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Technical question for the Ford 9” guys:
I’m going to have a Yukon posi unit installed in the rear end of my big block swapped 1963 Galaxie 500XL. Currently has the open diff from the factory.

I ordered the “aggressive” unit with 4 preload springs without realizing there was an option for a “smooth” 2 spring unit. Just how different would these two units be? And do you guys think the 4 spring unit will be ok on the street?

I’m building the car out for 80% street cruising and 20% burnouts for fun. Drag racing probably not in the cards for this car.
168103

168104
 

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I'd run it.

Be careful cornering, esp when "power on" during cornering and more esp if the road is slippery.

Adding throttle in a corner with a "posi", esp on slippery roads, and she will swap ends on you in an eye blink!
 

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I think Yukon's claim is ridiculous! I am POSITIVE using only two preload springs will cause the "plate" that the springs press on to crack prematurely. Ford traction loc units use four springs and are NOT aggressive. The sensitivity ( lock up) can be softened by reducing the shims ( in the cover) behind the clutch hub OR shortening the four preload springs on a bench grinder. IIRC Currie doesn't use any preload springs at all.
You will be fine with what you bought! Make sure you use friction modifier OR a compatible oil. My advice comes from 52 years of building Ford diffs after being factory trained.
Randy
 

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I think Yukon's claim is ridiculous! I am POSITIVE using only two preload springs will cause the "plate" that the springs press on to crack prematurely. Ford traction loc units use four springs and are NOT aggressive. The sensitivity ( lock up) can be softened by reducing the shims ( in the cover) behind the clutch hub OR shortening the four preload springs on a bench grinder. IIRC Currie doesn't use any preload springs at all.
You will be fine with what you bought! Make sure you use friction modifier OR a compatible oil. My advice comes from 52 years of building Ford diffs after being factory trained.
Randy
Thank you Randy. I appreciate the advice coming from someone who is so experienced with these rear ends. I will be certain to make sure my guy setting it up uses the friction modifier.

I’ve read that clutches are ideally pre-soaked in the modifier before being installed. Obviously my unit is already assembled. Will I need to “break in” the clutches after install?? I was thinking driving slow speed in a parking lot, making sharp turns would force the clutches to engage and disengage often - helping to speed this along? Or is it more of a “if it is set up right, it doesn't need to be broken in” situation?
 

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Thank you Randy. I appreciate the advice coming from someone who is so experienced with these rear ends. I will be certain to make sure my guy setting it up uses the friction modifier.

I’ve read that clutches are ideally pre-soaked in the modifier before being installed. Obviously my unit is already assembled. Will I need to “break in” the clutches after install?? I was thinking driving slow speed in a parking lot, making sharp turns would force the clutches to engage and disengage often - helping to speed this along? Or is it more of a “if it is set up right, it doesn't need to be broken in” situation?
You are right. "Ideally" the clutches are soaked. If they aren't you could experience a "popping" situation initially and slow tight turns would "work" the oil and friction modifier into them and stop the popping. There is no "break in" to do as the "slipping" only happens wen turning or spinning the tires LOL I've only had one "pop" and I didn't build it. A few slow circles cleared it up.
 

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The Yukon aggressive versions are aggressive, but nothing like a locker. Just make sure you have tires always at equal pressure and have a good additive in it. Arguments always arise, but the bevel cut gear that loads the clutches could swim in additive and still drive the side gears plenty, don't be afraid of too much, be afraid of too little. Also, good rule of thumb, if it's in the oil already, or delivers in a toothpaste tube, it's not the good additive. If it smells ugly in the bottle, likely good LOL

I would recommend you add a liberal amount of either Kendall or Mopar limited slip in the small plastic bottle. Then go out in the driveway and do easy low power slow circles to get it through the clutches without adding heat.

My favorite in Ford early clutch type

Second and almost equal favorite

Also good

Notice the pattern of the bottles, if it's in a taller bottle from Ford, it's the later version for Superduties, etc and doesn't work as well on the Traction Locks
 
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