8 1/4 strength ???

[Dakotamike]

Looking for some opinions on the strength of the 8 1/4 rear. I have a 1991 Dodge Dakota with 390 ci 318 , 904 trans with 3800 stall. The motor should be making around 450 hp. The stock 8 1/4 rear has all new bearing 4.10 gears with the factory sure-grip and a LPW diff cover. I've run a best 1/8th mile of 8.30 on drag radials. I'd like to put slicks on it but I'm scared the rear won't hold it. Any opinions??
Thanks,
Mike

[cudabob496]

Drive it till it breaks

[dodger1]

There was a write-up in Mopar Action on 8 1/4's, and they mentioned that the Dak unit was the best of them. As for how much power they'll take, I'd GUESS that you're on the edge - you'll have to find out the hard way. If I was you, I'd find a 9 1/4 (Ram??) and keep it in reserve for that day.

[dwc43]

I agree with Dodger1 on this one. You are right on the edge. Don't waste your money on an 8 3/4 either. The 1/4 and 3/4 are equal in strength. The 9 1/4 is a good choice too, if it's not too long.

[43 purestock]

I would agree you are on the edge there. The 9 1/4 is a very strong unit, I think thats what they put in the R/Ts but Im not 100% on that. The 8 3/4 is much stronger than the 8 1/4, But then you need axles to match your bolt pattern. The 8 3/4 also gives the option of easy gear changes, and a clutch style sure grip, which is superior over the cone type if you are running slicks. I hear the ford 8.8 can work too, but I really like to stick with Mopar as much as possable.

[dave571]

I agree you are on the line also. might hold up. might not.

If it does break, it might wreck your trans too. Very common.

I would talk to a guy on www.moparts.com named DoctorDiff
You can send him a mesage there if you are a member.

He is very knowledgable in the diff area, and will give some good advice.

[cudabob496]

http://www.moparaction.com/Tech/ques...OF_AXLES2.html

[Dakotamike]

Thanks for all the replys. It seems everyone shares my feelings that it might or might not hold up. I have alot of time and money into this truck it's not just a "beater". So I'm not going to chance it but I am still undecided weather to go with a 8 3/4 or a 9 1/4. Either way the rear will have to be narrowed. With the wheel combo that I am running now the wheels are out 1/2 inch. I'm looking to put them under a inch or so. Well I have a few more months to decide LOL..
Thanks again for everyones input,
Mike

[dave571]

If you are going to spend money to rnarrow one, I'm going to suggest you skip the smaller stuff.

Get a dana form a truck, and narrow it.

They can be got for almost free.
Get all the parts you need for the job from DoctorDiff, or for that matter, he can build one to your specs.

[Dakotamike]

I have a 8 3/4 489 case that I was thinking of using.(same rear a friend has in a 9 second Dart) I am planning on running in the 10's when I get my 340 done later this year. I also already have a set of Moser axles for the 8 3/4 that can be narrowed and resplined and a back brace for the rear. So money wise I already have most of the stuff for the 8 3/4.

Thanks,
Mike

[DJVCuda]

I run a 8 1/4 in my 66 cuda out of a 74 dart sport - mine has less splines inthe axles, 27 vs 29 for your dakota IIRC...

I run 12.56 @106 in the quarter and high 7's inthe 1/8th - 1.74 60' times with 3.23 gears on slicks... mostly street car but i have about 400 passes and 17000 street miles on that rear.
Holding strong!

[Dakotamike]

Glad to hear of one out there surviving the kind of et's I should be running on slicks! I'll probably just wait and put the 8 3/4 in late this year when I put the 340 in. I just talked to my friend with the Dart this morning and he has a set of 4.30 gears and a 35 spline spool he'll let me have for $150 so I'm pretty much set with the 8 3/4 project. Thanks to all that have responded.
Mike

[waynebo]

I would find a 85 or later 9.25" and fit it to the truck as a dakota is a heavy vehical and thats what will cause the 8.25" to puke with a 390" stroker torque motor,,just my opinion..Do a search on 9 1/4 rears on here and you will find the photos i posted of and 87 9.25" vs a late 70's 9.25"..
the later model is a way stouter casting.