Rear Axle Question

93gtmustang · Nov 24, 2007

I can push in and pull out my drivers side rear axle about 1/16 of an inch.
My passenger side moves less.
What is the normal amount of play.
Is this normal?
Should I check for a c-clip backing out of position?
I have 31 spline mosers with eaton posi. The install was done by a shop back in Jan. 2006.
Thanks

TRWXXA · Nov 24, 2007

1/16" of play isn't bad at all for a c-clip unit.

Prime Lord · Nov 24, 2007

Yeah, not at all. Especially for a car w/ some mileage on it. No worries. If a C-Clip blows, your tire will just start to wander away. heh.

In all seriousness though, a 16th of an inch is nothing to sweat

93gtmustang · Nov 25, 2007

So I don't have to take the rear cover off and check to make sure the c-clip is not coming off?

Mustang5L5 · Nov 25, 2007

The c-clip can't come off the way it's positioned inside the dif. It's recessed into a small circular pocket. Only way to take it off is to remove the center diff pin and push the axle in about 1" and only then will the c-clip come off.

93gtmustang · Feb 11, 2008

I going to go and check my C-Clips, just for saftey reasons.
A couple questions.
Will I be able to see the C-Clips just by removing the cover, or does the assembly have to be rotated 180 degrees?
Also, what weight gear oil and what type of friction modifier do I refill with? I have an eaton posi unit.
Thanks

Maryland Stang · Feb 11, 2008

I put Motorcraft 80w90 Premium oil in mine. DO NOT put friction modifier in when doing a refill. The plates have already been treated on the initial fill.

NKau · Feb 11, 2008

93gtmustang said:
I going to go and check my C-Clips, just for saftey reasons.
A couple questions.
Will I be able to see the C-Clips just by removing the cover, or does the assembly have to be rotated 180 degrees?
Also, what weight gear oil and what type of friction modifier do I refill with? I have an eaton posi unit.
Thanks

There's no reason to check them; it's physically impossible for them to work their way out of the axle tube without the center pin being removed as Mustang5L5 told you.

If you're bored, and want to replace your diff. fluid anyway, and want to see how the axles are actually held in, go ahead. Otherwise there really is nothing to 'check'.

93gtmustang · Feb 11, 2008

NKau said:
There's no reason to check them; it's physically impossible for them to work their way out of the axle tube without the center pin being removed as Mustang5L5 told you.

If you're bored, and want to replace your diff. fluid anyway, and want to see how the axles are actually held in, go ahead. Otherwise there really is nothing to 'check'.

Well, my main reason for checking the drivers side one is that there is some play in it.
And also, saftey reasons. I just don't want to have the axle let go at 104 mph going down the track.

I can see what you mean by saying that it's impossible for them to work their way out. I was thinking, maybe the c-clip could have been damaged or bent from coming out of a burnout sideways where it's wet and then having the car grab , which put's stress on the c-clips. I saw a SS Monte Carlo's axles come out at the starting line.

So, if they where going to come out, they would have already come out, or, I would be able to just pull the axle out anyways?

Thanks

93 LX · Feb 11, 2008

when C-clips "blow" its because of the axle sheering off at the tip or the spyder gears letting go.

Roland69 · Feb 11, 2008

Maryland Stang said:
I put Motorcraft 80w90 Premium oil in mine. DO NOT put friction modifier in when doing a refill. The plates have already been treated on the initial fill.

is there any truth to this...never heard that and I always use FM in a clutch style rear diff

Shakerhood · Feb 12, 2008

Roland69 said:
is there any truth to this...never heard that and I always use FM in a clutch style rear diff

You can "Try" to run without putting FM in, but if the Clutches start to chatter then you will need to add some.

NKau · Feb 12, 2008

93gtmustang said:
So, if they where going to come out, they would have already come out, or, I would be able to just pull the axle out anyways?

Thanks

The only way it can come out, is if you snap the axle itself which is typically done by launching on sticky tires. Once the axle snaps, the c-clip can do nothing to keep the axle in..........you never see an axle come out due to 'c-clip failure'; it just isn't possible to move the axle inward enough with the center pin installed to get them to fall off.

Every fox I have ever owned (3) have had some degree of side to side axle play; it's really nothing to worry about. If you do launch your car hard at the track on sticky tires, get yourself some hardened moser axles, and quit worrying

Maryland Stang · Feb 12, 2008

Roland69 said:
is there any truth to this...never heard that and I always use FM in a clutch style rear diff

Nevermind. I was given bad advice from another message board. Imagine that. Anyway, I checked my FSM and it says to put FM in with a refill. 4 oz of it.

TRWXXA · Feb 12, 2008

Maryland Stang said:
Nevermind. I was given bad advice from another message board. Imagine that. Anyway, I checked my FSM and it says to put FM in with a refill. 4 oz of it.

I had gotten some diff. fluid that supposedly didn't need FM added. Turns out it really did. After a few hundred miles, the clutched started to chatter when going around corners.

93gtmustang · Feb 12, 2008

NKau said:
The only way it can come out, is if you snap the axle itself which is typically done by launching on sticky tires. Once the axle snaps, the c-clip can do nothing to keep the axle in..........you never see an axle come out due to 'c-clip failure'; it just isn't possible to move the axle inward enough with the center pin installed to get them to fall off.

Every fox I have ever owned (3) have had some degree of side to side axle play; it's really nothing to worry about. If you do launch your car hard at the track on sticky tires, get yourself some hardened moser axles, and quit worrying

I have Moser 31 spline axles that where installed in Jan 2006 with an Eaton Posi.
I launch my car at 4000-4500 rpms on slicks, so it is a good shock load.
My wife and I alternate weekends drag racing this car. My 10 year old daughter goes with us. So I'm just trying to cover the saftey issues. I would hate to see an axle let go and have my daughter have to witness the circumstances.

twistedwankel · Feb 12, 2008

TRWXXA said:
I had gotten some diff. fluid that supposedly didn't need FM added. Turns out it really did. After a few hundred miles, the clutched started to chatter when going around corners.

I've found that even with FM a posi will chatter on the first couple of sharp turns after going a good distance in a straight line on a freeway.

It's the nature of the beast.

67coupe · Feb 13, 2008

The side to side play of the axles is caused by worn or improperly setup friction disks. Perfectly normal with mileage, esp hard use.

When you push the axle in, the end of the axle is hitting the diff pin. When you pull the axle toward you, the c-clip is hitting the spyder gear which is hitting/compressing the clutch pack against the diff carrier.

Before my gear install, I too had side to side play in the axles. In fact, you could hear them clanking back and forth while turning into a driveway. After the gear install and clutch pack rebuild. I noticed some slight resistance during install of the diff pin due to larger/unworn clutch packs replacing the stock ones. The play and the noise are gone.

93gtmustang · Feb 15, 2008

I had my rear jacked up tonight.
With the wheel mounted there is no axle play at all.
I noticed the play , which is about 1/16 on an inch with the wheel not mounted.
But with the wheel mounted there's no play at all.
I there a difference in this?
Thanks for all your help!

93gtmustang · Feb 19, 2008

I talked to Eaton tech today.
They do not reccomend synthetic gear oil with their posi units.
Coventional 80w-90 for the North Eastern part of the states.
Also, get the friction modifier from a Ford dealer. There is one that has a sea green color, that's the best one to get. And there is another that is an orange color, either one will work but the green one is the best I was told.
Fill 1/2 way with gear oil. then add 4oz friction modofier, then fill the rest with gear oil untill it flows out of the fill hole.
Clutch chatter when cornering after a drain is normal because the clutches are not fully lubed.
Go to a parking lot and do several figure 8's in each direction and that should get rid of any chatter.
This is what I was told at Eaton.
I thought I'd pass the information on to everyone.

Rear Axle Question

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