8.75 - Open to Sure Grip
#2714823
11/11/19 02:53 PM
11/11/19 02:53 PM
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Joined: Jan 2003
Posts: 1,412 Johnstown
69dart
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,412
Johnstown
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I'm swapping out the open differential to a Posi Unit ( https://www.jegs.com/i/JEGS/555/62820/10002/-1) for the the 8.75 in my 68 dart. Does anyone have any tips? Its a 3.91 gear if that matters and the front pinion seal needs replaced as well. I checked the tech archives but didnt see a walk thru. Thanks Guys!
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Re: 8.75 - Open to Sure Grip
[Re: dIc dOc Deity !]
#2714886
11/11/19 06:06 PM
11/11/19 06:06 PM
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Joined: Feb 2004
Posts: 855 ontario canada kingston
aspenrt360
super stock
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super stock
Joined: Feb 2004
Posts: 855
ontario canada kingston
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100% call DR Diff first he will set you up better than they will. i have bought a few things from the guy and am happy to say he is solid to deal with. and products are good too.
Last edited by aspenrt360; 11/11/19 06:07 PM.
2013 Chrysler 300 touring 1974 Dodge Charger SE. 360-727-8.75-3.23 sure grip 1972 Dodge Dart Swinger 1995 Dodge Ram 1500 4x4
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Re: 8.75 - Open to Sure Grip
[Re: 69dart]
#2714933
11/11/19 08:32 PM
11/11/19 08:32 PM
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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
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Bend,OR USA
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Which case are you using, 741,742 or 489?(last three digits on the casting number under the driver side of the pinion gear ) The case, carrier, determines which set of instructions you need when replacing the front seal If it is a 741 or 742 no big deal on replacing the front pinion seal, if it is the 489 case you need to follow the FSM instructions to the ninth degree, dang Mopar for going to a crush sleeve anyways 1969 was the change over year going from the 742 to the 489 cases for H.D. applications I'm sure them dang bean counter had a lot to do with that decision and change
Last edited by Cab_Burge; 11/11/19 08:33 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: 8.75 - Open to Sure Grip
[Re: 69dart]
#2714983
11/11/19 10:03 PM
11/11/19 10:03 PM
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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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What tools do you have now? You will need a good inch lb. torque wrench as well as a good foot Lb. torque wrench, a adjustable spanner wrench,a good dial indicator with a good magnetic base and a ton of patience AKA, buy a 1962 to 1969 Mopar factory Dodge or Plymouth service manual and read every part on how to work on their rear ends, the 7 1/4 inch ring gear rear ends all the way up to working on the Dana 60 rear ends as well as the 741 and 742 8 3/4 rear ends The 1969 FSM for Dodge and Plymouth may have a section on how to set up the 489 cases also, depending on when the manual was printed, the 489 cases came out in mid year 1969. On your deal with the 741 case you need to check the ring gear back lash in 4 different places, with a good dial indicator, 90 degrees apart, and write it down. Hopefully the four places are within .002 of each other on the backlash Once that is done you can remove the ring gear form the old center section, the opened rear end. Caution, all Mopar 8 3/4 rear ends have left handed threads on the ring gear bolts, all of them Don't strip or break one off loosening them up You will need to turn them clockwise facing them to loosen and counter clock wise to tighten them up Mopar recommends not reusing their stock ring gear bolts but I do. They come with a locking compound on the threads that was designed for one time use, I use blue Locktite on mine when I reuse them they need to be torque to 55 Ft lbs. You will need to mark both caps before removing them so they go back on the correct side that they where machine for The FSM calls for no more than .0030 run out difference on the carrier and ring gear backlash, I've learned that I can heat up the ring gear to around 140 F in a oven or on my wood heating stove in the shop in the winter and then the ring gear will drop right on the carrier and sit flatter than trying to pull the ring gear down with the ring gear bolts with the ring gear at room temperature, below 70 F I need to go eat dinner now so get the tools and FSM and let me know later when your ready to try this, their are several other torque specs you need to know about as well as some other things you don't need to worry about, such as pinion gear depth and pinion bearing preload on your deal now
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: 8.75 - Open to Sure Grip
[Re: Cab_Burge]
#2714990
11/11/19 11:09 PM
11/11/19 11:09 PM
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Joined: Jan 2003
Posts: 8,128 New Mexico
UCUDANT
Troll Hunter
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Troll Hunter
Joined: Jan 2003
Posts: 8,128
New Mexico
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Are you pretty mechanically inclined? If you mark the pinion and nut and count the exposed threads you can reset the pinion back as it was (if it was ok) Setting the pinion depth is the first step and it needs to be correct You'll need: Spanners Dial indicator and stand etc Torque wrenches I have a FSM but found the Mopar Action August 2016 issue to be very informative. If you use the ARP bolts TOSS the ARP washers they will not fit and the bolt heads will rub the case PM me if you need to
Last edited by UCUDANT; 11/11/19 11:18 PM.
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Re: 8.75 - Open to Sure Grip
[Re: UCUDANT]
#2715013
11/12/19 04:37 AM
11/12/19 04:37 AM
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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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You don't need to reset the pinion depth when changing the front seal on the 741 or the 742 third members Remove the pinion nut and replace the seal , retorque the nut back to the factory torque setting and then move the ring gear from the open carrier onto the posi unit and set the back lash and run out correctly on it and reinstall it back into the car and then have fun spinning both tires instead of one Been there done that a bunch of times over the years He is not replacing the gear set, he is going from a open carrier to a posi carrier reusing the same gears in the same rear end carrier BTW, I'm not mechanically incline, I'm a drag racer that does all my own engine, tranny and rear end work No painting or upholstery work though, I trade my labor for that work
Last edited by Cab_Burge; 11/12/19 04:41 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: 8.75 - Open to Sure Grip
[Re: Cab_Burge]
#2715214
11/12/19 07:27 PM
11/12/19 07:27 PM
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Joined: Jan 2003
Posts: 1,412 Johnstown
69dart
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,412
Johnstown
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Thanks Guys! I dig that bucket idea. I wondered how to secure the pig. I'll have to dig thru my mags - I might have that one down in a tote. I've built my engines, transmissions, paint, etc... so I'm fairly handy but I've never setup a rearend on my own. I finally have a shop with room for projects and my kids are grown so I want to learn some new tricks. I picked up the Jegs unit today at lunch - Any excuse to buy some new shop tools is good too!!!
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Re: 8.75 - Open to Sure Grip
[Re: 69dart]
#2715313
11/12/19 11:55 PM
11/12/19 11:55 PM
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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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Did you buy or do you have a good dial indictor that measures in .00010? Either way you need to use one to determine the run out and backlash on the ring gear on the new Posi center section, make sure the run out and backlash doesn't exceed .0030 If it does exceed that reposition it and make sure and get it warm enough, NOT HOT above 160F, to drop onto the posi unit and sits flat against its mounting surface I use some thick leather glove to handle it out of the oven, it should spin freely around the center section mounting surface for a few minutes so you need to get set up it so you can thread 4 bolts 90 degrees apart in it all the way(don't torque them yet, tighten them up a little, say 5 to 20 ft. lbs.) to hold it down square while it cools Once it is cool to the touch, at room temps. then proceed to mount it back into the carrier and set the carrier bearing preload and finish installing and torqueing all the rest of the ring gear bolts to 55 Ft/Lbs.(left handed threads) and then set the back lash back to what is was before you took it apart Let us know your results and what you think of doing these again Setting the pinion depth requires a pinion depth tool or a lot of patiences (SP?) using the contact pattern on the ring gear to set the depth and a lot more work removing the pinion gear and removing pinion bearing or race to change the shims, not my way of setting the depth
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: 8.75 - Open to Sure Grip
[Re: Cab_Burge]
#2715534
11/13/19 09:14 PM
11/13/19 09:14 PM
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Joined: Jan 2003
Posts: 1,412 Johnstown
69dart
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,412
Johnstown
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Thanks for the tips!!! I have a dial indicator so I'll be sure to check the runout. I'll use the wood stove to warm her up a bit if its too snug. Momma loves the smell of gear lube.
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Re: 8.75 - Open to Sure Grip
[Re: dIc dOc Deity !]
#2715615
11/14/19 02:57 AM
11/14/19 02:57 AM
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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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Last edited by Cab_Burge; 11/14/19 03:00 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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