Dear Brickophiles--

I just put Mobil 1 in my rear axle. Then hmmmmm--I remembered the threads about synthetic engine oil provoking leaks that weren't there before.

Does the same thing happen with gear oil? Should I be concerned for the health of my side axle seals and pinion seal?

Thanks for any help you can provide.

Doug Harvey

Mobil-1 in engines, Redline MTL in transmissions, and Redline 75W90 gear oil in diff's of both 240's. Many years, many 1000's miles, no leaks.
--
Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

I have not had a problem with synthetic gear lube leaks in the diff or the trans or the negine. old cars sometimes have gasket material incompatible with synthetics but the Volvos of the 1980's vintage are OK I guess.

It isn't common for that to happen in the rear axle.

However, if it is overfilled, it WILL leak somewhere, and it may be worse with synthetic fluid.

I just picked up a new Mobil 1 brochure from my supplier today. Although it speaks about engine oils only, it specifically states that Mobil synthetic engine oils are fully compatible with all engine seals, and will not cause leaks. In all of the used engines I have put it in, none have developed leaks. In fact I think the better film strength of synthetic prevents leaks by prolonging the life of the seal. Probably this applies to the differential seals. I wouldn't worry about it for a moment.

Synth oil "causes" leaks because it tends to dissolve dirt and deposits. Sometimes crud can build up around old, damaged or shrunken seals, plugging the leaks. Synth oil unplugs them. Unless you can't afford it or the car is a real beater, I'd go for the synth oil and replace any bad seals.
--
'84 '285' rice-eater with lotsa hp & performance goodies & an 8-legged tenant

Hi,

Yes, it applies in any application. However, at this point all you can do is monitor the possible fault points. If it does start to leak, you can switch back to conventional oil, and hope that the leak will stop. It might or might not. In general it's a great idea to change the rear end lube to synthetic, but I never wanted to risk a leak there. I wasn't aware that Mobil 1 was made in weights applicable to rear ends, but I guess I never actually looked into it. The top choice a few years back was Redline, but I have not kept up with the latest info.
HTH,

Balu
--
'89 780T, 223k mi; '80 245, 364k mi