My son came across a 66 Coronet v8 car with a removeable type thrid member rear. What kind is this and would it be a good choice for my 66 Valiant if it should not be too wide? I am going to check out the measurements today. Any words of wisdom?

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That's an 8 3/4 axle which is an excellent upgrade. On your Valiant, your axle width should be about 55.5 inches, vs. the 59.2 inch width of that 8 3/4.

The spring perches on your car are spaced 43" apart, where the perches on the 8 3/4 are 44" apart.

All you should have to do is move the spring perches in 1/2" each and it should drop in. Grab the brake lines that come with it, and the brakes themselves, as your stockers will not fit. Grab the Ubolts and shock mount plate too, for the same reason.

I did this swap into my '74 Duster using an E-body 8 3/4, which is 60.7" wide. Was a bit too wide, but I make up for it by backspacing the wheels a bit. The B-body rear should fit nicely.

I did a writeup with pics of thes swap on my site. Check the Duster page.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

66 Valiant with a 7 1/4" rear should have 53 1/4" between the flanges, and about 43" CL on the perches. The 66 Coronet, should be 55" flange to flange, and 44" CL on the spring perches...this is a pretty common shoehorn into A-bodies, most guys 'cheat' and just pull the leafsprings over 1/2" on each side (I wouldn't do that...but those V8 guys will do anything to get it going faster...)

Check the 3rd member to see if it's a '741' or '742' 8 3/4" rear (741 chunks are easier to come by in some parts of the country and cheaper)....

59.2" is the measurement for the 'fat' 1971+ B-body, and all C-bodies.....

-D.Idiot

I thought that was 63.4" for those year B-bodies. I guess it depends where you measure from.

Yeah, I wouldn't force those springs out to the perches. That'll bind the rear suspension quite nicely.

A common 4X4 swap is a Chevy front axle into a Dodge truck. The Chevy perches are 1" narrower. Some guys put a come-along on the springs and horse them in till they sort of line up, then clamp them down. Then, they complain about poor handling, worn-out bushings and broken parts.

The perches aren't really that hard to move. A few minutes with a torch, or a few more minutes with an angle grinder, and a few seconds with a welder is all it takes.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Thanks Guys,
A few twists of the wrench and $65.00 later I got this puppy home. Tag indicates 2.94 gears, which I suppose is common. As far as the 741 or 742 numerber I didn't see either, or I wasn't looking in the ritght place, I scraped some grease off the left side, there were a bunch of numbers but the only 3 digits were what looked like 358, I am looking in the wrong place? or does it really matter?

Happy motoring!

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go fast, turn left, don't screw up.
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You're really going to have to have some deep backspace wheels to get any kind of tire under a '66 with that rear.

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Official Cookie and Mater Tormentor.

somewhere on the bottom of the 'neck' (left side when looking straight at the pinion)...There will be a typical mopar part number...most people just recite the last 3 digits so the early ones are '741', later ones are '742', and the last evolution became the '489'...gears and chunks are available for all of them, but the popular ones like the 742 and 489 are getting $$$ in some areas just for the center 'chunk'. I've seen trucks, and some older C-bodies in yards that I've passed by with good chunks for the 741...a guy at work had an early 60's truck /6 hydraulic 11" clutch with a 741 suregrip 4.30 rear end....man was it 'granny'...

-D.Idiot

741 it is...I measured my 7 1/4 from outside of drums and came up with 59 1/2" did the same on the 8 1/2 and came up about 60", looks like a good fit...I know when I changed rears in my 64 cuda years ago, I got a sure grip out of a 68 cuda and just shortened drive line and got longer u bolts, didnt have to relocate the mounting pads, but that was from A body to A body. I do more checkin later...its about 10pm and the alarm goes off at 3:00am...later

c-dog

I was obviously asleep when I measured..from outside of drums my 7 1/4 measured 57 1/2 not 59 1/2. I am going to put on discs which might help with the width, but with some creative wheel selection it should work ok. I have about 13" from the "frame" to the inside of the quarter panel lip, I think the Valiant flairs out a bid more than a Dart. At any rate I'll make it work.

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go fast, turn left, don't screw up.
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I figured this one real quick. Does anyone have gear sets available for the 741? I have checked the usual places but all list for the 742 and 489. I would like something in the 3's or am I stuck with the 2:94?
also will these center chunks interchange? Can I put in a 742 or 489 should I want to lay out the cashola?

Thanks
C-dog

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go fast, turn left, don't screw up.
WWW.Mopardropheadcoupe.com

Cycledog......Yes, you can drop in a 742 or 489 "chunk" and that will upgrade you to the later diff. If you haven't yet, you might want to check with Randy's Ring & Pinion.....he might have something for that older rear.
You will run into a small "problem" now, as that B-body rear has a 4.5" bolt pattern where your A-body pattern is a 4" lug circle. Not a big problem, as the next good upgrade is a disc brake setup from a '74-'76 A-body, giving you discs with the larger bolt circle, (unless you've already done this).

BTW.....you'll also have to have your driveshaft shortened, as the 8.75 "nose" is longer than the 7.25.

Roger

Thanks Roger ,
Randy's does have 3 choices other than the 2:94, at least on their website. As far as the bolt pattern, I am planning on disc all the way around.

_________________
go fast, turn left, don't screw up.
WWW.Mopardropheadcoupe.com