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Discussion Starter #1
My car is a 1999 Mustang 5 speed with a 3.8.


I just got the car running after buying it with motor issues. While driving it for the first time, I noticed gear chatter in the differential when decellerating at lower speeds or corners. It does not happen while accelerating, sounded like a cracked disk brake, and seemed to happen only while slowing down. The brakes good.

I opened up the rear cover, and noticed that the fluid has very fine metal particles. Everything looks fine, but the pinion gear has a couple very small nicks. (I know, a picture would help, but I have no camera).

It has limited slip, no breather vent.

My question is, can anything be done to prolong it's life, such as a good cleaning and new fluids, or is this a common issue that happens right before a big explosion??


Thank you
 

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I use to put a heavy heavy oil in it, but the mechanics back in those days said it was a last resort. with the way tolerances are now I would step it up to a slightly thicker gear oil with a synthetic. Royal purple maybe. or buy the gear and get it replaced.
 

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Many times this type of problem can be fixed by changing the oil and putting in the correct limited slip oil additive. Use 80W90 gear oil and one bottle of FORD additive. You can only get this at you Ford dealer. Do not use the additive that the auto parts stores sell. Use the Ford additive only. while you have the cover off check the tabs on the clutch plates to see if any of them are broke off. I've seen this several times and it can cause a similar noise.
 

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Discussion Starter #5
Thank you for the replies. I appreciate the advice. Thicker gear oil makes sense. It would probably be a good way to reduce noise and prolong the gears. I'll check pinion play (is the supposed to be any play at all? what is the norm?). The clutch tabs are worn at the edges a little. I need a camera! How would I go about checking the clutch tabs?

Before I add the expensive stuff, I'll give the insides a cleaning, add 80w-90 or something, run it for 20 minutes, drain, inspect, and fill it with the good stuff. I'd like to get rid of the metal particles in the oil, so a flush can't hurt.

I don't have a qualified garage around my area to do gear replacements, so if anything, I will have to either attempt it myself, or try the oil change and see what happens, then drive it to the nearest shop. Thanks again
 

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Be sure to clean the fill plug. It has a magnet in it and it will probably be covered with metal. There are 3 friction discs on each side of the differential. Each disc has 2 tabs. If all of the tabs are there then it's good. There should be about .010 backlash between the gears measured at the ring gear. You will need a dial indicator to measure this. Check the gear teeth for scuff marks or obvious excessive wear. The teeth should be smooth and shiny.
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Discussion Starter #7
Be sure to clean the fill plug. It has a magnet in it and it will probably be covered with metal. There are 3 friction discs on each side of the differential. Each disc has 2 tabs. If all of the tabs are there then it's good. There should be about .010 backlash between the gears measured at the ring gear. You will need a dial indicator to measure this. Check the gear teeth for scuff marks or obvious excessive wear. The teeth should be smooth and shiny.
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I put new fluid in, drove around for a couple of miles (sounded better already), then drained the new fluid. I cleaned the magnetic fill plug, no pieces, just particles, checked the clutch tabs better, and can see that they have wear from moving back and forth. I assume that at some point, they need replacing, as do the gears, but for now, I'm going to add the best fluid I can find, which isn't great, but better than what was in there. I got the Ford additive (nasty smelling stuff), and 2 containers of Lucas heavy duty oil additive. Now, the label on the bottle says to use 50-100% `lucas oil` in differentials.

Has anyone used this? At what ratio?

I asked the service guy, he said use 100%, but then I asked about clutch plates, and he told me there is no such thing in a diff!! I won't take his word on the oil either.

That tool to check backlash,,,,I wouldn't even know where to begin. I think maybe the gears will need to be replaced by a proper mechanic, because I couldn't even hook that tool up! Thanks for all the info.
 

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Discussion Starter #8
Small change after new fluids, but still has gear noise, just not as loud. Looks like it'll have to do until I find a shop that can rebuild the diff properly. I'm done,

By the way, that Ford friction modifier,,, don't add that if you have anything to do within a day or so that involves being around other people. It smells so nasty, and it just won't wash off.
 

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Sorry it didn't work, but it's always worth a shot. Most of the time this will fix a noise in a limited slip rear end.
 

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Have you checked the air pressure in the rear tires? If the air pressure is not equal, or tread wear is not equal between the rear tires then it can cause problems with a limited slip differential. You should never run unmatched tires on the rear of a car with a limited slip differential. If the car was driven for a while with a low tire or any of these conditions then it might have worn out the clutches. The clutches in the Traction Lock wear quicker than the clutches in the old Eaton Posi or any other differential that has solid steel clutch plates. The clutches in the Traction Lock need to be replaced from time to time, especially if the car is used for drag racing or if a lot of burnouts are done. It may be that all you need to do is replace the clutches, but then you also might have problems other than that. Check the pinion for up and down or in and out movement. If there is any movement other than rotation then you have pinion bearing problems.
 

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Discussion Starter #11
When I first got the car last week, the tire pressure was off on every tire, and one rear tire was at 13psi. I'm not sure how long it was like that, but I doubt the former owner checked tire pressure. The air filter looked like a furry grease ball, a hole in the intake was covered by cardboard siliconed over it, and I'm certain it was used for burnouts, donuts and drifting!

I quickly checked the pinion gear, it didn't move up and down, but may possibly have improper contact with the ring gear. Although the gears are worn evenly, there is a little play when I turn the driver side wheel, from the axle, to the ring gear, and to the pinion. The clutch plates have been moving back and forth, judging by the wear on the tabs, probably 1/16th to 1/8th inch in either direction. All 3 of the tabs are worn at the edges, but can't move out of the slot.

Do worn clutch plates make any certain noise when worn, or do they just stop working? I hear more of a gear chatter than anything.
 

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"Back in the day" used car dealers stuffed bananas in the rear end to stifle any gear howl.
 

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Worn clutches usually make the most noise when turning a corner or just as the car comes to a stop or as you take off. They also cause excess axle end play. You say that you are hearing gear chatter. I don't understand exactly what that means. Most of the time a gear will make a whine or howl noise. I don't recall a gear making a chatter noise. That usually comes from a clutch.
 

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Discussion Starter #14
Worn clutches usually make the most noise when turning a corner or just as the car comes to a stop or as you take off. They also cause excess axle end play. You say that you are hearing gear chatter. I don't understand exactly what that means. Most of the time a gear will make a whine or howl noise. I don't recall a gear making a chatter noise. That usually comes from a clutch.

The issue is just as you describe. It makes the noise at very low speeds, mostly while slowing down and cornering. The noise I hear is from the rear, at least it sure does sound that way, like if I had a cracked disk brake (checked for that already),,, maybe chatter is the wrong way to describe it. When I take off from a stop, it sounds normal, but when I slow down, it's like meshing gears. Just like I would imagine it would sound like if the diff had no oil, just gear noise clicking together. More of a growling clicking, than a whine.

The sound would probably disapear if I put some bananas in there, as mentioned in a previous post, but that's not going to happen(they would freeze. I live up north). The new gear oil made some change, but not enough to say it's good. Does it sound like clutch plates, and can these be changed easily, or is this a job best done by someone other than myself.
 

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It's best to remove the differential and take the ring gear off when you replace the clutches. When you install the clutches you need to shim them for the correct preload.
 

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Discussion Starter #16
It's best to remove the differential and take the ring gear off when you replace the clutches. When you install the clutches you need to shim them for the correct preload.
I can take it apart with no issues, but I've heard so much about shims and clearance distances that can mess up a new gear set! Thanks for all the info, and I'll update this post once I've been to the garage for repairs. Just in case someone has similar issues.
 

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Do a quick check. Jack up the rear end and check the axle end play. Pull and push on the rear wheels and see how much they move in and out. If it's over 1/8 inch then the clutches are probably shot.
 

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Discussion Starter #18
Do a quick check. Jack up the rear end and check the axle end play. Pull and push on the rear wheels and see how much they move in and out. If it's over 1/8 inch then the clutches are probably shot.

I did a quick check on that when I was looking at the brakes, they don't seem to move at all by push/pull, but do have play while turning the wheel(tire). I also turned the wheel while the rear diff cover was off, and there was more play than I expected, though I have no idea what is normal. When turning the wheel back and forth, the axle moves a little first, then the ring gear, then the pinion. I'm not talking about a half rotation of the tire or anything, but I thought that the axle would act as a solid connection to the ring gear, and have no play what so ever!!
 
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