Just recently I've had a "grinding" noise coming from the rear of my '02 F-150 SuperCrew KR. It happened the first time when I was stopped on a very steep incline and then started up. It sounded like maybe the limited slip differential was slipping - the engine ran up some RPM's, noise from the rear, no movement. A little more gas, and it moved and drove OK. Now, every now and again, starting from a stop making a right turn (or left?) I get the same sensation/noise from the rear end. I'm guessing something in the diff? OK, here's what worries me - I took it to Jiffy-Lube 10000 miles ago and they recommended changing the diff fluid. I asked if they had the right stuff for a limited slip diff, and they said yes. So, I don't know if it's a fluid issue or mechanical. I don't see many writeups about limited slip differential problems, so I suspect this isn't a common problem. Have other had any problems like this? (My truck has not been off-road, is a 4x2, has 82000 miles and has not done towing.)

Duane in Austin, TX

 

Dig out the Jiffy Lube receipt and verify they used 75W140 full synthetic gear lube and 4oz of Ford friction modifier. Check under your truck for leaks and check the differential lube level.

 

Thanks for the tip - the receipt says "GL5 Syn 75/140 Pail", but no mention of any friction additive. It goes to the dealer on Monday, so I'll take this along. If that fixes it, I'll be revisiting Jiffy-Lube for a refund and to tell them it was my last visit. (Ford will do my oil change for $11.95, but JL is a lot closer.

Duane

 

I tried two things today. First I consulted the manual on the truck. No "friction modifier" is mentioned, just 74W150 synthetic fluid. Second, I stopped at Jiffy-Lube and they confirmed that they only put fluid in - if there is any special additive other than the fluid, they have no record of it, and they say they are following manufacturers specs. Tomorrow Ford - what makes me think I don't want to spend $$ for a diagnostic fee that isn't going to tell me anything? I guess as long as it keeps moving and an axle doesn't fall off, I'm ok!

 

Ford limited slip differentials require a 4 ounce bottle of friction modifier.

Controlled Slip Differential, Rear .....GL-5*[3][4]
All Temps......75W-140

3. Synthetic oil is required.
4. CS IDENTIFICATION: Letter & number on plate on door lock
pillar. (Models W/ Traction-Lok Rear Axle Add 4 oz of
friction modifier part no. C8AZ-19B546A (EST-M2C118-A)