I changed my rear fluid not that long ago with RP and added FM, but went through some water and now have that shudder...

Is it mandatory to use synthetic? Our Napa has Valvoline 75w140 for $6/qt or the full synthetic for $17/qt. Since I have the Sterling 10.25 I need almost 4 quarts and don't look forward to spending $70 when it could be $24...

 

Full synthetic is MANDATORY in the rear axle.

 

i dont think synthetic is required, just make sure you are using the correct weight and correct amount of FM in it

 

Well *****, that doesn't help lol.

 

have you looked in your owners manual yet?

 

Owners manual calls for full synthetic.

 

FWIW I pulled apart the read diff last weekend and changed the fluid to full synth and added the friction modifier. The fluid didn't look too bad and the clutch packs seemed to be in good shape - not alot of shavings or other crap in there. I've had it back together and drove it all week with no shutter - hopefully this lasts!

FWIW I checked the manual and it indicated 75W-140 SYNTHETIC [page 314 of my manual] so that's what I went with.

 

Sorry, Patrick - synthetic is required.

 

Alright, synthetic it is. Thanks

 

Good call! The way I looked at it while it did hurt to pay almost $60 for the fluid and another $8 for the FM it's a small price to pay for not having to pull the rearend apart again lol. Also, given the price of the clutch packs full synth seemed like a good investement.

 

I added two containers of the Motorcraft Friction Modifier over a year ago, the shudder has not returned.

 

Just took my 07 Screw into my local Ford service center today for this issue. I have under 40k mile on the truck. They replaced the clutch pack under the factory 60k powertrain warranty.

 

Unless you have a Detroit tru-trac LS (Aftermarket)...then Dino oil is mandatory (NO Synthetic). Just trying to avoid confusion..if stock axle..then it's synthetic.

 

Replaced with full synthetic and 8oz of F.M., got rid of the shudder for a bit, then it came back. 4 more oz of F.M, fixed for a day, then back. Asked ford and they said its probably the clutch packs going. I'm out of warranty so I'm just going to drive it as is for awhile. They said the most common effect is I lose limited-slip, worst case is my axle seizes. Oh well, saving for a True-trac right now.

 

I didnt do anything and the shudder went away completely.