8-3/4 sure grip only pulls 1 tire mark

[Wietse]

Hey guys,

A while ago i checked what type rear axle ratio i had and if there was a sure grip in there or not.
I found a 4.10:1 ratio and seen both wheels spinning the same direction when rotating 1 by hand, trying to hold the other locks up both so i was convinced there is a sure grip in there.
Lately i've seen the car only pulling 1 tire mark though if i take off hard hard, if just a light wheel spin it still seems to spin both tires.
I wonder, was i mistaken or fooled thinking it has a sure grip or could that clutch be worn out, or is this normal?
Someone that has any idea?

I haven't had it open as yet, only changed oil once with an LS 90 gear oil and added 1 bottle of Mopar friction modifier.
It's a 489 3rd member, since the car was originally equipped with a 22" radiator (no a/c or axle package) it is not the original rear axle and i believe it must have came from a '70 Coronet 500 donor car. (must have been an option on the '70 500 as well i think?)

Future plan is to change the rear axle ratio to a 3.55, i am thinking if there is still any repair/service kits to rebuild those sure grips that will be a job for the same time.

 

[AR67GTX]

If the other wheel spins in the opposite direction when you turn the other one you would definitely have an open rear due to the action of the spider gears. I supposed a heavily gunked up open rear and with heavy lube and cold temps might turn both wheels in the same direction at first but once warmed up they should start rotating opposite directions. But your description sounds like a limited slip, possibly one with wear. Some types are rebuildable and others aren’t.

 

[Durandal25]

.....the clutch is worn out.

 

[PRND21]

489 case originally had the cone style sure grip, more than likely worn out. Very hard to rebuild, replace with a better unit, clutch type or gear type when you change your gear set.

 

[Darter6]

cone style sure grip, more than likely worn out.

Yep.

 

[Wietse]

Thx for the replies guys, what does the "cone type" refer to? I believed all have friction plates and springs?

Looking at Doctordiff their stuff, seems like 2 options, the 8-3/4 helical sure grip (Sure Trac II) or the clutch type sure grip (Powr Lok)
Those are direct replacements in the 489 case? As they mention 30 spline side gears, should i check and confirm that or was that standard?

 

[Darter6]

Do a search here and punch in Sure Grip. I'm sure there will be several threads that cover all the different types Chrysler has used over the years.
Yes the 8 3/4'' rears have 30 spline axles stock from the factory.
They do make 35 spline in the aftermarket.

 

[66Satellite47]

With an 8 3/4 there are two types of limited slip, the early style is the clutch type, the later model is the cone type. The clutch type(Dana) is a simple rebuild, cone type not so much so. Both do wear out and loose their capacity.

 

[Fran Blacker]

https://www.doctordiff.com/8-3-4-cone-sure-grip-shim-pack.html

Scroll down and read instructions .

 

[440 Charger]

489 case originally had the cone style sure grip, more than likely worn out. Very hard to rebuild, replace with a better unit, clutch type or gear type when you change your gear set.

Currious what is the best type of Posi now not sure probly elockers is my bet best of each world.

 

[Wietse]

Currious what is the best type of Posi now not sure probly elockers is my bet best of each world.

Seems like the Eaton Truetrac is out of the question, if Doctordiff doesn't want to sell em anymore.
https://www.doctordiff.com/8-3-4-eaton-truetrac-differential.html

I am leaning towards the helical suregrip, just requires conventional gear oil and no friction modifiers are needed anymore.
https://www.doctordiff.com/8-3-4-helical-gear-sure-grip-sure-trac.html

 

[33 IMP]

489 cases usually came with cone style suregrips, as opposed to the Dana clutch type. (Not referring to the Dana 60, Dana corporation made the suregrip for the early 8 3/4).
What you are describing is typical of a worn cone type. They can be rebuilt/made to function again, and there are threads here and fabo that tell how. It takes a little machine work and some shims. A lot cheaper than a new suregrip unit. And considering your location, a lot easier than getting parts from across the pond.
Seriously, check out what Fran refers to in post#9. Those shims from Dr Diff, and some machine work on the cone, .(can and has been done with a hand grinder!) and you're back in business.Rusty rat rod has a how-to "How to recondition a cone suregrip" at fabo, in the how-to section.

 

[Darter6]

The best is the Dana Clutch Type. We called it the V-Ramp because of how the clutch engages. The more torque is applied the tighter the clutches grip.
Auburn makes a cone type that I believe is available at Summit or Jegs. All seem to be in the $450- $600 range.
. The Eaton trutrac can be noisy at slow turning speeds.
I have one.Mine growls at slow speed turns (we have a round-a-bout close to home) It works great. No where near as noisy as a Detroit Locker.Complaints of noise can be found on You Tube.
Some people say theirs is not noisy, others do.

 

[Wietse]

Scroll down and read instructions .

489 cases usually came with cone style suregrips, as opposed to the Dana clutch type. (Not referring to the Dana 60, Dana corporation made the suregrip for the early 8 3/4).
What you are describing is typical of a worn cone type. They can be rebuilt/made to function again, and there are threads here and fabo that tell how. It takes a little machine work and some shims. A lot cheaper than a new suregrip unit. And considering your location, a lot easier than getting parts from across the pond.
Seriously, check out what Fran refers to in post#9. Those shims from Dr Diff, and some machine work on the cone, .(can and has been done with a hand grinder!) and you're back in business.Rusty rat rod has a how-to "How to recondition a cone suregrip" at fabo, in the how-to section.

Spot on gentlemen, that's something i can work with. Thanks for that!
For sure its going to be pricy part to ship to Europe, i already had given up hope of rebuilding this and was looking for a new unit.
I will be doing the rebuild at some point as mentioned in the descriptions.

Just a question, DoctorDiff mentions to machine off .040" of the base of the cone, so that is over the full face or just that outer edge?
In the pictures at FABO it has been machined both, but the lip that was on the edge is completly removed.
Little confusing, i guess it needs a .040" cut over all face.

 

[Darter6]

Drop Rusty Rat Rod a message over on A bodies.Maybe he can explain how he did it better. Good guy.

 

[33 IMP]

Spot on gentlemen, that's something i can work with. Thanks for that!
For sure its going to be pricy part to ship to Europe, i already had given up hope of rebuilding this and was looking for a new unit.
I will be doing the rebuild at some point as mentioned in the descriptions.

Just a question, DoctorDiff mentions to machine off .040" of the base of the cone, so that is over the full face or just that outer edge?
In the pictures at FABO it has been machined both, but the lip that was on the edge is completly removed.
Little confusing, i guess it needs a .040" cut over all face.

I have heard of taking off .100, over the whole face, but if the Doctor says .040, I think that's what I would do. (The .100 might have been to accommodate a certain shim)
The metal removal doesn't even have to be precise. You are just taking off material from the end of the cone to keep it from bottoming in the case before it grips both axles.

 

[440 Charger]

Still bottom line is street or track full spool all fun things to consider.

 

[440 Charger]

I have heard of taking off .100, over the whole face, but if the Doctor says .040, I think that's what I would do. (The .100 might have been to accommodate a certain shim)
The metal removal doesn't even have to be precise. You are just taking off material from the end of the cone to keep it from bottoming in the case before it grips both axles.

The metal on metal is never fun.

 

[Wietse]

I have heard of taking off .100, over the whole face, but if the Doctor says .040, I think that's what I would do. (The .100 might have been to accommodate a certain shim)
The metal removal doesn't even have to be precise. You are just taking off material from the end of the cone to keep it from bottoming in the case before it grips both axles.

Doctor diff kit comes with a .030" shim, so i am assuming they want a .010" clearance behind the cone.
Doesn't sound like much actually.

 

[MoparLeo]

Here is a link from a while ago ( the info doesn't change though )
http://www.waywardgarage.com/tech/rearaxlemopar.html