8 3/4 Posi Gears

[darrin75]

I have a 742 case with no posi and was wondering,    I want posi traction with 3.91 gears.

1.  Would I do fine and be cheaper to buy the gears, posi unit and pinion myself and have them installed.
2.  Can I  do it myself.  How Hard Or

3.  Just buy a used one on ebay ready to drop in.
Looking for the cheaper version or best route to go.

4.  Or does anyone have one on here to sell me??

Thanks

[Ghoste]

If you have a shop that will install everything reasonably and you trust their work, that may be the least expensive way to go.  It is not impossible to do yourself but without knowing you personally or your automotive background, it's not something I would advise.  It isn't a job for basic tools and skills.
Buying a Sure Grip off e-bay isn't always a good idea either because it is going to be hard to determine it's true condition until it arrives.  I'm an e-bay cynic though.
A number of places (Manicinis, Randy's Ring and Pinion are just two) sell complete 8.75 rear end pigs in the ratio of your choice and with the limited slip unit of your choice already setup and good to go.  That may be the most expensive but it may not be a lot more than buying a used one and having it refurbished would be.

[Nacho-RT74]

for new unit at a reasoneable price:
http://www.marketworks.com/StoreFrontProfiles/DeluxeSFItemDetail.aspx?sid=1&sfid=92390&c=68053&i=18027296

Randy's sell these $100 more ( same ones, Yukon units ).

to install:
http://www.moparmusclemagazine.com/howto/155_0308_mopar_rear_end_gears_set_up/index.html

with proper tools and stuff yoiu can do it by yourself.

[my73charger]

Hi Darrin,

Point of clarification:  Posi is a Chevy term.  For Mopar it is Sure-grip.

[Silver R/T]

for new unit at a reasoneable price:
http://www.marketworks.com/StoreFrontProfiles/DeluxeSFItemDetail.aspx?sid=1&sfid=92390&c=68053&i=18027296

Randy's sell these $100 more ( same ones, Yukon units ).

to install:
http://www.moparmusclemagazine.com/howto/155_0308_mopar_rear_end_gears_set_up/index.html

with proper tools and stuff yoiu can do it by yourself.

I would recommend this place also, best price Ive found so far.

[Nacho-RT74]

I already paid for the SG unit ( and several more stuff from them... Scott looks a great guy ).

they carry the street and agresive version units at same price.

[darrin75]

thanks guys, I currently have 3.23 gears running about 70 mph around 3000 rpms, If I go to a 4.11 How much more rpms am I talking about here.  Just don't all bottom end...

[Nacho-RT74]

use this table and you'll get anything you want.

http://www.moparts.com/Tech/tech/img/AUTOMATICchart.xls

to manual:
http://www.moparts.com/Tech/tech/img/4SPEEDchart.xls

[darrin75]

thanks helps out alot..

[darrin75]

pricy, but I think this is what is needed
http://cgi.ebay.com/ebaymotors/Chrysler-Mopar-8-75-8-3-4-742-Rearend-3rd-4-10-Posi_W0QQcmdZViewItemQQcategoryZ33731QQihZ016QQitemZ260119777260QQtcZphoto

[Nacho-RT74]

you already have the case, dunno if ring and pinion, but if you don't:

suregrip $350+ ring and pinion $170 or so+maybe $130 for the job if you don't consider make it by yourself+$70 for bearings makes $720... just a little bit more than half of the price of auction.

Is a no brainer buddy!!!!

prices are aprox, but still

[darrin75]

I think I will go with the 4.10 or 3.91 gear,  What lots more torque with my 509 cam ,but still want to go no higher rpms around 70mph.  this should give me around 4000 rpms @ 70.  too much or not enough gear.

[darrin75]

bump

[Ghoste]

How tall are your tires?  You are asking for the whole cake and it's often a compromise at best.  If you want to run at high speeds and low rpm then your 3:23 is a good choice to leave in there.  If you want to really jump off the line then a 4:10 is a good choice.  You may want to consider a gearset between the two such as a 3:55 or maybe an overdrive transmission. 
4000 rpm at 70 is going to become tiring if you are doing it for long periods.  Not to mention fuel consumption and engine wear.

[darrin75]

good points.

By the way I have small tires 235 60 15

[Nacho-RT74]

THOSE are small

[Ghoste]

How do you intend to primarily use the car?

[darrin75]

driving on street mostly, but some have suggested that i need a cam swap, I can't smoke the tires at all  should have more damn power than that?  So my options are

just buy another rearend with bigger gear and swap in and out with the 3.23 depending on the needs or a cam swap, if I can find someone to do it???

[Ghoste]

Congratulations!  You've just opened the Pandora's Box of hot rodding.  It's all a package really and you can't make a change in one area without corresponding changes in about 6 others.  The 509 cam can work well but there are others on here far far far more qualified to recommend cams than I am.
Without knowing more about your combo and knowing that you already have a more aggressive cam and may pick a different one in the future, my opinion is that you should go to a 3:91.  Not too impossible on the highway, fun around town but not as deep as if you were racing the car once in a while.

[darrin75]

Firefighter suggests a engle k56 or k58, which very well maybe what is done on the cam.  However I can not do this job myself, so trying to find someone i trust enough to do it is where the real problems lays on cam swap.  Maybe just for now go with big gear in rear, firefighter also suggest if I am hell bent on keeping that cam, they I need a least 4.30 gears in the rear.  Sometimes I do however wonder if my carb is somehwhat responible for some of the low end not working correctly.  Can someone explain to me if you stomp the gas down all the way with it in gear from a stop does the vaccumm secondaries open like they should???

[SeattleCharger]

When you stomp on it at stop it just sputters?  rpms have to raise up some and car moving a little for the stomping on gas to wind it out?  you have a stock stall converter in there?    I don't know if the lower gears in rearend will totally take care of the need for a higher rpm stall converter, but a bigger cam will only add to your low end problem,  lower gears will help offset the bigger cam, but you may need a higher rpm stall converter in there,  others with more knowledge can help more,

[darrin75]

just done recently, tci 3000- 3500 converter.  That help greatly, but still either bigger gears or cam swap is my only way out.  Some people got to learn the hard way.

[SeattleCharger]

just done recently, tci 3000- 3500 converter.  That help greatly, but still either bigger gears or cam swap is my only way out.  Some people got to learn the hard way.

  Here are a couple threads I have linked to the site here that have some cam recommendations and info from firefighter and chryco and others, maybe these will help,

http://www.dodgecharger.com/forum/index.php/topic,21349.0.html     (cam thread)

http://www.dodgecharger.com/forum/index.php/topic,782.0.html       (cams, heads, etc. )

       http://www.dodgecharger.com/forum/index.php/topic,10041.0.html   (cam, Hughes, Engle)


   

[Ghoste]

Remember, your rearend ratio is just a lever to let the rest of the combo do the work it's capable of.  Overall, if Firefighter knows the rest of the combo, I'd trust his judgement.

[darrin75]

oK THIS ONE LOOKS GOOD TO ME. WHAT DO YOU THINK.  i ALSO i CURRENTLY HAVE 742 CASE INSTALLED NOW, THIS 489 SHOULD FIT WITHOUT ANY MODS RIGHT??

http://cgi.ebay.com/ebaymotors/MOPAR-3-91-489-CASE-POSI-RICHMOND-GEARS-SURE-GRIP-440_W0QQitemZ260166501557QQihZ016QQcategoryZ10076QQssPageNameZWDVWQQrdZ1QQcmdZViewItem