8 3/4 posi unit change

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dewsky

dewsky

1975 Duster 360
Joined
Mar 19, 2005
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Wichita, Ks
I currently have an 8 3/4 with a 489 case with a set of 3.91 gears and a posi unit installed. I am wanting the make the car (75 Duster) a bit more friendly on the highway by installing a set of 3.23 gears. I have a complete rear end out of a D200 with a 489 case that has the gears, but it does not have Posi. My question is, how hard is it to swap the posi unit from case to case? I dont know, but I believe it's a stock unit with the posi.
 
dewsky said:
I currently have an 8 3/4 with a 489 case with a set of 3.91 gears and a posi unit installed. I am wanting the make the car (75 Duster) a bit more friendly on the highway by installing a set of 3.23 gears. I have a complete rear end out of a D200 with a 489 case that has the gears, but it does not have Posi. My question is, how hard is it to swap the posi unit from case to case? I dont know, but I believe it's a stock unit with the posi.
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No such thing as a 8.75/8 3/4 Posi. It's called a Sure-grip or AKA Powr-Lok.

Now that is out of the way, its fairly straight forward swap. Just pull it out, swap the pinion and ring gear, set the lash and put it back in.
 
Check the backlash and write it down on both units before removing carriers. Swap carriers and ring gears and reset backlash to your recorded settings.
 
So, it would be the same as just changing the gears. I was hoping I could take the Sure-grip unit out of one and put it in the other.
 
dewsky said:
So, it would be the same as just changing the gears. I was hoping I could take the Sure-grip unit out of one and put it in the other.
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No need to touch pinion gear, check backlash, just remove open carrier, remove ring gear, reinstall ring gear on sure grip unit, put back into chunk, set backlash
 
Then I would lose the Sure Grip.....which I would like to keep. The 3.91 (installed in the car) has the sure grip, the donor rear end with the 3.23 does not. I've not taken either of them apart yet, just inquiring on doing this. To be honest, I've never taken changed a set of gears before, so this is new terrritory for me.
 
Sounds simple enough, just have to learn how to check the backlash......LOL
 
dewsky said:
Then I would lose the Sure Grip.....which I would like to keep. The 3.91 (installed in the car) has the sure grip, the donor rear end with the 3.23 does not. I've not taken either of them apart yet, just inquiring on doing this. To be honest, I've never taken changed a set of gears before, so this is new terrritory for me.
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Take the sure grip unit OUT of the 391 chunk, put it IN the 323 chunk
 
I would have thought the D-200 which is a 3/4 ton would have a Dana 60? But any way you need only change the SG unit with the open unit. Leave the gears in their original cases. Keep the ring gear bolts with the same carrier. Some were shouldered and some not.
 
dewsky said:
Sounds simple enough, just have to learn how to check the backlash......LOL
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It's not THAT hard to do. Get a FSM or at least the section on replacing the gears in an 8 3/4 center section. Go to Harbor Freight get a magnetic base for a dial indicator, and a dial indicator. Just saying this as you did not say you had equipment. You are gonna want something secure to hold on to the centers when you take them apart to swap the sure-grip into the 3.23 center, I made a fixture that bolts to my engine stand to hold the case while I worked on it. Mark the caps, and adjusters so you don't mix the pieces up between the two housings. FYI, ring gear bolts are left handed thread. I typically check and record back lash in 4 places, mark each point where you measure BEFORE you remove the ring gear from the housing, write the numbers down, these are the numbers you are going to adjust preload to when you reassemble. So long as you are careful and clean there is no reason why you can not reuse the bearings on the sure-grip unit. Reusing the ring gear bolts is flip a coin, local dealer can get them, or Summit, Mancini, Jegs.

Good luck, have fun!!
 
I could have been wrong.....Bought the rear from another guy, thought he said 200....must have been a 100. Just have to figure out what to do with the rear end when I'm done with it.
 
dewsky said:
I could have been wrong.....Bought the rear from another guy, thought he said 200....must have been a 100. Just have to figure out what to do with the rear end when I'm done with it.
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Narrow it to "A" body width and sell it!
 
dewsky said:
I could have been wrong.....Bought the rear from another guy, thought he said 200....must have been a 100. Just have to figure out what to do with the rear end when I'm done with it.
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Sell the truck housing and axles when your done. I'm actually looking for truck housing and axles right now!
 
SGBARRACUDA said:
I would have thought the D-200 which is a 3/4 ton would have a Dana 60?
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not always the case. 2 wd D200s could have either depending on package and year. Even the W200s didn't always come with dana 60s. Some got 9.25 corp in some years, 8.75s in the mid to late 60s, and even dana 44s in others after the 8.75 was discontinued.
 
Have you considered installing the 3.23 carrier as is and driving it for a while? You may find that it does quite well on the highway without the sure-grip feature. How often are you going to race the car?
 
dukeboy_318 said:
not always the case. 2 wd D200s could have either depending on package and year. Even the W200s didn't always come with dana 60s. Some got 9.25 corp in some years, 8.75s in the mid to late 60s, and even dana 44s in others after the 8.75 was discontinued.
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my 76 w200 had 9-3/4" dana rear axle. I don't think I've ever seen a 5 lug 3/4 ton, or an 8 lug 9-1/4" full floating Spicer. I havent seen it all, yet, but it would have to be rare for sure.
 
rustycowll69 said:
my 76 w200 had 9-3/4" dana rear axle. I don't think I've ever seen a 5 lug 3/4 ton, or an 8 lug 9-1/4" full floating Spicer. I havent seen it all, yet, but it would have to be rare for sure.
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There's a chart floating around one of the 4x4 forums that listed them all. I'll try to find it.

It's weird what axles mopar used back then. My 78 w200 has Dana 60s front and rear but standard was the Dana 44HD for the front and a 9.25 rear for that year.
 
DFX 340 Duster said:
Have you considered installing the 3.23 carrier as is and driving it for a while? You may find that it does quite well on the highway without the sure-grip feature. How often are you going to race the car?
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I dont plan on racing it, but would still like to have the Sure-Grip for fun.
 
POSI ???

Facepalm Picard.jpg
 
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