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Old 10-16-2011, 11:37 PM
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Default C3 differential/C4 batwing combo

Been playing around on occasion in the basement with trying to adapt a C4 D36 batwing onto a C3 iron differential housing. I presently have a late C3 batwing on the '69, but the D36 batwing is about 7 pounds lighter than the C3 batwing. I'm mocking up a 3/4" thick adapter "ring" to deal with the different gasket pattern and the difference in the cover depths.



I'm trying to get the batwing correctly located/down, and left/right. Left/right is pretty easy as the bolt patterns are reasonably symmetrical, but the up/down one is a bit more difficult. It can be done reasonably close by eye, but I'm trying to get the C4 batwing located at the same vertical position (relative to the output yoke centerline) as it is on a C4 differential housing. The cover height isn't important with a C3 suspension, but with a C4 suspension it has an effect on the rear toe geometry.

I don't know yet what the weight of the aluminum adapter ring will be (nulling out some of the 7 pound savings with the C4 batwing), but I'll know once I have the physical dimensions of the adapter. I can calculate the adapter volume and then multiply that by the specific weight of aluminum. A couple things in my case will help offset the weight of the adapter. I presently have a fabricated steel bracket that adapts the C4 toe-rod assembly to the C3 batwing. This bracket can be eliminated when using a C4 batwing. Also, due to the different rear spring mounting position I should be able to use slightly shorter (and lighter) spring hanger bolts.

If the adapter works out okay (functionally and weightwise) I'll try installing it over the winter. The batwing widths are different between the C3 and C4 units so I expect to have to cut out the old frame mounts and weld in new ones (again).
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Old 10-16-2011, 11:53 PM
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There are 2 D36 batwings, the one with the thin webbing like you have and with full width webbing. The one you are using is a lot weaker than the beefed up version.

This si the beefier one

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I'd be worried about breaking that one with that ZL powerplant you have

The strong ones were isntalled on the early Corvettes. My 84 Z51 had one of those beefy ones.
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Old 10-17-2011, 12:36 AM
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Interesting. I wasn't aware that there are two different D36 covers. The spare D36 in the background of the picture has the identical batwing. Well, I can still work on the adapter (I'm assuming the bolt pattern stayed the same) and keep an eye on locating one of the beefier batwings.

Thanks for the information. It's greatly appreciated.
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Old 10-17-2011, 12:49 AM
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Do a search on CF, years ago there was someone using a D36 batwing on a D44, the reason was the thinner batwing cover and this allowed the use of a steel stiffener plate that also adapted the bolt holes.

What I however don't understand is why not pick up a D44 and use the whole thing? all you need is to build a pinion mount.
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Old 10-17-2011, 02:50 AM
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Quote:
Originally Posted by Twin_Turbo View Post
Do a search on CF, years ago there was someone using a D36 batwing on a D44, the reason was the thinner batwing cover and this allowed the use of a steel stiffener plate that also adapted the bolt holes.

What I however don't understand is why not pick up a D44 and use the whole thing? all you need is to build a pinion mount.
I've got several spare C3 differentials (with varied ratios and plenty of rebuild parts) laying around, and I've had good luck with their durability. Also, sellers want an arm and a leg for D44 units. I just haven't talked myself into spending that kind of money on a (lighter) piece that's down low and in back.

I've got four D36 units, and they all have the same style batwing. The '84 has the original rear end, but I've bought a few extras over the years. I have (as far as I can remember) a '92/'93 rear suspension under my '51 Chevy pickup, and the assembly in the background of my earlier picture was advertised as a '96 when I bought it a dozen years ago. I can't remember the purchase details of the batwing (and its original differential) I'm using in the picture.

For my information, what D36 years had the beefier batwing?
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Old 10-17-2011, 07:04 AM
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Quote:
Originally Posted by Twin_Turbo View Post
Do a search on CF, years ago there was someone using a D36 batwing on a D44, the reason was the thinner batwing cover and this allowed the use of a steel stiffener plate that also adapted the bolt holes.

What I however don't understand is why not pick up a D44 and use the whole thing? all you need is to build a pinion mount.
Because the dana44 batwing brings a premium just by itself.
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Old 10-17-2011, 09:44 AM
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Didn't you have one cheap?

You could also grab a viper unit the later ones use SV joints and the thin style driveshafts as well.

As for the batwing, I never truly found out what the deal is there. It seems only early cars got them, never saw the beefy ones on the later cars.
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Old 10-17-2011, 01:29 PM
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Quote:
Originally Posted by Twin_Turbo View Post
Didn't you have one cheap?

You could also grab a viper unit the later ones use SV joints and the thin style driveshafts as well.

As for the batwing, I never truly found out what the deal is there. It seems only early cars got them, never saw the beefy ones on the later cars.
I sell nothing cheap! hahaha
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Old 10-18-2011, 02:43 PM
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I'm guessing you're going to coilovers? If not, are you having any issues with the spring mount location?
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Old 10-18-2011, 06:23 PM
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Quote:
Originally Posted by Ralphy View Post
I'm guessing you're going to coilovers? If not, are you having any issues with the spring mount location?
Staying with leaf springs. I'm using a C4 spring on my '69 right now. The C4 springs come in a variety of rates, and can be picked up cheap at swap meets. There's a slight difference in the vertical position of the spring mount (C3 versus C4) but the outer hanger bolt lengths are easy to change if necessary. I was surprised how well the spring swap went.
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