Let’s talk about the 8-1/4” diff

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TT5.9mag

TT5.9mag

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This should be a fun little topic. I’m planning to do something most car guys will say is not very smart. So I figured I’d ask and find out how many of you guys are just like me, dumb. How much power have YOU successfully put through an 8-1/4 rear end? Not just cruising around, but actually used and abused, street or strip. I am not yet to the point where I am ready to replace the diff in my D100 but I am to the point where I will be staging it at a drag strip and pushing the little red button (most likely after the 1-2 shift, but you know how that goes). This truck is 4200lbs has 3:55 gears with a peg leg on a street tire with stock type suspension and parts store shocks, so I’m not dead hooking even on chewing gum. The 360 magnum dynod at 365hp and I’m going to hit it with 100 shot of gas. What says you? Am I crazy? Will it last? Will it blow up on the first hit? Am I a glutton for punishment?Ready……..go!
 
if you're rolling on 400 treadwear tires i don't even think i'd worry about it, especially if the hit is from a roll after the shift.

not an apples to apple comp, but i had an 8.25 under the dart with 3.55's and abused the **** out of it side stepping the clutch on the street and banzai runs at buttonwillow, the springs and a bunch of autox.

i'd say if you keep the one wheel peels to a moderate amount that it lives just fine for awhile.
 
junkyardhero said:
if you're rolling on 400 treadwear tires i don't even think i'd worry about it, especially if the hit is from a roll after the shift.

not an apples to apple comp, but i had an 8.25 under the dart with 3.55's and abused the **** out of it side stepping the clutch on the street and banzai runs at buttonwillow, the springs and a bunch of autox.

i'd say if you keep the one wheel peels to a moderate amount that it lives just fine for awhile.
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I’ll look at the treadwear on the street tires, they’re light truck style so probably pretty close to the 400 mark. I do have a set of 325 drag radials on wheels that I considered briefly.
 
One of these might help a little
LPW
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There was a point where I just really wanted to get an 8.75 under my stock ‘73 340 4-speed Duster because of the perceived weakness of the 8.25. Then I read some old HR magazines from the mid-70’s about some dudes running the 8.25 like Glidden and also Judy Lilly
 
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The Chrysler 9.25 from the 1st gens is a direct bolt in swap same width and all even the driveshaft length stays the same.. Just get a pre 85 axle to keep the 5 on 4.5 pattern.
 
go-fish said:
One of these might help a little
LPW
View attachment 1716433638

There was a point where I just really wanted to get an 8.75 under my stock ‘73 340 4-speed Duster because of the perceived weakness of the 8.25. Then I read some old HR magazines from the mid-70’s about some dudes running the 8.25.
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Well I like the idea but I probably won’t be spending any amount of money on the stock diff. It’ll live till it doesn’t then get replaced. At least that’s my current thinking.
 
TT5.9mag said:
I’m planning to do something most car guys will say is not very smart.
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I like the sound of this. It is right up my alley. I've done things that were not smart.

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In 1998-99, I made a couple home movies where I jumped and crashed a few A body cars.
Good times....
 
318willrun said:
8.25 rear ends are tougher than most give credit. But many don't run them because the drag strips don't like C clips
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I think that’s a valid argument. I’ve certainly never blown one up, but also I’ve never tried. I just get rid of em. This time I figured why not see what it’ll take. I could be talked into doing a c-clip eliminator type deal for saftey reasons. I’ll look in to that. Thanks.
 
I ran an 8 1/4 in the 73 Scamp (my avatar) that I had for many years. Aftermarket 3.90 gears with an Auburn cone type sure grip. Factory axles. Factory cover. No bracing or anything. Car was not lightened at all.

It had multiple engine combinations. One was a mild 360 with a 100 shot of nitrous. 235/60/15 Mickey Thompson drag radials at the strip. Best time was in the 12.2s if memory serves. Lots of passes on that combo. Also ran a hotter 360 with better heads and no nitrous with the drag radials. I think that combo ran very low 13s. Never had a single problem with it. I sold the car to a guy I know several years ago and it's still going strong (he rarely races it - mostly street driven).

Your truck is obviously heavier than my Scamp so that is an additional factor. But overall I was very impressed with the 8 1/4.
 
8.25 were behind 340's, 360 4bbl's, in D150's that pulled and worked, and I do believe some C-bodies with big blocks... All that speaks something for the 8.25 rear ends...
Now, with 27 spline axles I wouldn't use a transbrake or dump a clutch with slicks and 500 ft lbs of torque... you know what I mean
 
I really doubt the 8 1/4" axle was ever behind a C body with a big block when the 9 1/4" axle was commonly used.
 
Some 80's dodge vans had the 8.25. My dad had an auto repair shop and a customer had a van with the 8.25. Never did my dad do any work to the rear. Just fluid changes and brake jobs. As a matter of fact he rarely had mopars for major repairs. Only when people really neglected the poor mopars!
 
QuickDart360 said:
Some 80's dodge vans had the 8.25. My dad had an auto repair shop and a customer had a van with the 8.25. Never did my dad do any work to the rear. Just fluid changes and brake jobs. As a matter of fact he rarely had mopars for major repairs. Only when people really neglected the poor mopars!
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B250 vans were 8.25 as well as the B100's and such for years and years. 8 lug bigger rears were B350's
Let's not forget all the Dakota's and Jeeps with 8.25 rear end...
 
Out here, I have never seen an 8 1/4" axle in a 3/4 ton anything. It has been the 9 1/4" axle on light duty GVWR 3/4 tons then the heavier duty ones stepped up to the Dana 60.
 
Kern Dog said:
Out here, I have never seen an 8 1/4" axle in a 3/4 ton anything. It has been the 9 1/4" axle on light duty GVWR 3/4 tons then the heavier duty ones stepped up to the Dana 60.
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If you are talking vans, I can tell you, i have currently in my possession a '89 B250 with a 8.25. In fact, if you see a pre-94 Van with 5 lugs, I'm betting 8.25 for yes, even the B250's
 
And Ramchargers.... many ramchargers came with 8.25's
 
That is fine.

318willrun said:
Lets clarify, it's often called the 8 3/8 rear in trucks and such LOL
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I don't know why you would actually laugh out loud about a rear axle but I do laugh at other things that you may find strange.
The 70 Charger standard axle was an 8 1/4" unit. Slant six, 318 and 383 2 barrel cars got this axle. The 383 4 barrel got the 8 3/4" axle.
I'd be surprised to see any C body with an 8 1/4" unit. Years of junkyard crawling and I've never seen one. If they were built, I have yet to see them.
Maybe the early 70s 360 Newports?
As far as vans, I admit that I'm not as familiar with their equipment since I've never owned one.
The trucks though. I've seen 8 1/4" axles in Dakotas, Durangos, D100 trucks but never a 4wd, never a 3/4 ton. If they were built, I've never seen one out here.
 

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