I was wanting to change the oil in my differentials. I bought some Mobil 1 75-90 syn to replace what's in there (most likely a non-syn). Does anyone see a problem with switching to a synthetic oil or is it best just to stick with the conventional?

 

shouldn't really be an issue, as long as it's a GL-5 oil. It's cheaper to stick with conventional, but other than that.

 

I'm using the Mobil 1. I switched to it after I broke-in the gears though.

 

Shouldn't have a problem. I switched to Royal Purple when I swapped my 3rd member - 140K on 3rd, 268K on housing.

 

[sorry to highjack your thread] mine has never been changed it has 140k plus and all my other yotas had 170k on the stock oil is the good or bad for it ?

 

I think it depends on what kinda drivin your doin...
I change mine every 15K like supposed to...
Also I do alot of muddin so I kinda need to...

 

It's good insurance to go ahead and do it. If you go synthetic it should be about $30 a diff, probably a little more than half that for dino oil. I think most people change it about every 30K (or less if you do alot of mud and water crossings like YotaFun was saying). I wouldn't go more than about 50-60K even for a vehicle that doesn't get wheeled.

 

great more money to spend thanks for the info and i sorta wheel my truck nothing like i did to my last truck

 

Syn is perfect. Switch. Then keep an eye open for leaks. If no leaks, good to go!

 

? why would switching from regular gear oil to syn oil cause leaks, ?

 

Synthetic tends to clean sludge better. Generally you get a buildup of sludge behind your seals (which helps it to seal better) and when you switch it out it will get rid of that and will either make an old leak worse or make a weak seal leak. This happened when I swapped my transfer case over to synthetic. Had no leaks but drove it for about 2 weeks and it started leaking from the rear output seal. Just keep an eye out for leaks for a month or so after you switch. If you have any existing leaks change the leaking seal/gasket before you switch.

 

I've also heard of people who used RTV on their axle seals that had issues with syn disolving the RTV