8 3/4 discussion/questions.

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Dusterdude72

IN MOPAR MUSCLE MAGAZINE
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My 72 duster I knew had an 8 3/4 in it and i knew it had recently been built with 4.10 sure grip prior to me buying it but I just recently checked it all out while I was in the middle of bleeding my brakes off and I took pictures and took note of the part numbers.

I have a few questions for the experts as to if this is the most desirable 8 3/4 and if so ....why? anything special about my set up? and anything anyone might think would be good knowledge to know that I had not asked a question about please feel free to mention.

I have seen alot of pictures of dusters that showed how tight there wider tires sat next to there leaf spring and this is not the case with my set up...... I have 275/60/15 bfg g force T/A drag radials and I have about 4 or 5"'s between the tire and the leaf spring on each side.

Now where it gets interesting..... it looks as though there has been some new boxed leaf spring mounts have been added and welded into place and relocated the springs inword? I also see that new perchs were welded onto the axle and I can see where the old perchs sit a few inchs off to the sides of the new ones.

The 8 3/4 center section part numbers are 2070742 with a number 2 above it and a letter A with a circle around it and a large number 2 off to the side .also below the part number is the casting AAPW and 1299? im trying to read from the picture because I forgot to take note while looking directly at it.

so I believe it is the 742 set up. and should have the large stem 1 3/4 pinion.

I am no expert when it comes to this area which is why im looking to fabo for opinions and info!.

the entire under carriage has been updated prior to me buying it and has new bushings,front shocks,tie rods,ball joints,kelsey hayes 4 piston disc front brakes,russel stainless steal braided brake lines,rear end rebuilt...all of it. I am just rebuilding the rest of the car. (resto thread in my signature )

sorry for the long post. just trying to get out as much info as i can , Thanks everyone in advance!
 
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I just went ahead and added all my under body pictures for the heck of it....hope this gives you guys an idea of what all I am talking about, thanks again!
 
742 is a great unit to have.There are others who like the 489 better but I think they are pretty equal.

Your springs have been relocated inboard roughly 3". And it was done correctly as the spring is located inside the longitudinal.This is much stronger than simply putting them on the inside of the framerail and the car should handle well.The springs have 5 leafs apiece if I counted right,so they are not ss springs.Maybe HD springs?
 
742 is a great unit to have.There are others who like the 489 better but I think they are pretty equal.

You springs have been relocated inboard roughly 3". And it was done correctly as the spring is located inside the longitudinal.This is much stronger than simply putting them on the inside of the framerail.


Good to know, thanks buddy!

any other input from anyone else?
 
Yup the 742 is my favorite, problem with finding out which sure grip you've got (clutch or cone) you've got to pull the pumpkin for a look and I prefer the clutch type cuss they're rebuildable. Here's a picture and story that talks about all 3 8 3/4"'s. Also get yourself a pinion snubber to help control leaf spring windup on hard launch. http://www.moparts.org/Tech/Archive/axle/1.html
 
Yup the 742 is my favorite, problem with finding out which sure grip you've got (clutch or cone) you've got to pull the pumpkin for a look and I prefer the clutch type cuss they're rebuildable. Here's a picture and story that talks about all 3 8 3/4"'s. Also get yourself a pinion snubber to help control leaf spring windup on hard launch. http://www.moparts.org/Tech/Archive/axle/1.html

Thanks for the link!

and yes I have no clue which sure grip unit I have and I guess that will remain a mystery until I have to change a bearing,axle,gearing and so forth because I do not feel like ripping it all apart to find out right nowl ol.

and thanks for the tip on the snubber...I will keep that in mind
 
742 is a good diff. 742 has the slightly smaller pinion than the 489, 742 has a straight pinion abd the 489 has a tapered pinion, gears are also cheaper for the 742. there is a 741 diff which is the weaker unit
 
742 is a good diff. 742 has the slightly smaller pinion than the 489, 742 has a straight pinion abd the 489 has a tapered pinion, gears are also cheaper for the 742. there is a 741 diff which is the weaker unit


I looked on a thread at mymopar and found that same info but thank you for the input.

either way it should hold up plenty well for what I plan on using it for.
 
I looked on a thread at mymopar and found that same info but thank you for the input.

either way it should hold up plenty well for what I plan on using it for.

Oh hell,they'll stand up to hemi's and big blocks all day long.No worries there mate!
 
seems like quite a small hole to peep into and clearly identify anything?
 
All you,ll need to see is the springs for the clutch-syle.Can,t believe your just finding out now,that your car has the spring relocation done on it?

HAHA Im just as surprised im jsut now finding out also lol.

I have had the car about a year now and i have done TONS of work on it but not to much on the under side.

I looked everything over on the underside a few times but never really payed close attention to what was going on in the rear of the car....and today when I was bleeding the brakes off I happened to look and see that they had moved the springs and welded in new box's and perchs and it was one of those " DOH " moments lol....all this time and just now noticing...I know....I know lol :banghead:

so while I was there I figured it was about time I ran the numbers on the rear end (been meaning to for awhile now)
 
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