I have recently developed a cricket-like chirping noise somewhere in the rear part of my drivetrain. It's a '95 Bronco with limited slip rear differential.

I drained the differential about a month ago and replaced the oil with Pennzoil 80W-90 GL-5 spec. Since then I've driven it about 600 miles. The oil container indicated it was for limited slip differentials and that friction-modifier additives were unnecessary and not recommended. I'm wondering if I need to add the friction modifier anyway.

The chirp only occurs while the drive train is under load and is at any speed. When I let off the accelerator or take it out of gear the noise ceases. The U-joints are tight and have been recently lubricated.

Anyone got any ideas? It's very annoying.

 

Might try greasing the leaf springs. I've had a chirp from the rear end that was that. If that doesn't do it then you might wanna try a re-drain with regular oil and friction modifier. Doubling the friction modifier may not be the best of ideas.

 

The usual way to check if you need friction modifiers is to do very slow speed tight turns. I find backing up and turning, like out of a parking space will do it.

If the wheels chatter, you need friction modifier. Chatter feels kind of like the tires are rubbing the fender well. Kind of a rough start stop chattering feel.

Previous expereince with other LS diffs that chattered was that the gear lubes saying they didn't need additive, often did need it.

BUT, you don't want to add additive unless you are sure you need it. Additive decreases the Limited slip capability of the diff from what I have read. You want a little slip so it doesn't chatter, but you don't want so much that you become one legged.

Not sure about the chirp. Any of the diffs that I had that chattered did not chirp.

Maybe you have a small rock in the drum or dust guard around the discs?

Good Luck,

Jim Henderson

 

Thanks for all of the suggestions. I think I'll focus on something other than the limited slip. It seems more likely to be u-joints or something else based on feedback so far.

I'll investigate it further in a week or two and post anything that I find.

 

Good post Jim.

 

Did this "chirp" exist before you drained & refilled the differential, or relubed the U joints, or did it come about afterward?????

 

The chirping noise began after I changed the differential oil & greased the u-joints. However, it occurred about 700 miles & 45 days later.

It sounds like crickets.

 

You ever find out what the noise was coming from? I've got the same cricket-like sound.

 

I don't have any idea what the problem is and haven't had time to try and diagnose it. I may run a piece of plastic tubing underneath the vehicle and listen at the other end to see if I can determine where it's coming from.

I have no idea if this will work, but it beats hanging on to the underside of the beast while somebody else drives it!

 

If it happens at a slow enough speed like just as you take off, have somebody watch, or use marks/measurements, count how many chirps per tire rotation. if you get about 4 chirps per tire rotation, it's most likely something in the driveshaft... maybe the steady bearing.

 

Well with it doing the "chirp" only when the driveline is under load, but stopping when you let of the gas, or shift into neutral, should be a good clue.

Kinda makes me think thust washer.

Maybe jack the rear end up on jack stands, so both wheels are off the ground & have someone run the thing in gear & you listen & see if you can determine just where the noise is emanating from.

Maybe use the tubing you spoke of, to pinpoint it.

Have you been able to determine which side it's loudest, like around the wheels, or if it's coming more from the center, around the differential, or more from the middle, around the drive shaft or tranny????

I suppose if you doubt the differential lube, you could just drain it & replace it with Motorcraft & the Ford specified friction modifier.

I see your down in the "Loan Star" state, any chance your in the area with all the Big Wet????? I'm thinkng maybe that may be the wild card here????

 

The thrust washer is inside the differential, but I wouldn't worry about it just now.

The reason I suggested it is, seeing as how we don't really know if you've used the correct amount/level of differential lube, viscosity range, or limited slip additive level, I just thought the thrust washer may be complaining!!!!!

Better to try & locate the noise area first, before jumping to conclusions imo.

 

I found the problem. It's the centering yoke bearings in the centering ball. They're completely rusted. The previous owner must have run it through some high water. The u-joints are okay, but I'm going to replace them anyway.

Does anyone know how difficult it is to replace the centering ball? It's a press fit. The choices are a repair kit or an entire new centering yoke. Also, there are no identifying marks on it other than Spicer S 259. None of the parts houses in southern Colorado carry it, and they can't really identify a proper part to order.

 

Thanks to AndyM! I took his advice on removing the centering ball.

I just popped it out and it was very easy actually. I tilted the ball all the way to one side of the yoke, put some cardboard under the edge, and put a screwdriver into the center hole of the ball. I then hit the screwdriver handle a couple of times with a 4lb hammer and it popped right out....no apparent damage done to anything in the process.

 

There's a good possibility this could also be my problem, there is an excess amount of rust under my truck.
However I could use some education on the center yoke bearings. Is this the part that the driveshaft goes into? Did you replace the bearings and the ball? Finally where, and how much did the parts cost you?
Thanks