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Discussion Starter #1
i got a 1971 cougar with 2.73 gears and looking for some tire squelling fun, its a 28 spline 9 in and
i have a 351 with the 4v heads, cam and holley 750 and a built fmx , thanks for any help
 

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open diff, take out old diff. put in new posi diff, close diff.
 

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Try to find a hoghead already set up that has a posi, (and my favorite) 3.25 or 3. 50 gears, then you swap out the whole thing, or buy the posi. unit and swap out your gears onto the new posi. unit and install, ( best left for trained mechanics).
DIY, remove drive shaft,wheels,bolts that hold backing plate and pull out axles, remove bolts that hold hoghead in, drain grease, then remove hoghead. It's heavy! Put back in-- New gasket, reverse procedure.
 

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Try to find a hoghead already set up that has a posi, (and my favorite) 3.25 or 3. 50 gears, then you swap out the whole thing, or buy the posi. unit and swap out your gears onto the new posi. unit and install, ( best left for trained mechanics).
DIY, remove drive shaft,wheels,bolts that hold backing plate and pull out axles, remove bolts that hold hoghead in, drain grease, then remove hoghead. It's heavy! Put back in-- New gasket, reverse procedure.
You make it seem so easy :d
have no experience myself in it but am looking to install a new diff in the near future ,
So based on this topic, NO SWEAT :D
 

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Don't forget about the copper washer 'seals' that are on the housing studs under the nuts holding the punkin... You might have to chisel them off since they tend to 'flow' into the threads of the studs.

BTW, 9" rears came with 2.75s, not 2.73s... Are you sure you have 4V heads? Are they factory? (VIN code M) Most 351C-4Vs had 3.00s or 3.25s. Most 351-2Vs (VIN code H) had 2.75s... If the aluminum tag is still on the rear end (found under one of the punkin nuts), it will have all of your rear end info.
 

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Chevys have posi... Ford & Mercury have Traction lock and Detroit Lockers. Just a pet peave of mine when I hear someone say they have posi in their ford, I realize it's a loose term most people can relate, but you'll never hear me refer to a Ford locking differential as a positrac.
 

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Chevys have posi... Ford & Mercury have Traction lock and Detroit Lockers. Just a pet peave of mine when I hear someone say they have posi in their ford, I realize it's a loose term most people can relate, but you'll never hear me refer to a Ford locking differential as a positrac.
You're forgetting the Ford Equaloc, the precursor to the TractionLoc...
 

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Cool, thanks for the clarification (peeve) I'll remember that from now on.

He need an axle puller or inverted brake drum sometimes works. I would recommend new axle seals and dust seals behind the brake backing plates.
Pulling the 3rd member out can be a chore, it's hard to find a place to pry but once it's broke from the gasket just work it slowly back and forth till it's right on the verge of clearing the studs then get ready for it's full 100lbs of awkward tail heavy mass on your chest. You can use a floor jack under it too but it's a balancing act, I'd just muscle the pig out.
 

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Don't forget that when you break it loose you'll have old (probably stinky) gear oil coming on out. Catch pan.
A ratchet strap on a floor jack, or a motorcycle jack (the flat kind that lift a bike by the frame) works well.
 

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If you don't have an axle puller (slide hammer) handy, find two bolts that will just fit between backing plate & axle flange. Put nuts on the bolts and then turn nuts to loosen, pushing flange away from backing plate, sometimes takes three hands to do this.
 

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why not just use the rear wheel as your "axle puller"? After you take the retention plates off, slap the wheel back on, spin a couple lug nuts on and now you have a big soft (tire) "handle". For the hogs head, if you have a foot-long or so piece of tubing or steel, you could drill to holes in it that will allow 2 bolts with nuts to bolt the makeshift handle to the pinion yoke using the universal joint bolt holes. This would allow you a "lever arm" to try to pry the hogs head free, and since it's on the pinion, it can be repositioned and/or rotated easily to work it free in multiple directions. I'd put the floor jack with a piece of cardboard on the cup just in front of the housing opening such that when it does come out, that tail'heavy mass can tranfer to the jack with wheels for hopefully an easy transition and way to remove from underneath the car.

Kevin
 

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I use a floor jack placed just forward of and level with the diff. so the pumpkin ends up on it instead of dropping on my chest or the ground.
 

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Discussion Starter #19
thanks for the info , i added the 4v heads and cam 2 years ago, and when i run it to the red line the car doesnt shift to 2nd gear till i hit 60 , so i was looking for more of an impressive off the line , i dont have one lined up and rarely see one on craigs. i got some time this spring to do it , just lacking the smartz in that area and i know that its a delicate project... but again thanks for the info ...for the love of cougar go I
 
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