Synthetic lube in rearend okay?

I remember something about using only a certian type of regular oil in toploaders because of the type of blocking rings or sycnros materials. I think it is GL2 or 3.

I am unsure about the rearend though.

personally and professionallyi dislike synthetic gearlube. i am a truck mechanic and it seems that 80% of all premature failures ive seen in trannies and rearends that wernt low or out of oil had sythetic in them. but i can see that it is more slippery because the gears always look good for the usage they have on them, its always bearings and synchros that go bad.

ashford said:

personally and professionallyi dislike synthetic gearlube. i am a truck mechanic and it seems that 80% of all premature failures ive seen in trannies and rearends that wernt low or out of oil had sythetic in them. but i can see that it is more slippery because the gears always look good for the usage they have on them, its always bearings and synchros that go bad.

Click to expand...

So are you drawing the conclusion that synthetic oil is to blame for premature failure? I'd imagine if it's the correct oil (weight wise) and it's not low then it's doing its job and wonder how it can be blamed. I'm curious from your standpoint tho, please explain more.

BTW, I have not had a problem running synthetic oils in any of my cars and would recommend them if someone wanted to spend the extra cash. Whichever way they went I'd recmnd make sure they are topped off.

Replies from others and my personal use synthetic oils are more prone to leak. I switched out my synthetic oil (Redline) in my 9" for some conventional gear oil because of this, but I will continue to use synthetic oil in the motor because of the harsher environment.

I run synthetic oil in all my vehicles as well with no issues. I run 140 wgt gear oil in the rear end of my cars and my F250 came with it from the Ford factory.

synthetic oils are great for use in the driveline as well as the engine. any leaks, like in an engine, were already there, the synthetic though is more agressive in keeping things clean and thus the sludge buildup at the point of the leak is gone, and that is why the lube is leaking. as far as premature bearing failure goes, that is likely due to the wrong weight lube being installed. too thin and the load capacity drops, too thick and hte lube cant get to the bearings.

I run Redline Shockproof in the T10 and the 9" rear with no leaks or problems!

67Dylan said:

So are you drawing the conclusion that synthetic oil is to blame for premature failure? I'd imagine if it's the correct oil (weight wise) and it's not low then it's doing its job and wonder how it can be blamed. I'm curious from your standpoint tho, please explain more.

BTW, I have not had a problem running synthetic oils in any of my cars and would recommend them if someone wanted to spend the extra cash. Whichever way they went I'd recmnd make sure they are topped off.

Click to expand...

this is an observation not a lab test or an unfounded opinion. ive seen alot of fuller road ranger transmisions that have had bearing and synchro failures before 150,000 miles(about 1-2 years of operation for over the road. these are trucks now not cars)which are factory filled with synthetic(aka extended drain). then again when you have a truck from 1995 come in with the same tranny with 600,000 miles on it beat to hell and the origional tranny finally goes out of it, it makes you start to wonder. this is a common occurance. also factor in the price of 4 galons of syntehetic, and see how often people will want to change tranny oil.
as for differentials failures arnt all that often in the big trucks. its the mid size that takes a beating. for example one customer has a gmc delivery truck. it has a dana 80 diff in it the pinion bearings failed at 40,000 miles(factory filled synthetic)just out of warenty. so it was rebuilt and ran about 50,000 this time and again the bearings failed. the customer complained about the price of gear lube so i put in 80w/90 gl-5. the next time the diff failed it had 130,000 miles put on it. as for car useage i can't tell you what is better. but this is what iv'e ran across in the heavy duty field.

Everywhere I asked about synthetic in a Ford rear end, they said ABSOLUTLY NOT.

The Ford rear ends have an extreme hypoid angle (or something to that nature) I was told synthetics in the rear end would ruin it.

Dont take my word for it, call
Currie Enterprises (714) 528-6957
or Toms Differentials (208) 265-8111
they'll tell you the same.