75w140 is not destroying rear ends. It is the proper weight oil to use.

JMC

 

This has been my experiance I changed my Rear end oil on my 97 4x4 w 3:55LS and put Stalube sythetic 75w140 like it said and the friction modifier well after about 200 miles I stsrated getting this terrible shudder in the rear end when going around corners. Truns out the clutch pack in the LS were not releasing. So i consulted a rear end shop and they said get that stuff out we see this probelm all the time.They told me go get some Redline 75w90 and put that in and it should take care of your problem if not you will need to replace the clucth pack in the LS. So i did as he said and within about 20 miles the Shudder went away and all has been fine since then. I highly recomend Redline oil after that experiance. Alos with the Redline 75w90 you DO NOT need to add friction modifier as it is inthe product already.. I run Redline in everything now both Diffs Transfer case. EDIT:Well with all this talk about the diff oils i decided to go check the truck owners manual and the tag on the rear diff cover,The manual says 75w90 for the front, And all it says is High Performance for rear but no weight and the tag says 75w140 synthetic. So like i have said I will be calling Redline tomorrow again to see what they say Why would Ford have two different oils for each axle and why is the rear weight not given in the manual I have always ran 75w90 in previous Ford LS rear ends

Richard D.

https://www.f150online.com/galleries....cfm?gnum=2479

 

Well I made two phone calls today one to Redline and one to my local Ford Dealership. Dealership says they put the 80w90 in. So I called Redline they say the 75w90 should be ok but since they now make a 75w140 you should probably use it. But using the 75w90 should be ok. so I will be changing mine out as soon as I get my new Diff cover form Mag-Hytec. Talk about getting the run around. When I told the dealer the tag says 75w140 they said we know but all we use is the 80w90. Go figure.

Richard D.

 

Gee, now I'm really confused. If the tag says 75w140 then why would a dealer put in 80w90? If it came with 75w140 from the factory ( which it should of because of the tag ) then why would the dealer switch it?

 

ok originally it was thought 75w140 would be best. However many many many techs started discovering through experience that the 75w140 that they had facotry installed was making for bad differentials. The compaint ive heard is that the 75w140 that they used (i dont believe this applies to all 75w140 but im not sure) is unable to absorb moisture that well leading to component failure. Because of this many dealer techs recommended sticking 75w90 (i believe) in there. Personally i stand by mobil for many products so i went to mobil synthetic gear oil 75w90 for my differential, 17k miles and still working great, although thats hardly a great length of time. Im sure it depends on many variables but since it seems many veteren ford techs follow this course im sure theres a reason. Im not a huge dealer fan but there are some excellent techs (yes its true) and ill trust their judgement

 

See this is getting crazier as the moments go by. I myself have been running the 75w90 in my Rear End with the 9.75 LS for about 2 years now and it seems to have been working fine ,like i said the very first time i changed my fluid i went with Sta-Lube 75w140 Synthetic and after about 200 miles I got a trerrible shudder when going around turns so I took the truck to a Rear End shop they could find nothing wrong and suggested that i swicth over to the Redline 75w90 which i did and after only about 20 miles or so the shuddering went away and all has been fine since then. So now it is time for another fluid change and since I am upgrading to a Mag-Hytec Cover I am going to put in the Redline 75w140 since that is what Redline is now suggesting. They found it odd that the front requires 75w90 but the rear is 75w140 so my question is was it strictly the Ford 75w140 that the Dealers were having problems with? I myself am going to go with Redline 75w140 even though i have been using the 75w90.

Richard D.

 

i believe it was only ford 75w140 that was causeing the problems though im not sure. I would put much faith in redline. If they say its good to go, you can pretty much count on it to be fine.

 

btw that "shudder" doesnt sound like the wrong grade of oil or even bad oil properties, sounds like they just forgot the friction modifier. Ive heard of that cause shudders esp while turning. Is that what you had? Maybe they just forgot that part. In any case report back on the 75w90, it should look fine coming out.

 

No the friction modifier was not forgotten I am the one who did the change and put the Ford friction modifier in myself.

Richard D.

 

I use either AMSOIL or Redline 75W140.
I doubt that water is causing most of the problems with these differentials. I have broken four 8.8 diffs. Trust me when I say water was not the cause. The front differential can use a lighter oil because it doesn’t do any work at high speeds. Run your truck at 70 mph for ½ an hour and then pull over and touch the diff cover. Touch the brake disks. Don’t forget this oil lubes the bearings out by the wheels. Cheap insurance by running the heavier weight oil.

Regards

Jean Marc

 

Thanks JMC.

 

Well I have had no problem with my rear-end with the Royal Purple 75W-140. I do not believe the 75W-140 would be a problem could be the techs not knowing what they are doing, the quality of parts etc.

Anyhow, "if" 75W-140 is a problem then great, means I get a FREE rear-end if it goes bad since I am FOLLOWING what Ford recommends.

It's like saying since Ford recommends using 5W-20 motor oil why not use 0W-5 (if one exist) it's thinner so it should be better right?

Moral of the story, unless you get something in writting from your "tech" or dealer stating it is ok and RECOMMENDED to use the lighter weight oil in the rear-end stay with what is recommended, or when you take it in for failure, the same "tech" that said it was ok to use just may say "sorry, your not covered under your warranty since you are NOT using what is recommended"

Wouldn't that be a bitch...

 

I'm running Royal Purple "Max Gear" 85-140 with no problems and no additives.

 

Just to note, that I am using Royal Purple in my L/S and the Ford friction modifier. I asked Mike from Superships about it and it suggested that I add the friction modifier because that is what they do regardless of what the claims are.

 

I run the Redline with no Friction modifier as Redline puts the additive in there oil. Will be putting the 75w140 in later this week whne i get my Diff. Cover.

Richard D.