Rear End Questions...

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myasylum

myasylum

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O.k. I have a 8 1/4 rear end... Stock 3.23 or something?

I took it into a shop and they said they can add a sure grip/w 390 gears that they promised me it will hold up for about $1200.00.

I thought that was quite a bit of cash. I think I am running at about 400hp.
This rear end was originally behind a slant 6, and is holding up VERY well (so far) considering the 300 HP difference! I've roached the tires quite a few times, and it's holding up well.


I am however leery about the 8 1/4, and for $1200.00 I think may be better invested into a 8 3/4.


Could someone give me an opinion here, and perhaps if I go the 8 3/4 route advise me of parts I need and the money involved with this?


How hard does this rate on the "Do it yourself" scale? :)



Thanks much!!
 
I don't know TOO much about rears, but $1200 seems high considering what you could get a nice 8.75 setup for.

That shop is probably near here, I guess I won't be going to that one for anything!
 
Depending on what brand of sure grip unit and gears, 1200.00 could be fair. To spend 1200 on a 8.75 you first need to own one.
Besides, you can tear up any rear end if you try hard enough.
Difficulty and skill level for rebuilding a differential is a strong 8 on a 1 to 10.
 
Hey, wow! Nice to meet you fellow Wisconsinite! Its in Germanton. They did my tranny for a pretty good price, so I thought they'd give me a pretty good price on the rear end too. I guess maybe not?
 
Like I said, I don't know too much about them, but put it this way, you could spend less, even for a complete 8.75. You are doing 400hp, so maybe a $1200 rear is overkill for you? What's your goal? What were they putting in there? I'll leave it to others who can answer more specifically from here out.

Germantown... that's only about 3 miles from where I am (Falls). Maybe I will check them out after all if they do transmissions and especially if they do motor/machine work. Name?
 
You could probably find a complete 8 3/4 s.g for alot cheaper,if not the same amount($1200)and bolt it in.All your brakes from 8 1/4 will fit the 8 3/4 rear.Might need to shorten your d.shaft.
 
May car will stay in the 400-500hp range. Thats enough for me. I don't know what brand gears they were going to use? When they said $1200.00, I just said, "Oh??" and left it at that. I thought maybe I could find a 8 3/4 for that??

What brand gears are good?? I don't even know what to look or ask for?

Here is there web site...
http://www.autotransdesign.com/

I have heard some complaints about them, but personally theyve been good for me.
They put in 3.73's behind a LT1 motor I had at one time, it worked great till the day I sold it. They also did my friends tranny on his V-6 '95 Grand Am, and now a "Street/Strip" 904 on my Duster. No complaints from me personally??!? I guess they somehow make there own stall converters, and that kind of freaks people out.
 
Okay, thanks... I'll check them out, maybe let them do my 904 or 727 when they need it. Right on 145, eh? Couldn't be more convenient for me location-wise.
 
I'm in Cedarburg... So I'm pretty close to you as well. I think They charged me $400.00 for the tranny that included a 2400 stall converter. Don't quote me on that though... Can't quite remember. They even painted it all pretty :)
Yea, just talk to them and see if they make sense to you. Like I say, a lot of people are scared off that they make there own stall converters. They don't trust that or something? There are two guys that are in charge. It's kind of funny because they remind me of the Mythbuster guys. One guy is all funny and talkative the other is just straight forward, doesn't say much and your in and out.

Yea, I thought $1200.00 was a lot too. Thats why I left to explore other options.
This is what I "Plan" on doing with my tax returns. So i really need to know what parts to look for and all. It's good to know my old brake lines will still work! I need a Large bolt pattern too.
 
I'll check them out, thanks for the info. Doesn't make sense to stick my 727 in without having it gone through if I can get it done for anywhere near that.
 
Do what pettybludart said, if you're pushing 400+ hp the 8 1/4 will not stand up. 83/4 might not either, but ya get a hell of a lot better chance. You should be able to get complete between the $750-$1000 range...good luck!!
 
Not sure for an 8 1/4 diff, but for an 8 3/4 considering the cost of all the parts that will be required, remember the sure grip unit alone brand new is $400-$500 and a new crown and pinion gear set is $200, complete bearing and seal package new is $100. Average labour rate these days is around 65 an hour, your looking at 5-6 hours for the entire job, set up carrier (an 8 3/4 carrier is not a straight forward job to get the teeth to line up right) and to re & re the 8 1/4 axle from the car to a 8 3/4. I wouldn't spent $1200.00 on an 8 1/4 but on a 8 3/4 that's an average price.
Like someone else mentioned buying a complete 8 3/4 already done that can be fired straight into the car, usually will be cheaper.
 
JTG said:
Like someone else mentioned buying a complete 8 3/4 already done that can be fired straight into the car, usually will be cheaper.
Click to expand...

But then the problum comes in... where to find one??? A, A-body one at that!

Would you trust E-bay for something like that?
 
myasylum said:
But then the problum comes in... where to find one??? A, A-body one at that!

Would you trust E-bay for something like that?
Click to expand...

Due to size and weight of one these axles complete, shipping will probably cost huge, I picked one up at the last Mopar national show I attended. From a cost prespective unless your picking it up yourself, not sure how the shipping would be reasonable. There is guys at the shows and a few sellers on ebay and that's all they do is assemble and sell complete rear differentials.
 
Paying a shop to install all new parts (sure-grip, gear set, bearings, seals, etc) is going to cost a bunch no matter what axle your dealing with. Even the weak 7-1/4 axle. Even if you did it yourself the parts alone would probably be $900 and for a shop to stay in business they have to charge for their labor. We have to look at things realistically. In my opinion I don't think their ripping you off cause as I said it'd cost nearly that much, if not more to do any axle.

With that said my preference would be to start with a better axle, like the 8-3/4. I've seen them sell on this board and others (Moparts.com, Racingjunk.com, etc) quite often for $800-1000 rebuilt or in near new condition. Even if you had to pay $200 to have it shipped you'd still be ahead in the game cause you'd have a much better axle. Just make sure of the person your buying it from is reputable. One way to do that is if you find someone on the board that lives near the seller ask them to go look it over for you. I would be happy to go look one over for you if you found one in my area for sale. I think a lot of other guys would too.
 
Kind of like Fishy said... You're looking to get a solid axle under the car with a grip and gears of your choice. Type of axle means little, and in some cases the smaller stuff coupld be more expensive. I dont think $1200 is anywhere out of line to walk out with everything new (besides brakes) and what you wanted. As an example, for me to rebuild an 8 3/4 open chuck completely and give you gears and a new limited slip you're going to drop $1300. The 8 1/4 has more parts because it's got a the full housing with axle bearings and seals, and I'm sure the limited slip units aint cheap. The work is more too. But again, if you take an 8 3/4 case and axles, replace the bearings and seals, plus do a chuck, you will spend closer to $1500 to get an apples to apples comparison. You might find a used Dana 60 for that but I seriously doubt it. I've never seen one compelte and ready to install with new parts for anywhere near that figure. If it was me, I'd take the $1200 and find a complete usable 8 3/4 with 3.55s and bolt it in with new brakes. Run it for a few years, then go thru it.
 
You guys make a lot of sense!

I guess what doesn't make sense is too spend $1200.00 on a 8 1/4, when I can spend $1200.00 - $1500.00 on a 8 3/4.

Since the car is put away for winter that gives me some time to browse around and see what I can find... Maybe even a Dana 60! :p

What year a-body rear ends will fit my car? I have a '73.

Thanks You!!
 
myasylum said:
What year a-body rear ends will fit my car? I have a '73.

Thanks You!!
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Late 65 through 72. A Body 8 & 3/4's came out in late 65 and were used with the 273/235 motor with a 4 speed. I parted out a 65 Dart with a build date of 7/23/65 with that combination. I'd have to look but think the rear was dated late Jun or early July of 65
 
Isn't there a certain "number" to look for that is better then the others??
If so, what makes that number better??

Thanks!!
 
myasylum said:
Isn't there a certain "number" to look for that is better then the others??
If so, what makes that number better??

Thanks!!
Click to expand...

Here's 2 links that should answer your questions, and if it's not enough detail, just google Mopar rear end info and you'll get tons of hits. Technically, the 489 is the strongest, but from what you've said, any would be fine for your car. I have a 741 that I was going to use in my Dart and I'm sure it would have been fine, but I happened to get a 489 so will use that and will save the 741 rear for another car. I wouldn't have hesitated to use the 741 though, based on everything I've read.

http://www.planethoustonamx.com/main/chrysler_8_34_rearends.htm

http://www.moparfins.com/repairs/8-3-4_Rebuilding/Information_on_Mopar_Rears.htm
 
What about a B-Body 8.75? More affordable. You'll just have to move the spring perches.
 
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