dumb ? #2 - iroc rear end vs 76 dart swinger rear end

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jasonmrenda

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well i have the 76 parted and gone to Joe for his shriners build. so as he was looking the 76 over befor ehe left he said he thinks the rear axle i have is a Dana 60. i'll snap some pics but i have no idea.

so assuming it is NOT a D60, and it is the stock unit for the 318 equipped 76 swinger, what is a better axle to use? this one or one from a 88 iroc? i have the iroc one and it has disc brakes on it - that's the only reason i was cnsidering it. are the disk conversion kits for the rear axles of the swinger super expensive?

just curious.
 
Its probably an 8 1/4" rear, you can check with this...

moparaxleguide.jpg


If it is, I'd definitely stay with it, the 8.25 isn't a bad rear behind a mild small block. There's a chance its also a 7 1/4", although I think by '76 they had gone away from those ( I have a '74 Dart with a 318 and a 7 1/4 though, bad luck!). The 7 1/4 is a time bomb, it will break eventually. But I still wouldn't swap it with anything off an IROC.
 
cool - i just degreased it a bit and compared it to that chart and it most resembles the 8 1/4. good enough for me as i dont plan on any racing. is it worth/expensive to get rear discs or just keep the drums? i may need to replace the drum internals just to be sure that everything is all set.
 
You can just count the # of bolts on the housing, the 7 1/4 has 9, the 8 1/4 has 10. Also, the axles tubes for the 7 1/4 are 2 1/2" in diameter vs 3.

I had thought that by '76 the 7 1/4 had been phased out, but I'm not 100% on that. The one source I found said it was gone in '73, but since I have one in my '74 I guess not.

As far as the brakes go, the drums will really be fine. Mopars had pretty decent brakes on them to start off with vs other makes, and if you're not planning on racing the rear drums, when adjusted properly, work great.

If you really wanted to improve the braking, find yourself a pair of 11 3/4" caliper adapters off a later model Chrysler (cordoba, diplomat etc) and buy a set of 11 3/4" front disks. They offer a significant improvement, and since you've got a '76 they'll fit right onto your spindles. They also use the same calipers, so really the only thing you'll need is the caliper adapters and new rotors. Since somewhere between 70-80% of the braking is done with the front wheels this will be a much more effective upgrade.

Adaptors

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=150358672381
Rotors

http://cgi.ebay.com/ebaymotors/1975-1983-Chrysler-Cordoba-Mopar-Cross-Drilled-Rotors_W0QQitemZ250359352790QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item3a4a948dd6&_trksid=p4506.m20.l1116


I run the 11 3/4" set up on my Challenger, works great even for the bigger car.
 
Not all 8 1/4 rear ends are the same, those with a 2.45 ratio only can fit that ratio.

I personally never have been in or driven a stock A body w/discs that didn't try to spin like a top during a panic stop because the stock one size fits all proportioning is so far from right. And if it's raining, forget it, it WILL spin like a top.

An adjustable proportioning valve will help controllability, just remember it always dials out rear braking to slow down the onset of lockup and reduces overall braking. It NEVER adds to the total braking.

A better solution is to slightly reduce the brake cylinder piston diameter.

The best solution would be rear discs, with rotors and calipers sized proportionally to whatever is being run at the front.
 
Reducing the size of the rear wheel cylinders will help bias a lot. Also, I think the caliper piston diameter was increased in 76 to address this. 11.75" front rotors with stock A-body 10" rear drums would be a good place to start.
 
I have 73+ A-body disks and 10" by 2.5" drums out back with the stock proportioning valve in my 68 Barracuda. In the almost 40k miles I have put on this set-up I have not had any issues with premature rear wheel lock up.
 
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