Any rear end experts in the house?

[TripleDigitRide]

When you are under the truck read the tag, or take a picture, that is on the back cover. It will let you know if it is posi and what gear it has. The tag should look something like this:

If the ratio says something like this "3.00" then it is an open differential and should not be chirping at all. If the ratio says "3L.00" then it is a locker and may require the friction modifier. The numbers are the gear ratio so it may say "3.00", "3.55", "3.73" or even higher. If it is missing the "L" in the ratio then it is an open differential and should not be acting like a locker. The "L" in the ratio is the indicator for a locking rear end.

 

The chirping is because the two axles are locked together now. Normally there is a friction setup that locks them together under high load situations but lets the outer wheel spin faster when turning. But because they are locked together now the inner wheel chirps as it tries to keep up with the outer wheel.

 

The friction modifier is actually supposed to let the differential slip some. Without the friction modifier the wheels will act like they are locked together. I would say to try adding the friction modifier and then turn a few circles in both directions. Do not try to do donuts because the axles will just lock up under load.

The codes on my tag:

3 L 55 9 75

 

I am assuming that means 3.55, Limited Slip, 9.75

[TripleDigitRide]

You need this

http://www.amazon.com/Ford-XL-3-Friction-Modifier-Additive/dp/B000NU5LP6

If I don't see any improvement in the next few days, I will try that. Thanks.

[Raoul]

Sorry, but I have to say this. Yes I am, and I like limited slip.

[BrasilNuts]

I had a '95 Mustang GT with a similar problem. It's been many year and I'm a little fuzzy on the details, but I added dif. fluid and it still made the noise. A mechanic friend of mine told me to buy the Ford dif. fluid and it would work.

He was right.

If you're going to add dif. fluid, get it from Ford. Edited February 22, 2014 by BrasilNuts

[TripleDigitRide]

I had a '95 Mustang GT with a similar problem. It's been many year and I'm a little fuzzy on the details, but I added dif. fluid and it still made the noise. A mechanic friend of mine told me to buy the Ford dif. fluid and it would work.

He was right.

If you're going to add dif. fluid, get it from Ford.

I already changed the fluid (before this thread), and I believe it was Valvoline from Auto Zone. Someone posted a link to some Ford specific (Motorcraft) friction modifier additive. I think I will try that before draining all of the new fluid and buying more.

[BrasilNuts]

I bet that's your problem then.

I had a Auburn Dif. put in my Mustang, the guy that put it in told me to just get the dif. fluid from Autozone. A few days later it started popping in tight turns.

Added the Ford fluid and never had another problem, well until I got rear ended and the axel was ripped out of the car.

[TripleDigitRide]

I bet that's your problem then.

I had a Auburn Dif. put in my Mustang, the guy that put it in told me to just get the dif. fluid from Autozone. A few days later it started popping in tight turns.

Added the Ford fluid and never had another problem, well until I got rear ended and the axel was ripped out of the car.

Did you use the Ford additive, or replace all of the fluid with Ford's brand?

[BrasilNuts]

If memory serves, I just dumped it in with everything else.

Just the Ford additive. Edited February 23, 2014 by BrasilNuts

[DixieDawg]

I had a 2000 model that rear end should take the synthetic 75w-140 or the 90weight synthetic I had a popping and chatter in mine turned out to be a wheel bearing going bad check the inside of your rear wheels for any signs of oil another thing check your vent on that rear end if it gets stopped up it'll heat up which breaks down the oil in the differential and causes a loss in viscosity but before I go changing the fluid again I'd add the motor craft (made by ford) additive to it and check the inside edges of my rims and inside walls on my tires for signs of any leaks if you see any sign of oil your grease seal and possibly your wheel bearing could be bad any of these will cause that popping and rattling especially in a turn I had the same issue once before -Dusty-

[jtmaze]

[quote name="mrstaylor0602" post="1114870" timestamp="1393041399"]Add some friction modifier, do some figure 8's and report the results.[/quote] This JTM We the People of the United States, in order to form a more Perfect Union......

[Luke E.]

The codes on my tag:

3 L 55 9 75

 

I am assuming that means 3.55, Limited Slip, 9.75

 

 If what Dolomite said it correct and I have no reason to think that it's not, the "L"  is the designation for "locking rear end" I'm assuming that he's pulled this info from somewhere online. It would seem odd to me that a half ton pickup would have a locking rear end unless special ordered that way but weirder things have happened. 

 

 I forgot to ask before but does it do it when turning left and right or one or the other?

[DixieDawg]

You have a limited slip 3.55 rear end with 9.75" rearend -Dusty-

[Sam1]

misadvertising! 

[10-Ring]

Check your drive shaft U-joints.  Rear end problems stink!

[TripleDigitRide]

[quote name="10-Ring" post="1115377" timestamp="1393163827"]Check your drive shaft U-joints. Rear end problems stink![/quote] Yeah, he/we checked them while it was on the lift. They appear to be OK.

[Superman]

 If what Dolomite said it correct and I have no reason to think that it's not, the "L"  is the designation for "locking rear end" I'm assuming that he's pulled this info from somewhere online. It would seem odd to me that a half ton pickup would have a locking rear end unless special ordered that way but weirder things have happened. 

 

 I forgot to ask before but does it do it when turning left and right or one or the other?

Ford used the trac-lok limited slip in a lot of their trucks, 2wd and 4wd. Its not locker like some people think, like a detroit locker. Its a limited slip, it uses clutches on either side behind the side gears in the diff. They work good on the street, not so much offroad.

 

TDR-What you described in the OP sounds exactly like the limited slip chatter. We get them in the shop doing exactly what you describe and the friction modifier from the parts store works just as good as the Ford brand.

[Tncobra]

First thing I thought is what Dixie said, a outside bearing. 8 inch rears are known for that.

Sometimes you can narrow down a vibration by seeing if it's speed related or rpm related. Get it vibrating and note the speed. Put the trans in another gear and get it too vibrate. If it vibrates the same speed in any gear it is usually from the tail shaft back. Shaft/joints/rear/drums/tires/wheels. RPM vibration is usually trans forward.

Put the truck on blocks and run it. Also you can lift up on the tire/wheel and find bearing play.

[Dolomite_supafly]

I pulled the info from 2 decades of building hot rods, mostly Fords.

I would add the friction modifier and drive it around for 10 minutes. The problem should be gone.

[TripleDigitRide]

While the issue seems to have cleared up within the last day or so, I decided to add a bottle of Motorcraft Friction Modifier for good measure. OMG! Why didn't someone warn me of the god awful stench of that stuff? I'm not sure there's another substance on earth that stinks so bad.  :puke:

[Guest RebelCowboySnB]

lol Gear oil will gag a polecat... We assumed you knew...

[dralarms]

My wife says as big as mine is I should be an expert.