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  #1  
Old 08-27-2008, 01:24 AM
70moparfreak 70moparfreak is offline
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Question 8 1/4 swap to 8 3/4 rearend

I have a '72 satellite with an 8 1/4" rearend and I found a 8 3/4" 489 rearend out of a '74 Polara that I would like to install. However, I am concerned after looking at the perch widths, track widths and center section depth that it may not work. The perches differ by 1.3" overall and the inside drum to inside drum differs by 1.6" overall. Does anyone know how much tolerance there is? Will I need to modify my perches and drive shaft etc? Is this a big deal? Or, will it bolt right in??
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  #2  
Old 08-27-2008, 02:47 AM
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dwc43 dwc43 is offline
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Well, it wont fit. IT would need new perches welded on and the old ones cut off and the pinion angle set before welding on the new perches, plus it's too wide for your car. You don't need it anyways. The 1/4 will take just as much as the 3/4 that's why it replaced it and has the same gear sets and sure grips available as well. I'd just get a gear and sure grip from Randy's Ring and Pinion and be done with it. www.ringpinion.com
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Old 08-27-2008, 09:54 AM
peg leg peg leg is offline
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Default Diffs

Look at the top of this website, and you will see a section on rear ends. Print this info, and you will have all the dimensions and info you need to identify and position your new axle, if you go that way.
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Old 08-28-2008, 12:11 AM
dave5711 dave5711 is offline
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The chart in the tech archives is very usefull.

If memory serves, an early(68 or 69) C body 8 3/4 is pretty close to the right dimensions for a 72 B.

Use the chart and hit the junkyard.
Once you find one that's close, I'm reasonable sure the driveshaft length you have will still work.
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  #5  
Old 08-28-2008, 04:57 AM
namvet67a1f namvet67a1f is offline
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An 8 1/4 will work fine ...unless the car is running in the 10's.
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  #6  
Old 08-28-2008, 11:25 AM
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70moparfreak, welcome aboard.

Namvet, youre back. Did you go for a trip? I figured it would take awhile to find that mysterious info on extreme mileage and there part numbers.
Looking foward to your next post.
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  #7  
Old 09-01-2008, 11:15 PM
70moparfreak 70moparfreak is offline
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Default rearend update

Well, I found an 8 1/4" complete rearend with 3.23 gears and a suregrip for my '72 satellite. The only identification on it are several numbers. Can anyone identify the numbers 48674 & 3723599? Also, KD 3 4 & 2 80. I have found very little information on 8 1/4" rearends in general.
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Old 09-01-2008, 11:48 PM
cudabob496 cudabob496 is offline
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http://www.moparaction.com/Tech/index.html
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  #9  
Old 09-06-2008, 08:08 PM
dodger1 dodger1 is offline
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70, you didn't tell us how much power you are putting into the axle. The 8 1/4 is not a bad piece, but if you're running a strong big block, you might want to upgrade to a 9 1/4 or 8 3/4. As Ehrenberger and namvet say. Also, if you keep the 3.23 unit, be sure to inspect the axle and bearings and replace as needed. The axle shaft runs directly on the bearing element (no inner race) and can get worn. Moser (I think) will sell you new, stronger, axles if needed. I'd change bearings in any case.
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  #10  
Old 09-06-2008, 08:42 PM
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Here is a great chart, from our tech archives.

http://www.moparchat.com/forums/atta...3&d=1082588397
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  #11  
Old 09-06-2008, 08:47 PM
70moparfreak 70moparfreak is offline
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Default '8 1/4 swap to 8 3/4 rearend'‏

Thanks Dodger...

Been reading up on the 318 performance builds. I am anticipating in the neighborhood of 350-400hp depending on what it would take to achieve. I would like to keep the matching numbers small block motor/tranny. Would an 8 1/4" handle this?
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  #12  
Old 09-06-2008, 10:39 PM
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I am running a mild 360 (300 hp?) through a 999 and 2.94 geared 8 1/4 in my 3600 lb. Mirada, so I can't say yours will handle 400 hp. I will offer a guess, though. Considering the 'teen won't have the bottom end whack a big-block would have, I think you'll be OK as long as you go through the axle and do the maintenance items. Mopar Action had an article on these axles as found in Dakotas, and, although they had a slightly larger ring gear (8 3/8"?) they were thought to be pretty strong. If it was my choice, I'd stick with the 3.23/Suregrip unit you have found. Hard enough to find axles that are bolt-in for the year of your car as it is.
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Old 09-07-2008, 09:01 AM
dgc333 dgc333 is offline
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Quote:
Originally Posted by 70moparfreak View Post
Thanks Dodger...

Been reading up on the 318 performance builds. I am anticipating in the neighborhood of 350-400hp depending on what it would take to achieve. I would like to keep the matching numbers small block motor/tranny. Would an 8 1/4" handle this?
I have a 360 with approx. 370 HP in front of a rebuilt but otherwise stock 8.25 with 3.55 gears and a sure-grip. I have been driving this combo hard for 22k miles now and the 8.25 has held up just fine.
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  #14  
Old 09-07-2008, 03:13 PM
70moparfreak 70moparfreak is offline
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Default 8 1/4 swap to 8 3/4 rearend

That's great news! I'd love to fall in the 370hp range. It sounds like for what I need the 8 1/4" will suffice.
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  #15  
Old 03-14-2010, 02:25 AM
70moparfreak 70moparfreak is offline
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Hey

Finally did the swap to Sure grip with 3:55 gears and LPW ULTIMATE 10 diff cover. Only problem I'm having is a huge amont of gear noise when I'm driving. Accellerating and decellerating. Any idea why this would be happening?
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  #16  
Old 03-14-2010, 01:10 PM
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did the rearend sit for a long time? had that in my dad's roadrunner once with his 83/4, we swapped in some 4:56s that had been in the shed for a few years, drove it hard about 4 or 5 miles, and then you heard the awfulest roaring noise, with the loud exhaust of the car and all we thought the gears done tore up the 4 speed tranny, we swapped out another 4:56 pumpkin and had her up and going in about 30min and hasn't made any noise since, thats what i love about the 83/4 to change gears all you have to change is the pumpkin, and it has the bolt in axles while the 81/4 has c clip axles with an 83/4 you break an axle it will stay in, and you can make it home, break an axle in an 81/4 that wheel is coming off, and you may say you won't break an axle with that 318, but i broke an axle in my old pickup with a stock 318, was spinning my tires and pop!!! i'm looking at my tire passing me up...
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Old 03-14-2010, 02:11 PM
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Quote:
Originally Posted by 70moparfreak View Post
Hey

Finally did the swap to Sure grip with 3:55 gears and LPW ULTIMATE 10 diff cover. Only problem I'm having is a huge amont of gear noise when I'm driving. Accellerating and decellerating. Any idea why this would be happening?
This is still with the 8 1/4 right?

Noisy on accell, and decell... well if the gears are new, they weren't set up properly. Pinion depth is likely out.

If they are used, either they aren't back the way they were, so they will be noisy, or they were noisey in the old diff, so they are going to be noisy in this one too. The wear pattern on used stuff is crucial. Without recording the backlash etc.. at dissasembly, getting it the came on reassemble is virtually impossible. THUS the reason why the 8 3/4 (and the ford 9") is popular. Removing the entire center chunk and reinstalling it in another car, does not change the set up in any way.
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  #18  
Old 03-14-2010, 05:41 PM
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Ray Bell Ray Bell is offline
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Getting good tooth mesh is one thing in setting up the hypoid gears... getting quietness is yet another...

Very tricky job to get right.
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Old 03-14-2010, 06:03 PM
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i thought he meant he swapped out the whole rear, and sometimes like in my case if it sets for a long time, the bearings and clutches get dry, and will make noise after ran for a while
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  #20  
Old 03-18-2010, 02:18 AM
70moparfreak 70moparfreak is offline
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Yes, this is still my original Satellite 8 1/4 rearend. I just swiped the sure grip out of the polara unit and also added a brand new ring & pinion. So what I think I'm hearing is that possibly the pinion depth needs adjustment so the gears mesh properly. I know he had a hard time getting them set up.

Just seems like the whole car is more sluggish and doesn't role like it used to. Takes a lot to get it up and moving and then slows down quickly....much more than I expected. Not sure if this due to the change from the 2.?? to 3:55 gears or if there are some serious adjustment problems. I expected some difference but not this much. Would this all be attributed to pinion adjustment?
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  #21  
Old 03-18-2010, 08:19 PM
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If you went from a 2.?? to a 3.55 the car surely should not be more sluggish. Something is wrong with the diff. set-up and I would get to the bottom of that without driving it more.
Get a factory manual or get a reputable shop before you ruin the whole thing.
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  #22  
Old 03-18-2010, 10:06 PM
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Ring and pinion suggest you run a new setup for 10 minutes and let cool:

A new ring and pinion installed with new bearings will initially generate higher than normal operating temperatures. It is advisable to use whichever of the following break in procedures matches your application.

1. With vehicle still on jack stands and rear-end filled with proper amount of lube, run in forward and reverse approximately 2 to 3 minutes. **
2. Drive vehicle approximately 10 miles at normal operating speeds. Accelerate and decelerate several times conservatively, then let cool for 45 minutes
repeat 2-3 times
3. Do not do any heavy towing for 300 miles.
4. change gear oil 2500-5000, then every 20-30k

condensed from numerous gear manufacturers (on the liberal side, many just say 20 miles and let cool then EZ for the next 500 miles, done)
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