trying to better understand my new to me 1993 F150 4x4 rear differential. Trying to learn more about it so i can chage gear oil on my own.
I'm afraid my differential needs some attention (grinding when warm in 1st gear when cornering from 35 to 90 degree turns)?
I plan to at least change the gear oil before taking to my mechanic for further inspection. Hoping my gear oil change will fix issue. I know at least at this point that if differential has 'Limited Slip' then add 'friction modifier' to the gear oil.
Any input is greatly appreciated.
This is my 3rd post! go EZ!~

 

Three ways to tell what rear axle you have and if it has L/S. Check the safety sticker in the driver's-side door jamb for the axle code. If it starts with "H", (i.e., "H9") the axle came with L/S. Check the metal I.D. tag bolted on the rear inspection/ cover plate, which you'll be removing to change the oil and look for metal pieces or damaged gears. The bottom line of the ID tag starts with the gear ratio and will have an "L" for the 2nd character, (i.e., "3L55 8 8 ...). Sometimes the bolt holding the tag covers up the 3 or first digit, so you may see "L55 8 8 ...). Final method is to lift one tire off of the ground with a jack and see if it spins. With L/S, it should not. Or if you raise both rear tires up, one will turn the same direction as the other side while turning one wheel by hand. An "open" diff will have each tire turn opposite directions. A grinding or groeling noise is a bad sign for the 8.8" axle, but the problem could simply be a worn u-joint in the driveshaft. Good luck!!! JSM84

 

ok I believe the friction modifier is not doing its job any more. I plan to change R Diff gear oil tonite and add friction modifier as well. I confirmed this week at the Ford dealership that FM is needed for my R diff
thanks for your help JSM84
Adipose
will let you know how the gear oil change goes result wise

 

What problem are you having? Does the L/S not seem to engage? I doubt new oil/FM will help if the clutches are worn, but it's worth a try to get a bit more mileage out of the L/S. The factory Ford Trak-Lok can be replaced for about $200 with a Dana Trac-Lok or a bit more for say a Detroit EZ-locker or similar. IT's real simple to pull the 'chunk' out of the 8.8" and have it worked on if needed. My 88 Bronco with the 8.8" ran O.K., but when I pulled it I found a chipped tooth on the pinion gear. ANY grinding. howling, whining or other noise from the rear axle usually indicates a big problem like posted earlier, but is normally not a major cost to fix or upgrade. There is a ton of info on the web on mods and upgrades for the Ford 8.8" axle to strenghten it if you plan to keep the truck for a while. I go through trucks about every 2-3 years by wearing them out on the farms I survey. Check your oil with a magnet, too, for any metal particles indicating wear. I looked at a ring gear last week that was flat over half the circumference, and the rest of the teeth weren't much better. Severe abuse and lack of oil was the problem. The regular 90wt gear oil can overheat, so a synthetic or 'friction modifier' may help reduce that type of wear. JSM84