Will an 8 3/4 rear end fit in a 73 dart sport?

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ratty dart 340

ratty dart 340

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Hey there, I have a 73 dart sport 340 car. Previous owner swapped in a 1971 360 with 727. Transmission is believed to be numbers matching(not sure). I finally fixed an issue where it would stall after pressing the brake, but now whenever the car starts moving, the rear wheels spin back and forth. Seems like center gears might be shot or the axel bearings. The previous owner swapped in a ford 9 inch from something like a 69 mustang. He put 4.11 gears in it. I am wondering if it’s worth it to put an 8 3/4 in it, or just a different center section for the 9 inch. I would like to avoid shortening the driveshaft if possible. I do know that even with the 340, this car would never have come with a 8 3/4. Thanks
 
If it was done right, I'd leave the 9" in it. It's not like it's a numbers car or anything. It certainly won't affect the value and it's arguably stronger than the 8 3/4.
 
Professor Fate said:
Please elaborate/clarify. Not sure what you mean there.
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Whenever the car has forward inertia, the back wheels will wobble back and forth despite going forward. Kind of hard to explain. In other words, the rear wheels have play. You can manually spin them and there is play. When going to drive, upon releasing the brake, the rear wheels will stop spinning, then spin forward, and will repeat this. If that makes any sense.
 
ratty dart 340 said:
Whenever the car has forward inertia, the back wheels will wobble back and forth despite going forward. Kind of hard to explain. In other words, the rear wheels have play. You can manually spin them and there is play. When going to drive, upon releasing the brake, the rear wheels will stop spinning, then spin forward, and will repeat this. If that makes any sense.
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It doesn't. At least not in print to me. I'm kinda thick when it comes to reading text and applying it without pictures sometimes. But then, I'm kinda thick anyway. lol Any way you can post a video?
 
RustyRatRod said:
It doesn't. At least not in print to me. I'm kinda thick when it comes to reading text and applying it without pictures sometimes. But then, I'm kinda thick anyway. lol Any way you can post a video?
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Unfortunately don’t have a video. And can’t get one for at least a week.

Another thought I just had, is that issue is possibly brake related. Front discs, rear drums. The rear wheels are acting like they are getting caught on something when spinning… so they hesitate(slow down) then spin forward normally for about a quarter turn( of the rear wheel) then seem to get stuck(hesitate) again.
 
Personally, I would find what's wrong with your nine, and fix it. 8 3/4 is not an improvement over a nine, nine parts are EVERYWHERE, and a-body 8 3/4s are ferociously expensive (and have the wrong bolt pattern for you). Early b-body could work, but the nine is already there.
Just as an aside. With both rear wheels off the ground, when you manually spin one rear tire, what does the other rear tire do?
Also: are you dead certain its a nine inch, and not an eight inch?
 
Let's get a bit more info before you start replacing parts.


Do you have the rear end off the ground?

Is the engine and trans and driveshaft turning the rear, or are you spinning a wheel by hand?

What you are describing sounds like 1 of 2 things.

1. The brake drums are out of round and are dragging at the low point
2. The pinion angle is really off and the angle is causing the rear axle to speedup and slow down as the drive shaft rotates
 
ocdart said:
Pics needed! Worth a thousand words each...
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Yea. Just getting some information before I really dive in. I won’t be able to get pics and or videos for at least a week, due to being in a college. The solution might be very simple, I’ll update once I’m able to start wrenching again.

Thanks.
 
Dana67Dart said:
Let's get a bit more info before you start replacing parts.


Do you have the rear end off the ground?

Is the engine and trans and driveshaft turning the rear, or are you spinning a wheel by hand?

What you are describing sounds like 1 of 2 things.

1. The brake drums are out of round and are dragging at the low point
2. The pinion angle is really off and the angle is causing the rear axle to speedup and slow down as the drive shaft rotates
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We had it tested a couple months ago and nothing stood out to us. We had the back on jacks, and manually spun the wheels. Slight play in wheel but we were focused on getting running. Hopefully next weekend I will be able to do more testing and should find the problem. I should have been more clear. The main idea of this thread was to hear opinions on weather or not I should replace the rearend, while I’m back there. Thanks
 
It is absolutely normal for the rear drum brakes to drag in a spot. When you spin by hand you would feel and hear a scrap scrap scrap sound.

As for looseness. How loose is loose? There will be a little play in and out or up and down but it should be more of a sound you can hear rather than feel.

As for replacing the rear...

If it was professionally installed no reason to change. ford 9" are bullet proof as compared to 8 3/4 and probably a Dana 60 as well (I'll get flack for that)

Plus parts are readily available and cheaper with more variety.
 
Dana67Dart said:
It is absolutely normal for the rear drum brakes to drag in a spot. When you spin by hand you would feel and hear a scrap scrap scrap sound.

As for looseness. How loose is loose? There will be a little play in and out or up and down but it should be more of a sound you can hear rather than feel.

As for replacing the rear...

If it was professionally installed no reason to change. ford 9" are bullet proof as compared to 8 3/4 and probably a Dana 60 as well (I'll get flack for that)

Plus parts are readily available and cheaper with more variety.
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When I drove it the other day, there was a slight shake on whole car, and a faint sound. Sounded more clunky instead of scrapey like brakes.

Have many things to check when I can next..

And yea I think I will keep the 9 inch, but will replace the spider gears, if that’s what the problem ends up to be.
 
(I'll get flak for that) LOL. Good natured flak only, from me.
Comparing a 9" to a 60, it depends a great deal on what's inside, or done, to the 9". ALL car Dana 60s are strong. Good clutch suregrip, 35 spline axles most of the time (the 23s and 30s aren't bad). Giant r&p.
I'd put my nines up against a Dana, but there's LOTS of good aftermarket parts in them. I would NOT put a gray iron center, weak stock Ford posi, 28 spline axles, in the same strength universe as a Dana 60. Maybe not even as good as an 8 3/4.
(My nines have strange 33 spline axles and spool, rear brace, nodular case and pinion support, billet yoke, and jfz disc brakes. I think the only Ford part is the narrowed housings.)
 
33IMP said:
(I'll get flak for that) LOL. Good natured flak only, from me.
Comparing a 9" to a 60, it depends a great deal on what's inside, or done, to the 9". ALL car Dana 60s are strong. Good clutch suregrip, 35 spline axles most of the time (the 23s and 30s aren't bad). Giant r&p.
I'd put my nines up against a Dana, but there's LOTS of good aftermarket parts in them. I would NOT put a gray iron center, weak stock Ford posi, 28 spline axles, in the same strength universe as a Dana 60. Maybe not even as good as an 8 3/4.
(My nines have strange 33 spline axles and spool, rear brace, nodular case and pinion support, billet yoke, and jfz disc brakes. I think the only Ford part is the narrowed housings.)
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Very interesting. It sure does suck being away from it. Every second I want to go work on it. Too bad college is somewhat important.
 
Wheels wobbling? Are they fully seated on the drums? If steel wheels, usually, the center register to wheel fit is very important (hub centric).
 
crackedback said:
Wheels wobbling? Are they fully seated on the drums? If steel wheels, usually, the center register to wheel fit is very important (hub centric).
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There is a difference between the Ford and Mopar hub size as well. I don't remember for certain but I think the Ford hub is smaller.
 
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