8 3/4 life span.

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needsaresto

needsaresto

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Hey all,was just jawing with a mopar guy at the local tire shop,who has had zero luck with 8 3/4 diff's

He killed one in his dakota which only has a 360. Mind you it is on juice.

He did admit that the gearsets he was using were used and used hard previously.

Im of a mind that the 8 3/4 will survive a big block when it is bilt up with fresh quality parts.

It's what I'll be using behind my 451.

Tell me your opinion and experiences. I need to take the right approach when I go to build this 8 3/4.
 
Too many variables to give a specific lifespan. Torque, high vehicle weight and traction are major factors that hurt 8 3/4's. The hard shock from 4-speeds and trans brakes tend to shorten their life too. Some have been getting by! Set-up is also important, and my differential guy seems to have been doing a very good job.

I pull high 1.40 and low 1.50 60's with the wheels in the air every run. I've gotten 2 hard seasons out of gear sets which didn't completely break, but either had some cracked/broken teeth or were worn to the point where it was suggested that they be replaced. I have been using a set that's been "Finished" with a surface treatment and cryo which I'm sure helps. But I'll be checking them in the off season to see how they've been doing. I have also been using the Mopar aluminum center section which I'm sure helps with gear life and cap strength. But I never blew an 8 3/4" in the many years before that either.

I even know of a guy who runs Stock with a 360 Mirada, mid-high 11's, and he's been running an 8 1/4" rear! Yes Eight and ONE-quarter ring gear. Don't know how often he changes gears.

A Dana 60 will certainly extend gear life and will give long-term peace-of-mind (properly set up). Axles are actually the same size as an 8 3/4" when using 35 spline axles. I broke a couple of Strange axles many years ago, but after about 9-10 years in my automatic 10 second Challenger. I think I wore out one or two gears. That's putting between 300 and 500 runs a year! I raced 2 tracks a week and sometimes 3 back then.
 
If the car is a street only then yeah, a 8 3/4 will work just fine. If you're going to take it to the track more then street go with the Dana 60. Sell the 8 3/4 to fund the dana.
 
I don't know about life span-too many variables.I could take you out to the bonepile at the salvage and you can see all types that have broke,some behind 4 cyl and some behind diesels.All in all the 8 3/4 is a great rear,used behind /6 all the way up to 440's ,can't say much more than that.
 
From what I understand, Hemi cars with automatics got the 8-3/4

4-speed Hemis got the Dana 60

I think they are just fine myself.
 
Some people can tear up an anvil.
 
The newest 8.75 had probably been used hard for decades before someone swapped it into a Dakota. Abused, used axle + swapped and run hard = good way to break parts. Why would someone go through the effort of swapping a rear end into a truck without going through it before using it? I guess we don't have the whole story, but it's no direct swap.
 
Lets see...Arlen Vanke was using the old style 8 3/4" with the keywayed drums behind his Hemi in 1964 doing neutral drops off the line and nary ever even broke a drum key, but your buddy can't keep one behind a 360 Dakota?? Sounds like someone needs to be enlightened as to how to go through one and set it up BEFORE putting it in!!! JMO, Geof
 
me and my brother run 8 3/4 in our drag cars and haven't had any problems yet all big blocks even 741 cases which are suppose to be the weak one. my duster ran 10.91 and his dart ran 10.48 both all steel cars with all glass foot braking them.
 
A friend of mine just pulled his 742 cased center from his Challenger, it had chipped most of the teeth, (car ran a 9.60 with a 1.3 60' time). He went with a Dana after seeing the condition of the 8-3/4, but it had many passes on it. In an A-body running 10's-11's, I would bet a decent condition one will last quite a while.
 
I think it was more to do with running used 4:10 gears,and the gears having been used hard before he got em from his Dad.Could also be that he set the gears up incorrectly.
He was using 35 spline axles. Perhaps it was a stick shift,I never asked. That would make life more difficult for the 8 3/4.I didnt ask about why there was an 8 3/4 in his truck.
Personally I feel pretty safe running it behind my 451 with 727. I just thought I'd relate his story and get some real world experiences from my Fabo brothers.

He seems to think a ford 9" is a better option,lol. After he said this I thought,yup here comes the offer to buy my piece of crap 8 3/4 but he didnt. I told him the Ford 9" is no stronger than an 8 3/4 and definitely not cheaper to build. Lol,he's a young guy and will learn eventually.
 
needsaresto said:
I think it was more to do with running used 4:10 gears,and the gears having been used hard before he got em from his Dad.Could also be that he set the gears up incorrectly.
He was using 35 spline axles. Perhaps it was a stick shift,I never asked. That would make life more difficult for the 8 3/4.I didnt ask about why there was an 8 3/4 in his truck.
Personally I feel pretty safe running it behind my 451 with 727. I just thought I'd relate his story and get some real world experiences from my Fabo brothers.

He seems to think a ford 9" is a better option,lol. After he said this I thought,yup here comes the offer to buy my piece of crap 8 3/4 but he didnt. I told him the Ford 9" is no stronger than an 8 3/4 and definitely not cheaper to build. Lol,he's a young guy and will learn eventually.
Click to expand...
Hey,
I wil buy that piece of crap 8 3/4 he broke!!!
LoL
Hey I am cereal !!!
Thanks,
Frosted Flakes
 
Like most of the people said its depends how hard you are on it, what case you have, and what kinda torque you putting to it
 
cosgig said:
Lets see...Arlen Vanke was using the old style 8 3/4" with the keywayed drums behind his Hemi in 1964 doing neutral drops off the line and nary ever even broke a drum key, but your buddy can't keep one behind a 360 Dakota?? Sounds like someone needs to be enlightened as to how to go through one and set it up BEFORE putting it in!!! JMO, Geof
Click to expand...

Now thats "funny" & i totally agree, I have had i don't know how many 8.3/4s behind many BBs & a few SBs & never broke one, not to say it can't happen, I was told never use the 741 case, yeah right, They are stronger then most give them credit for.

To the OP, I ran one for 2 yrs. & over 250 passes in my 3200 Duster with a 451 running high 10s & NEVER EVER an issue, many 1.52-1.54 60fts, stock axles & the splines never twisted, Now not that things cannot happen, because anything can break, even a Dana, A guy i knew chunked the guts out of one, get this, behind a SB Vega LOL, saw it happen with my own eyes.

The set-up is very important, & I highly suggest running a "full spool", this makes them much stronger & less likely to break, Back brase also helps but mine didn't have one, just a full spool with 4.10 gears.
 
Hey joe dust,how much h,p/tq were you pushing through that 8 3/4? With a 451 it could be anywhere from 550-800 .

Maybe thats what I should have called this thread. 8 3/4 h.p limits..

Im probably going use a suregrip,not a spool as my car will be street/strip.
 
But.... If you are BUILDING one and you know your motor is going to be stout why not build a Dana? And have that peice of mind. I built my Dana from the ground up including shortened and axles for about $800. Now add in the fact you are going to pay at least $500 for a A body 8 3/4 and its stock?
 
72ScampTramp said:
But.... If you are BUILDING one and you know your motor is going to be stout why not build a Dana? And have that peice of mind. I built my Dana from the ground up including shortened and axles for about $800. Now add in the fact you are going to pay at least $500 for a A body 8 3/4 and its stock?
Click to expand...

Already have the 8 3/4,came with the Dart and a runing 318/904 combo. Good deal considering I actually drove the Dart for 1.5 yrs before parking it.

I dont know any machinist locally who I would trust. The closest one is 3.5 hr drive. Really great engine builder/machinist who is a mopar guy.

Im in Canada,so I think I can automatically add 20% on to your estimate. It's a mystery why us Canadians pay on avg 20% more than americans. The govt simply says it's not likely to change,even though our doller has been substantially higher and consistantly stronger for the most part than the U.S buck. I think it's just greed personally.

Isnt the Dana a bit heavier than an 8 3/4?

I do already have a spring relocation kit (thanks Doug!!) so that is something I dont need to buy.
Axles,probably gears and rebuild kit,plus the misc stuff like brake parts,lines,etc etc.

I'll shoot my machinist friend an email,see if he can help with an estimate for shortening a Dana

Lol,probably wont have any problems selling that A body 8 3/4 IF I decide on this route...
 
needsaresto said:
Hey joe dust,how much h,p/tq were you pushing through that 8 3/4? With a 451 it could be anywhere from 550-800 .

Maybe thats what I should have called this thread. 8 3/4 h.p limits..

Im probably going use a suregrip,not a spool as my car will be street/strip.
Click to expand...

The engine in reality had about 520-530 HP tops, Thats FWHP, But it wasn't pulling much LOL.
 
$40 Purchase of the Dana with Power Lok.
$250 to shorten weld new ends and nickel rod the tubes including set up of gears and swap new bearings
$120 new bearings and seals (Timekin)
$300 axles bearings (Moser)
$75 new ends (Strange)
$20 brakes backing plates (Used)
$40 new front yoke 1350 (Dana Spicer)
$10 for lines tee block. (Used)
$10 new bolts (Dana Spicer)


So about $900 total on the rear with all new parts and brakes. Most of this stuff was NEW parts sourced from various places.
 

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if in doubt go with the 9". but dana makes a good axle too. but i've diesels mulch a dana 80 while the 9" laughs at them. typical rear ends have 2 pinion teeths contacting 2 ring teeth while the 9" has 3 pinion teeth touching 3 ring teeth. every serious machine ive ever seen had a 9" and i'm a firm believer.
 
9" is a good rearend, less then a Dana, But if the race weight isn't high the 8.3/4 should hold.

I run spools on the street all the time & all is good, tires don't like it but oh well, Just don't put yourself in a tight perdicument, Running a spool keeps cost way down & there stronger & more stable, a win'win IMO.
 
I shelled two Dana 70's in my '93 Cummins, then went with a Detroit locker center, no more problems.
 
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