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1985 Dana 70 gear oil API spec? #5158728
07/12/19 02:22 PM
07/12/19 02:22 PM
Joined: Mar 2013
Posts: 368
Tacoma, WA, USA
Cubey Offline OP
Cubey  Offline OP

Joined: Mar 2013
Posts: 368
Tacoma, WA, USA
I have an 85 E350 chassis RV with a Dana 70 4.10 rear end. It has potentially been 25-30 years since the oil was changed, if it was EVER changed at all. I want to change it a few times with cheap conventional gear oil to help clean it up before I put in more expensive full synthetic.

I have my eye on a $15 gallon jug of SuperTech 80w140 for a short change interval of maybe 500 miles, but it's only spec'd to API-GL5. Would that be acceptable?

I haven't opened it up yet so I don't know if it's an open or limited slip diff. Adding a $10 bottle of Motorcraft friction modifier still makes it only $25 total.

I plan the "final" fill to be Valvoline full synthetic 75w140 which is over $50 for 4 qts, so obviously I don't want to use that for the short term use cleaning process.

I ordered a $22 "Lube Locker" rubber differential cover gasket so I can easily pull it back off multiple times in a relatively short amount of time for changing the oil. No RTV required, so I will only have to scrape the surfaces of RTV/gasket the first time.

If it's an open diff, I might even just stick with the cheaper $15/gal conventional instead and change it every 12 months since the rubber gasket makes it so easy.

Last edited by Cubey; 07/12/19 02:23 PM.

1985 Ford E-350 27ft Class C RV (6.9L IDI w/ ATS 085 Turbo, C6 A/T, Dana 70 4.10) MPG @ Fuelly
Re: 1985 Dana 70 gear oil API spec? [Re: Cubey] #5159152
07/12/19 11:12 PM
07/12/19 11:12 PM
Joined: Dec 2002
Posts: 42,971
New Jersey
JHZR2 Offline
Global Moderator
JHZR2  Offline
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Joined: Dec 2002
Posts: 42,971
New Jersey
Its not a bad idea to do a first drain and fill with something cheap; replacing in 500-5k miles. Supertech has a 75w-140 synthetic that may be a good bet and might actually be nearly the same price as the conventional.

Re: 1985 Dana 70 gear oil API spec? [Re: JHZR2] #5159799
07/13/19 07:19 PM
07/13/19 07:19 PM
Joined: Mar 2013
Posts: 368
Tacoma, WA, USA
Cubey Offline OP
Cubey  Offline OP

Joined: Mar 2013
Posts: 368
Tacoma, WA, USA
Originally Posted by JHZR2
Its not a bad idea to do a first drain and fill with something cheap; replacing in 500-5k miles. Supertech has a 75w-140 synthetic that may be a good bet and might actually be nearly the same price as the conventional.


Nope. The SuperTech 75w140 full synthetic is $11.72 while Valvoline's is $12.47, all of 75 cents per quart difference. $3 isn't much savings to fill.

Now on the other hand, SuperTech full synthetic 75w90 is about $5.86/qt vs $9.48 for Valvoline's.

If I went with the SuperTech 75w90 full synthetic instead of 80w90 conventional, then yeah, it's not that much more expensive.


1985 Ford E-350 27ft Class C RV (6.9L IDI w/ ATS 085 Turbo, C6 A/T, Dana 70 4.10) MPG @ Fuelly
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