Rear-End Help

[HP2]

Go with goodys sugestion and only jack up one of the tires leaving the other one on the ground. Spin the free wheel by first putting the valve stem at 12 oclock. Like before, count how many times the U joint turns but now spin the wheel two comeplete times around making sure the valve stem is at exactly 12.

I agree with these guys. If both tires are in the air, you are getting an inaccurate reading. Keep one fixed so it cannot move, then check it. You'll get different results.

Sure Grip, Positraction, Trac-lok, Power-lok, etc are all band names, like Kleenex or Thermos. They all perform the same function of providing a limited slip action to the differential.

Check for the number cast into the nose of the third member. This is on the driver side just behind the u-joint saddle. Let us know what the last three numbers are. They should be 741, 742 or 489, IF, you have an 8 3/4 rear end. This is identifiable by the smooth, bolt less backside when viewed from behind the car. If you can see bolts from behind the car, you have an 8 1/4 rear end which you will want to ditch with a 440. If you have the 8 3/4 rear end, then you will want either the 742 or 489 case with a 3:23 or 3:55 gear and a new sure grip, or some other limited slip carrier in it, to back up your upcoming 440. Unless you building some mega powerful, 700 horsepower killer big block, or a performing 6000 rpm launches at the drag strip, you can use the 8 3/4 for many years without incident. If you are tending to lean towards the radical power side, then go for a Dana 60. 

[RDF]

I agree with these guys. If both tires are in the air, you are getting an inaccurate reading. Keep one fixed so it cannot move, then check it. You'll get different results.

Will do....I will try again this weekend.

IF, you have an 8 3/4 rear end. This is identifiable by the smooth, bolt less backside when viewed from behind the car.

This is my car......sealed from behind but bolts on the inside, facing the driveshaft.

Unless you building some mega powerful, 700 horsepower killer big block, or a performing 6000 rpm launches at the drag strip, you can use the 8 3/4 for many years without incident.

  I will build something powerful, but not inthe 600hp range.  Probably closer to 450-500hp.

So from what it sounds like, I should be able to get new "guts" for my existing rear end and have them put in and I could be all set?

[HP2]

Yes. Since you have the 8.75 rear it is very easy to have the gears changed in it. You need to drop the driveshaft, remove the rear wheels and drums, unbolt the axle retainers inside the brake assy, pull the axles out about 6 inches, then under the car unbolt the main carrier from the housing and pull it out. That is the third member. You can now take it to any differential shop and have them rebuild it with gears of your choice and reverse the procedure to put it back together. 

[RDF]

Yes. Since you have the 8.75 rear it is very easy to have the gears changed in it. You need to drop the driveshaft, remove the rear wheels and drums, unbolt the axle retainers inside the brake assy, pull the axles out about 6 inches, then under the car unbolt the main carrier from the housing and pull it out. That is the third member. You can now take it to any differential shop and have them rebuild it with gears of your choice and reverse the procedure to put it back together. 

Ok, sounds good.  From my old days of being a mechanic, I can remember changing axles in older cars so let's hope my memory doesn't fail me.  As far as Posi, limited slip, etc. I'm still a little lost; does changing the 3rd member change this as well?  What if I didn't want the limited slip in there now, how could I make it posi? 

[73Chally]

Posi and limited slip are the same thing, just a different name. If your rear end already has one, you can see about getting it rebuilt.  If it does not have one, then you will want to buy one.  You just need to research the best prices through any number of sources (Summit, YO, Paddock, etc).  I believe Eaton is about the biggest supplier for the Chrysler 8-3/4 sure grip.

As far as changing the 3rd member, it just depends on what you currently have and how much you want to spend.  If your current setup does not have the sure grip, then you either want to add it to your existing 3rd member, along with the new gear set, or as I mentioned before buy an entirely new 3rd member with the sure grip and gear set already installed.  It will be a bit more expensive doing it this way as opposed to rebuilding your existing 3rd member, but what you are buying is a completely finished piece that is ready to bolt in, as opposed to having to find a shop to put in the gears.

I changed my rear last year, using my existing 3rd member because I already had a good sure grip in it, and only needed the new gear set.  Even with that, it still cost me about $500 including labor, so if you can find a complete 3rd member with sure grip for around $600-$800, you will be in real good shape.

[RDF]

I guess my question is what makes a rear end sure grip, posi, etc.?  Is it a component within the 3rd member? 

[cowboy]

-
Yeps.... 

It can be cone type, clutch type or...  to get power to both wheels equal...

[tactransman]

Robert,here is some good info on the 8 3/4 "sure grips"

http://www.moparts.com/Tech/Archive/axle/13.html

[HP2]

I guess my question is what makes a rear end sure grip, posi, etc.?  Is it a component within the 3rd member? 

The carrier that the ring gear bolts to determines the open/limited slip status. This carrier is either an open case with some gears and pins in it for an open case, or it is an mostly enclosed case that is full of clutch packs and springs, or cone and seats, or helical gears that provide the locking mechanism.

If you already have a sure grip carrier, it may be rebuildable with just a kit. If you have an open carrier, you will need to purchase the sure grip carrier to convert to the limit slip option. However, if you have a decent gear set of a ratio you like already installed, you do not need to change gears just to get the sure grip. The limited slip carrier is independant of the actual gears. However, until you get an accurate count of the revolutions, or you tear open the rear end, you won't know if the gears you have are a ratio you would want to keep.

[ChallengerHK]

Sure Grip, Positraction, Trac-lok, Power-lok, etc are all band names, like Kleenex or Thermos. They all perform the same function of providing a limited slip action to the differential.

I'm confused. Are you saying that I should stuff my differential full of Kleenex, or connect it to a Thermos?

  Couldn't resist.

[RDF]

http://cgi.ebay.com/ebaymotors/mopar-8-3-4-dana-suregrip-3-91_W0QQitemZ230208137463QQihZ013QQcategoryZ33731QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


or


http://cgi.ebay.com/ebaymotors/Mopar-Dodge-8-3-4-center-section-3-23-gears_W0QQitemZ150199032751QQihZ005QQcategoryZ33731QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Would something along these lines work?

[MEK-Dangerfield]

http://cgi.ebay.com/ebaymotors/8-3-4-mopar-POSI-489-rear-end-project-CUDA-dart-340-426_W0QQcmdZViewItemQQcategoryZ33731QQihZ019QQitemZ290193888906QQrdZ1QQsspagenameZWDVW

or


http://cgi.ebay.com/ebaymotors/Mopar-Dodge-8-3-4-center-section-3-23-gears_W0QQitemZ150199032751QQihZ005QQcategoryZ33731QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Would something along these lines work?

Do you know if you have a 489, or 471 rear? That might make the choice easier.


   Mike

[RDF]

 

yes that would help.....no I don't know....I need to figure that out first. 


See?  Without this forum, I'd have all sorts of parts....just not meant for my car! 

[RDF]

I've got a 489 case.....so the 741 case won't work?

[FJ5_440]

The 741 case will "work", but it is the weakest of the three with the smallest pinion and may not hold up to the higher horsepower levels.  The 489 that you have is probably the strongest.  If you have a sure grip unit installed with the gear set you want, you should have a bullet proof rear for the horsepower levels you are talking about.