8-1/4" to 8-3/4"

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DakotaDuster

DakotaDuster

"I'm all in."
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Ok, for now my main question is will I have to get a shorter driveshaft? The car is a 727 & 8-1/4" right. I'd like to keep the 727, so just wondering if there's a driveshaft length difference between the two rearends?
 
Did it to a F-Body and was able to use the same shaft. On a A I went the from a 8 3/4 to a 8 1/4 and used the same shaft.
 
Converted from a 8.25 to 8 3/4 on my 73 Duster

used the same drive shaft.....and that was 11 yrs ago.....
 
If you need a bit of room;you can move the rear springs back .25 on the front perches, and gain another .25 to .5 by moving the banjo back on the springs. Too much more than that will put the shock bodies into the fuel tank pinchweld. The pinch can be manipulated a bit. But IIRC the difference between those noses is less than 3/4 inch. That axle has to be moved back anyways for big tire clearance.
 
Ok, so it sounds like I'll just have to see when it comes time. That's the first major change to the car. Not that the car if an axle breaker or anything. But there's no point in investing any money in the 8-1/4 if I want to make any decent power and race it(not competitively) later on down the road.
 
Plus you can have multiple chunks, and swap them around as desired. About 1.5 to 1 hrs to do a swap, including the matching speedO gear. Thats a huge advantage,right there.
In the early years of my project, I had different chunks in it several times a year. I had the race chunks (4.30,4.89,and 5.13), the cruisers (2.76 and 2.94), and the streeters (3.23,3.55 and 3.91). I never had a 4.1, or a 4.57 in it though, nor a 3.73.
Enjoy
 
Thank you for the information. I really appreciate it.

When looking for a 8-3/4" rear end are there multiple widths? If so what will or won't fit... If any?
 
Yes, there are several different widths; The As, The early Bs, the Late B & Es, The Cs, and D series pick-ups .There may be more,IDK
Only the As have the sbp( 4" small bolt pattern).All the rest have the lbp( 4.5" large bolt pattern).
The As are 43.5" c/c( center to center of the perchs).Early Bs can be installed by spreading the springs a hair(IIRC they are around an inch wider, c/c).

You didnt say what body or engine you have.Ima guessing its a 73up Dart 318. You should know that the little 8.25 can take quite a licking.So if its a mild 318, you might just slam a SG into that go have fun. Its been said, that the bigger sbms will break it sooner or later, especially on slicks, if they hook.On the street with a teener, I ran the heck out of one, and never killed it.

If you are thinking of tracking your car more than occasionally, this is all moot though,as you will be wanting to fit tall slicks, on wide wheels. This will require custom sbp wheels, or off-the-shelf lbp 15s. And so you will need to have the diff narrowed and custom lbp axles built. In this case just about any old set-up will work for you.
If you go this route, I suggest you buy your wheel and tires first. Then rip all the old stuff out to get it out of the way. Set your new assembled wheel/tires in the tubs,center them up, drop the car down to ride height, and re-center. Then measure the flange to flange distance, and send your rear end out for adjusting.
Of course,you can do it the other way, but IMO it never seems to fit right if you do.And if it ends up too wide, youre almost screwed. If its too narrow, you can always space it out. So measure very, very, carefully. I narrowed mine to fit off-the-shelf, 4.5" bs 15" wheels,of which I had several to chose from.And I liked the look of a 15 x 10 al slot with that bs.
If you are only going to track it a time or two, then a stock-width set-up will do, with custom back-spaced wheels.
 
Well, the previous owner thinks it was originally a slant car but he never really clarified as to why other then mentioning the small axle. Which doesn't necessarily mean it was or wasn't a slant 6 correct? The car is a 74 and currently has a 360 in it, that in my mind is very mild. Any serious track time(as in most weekends out of the summer) won't be for several years I imagine. I think the biggest tire I'd want would be a 275/60/15 drag radial. IMO the car has a really goofy wheel and tire set-up on it now. Well, more so the wheels. The back wheels look like front wheels to me and the front wheels look like back wheels although they are 14s and the rears are 15s.
 
Fronts 14x??

10388194_10153248520051730_5311377903398128862_n.jpg


Rears 15x??

11206053_10153248517846730_502729224991459538_n.jpg



Supposedly the rear wheels have a 1" spacer so they wouldn't hit the leafs. Which to me seems even more so that they were intended to be a front wheel but maybe I'm wrong.

11150995_10153248516861730_6896553191227916358_n.jpg
 
I think slantys got the 7.25. The VIN tag on the apron will tell you what engine,tranny and diff, it came with,as will the build sheet.
The covers on those diffs are different. The 7.25 is kinda odd looking, while the 8.25ers are either roundish or slightly oval, depending on the years.The 8.25 has 3" axle tubes, while the 7.25ers are smaller,perhaps 2.5?
The wheel appearance may be a wheel offset thing. Rears are usually deepdish while fronts are not.I cant say.
If the 360 is mild, staying mild,staying 727, and 275 street tires are going on, the 8.25 with a SG and 3.55s or better, should serve you well.Especially if you can get a 4-spider trac-loc into it.
The thing that kills rear-ends is shock. If the rear tires have excellent traction,and the engine rpm is brought up into the torque band, and is unleashed, all that torque goes into the case/cross pin, then to the spiders and side gears.And finally out the axles.The case to crosspin takes a beating.
So if youre staying A/T, not going to a trans-brake, and installing a 4-spider trac-loc, youre miles ahead.If the diff. is in good shape,currently, it will last thousands and thousands of miles, behind a mild 360, even tracking it.
If you go to slicks, superstock springs and traction aids, all bets are off.
 
Yeah, youre right. That does look odd.It does appear though that you could fit a lot more rubber in the back, which will require a wider wheel, with a deeper dish, and then it will look right again.
 
Oh yeah I know all about shock loading. I have a diesel sled pulling truck lol.

Here's a picture of the rearend. My buddy thought it was a 8-1/4 because the cover on the back side of it.

11053341_10153247995166730_3126245861035772886_n.jpg
 
I will be staying auto as I'm a right leg amputee, but eventually I'd like to get quite a bit more serious with the car but for now... as cheesey as this may sound to hard core racers... I just want it to look some what fast for now and enjoy driving it while I keep learning about it.
 
Yeah it does look like the smallest. Plus the springs look like 4 packs, so that wont do either. Well from what you are saying,Im still inclined to recommend the 8.25er for now, as they are cheap and plentiful. But now you will also need springs,shockplates and a set of U-bolts.This rear will come with 10 x 2ish brakes as well. So if your current rear has 10inchers, you shouldnt need anything else.Dont pay much for the 8.25 unless it comes with a trac-loc, and 3.55s.Most I have seen are 2.76s/2.94s/some 3.23s. A while back, guys here on FABO were practically giving them away. Actually IIRC one guy was giving one away.
 
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