using brackets from CaptainFab and '93-'97 F-body calipers with integral park brake or a Wilwood product with the separate small drum brakes in the hub as the park brake..
The questions that I have are:
1. Which rear end to use, Dana 44 or Truck 12 bolt.
2. Which gear ratio to run. (looking to improve off line performance over
the current 3.07:1 in the truck now).
3. Which is better, calipers with integral park brake or the Wilwood style
with the small drum brakes used for the park brake.
Any help or advice that you can offer is appreciated.
Thank you,

[blackedoutharley]

Either differential is fine; the Dana44 is popular with the 4X4 crowds and parts are readily available.
The 12 bolt has been (or was) in use for years and also has good parts availability.

Given that you already have the Dana I vote to reuse that being that there is no fab work needed. Rebuild what you have and go.

Gear ratio would depend on what size tire you are running and what rpm range you want to run in. Given that you have 3.07's now I would say nothing steeper than 3.55's for a good blend of freeway flying with the 700R4 but still enough for better performance.
Again, tire size is going to be a factor in your decision.

As far as the brakes; I am not a fan of the drum type parking brake set up just due to the addition of more parts.

YMMV

[Rob Fisher]

The tires I have are 29" tall and according to an RPM Calculator at Jaws Gear
www.jawsgear.com running a rear end with a ratio of 3.73:1 with the gear ratios of the 700R4 at 60 MPH the engine would be at 1804 RPM, at 70 MPH 2105 RPM and at 80 MPH 2406 RPM. Do you think those RPM's would be OK.
Unfortunately there will be some fabrication involved if I stick to the stock Dana 44, I am installing a Porter Built Stage II rear drop member with trailing arms and air bags, and right now the truck has leaf springs. Not a big deal but I will have to modify the axle perches.
I am also not a fan of all the extra parts in the drum style parking brakes, just not sure which works better.
Thanks again for your input.

[blackedoutharley]

What size tire are they?

If your numbers are correct then go with the 3.73's... in fact you might even run the calculator to see what rpm's it would do with 3.91's.

[Rob Fisher]

The tire size is 29".
I put together a little chart showing engine RPM's at different speeds based on the 29" tall tire and the the 0.696:1 4th gear ratio of the 700R4 for 4 different rear end ratio's.
Still not sure about the Dana 44 though, you do not hear much about them other then on the 4 x 4 sites.

[Rob Fisher]

Does anybody else want to share what they know about the Dana 44.
Any information is appreciated.
Thank you

[Rob Fisher]

Anybody, anybody at all.

[jimmydean]

Capt Fab also makes a kit for the Camaro/Firebird caliper that has the integrated e-brake. I want to go this route on a 12 bolt if I end up passing on the Impala SS rear I am looking at this weekend.

The Impala/Caprice use a lame e-brake setup, but the axle is posi and 3.08 (what I need), so it's a toss up.

[66-PMD-GMC]

There is a 66 BBW in my build area at this moment that I am working on.
It has the same motor/trans combo you have and the small block in that truck likes the 3:73 gears in the 12 bolt that it is sporting.
Having too tall a gear can cause mileage problems just as a gear too low will.
I have a 97 350 vortec powered dually with a 3.42 geared screw in the rear and it get phenomenal mileage on the freeway but suffers a bit on the stop and go city stuff.
These are the only 2 SBC powered truck that I have experience with and the motors seem to like the lower gear over the taller.
I had a dana 44 in my 67 firebird with a 500+ pony Pontiac motor powering it and never once had an issue.
They are very good rear ends. Easily equal in quality to the 12 bolt. I am running a 9" in my 63 pro-street truck.

[Brad54]

The Dana 44 is an EXCELLENT rear end... it's also the longest running rear end in the industry; it's been in everything from Studebakers in the early '50s, to Vipers and Corvettes.
Jeeps, Ford Explorers and Excursions used them too.
Because of their use in Jeeps, take-out posi units are cheap and plentiful: the differentials have "case breaks," meaning a 2-series, 3-searies and 4-series gear set will need a different differential. I don't know what the exact breaks are (they're usually not straight along 2-, 3-, and 4-series lines... it's probably high 2s to low 3s, low- to mid-3s, high-3s and 4s). When Jeep guys need to put 4.11 gears in, their 3-series case ends up on ebay or on the shelf of the local Jeep shop.

Another advantage is that you can get OE rebuild parts, which are superior to aftermarket pieces, including gear sets that set-up better and aren't as prone to whining. They cost more, but are worth it in my opinion. Because these rear ends have been around so long, bearing and seal kits are available at your local parts store, and are pretty affordable.

Posi rebuild clutch kits are also readily available, rather than having to buy a brand new $400+ posi unit.

You can also find an OE finned aluminum rear cover for them... I can't remember the original application, probably Explorer, but I've got one on the wall waiting to go under the truck the next time I change the fluid.

I have a Dana 44 in my '61, with 3.42 gears and 235/75/15 tires, with a NP 833 4-spd OD manual trans, with .73:1 final drive. I haven't done the math in a long time, but it lopes down the highway effortlessly at 80mph.

The gear splits in my trans are pretty close, if not exactly, what yours will be with the auto overdrive.

The only thing to watch out for are axle spline counts: there were 17 and 30 spline axles. Mine originally was 30-spline, and that's what the Jeep axles are. There are a lot of 17-spline applications, so be sure to check that when shopping for a dif.

I'll be putting a Dana 44 under my '54 Buick hot rod when the time comes, rather than the more common Ford 9-inch.

-Brad

[66-PMD-GMC]

Originally Posted by Brad54

The Dana 44 is an EXCELLENT rear end... it's also the longest running rear end in the industry; it's been in everything from Studebakers in the early '50s, to Vipers and Corvettes.
Jeeps, Ford Explorers and Excursions used them too.
Because of their use in Jeeps, take-out posi units are cheap and plentiful: the differentials have "case breaks," meaning a 2-series, 3-searies and 4-series gear set will need a different differential. I don't know what the exact breaks are (they're usually not straight along 2-, 3-, and 4-series lines... it's probably high 2s to low 3s, low- to mid-3s, high-3s and 4s). When Jeep guys need to put 4.11 gears in, their 3-series case ends up on ebay or on the shelf of the local Jeep shop.

Another advantage is that you can get OE rebuild parts, which are superior to aftermarket pieces, including gear sets that set-up better and aren't as prone to whining. They cost more, but are worth it in my opinion. Because these rear ends have been around so long, bearing and seal kits are available at your local parts store, and are pretty affordable.

Posi rebuild clutch kits are also readily available, rather than having to buy a brand new $400+ posi unit.

You can also find an OE finned aluminum rear cover for them... I can't remember the original application, probably Explorer, but I've got one on the wall waiting to go under the truck the next time I change the fluid.

I have a Dana 44 in my '61, with 3.42 gears and 235/75/15 tires, with a NP 833 4-spd OD manual trans, with .73:1 final drive. I haven't done the math in a long time, but it lopes down the highway effortlessly at 80mph.

The gear splits in my trans are pretty close, if not exactly, what yours will be with the auto overdrive.

The only thing to watch out for are axle spline counts: there were 17 and 30 spline axles. Mine originally was 30-spline, and that's what the Jeep axles are. There are a lot of 17-spline applications, so be sure to check that when shopping for a dif.

I'll be putting a Dana 44 under my '54 Buick hot rod when the time comes, rather than the more common Ford 9-inch.

-Brad

[GVDobler]

Originally Posted by Brad54

I have a Dana 44 in my '61, with 3.42 gears and 235/75/15 tires, with a NP 833 4-spd OD manual trans, with .73:1 final drive. I haven't done the math in a long time, but it lopes down the highway effortlessly at 80mph.

-Brad

I get 79.19 mph at 2,300 rpm. Not too bad.

[Brad54]

Originally Posted by GVDobler

I get 79.19 mph at 2,300 rpm. Not too bad.

That sounds right... I don't have a tach, but the thing isn't screaming at all.

Wind resistance is knocking down my Miles Per Gallon a LOT more than engine rpm.

-Brad