Diff and T-case lubes

[CAROLINA CUMMINS]

Last time when I changed my diff fluid, I didn't have the helpful advice of you guys on TDR. Only local mechanics; so it seems they are all in cahoots with DC, so they told me I had to have factory stuff At 15 bucks a quart I'll probably be buying a Mag-Hytec before long, so I'll change the Transfer case lube too. My question is; Can I buy one weight of gear oil(90wt, 85-90) to put in all three; F/R diffs, T-case. It'll probably be fully synthetic, I just need the weights. Thanks









Steve

 

[DPKetchum]

YES!. front and rear diffs,of course take take the same fluid. 80w90 is fine. The np205 transfer case in the manual depending on climate can run a multitude of weights but generally 80w90 is cool for it also. Makes it kinda simple.

 

[dusthomps]

Steve,



There probably are a couple of choices for you for diff and tcase lube, but it probably boils down to preference. I also run a straight 80-90w in the diffs and tcase. If you're looking towards synthetic, maybe a 75-140 or a 75-90w is what you're looking for.



Dustin

 

[bgilbert]

Yes same for both. I used Mobil 1 synthetic 75-90W in transfer case last time and NAPA gear oil, I think the weight was 80-90, in my diff's. I suggest using the best stuff in all three the first time since you probly wont change them for awhile. Dont forget the friction modifier- diff additive for both rear ends. I used what NAPA had. Bill

 

[MFalkinham]

I also want to change both my diffs and the transfer case to synthetics soon. How many quarts of fluid should I buy to change all three, with a little left over for good measure? I know I can find the technical answer if I search, but I'm just looking for a ballpark figure so I can buy the fluid without making two trips to the store.



Thanks a bunch, guys!



- Mike

 

[DPKetchum]

10 pints or so

 

[bgilbert]

Mike, from 93 service manual . capacities- Dana 70 rear axle 7. 0 pints/ 3. 31 liters. Dana 60 F front axle 6. 5 pints/ 3. 07 liters. NP-205 transfer case 4. 5 pints/ 2. 13 liters. Conversion - 2 pints=1 quart. Dana 70 3. 5 quarts. Dana 60 F 3. 25 quarts. NP-205 transfer case 2. 25 quarts. 3. 5+3. 25+2. 25= 9 quarts of gear oil. Get 9 quarts, maybe 10 to have extra, plus 2 tubes of additive usually comes in 8 oz tubes.

Recommended SAE grades for diff's are 140, 80-140, 85-140 for anticipated temperature range of ABOVE 90F. 90, 80-90, 80-140, 85-140 for ATR of 90F to -10F. 75, 75-90, 80, 80-140 for ATR below -10F. As you can see the different grades overlap for different temps so you probly be ok with any of them depending your service. Mine I believe was 75-90 mobil one sythetic. Bill

 

[DMC]

I have change my transfer case to 75-90 Mobil 1 about 15000 miles ago and seem to be suffering no ill effects. I even think the T-case is running cooler since the change from ATF. Has anyone been running gear oil in their T-case for a substantial number of miles? Just wondering if it actually protects better than ATF?



Thanks

Don

 

[bgilbert]

I'm sure someone could correct me hear, but Don, I imagine you have a different transfer case than the 1st gen trucks. Our NP205 is gear driven hence the gear oil. I think you have a NP241 which is chain driven and requires ATF. I'm sure someone will correct me if I'm wrong.

 

[DKasper]

One word of caution when going to synthetics in your differentials: Often RTV sealant does not hold up very well and develop a little bit of a leak after a year or so.



This happened to me a little over a year ago, I had changed to Royal Purple gear lube, which was working great, but I developed leaks in both the front and rear after 11-12 months. I contacted Royal Purple and they indicated that this was not uncommon for RTV to not quite do the job. They recommended using a real gasket-quality sealant.



I went to NAPA and got a can of "The Right Stuff" gasket maker, which worked great. A little pricey -- about $15 -- but it is working much better.



Have Fun!



Dave

'93 D350

 

[bgilbert]

Anybody using gaskets anymore? Spend the extra cash and buy gaskets for the front and rear. I use ultra copper high temp gasket RTV silicone on both sides of the gasket with no leaks. Bill

 

[MFalkinham]

I'd prefer to use paper gaskets as well, but the Weaver parts store where I'm buying the synthetic gear fluid doesn't carry Dana gaskets. Does Napa carry them, or where else could I look? If I can't find them, I'll try that "Right Stuff" stuff that DKasper mentioned.



By the way, Castrol Syntec 75w90 costs $7. 50 per quart at Weaver. Does this price sound normal, or could I do better at Napa?



Thanks again!



- Mike

 

[DPKetchum]

Been running synthetic gear oil for four years in my diffs. Used Mopar rtv when it was serviced. No hint of any leak or weepage. In another month or so will service diffs and t/case. But it has been four years since I put Amsoil synthetic in.

 

[DMC]

You guys can get your Dana Gaskets at advance auto parts. I don't know about getting them at auto zone. I used the aerosol type rtv on each side of the gaskets. No leaks with synthetic gear oil.



Good Luck



Don

 

[CAROLINA CUMMINS]

I finally got around to four different auto parts stores today and I couldn't find any that were exactly what I wanted. The closest fully synthetic was Mobil 1 75w90. I seen where they had 75w140 in Mobil1 but they were sold out. Since it is fully synthetic, how would the 75w140 work in all three applications?



Thanks, Steve

 

[KBalzuweit]

I am running the 75/140 in my dana 70 and it has worked great. Make sure you put in the Mopar friction modifier. I had all kinds of binding and such until I put it in. I just figured since the oil bottles said Ok for limited slip I was fine, WRONG. I am planning a switch to all amsoil the next oil change, have heard and read nothing but good about the stuff. I just want to give the old truck the best so it keeps working hard for me.



Karl

 

[CAROLINA CUMMINS]

So will the 75w140 work okay in the np205? will the heavier weight cause too much drag(resistance). Whatever I'll get will be synthetic, either Mobil1 or Amsoil. I aint decided which weight would be right for all three.





Thanks Steve

 

[DPKetchum]

In the past I tried the 75w140 in some manual transmissions(synthetic) and in anything below 70 degrees about could'nt shift without binding or gear grinding. In lower temps it was really bad. Max weight I would use in all unless you live in Egypt is 75w90 or 80w90. Just my two cents worth.

 

[CAROLINA CUMMINS]

I just ordered a case of Amsoil Series 2000 SAE 75w90. I hope it is worth the money.





Thanks, Steve

 

[DPKetchum]

So far I found all Amsoil oil/lube to be super.