Folks,

Still having a problem getting an Absolute Confirmation of the correct fluid to use in the REAR gears.

Got an 98 XLT 4x4 SOHC 4.0

There is one Tag bolted to the rear cover. It reads....
(2 rows of numbers):

S612B
55 88 7J15

The parts guy at the dealer said that there is often a second tag that reads "synthetic only" and that most XLTs are LS.

He said that the door sticker code (which is "axle: 42") does not identify LS or not. He also said that there is no the way to be SURE which to use except for that tag (not even the VIN).

My concern is that IF there was a second tag...it may have broken off...or been lost some other way.

The Ford guy said he didn't "think" those number referred to LS...but could not tell mean what they DO mean. I KNOW they mean SOMETHING, or they would not be there. I need to know exactly what so I can be SURE what kind of fluid to use.

Anybody know or have a reference?

THANKS!

 

The S612B is the axle model number, and, from my experience, should be enough to identify the axle except for the gear ratio.
The gear ratio and LS are also encoded in the first entry on the second row. There should be a 3 before the 55, indicating a 3.55 gear ratio. A limited slip will be indicated by an L between that 3 and the 55 (3L55 is limited slip vs. 3.55 which indicates open)

 

Actually, on my '97 the first digit of the ratio is not on the tag. My tag reads "L10 88 7E27". Mine has a 4.10, limited slip also verified by the D2 on my door jam certificate and my window sticker.

Now as far as Kev100's Explorer goes something has happened to cause the inconsistency. Either his door was replaced with another Explorer's which resulted in the wrong tag or the original 4.10 open differential was swapped out for an open 3.55 open differential or the tag got mixed up when someone serviced it. The differential tag definately indicates an open 3.55 axle. The 42 on the door tag definately indicates an open 4.10 axle. Kev100, what size tires are on your Explorer now? The only tires that came with the 4.10 were 255 70R16 tires. What are your RPMs at 60 MPH in OD and D? With 255 70R16 tires and 4.10 axle you should be turning about 2600 RPM at 70 MPH in OD or 3450 in D. If you have 255 70R16 tires and someone swapped your axle for a 3.55 then you will be turning about 2250 RPM in OD and 3000 RPM in D. You might have to put your transmission in N and turn your rear tire one revolution and count how many times your driveshaft spins to be certain (without opening up your differential). If your driveshaft only spins about 3 1/2 times then you have a 3.55. If it spins a little over 4 times then you have the 4.10. The only reason this is important is because Ford specifies that the rear axles in all V8 equipped Explorers, all 3.73 and 4.10s and all limited slips get 75W140 synthetic fluid. All others only call for 80W90 axle lube. The 75W140 will resist heat better and provide better cooling and would be an improvement to your 3.55 (if thats what you have). I wouldn't go the other way though and put the 80W90 in a 4.10. You are safer if you go ahead and put in the synthetic fluid until you know what ratio is really in your differential.

Finally, compare the VIN on your sticker in the driver's door with the metal tag on top of the dash on the driver's side and on your title to be sure they match up. If they do, then you can be reasonably certain that your Explorer was originally equipped with an open 4.10. The only thing left to find out is if someone mistakenly put the wrong tag on during a prior service or if a previous owner swapped out the rear end for a 3.55.

 

I just went through this nightmare with another vehicle of mine. No one could tell me if it was LS or not. I finaly did the "ultimate" test. I jacked up the whole rear end and spun one tire. If the test holds true for everyone, then if the other tire spins the same direction then you have LS, if it spins in oposite directions then you don't. The truck has to be in Nuetral. You might want to verify that this test is for your exact truck, but it worked for me. Side note : Once I determined whether it was LS or not, I went on my merry way to purchase some Mobil 1 Synthetic Gear lube and guess what..... there's only one kind and it's for LS and non-LS. What a waste of time. Better to be safe then sorry I guess.

Good luck !!!

 

Is it me or am i missing the boat. He has a 4x4. Look at the front axle to confirm what everything else is saying. The front and rear should be dang close.