Synthetic 75w90 for Dana 70 open diff in Class C?

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Is anyone with a Dana 70 open diff in a Class C motorhome running synthetic 75w90 oil?

Based on the official Spicer manual, it calls for 80w90 except in steering situations (dually steering??) when it calls for 85w140.

Quote
DIFFERENTIAL LUBRICATION
It is not our intent to recommend any particular brand or make of lubricant for the Spicer hypoid axle.
However, an S.A.E. SOW-90 multi-purpose gear lubricant meeting Mil. Spec. L-2105-D, and suitable for 1A.P.I.,
Service Classification GL-5, is suggested as a minimum requirement

Source; page 5-1: https://media.spicerparts.com/cfs/files/media/Nwh6LfbHWPgh9aKS3/5312-9.pdf?store=original


It does go on to say you should use whatever vehicle manufacturer it got put on says to use, but needless to say, I don't have the 1985 owner's manual since I'm not the original owner.

The gear oil was probably the original from 1985 based on how bad it looked when I drained it back around August. I put in cheap SuperTech conventional 80w90 ($15/gal) as a means of cleaning it up before I put in more expensive synthetic. It's been roughly 1400 miles so far. In about another 800mi/1 month, I will dump it and put in synthetic, when I get to a place I can work on it without hassle. There has been no noise from the diff so it seems to be playing okay in there.

For some odd reason, Super Tech Full Synthetic Gear Lubricant 75W-90 is dirt cheap vs 75w140. Since the tech spec (roughly) matches the Spicer manual, I would think it should be fine.

I never tow, so that's not a factor. I stay at 55-60mph most of the time for better fuel economy so it's not being run as hard as it could be. In addition, I am full time RVer, and I typically stay out of very hot places. 85-90 is usually the highest I ever see and if it's that warm, you can bet I'm already heading north.

It's got a 6.9L IDI (with ATS 085 turbo) and a C6 (3sp A/T) up front, with 4.10 gears in the D70, for those wondering.

I reckon that the ST full synthetic 75w90 will be fine for my application given those operating conditions, but I'd like to hear other's input. Being full synth, it should hold up better than conventional, even if it gets hotter now and then, a few times a year.

Below are the pics I took when I drained it. Due to the rotation of the carrier, it was hard to see inside. I got my camera positioned just well to take a shot and it's definitely open, not LS.

[Linked Image]


[Linked Image]


The RV itself:

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The Dana 80 in my (approx.) 14K pound F-450 in my sig has 80W90 in it, seems to handle it OK. Not exactly the same, but the weight is probably close. I'm going to change it to 75W140 the next time I change it, though, because the 80W90 actually BOILS OFF in summer under heavy use, disappears with no visible leaks. I;ve used 75W90 full syn before, but in a truck as heavy as my F-450 (or your F53 chassis), I would go thicker.
 
Originally Posted by bullwinkle
The Dana 80 in my (approx.) 14K pound F-450 in my sig has 80W90 in it, seems to handle it OK. Not exactly the same, but the weight is probably close.


My weight specs. For some reason the RV conversion tag shows a 700lb higher GVWR than the Ford cutaway ("incomplete") tag says.

[Linked Image]


[Linked Image]
 
Originally Posted by bullwinkle
The Dana 80 in my (approx.) 14K pound F-450 in my sig has 80W90 in it, seems to handle it OK. Not exactly the same, but the weight is probably close. I'm going to change it to 75W140 the next time I change it, though, because the 80W90 actually BOILS OFF in summer under heavy use, disappears with no visible leaks..


Umm, unlikely it boils off.The boiling point is 425 F. More likely it's weeping from your pinion and wheel bearing seals.

smile.gif
 
Originally Posted by bullwinkle
I'm going to change it to 75W140 the next time I change it, though, because the 80W90 actually BOILS OFF in summer under heavy use, disappears with no visible leaks. I;ve used 75W90 full syn before, but in a truck as heavy as my F-450 (or your F53 chassis), I would go thicker.


I have an E-350 van chassis, same as an ambulance, shuttle bus, or small box truck. Class A motorhomes are what get the F53.

As Snagglefoot said, it's probably not boiling off. Not unless you have some really insane temperatures going on in there! Do you have drum rears? The inner wheel seals on full floaters can leak into the drum, causing oil loss that way, kind of hiding it.
 
Originally Posted by SteveG4
An F-350 with a 6.9 IDI and a Dana 70 rear diff calls for 75W-90 or 75W-110, according to the AMSOil website.
That site also calls out: Dana 70 HD Rear 7.4 pints Fill to no more than 1/4 to 9/16 inch below fill plug hole.
https://www.amsoil.com/lookup/auto-...-8-cyl-engine-code-1-1-diesel/us-volume/

I hope this helps.

Also, I'd likely go with that Mobil Delvac 1 75W-90 recommendation made earlier as well:
https://www.amazon.com/Mobil-Delvac...ative=165953&creativeASIN=B007WVI5G6

Good luck.


Valvoline makes a synthetic 75w90 too. No love for that oil? Mobile 1 is way too expensive IMO.

I will probably just get the SuperTech full synthetic 75w90. 4 Quarts of it costs all of $28. It seems to have good reviews, not only on WM but on BITOG.

This is a good price for Valvoline in a gallon jug, but it still costs more. https://www.walmart.com/ip/Valvoline-SynPower-SAE-75W-90-Full-Synthetic-Gear-Oil-1-Gallon/593112274

7.4 pints (3.7qts) sounds about right for what it took to full it after I drained it and refilled with conventional 80w90 for the short oil change interval to clean it up.

But you know, being as old as it is, maybe dino is better to stick with, as far as the seals and all. It has no leaks right now and I'd like to keep it that way. I have a reusable "Lube Locker" diff cover gasket on it so I can change it often with half as much labor. No scraping RTV every time. Just loosen, drain, remove, wipe, install/torque, refill. It hasn't leaked a drop either. Plus dino is all of $15/gallon. I can change it annually for that low price.

I run dino in the engine, so I might as well in the diff too. It's primitive tech that is happy with primitive oil.
 
synthetics can get better mpg's even fake group III's as most are + even conventional lubes add some synthetic to meet a spec. i changed the cheap OE semi syn in my frontiers nissan-dana 60 to redline 75-90 pre spicers site, it had 75-140 semi factory lube in it. i only haul a little coal yearly on a short run + am enjoying about 3 mpgs more from going to ALL redline real synthetics in all driveline units. as noted the 75-110 synthetic is a good option if needed + you can blend your own using the same manufactures lubes of varying viscosity. with todays minimal cost increases using cheap synthetics generally group III lubes is just smart!
 
Originally Posted by Cubey
...
But you know, being as old as it is, maybe dino is better to stick with, as far as the seals and all. It has no leaks right now and I'd like to keep it that way. I have a reusable "Lube Locker" diff cover gasket on it so I can change it often with half as much labor. No scraping RTV every time. Just loosen, drain, remove, wipe, install/torque, refill. It hasn't leaked a drop either. Plus dino is all of $15/gallon. I can change it annually for that low price.

I run dino in the engine, so I might as well in the diff too. It's primitive tech that is happy with primitive oil.


I tend to agree with you on the dino based on the age of your ride. I would just change it again. I might go with a little heavier dino.
 
Originally Posted by Gebo
I tend to agree with you on the dino based on the age of your ride. I would just change it again. I might go with a little heavier dino.


There is conventional SuperTech 85w140 for $15/gallon also. I'm never anywhere cold enough that 85w would really be a problem when the spec is 80w. Usually low 20s is the coldest I ever see. Maybe mid teens one or two days a year.

Both the 80w90 and 85w140 are also available in 1qt bottles for about $5/qt. For an extra $5 for 4x 1qt (vs $15/1 gallon), I could roughly mix 50/50 of 80w90 and 85w140 to get slightly thicker oil. But that just complicates things when it's probably not needed.
 
I'd probably add 2 qts 80w90 and fill with the 85w140

If you search it out (somebody here may help) a few years ago they divided the 90W viscosity into a high 90W and a low 90W. The high 90W became the new 110W and the low 90W stayed 90W. Based on this change, I now run 110W where my owners manual calls for 90W. But as you can see, all my cars are old.

If I am wrong I stand to be corrected.
27.gif
 
Originally Posted by Gebo
I'd probably add 2 qts 80w90 and fill with the 85w140

If you search it out (somebody here may help) a few years ago they divided the 90W viscosity into a high 90W and a low 90W. The high 90W became the new 110W and the lie 90W stayed 90W. Based on this change, I run 110W where my owners manual calls for 90W. But as you can, all my cars are old.

If I am wrong I stand to be corrected.
27.gif



That was my exact thought for the mix ratio. Being an open diff makes everything so much easier. No worrying about friction modifiers. Just put in cheap gear oil and go.
 
Originally Posted by Snagglefoot
Originally Posted by bullwinkle
The Dana 80 in my (approx.) 14K pound F-450 in my sig has 80W90 in it, seems to handle it OK. Not exactly the same, but the weight is probably close. I'm going to change it to 75W140 the next time I change it, though, because the 80W90 actually BOILS OFF in summer under heavy use, disappears with no visible leaks..


Umm, unlikely it boils off.The boiling point is 425 F. More likely it's weeping from your pinion and wheel bearing seals.

smile.gif


All new, had the rear axle rebuilt with new pinion shaft, ring & pinion (stupidly on my part with 3.73 gears, too high), and Eaton gear lock differential. I did have a plugged vent (which forced gear lube out of one wheel seal), new vent fixed that. It is going somewhere... Fortunately WM put Valvoline dino gear oil on clearance for around $1/quart! Weight on the F-450 & the OP's RV are close, I'm surprised he only has a Dana 70 & not an 80. Dodge has recommended 80W90 or 75W140 on these for a really long time, but I would expect leakage issues on a 35 year old rear end with 75W90 syn gear oil.
 
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