Here's my story...
A couple of months ago I noticed my differential pinion seal was leaking. I took it into a dealer and they changed the seal and added fluid for me.

Recently, my differential has started to howl. My first thought was that they didn't fill it back up. I checked the oil level and it was full.

After researching the problem I found out that I have the 3.55 limited slip differential which supposedly requires the friction modifier additive.

I looked at my repair invoice and unless they threw the friction modifier in for free, they didn't put any in.

Any advice? Should I just get some and put it in and hope for the best? Is it too late? I'm sure if I ask them they'll say that they put it in rather than possibly buying me a rear end. HELP...

 

Hi Dias3,
I too have that noise only when accelerator is applied, goes away when coasting.
I Cannot tell where noise is coming from.
I thought it was the tires, but, the noise goes away when accelerator is released.
Sorry, I do not have an answer, have the same problem. So instead of starting new thread, I replied to yours. Hope you do not mind.
Any and all help would be greatly appreciated......Bill

 

Mine had done that since new, it is 3.55 limited slip. Maybe they never put the additive in at the factory? Iv'e had the bearings changed and it still whines at 60 mph with slight acceleration. It's very annoying. Anyone know of a fix I'm sick of it!

 

Hey Dias3

Does your truck howl all the time, or just on accel/decel? Does it howl at any specific speed? The friction modifier is in the oil for the limited slip clutch plates, prevents chatter and grab when turning. When changing the pinion seal, the oil would only need to be topped up, not changed, so fricition modifier may not have been added, and probably won't affect the limited slip. Sounds to me like you pinion bearings are damaged/failing. If the person replacing the pinion seal is not carefull or experienced enough and over tightens the pinion nut, you bearings can(and usually do shortly after) fail. Pinion bearing preload is very sensitive, more so with used bearings. I have seen many trucks that have a pinion seal replaced and then the bearings fail a month or two later due to overtightening. Just something to think about.

Orlando and wl6, I think your noises may be different than Dias3 because yours have been there since new and his started after they replaced the pinion seal. I have seen many trucks with gear noise concerns, usually occurs at 50-60mph, ok the rest of the time. There are a few threads discussing this and what Ford is doing about it. I will check for any updated info and get back to you.

Later