Rear diff fluid

[dieselcrawler]

Hey all...

A few weeks ago I drained and changed the rear diff fluid in my DRW F350. I have no idea what came out of it, viscosity or if it's sinthetic or dino juice. In a pinch, I just put back in what was availible at my buddy's garage, which turned out to be 75/90wt. Took almost 2 gallons, and a dash of Posi additive.

What I want to know is if this is the right fluid, (I'm thinking it isn't, should it be 90/140 sinthetic?) and if I'm hurting the diff running the lighter wt fluid.

The reason for the fluid change in the first place was a noisy pinion bearing. I had the truck up on a lift to try to find drivetrain noise, and using a mechanic's stethascope, found the pinion bearing quite noisy. There was no metal in the fluid I drained out... looked real good. So I filled it back up with what we had there that nite.

Thanks for any feed back...

[countryraised]

It does call for 90/140 synthetic on my 350 srw, I would bet your drw needs the heavy synthetic also, I don't know if it will hurt it short term, but any distance or heavy loads might?

[Tony V]

yeah man i'd change that.

[dieselcrawler]

I wish I were more sure that the rearend bearings are ok... hate to spend $100 on oil just to have to drain/waste it in a few months if the pinion bearing goes... how common is pinion bearing failure?

[Tony V]

Not real sure. I honestly dont think its very common. I have 200k and never had a prob yet.

[no-tel-in]

did you say you put 2 GALLONS in it??

[Tony V]

yeah I just noticed that. Where did it all go?

[countryraised]

in his dually 2 gallons is probably right. it's a dana 80 axle, larger pumpkin and in our trucks the rear axle oil fills all the way out into the hubs, not just the pumpkin.

[dieselcrawler]

Yup, almost 2 gallons. I bought one at the parts store that night before I tore it apart, about 7:30 PM. By the time I got to filling it back up, around 9:30, after the parts store is closed, I find myself rather lucky to have an extra gallon stashed in the underbody box... it took over 7 quarts, the 2nd gallon only had a little bit left when I was done.

So that big ol' pig is a Dana 80? I didn't know, I should have copied down all the numbers on the diff tags while I was there, just for the info... Do know it's 4.10 gears with a posi...

So how long can I get away with this lighter oil? I haven't been pulling anything, just daily driving. The ammount of noise the pinion is making makes me uncomfortable, but it's not so bad you can hear it over the noise of the truck while driving. I only heard it 'cause I had a sethoscope and was under the truck while it was on a lift, running. Everywhere I put it, brake backing plate, center section housing at the axle tubes, and at the pinion, the center drive shaft support bearing, the transfer case tail housing, all had a nice smooth hum, exept the front of the pinion snout buy the yoak. Noticeable diffrence there. And this is with the drivetrain running at 50-60 MPH... (I have to admit, I was scared... I don't like being under a 9K lb truck on a lift in the first place, but while running also?!?!?!)

[Highbeam]

To verify whether that pinion noise is normal I'd see about putting another truck up there. I've had a bad pinion bearing before on a GM product and they do get really noisy. 100$ in gear oil is cheap compared to what that rear end job will cost. If you are certain that the bearing is toast then just change it, no reason to think anymore about it. Then refill with the right oil.

BTW, I just changed my diff oil last month and syth 75-140 was 17.99 per quart. More than double the synth 80-90. Both Mobil1 products.