Hi all. First post. I have a 97 Ford Expedition that has a slight leak at the rear axle seals, even though the seals are new. With that in mind, I have a couple of questions:

1. Would Valvoline 85w140 semi-syn. tend to be less "leaky" than Motorcraft full-syn. 75w140? Why?

2. Would it be safe to use 85w140 semi-syn. in a rear differential that calls for 75w140 synthetic?

Thanks in advance

WW:

Nice to see you here. I'm just back after not visiting for a while. I've heard a variety of thoughts on this sort of scenario. Between the lack of consistent approaches, and my own lack of technical expertise, if it were me, I'd just conduct some comparisons with the vehicle and see which product leaked the least, and then go with that.

In my 99 expy I use RL 75/140 has never leaked has a good slug of ester seal swell/condition additive of which some brands do not that is why they still leak after a seal change unless you have a grove worn into the axle.
bruce

I put Redline rear end lube (can't remember which grade) in my 1990 E350 motorhome and had new seals installed at the same time. Have run about 7000 miles since then and no leaks, other than some throw out the floating axle hub because the bolts were loose. Once I tightened it down, no more throw.

Thanks for the responses, guys. It's sort of funny that every response in this thread is from a BITOGer. I think I'm going to like this forum. It's a lot less "noisy" than BITOG has become as of late.

I'm going to try Redline gear lube next, & see if that helps with the leak. If not, I may have to replace the axle shaft. grrrrrrrrrrr. It's getting to the point now that my wife sees my "maintenance" projects as "car problems", & I'm feeling the pressure from her to buy something newer. I don't like that idea.

Thanks again, guys.