I was pulling my 9000lb trailer and when going up a very steep hill I heard like a grinding (grrrr) sound from the rear diff (i think). It hasn't done it since but i decided to check the fluid level in the rear diff. When I took out the plug the oil was really black and on the inside face of the inspection plug is this metallic silvery paste. Is there suppose to to be a gear friction reducer additive in this or is this paste fine metalal bits due to something wearing really bad?

 

How many miles on your truck. When it comes to gears, a silver grey paste on the magnets is fine. It's normal wear. Now if you feel chips and pieces with your fingers then that is abnormal. You would have to find out where the pieces came from, whether it be the teeth, bearings, pieces of the limited slip clutches if you have a LS. Hope this helps.

 

The gear lube shouldn't be black. The color is an indication the lube was overheated. Remove the cover and inspect for metal chips in the bottom of the housing. Check the gears for wear and backlash. Rotate the pinion and check for roughness in the bearings. If eveything checks out OK, install a synthetic lube.

 

Sorry I forgot to post year and milage. the truck is a 2003 (2 yrs old as of November), CC DRW 4:10 gears 6.0 litre, it has 40,000 miles (actually 63,000km..that is just 3000 km over warrenty...just my luck). When I said there was a slivery metallic paste I mean there is enough that when wiped off it can make a ball the size of an acorn. Yes , my next step is to remove the cover.....eck.

 

Usually it is little more than a heavy film. You might want to touch base with you pruchasing dealer. If it can be deamed a defect, Ford may absorb some or all of the cost of repair. Don't change the fluid until you talk to them or a Ford rep.

 

I did just that , took it in to dealer. They said it was normal. The diff cover was seaping so i had they pull it inspect and cahnge fluid while it was theer. no things get interesting! when i get it back I see that they put 80W90 hypoid oil in. i question them because teh manual says to put 75W140 synthetic with friction modifier (mine is limited slip). The service manager says that he has talked to Ford tech hot line (only dealers can access) and they have indicated that the synthetic has been causing problems so they advised them to put conventional 80W90 in. I took his word for it but decided to call two other dealers. the other dealers do not have a clue what he was taling about..so i call the Ford customer service 1-800 # explain my problem and they take a while to investigate and come back to me to say that there are no TSBs out on this and that the synthetic 75W140 is what is reccommened. i call the service manager back and he says that he once again confirmed with Ford engineeris that 80W90 is what they are reccomending in my type of diff (a worm gear type of limited slip). they have no TSB on this but the service manager said he would put it in writing for me if i want it. He also said they would put the synthetic in at no cost for me if i wanted but itr may cause me trouble in long run. What to do??????

 

I would do what Ford Customer Service said. Put the 75w140 synthetic back in the dif.

 

When Ford went to the 75W140 we started seeing a lot of bearing problems. I've heard debates on whether the problems were caused by the oil or maybe Ford changed specs or suppliers of the bearings.
Hotline sometimes gives "off camera" suggestions based on what they see. They can't officially tell you to go against what Ford says.
Usually if the customer is paying for the oil I'll put in 80W90. If warranty is buying I'll use the ridiculously expensive Ford 75W140. I've never heard of a problem caused by using 80W90 instead.

 

If you go with the 80w-90 include gear oil change in your maintenance schedule.

 

I would want synthetic back in there. That is what Ford recommends. Ford syntheric gear lube, 75w140, is the color of motor oil. If the color of the fluid was black it is an indication of overheating and synthetics takes heat better than petroleum base lubricants. Either way monitor the fluid closely for both metal and discoloration. Do you have limited slip differential?

 

Yes i do have limited slip, 4:10. The service manger noted that alot of the trow truck applications have the same diff as mine and that is where the problem with the synthetic was being discovered. I will be going back to the dealership this week to sit down with the service manager to try and detetrmine the best solution (to keep the 80W90 in the diff or chnage back to 75W140). At this point Ford customer service has documented all this and have told me that they reccommend the synthetic therefore i feel that I need to put that back in or in the future if there is a problem they could deny any fault (if I keep the 80W90). On the other hand the service mamanger has assured me the best thing to do is to keep the 80W90 and he is prepared to put this in writing, and has told me that he , and ford engineers, will stand behing his reccomendation. Anyway , when i meet with him i will have to make my final decision.

 

I suspect the limited slip as the cause for the problem with gear lube. IMO, the LS is slipping excessively and that is what gave your the sound (grrr) you heard and the discoloration of the fluid. To a degree, a small amount of silvery paste on the plug is normal, but black gear oil is not. If the gears and bearings were the problem the rear would have definate signs of deteriation. The LS can be checked without disassembly, but I prefer disassembly and inspection. If there is a problem, now is the time to get it resolved before you get too many more miles on the truck.