i accidentaly read the wrong oil weight from my manual when i bought new differential fluid. i filled the rear diff with 75w-90 instead of 75w-140. i used lucas synthetic, not cheap. should i change it out with the 75-140 or am i safe with the 75-90??? i would hate to have to drain out the new oil i just put in.

 

If you used synthetic, you *should* be okay, but I'm not certain.

If you have limited slip, you need a bottle of friction modifier from Ford. I don't think Lucas puts it in like some other synthetic gear lube manufacturers.

 

I've used Lucas Oil and it does contain the friction modifier. No need to worry about that. But for peace of mind, I would just go ahead and get the right weight oil. Do you really want to run your truck with the wrong gear oil?

gotlucasoil.com carries LUCAS 75/140 SYNTHETIC GEAR OIL in quarts, gallons, and 5 gallon buckets.

And if you want a fine steak, Lucas Oil also has cows.

 

thanks for the replies. i was kind of leaning towards switching it out anyway. i dont tow anything on a regular basis so im *guessing* the 75-90 is will work till i order some 75-140

havent you seen the commercial? cows are always happier in california

 

If you have a 4x4, drain it out and put it in the front, that's the right weight for up there.

 

Drain it.....you're better off without the Lucas anyways. Have you actually SEEN this stuff after it's put in something?? It turns into FOAM!! I put some in my manual transmission, and left the shifter off so I could see for myself. I cranked the truck, and put it in gear with the transfercase in neutral. Looking through the top cover you could see foam slinging around everywhere. I immediately drained it.......the stuff came out pure white. I tried flushing it out 3 times with ATF.....ended up having to fill the case with diesel to get all that crap out of there......

Don't believe me? Go to a parts store that has one of those Lucas displays with the gears that you spin. Turn that crank really fast for about 10 seconds and see for yourself.

Also, I'm curious......why did you change the fluid? Did it get contaminated?

 

Will it hurt anything?? No. Is it right? No. Would I be able to sleep at night knowing I had done that?? Absolutely not. Good thing you're changing it...now you can put some good oil in it. Amsoil's Severe Gear is really really good stuff! They have the 75W140, plus others for the front.

 

i always thought lucas made quality products. guess ill shop around some more to see which brand to buy. i changed it out beacuse i just hit 98,000 miles. just for a little peace of mind. im also doing the brake fluid and power steering fluid.

 

I'm gonna take mine to the dealer to do mine real soon - I also have 98k. I'd rather pay them the $140 than mess around with trying to make sure the RTV sets up right and it doesn't leak. They use 75W140 Motorcraft full synthetic and Motorcraft friction modifier.

 

$140 is not too bad if that includes the fluid and having someone else do it too IMO.... I think I paid around $50 for the various aftermarket syn fluids out there when I've done it myself... I've used Amsoil a couple of times and now I'm on my first run of RP.

I've got 190k on my rig now and did the first change at around 100k just 'cause I think that's what was listed in the service manual?

Anyway, that was the first time I had to deal with a rear end pan that didn't have a gasket! Had a little learning curve that first time around to say the least! Used the RTV stuff, but didn't let it setup long enough and torqued the bolts down too much when it was still wet, then poured $50 worth of fluid in the hole!! Guess what happend!

So, I drained it into a clean pan and redid the RTV and let it setup and only finger tightened the bolts then let it sit overnight! Tightened up the bolts a bit more, then poured in the fluid.. Worked great until a couple months later, when one of the axle seals started to leak....

So, pulled the nice leak free pan off again to change the seals, but I decided to get new fluid, because even that couple of month old stuff reaked as bad as the 100k mile stuff did! (oh yeah, don't leave the drain pan full of that old smelly stuff in your garage overnight!! You will have that smell linger for awhile, even after you get it out of there!)

I let that stuff run for about 75k miles and by then, I was towing more, so I think about a year ago is when I tried the RP.. No reason for the change, other then it was right next to the Amsoil on the shelf in the store (sorry Galaxy!) and cost a little less too....

Had to do the same overnight 'cure' of the RTV, but it worked great and no leaks. I did have to 're torque' the pan bolts recently, as I did notice some weaping around the edges, but the bolts were loose too! Once I re torqued them, it's since dried up fine...

So, it's some work and you can't just do it in a couple of hours and then drive away... Well, at least not the way "I" do it.... But, I may consider having it done at Ford if they do it for $140 and it's out that same day...

Mitch

 

i bought the lucas stuff for $10 a quart. i needed about 3 and a half, plus the rtv sealant, i spent 35 bucks and 45 mins changing it out. i didnt wait to let the rtv "cure", and no leaks. guess i got lucky, but i did put a double bead on the cover.

if you have basic auto knowledge and the tools, its easy. just make sure you read the right oil weight in the manual lol oh well, live and learn

 

Get in touch with gotlucasoil@charter.net for pricing. They'll get you the Lucas Oil at a much better price. But if you are in Southern California, you can buy it direct. Just go to their warehouse in Corona.



In Northern California, you can buy Red Line from their Benicia location:
Red Line Synthetic Oil Corporation
6100 Egret Court
Benicia, CA 94510
PHONE: (707) 745-6100


75W140
Our 75W140 gear oil is a GL-5 rated product recommended for street-driven road car differentials where that viscosity is specified, providing excellent performance in both conventional and limited slip units. Popular in late-model Ford truck rear differentials as well as many other common models.

 

I use a gasket for the diff. No more RTV set up time. Drain and go.

Regards

Jean Marc Chartier

 

I have 75-90 in my rear end and its been fine so far, I don't do any really heavy duty hauling at all though, so its probably fine for my daily driver uses. Been on many many 250 plus mile trips, one way.