EP 80 replacement in manual transaxle

[kreigle]

Does anyone have a recommendation for a replacement lube in a manual transaxle that specs EP 80 gear oil? This trans is used in the '60-73 Saab 95, 96 and Sonett. I know someone who recommends Amsoil 75w90, and my brother suggested Redline MTL since that is what he uses in his Saab 900 transaxle.

My dad is leaning towards the MTL since it is available through Advance Auto, but wants to know if there is something better suited.

This car is going to be rarely driven, has been in the restoration-assembly stage for +5 years now.

 

[MolaKule]

I would recommend the 75W85 MTL-P from Specialty Formulations.

http://www.specialtyformulations.com/index_files/Page625.htm

 

[kreigle]

Thanks.

I have a question; however about the "not for use in hypoid-type differentials" disclaimer.

This transaxle, along with the Saab 900 trans both have helical ring and pinons. How does this differ from a hypoid differential?

If the Redline gives good performance with the 900 ring and pinion, does that mean that MTL-P and Redline should work in the Sonett? The only reason I wasn't sure about using the Redline is that the 900 trans specs 10w30 rather that EP80.

Is the EP80 vs 10w30 spec difference the reason you recommended MTL-P over SynchroGlide (which seems to more closely match the Redline MTL that my brother want to use).

edit:

I just did some more reading online and noticed that is seems like this oil "should have a GL-4 or GL-5 spec". This is not mentioned in the manual, which only states EP80. Does MTL-P have a GL spec?

edit:
Ok I'm not sure about the accuracy of the GL-5, this trans has brass/bronze syncros.

[ February 21, 2005, 12:06 PM: Message edited by: kreigle ]

 

[Big Jim]

Hypoid refers to the geometry necessary to pinion gear at the bottom of the differential and so doing increases the tooth preasure tremendously, thus the need for "EP" (extreem pressure) additives. The angles are not so steep on transaxle ring and pinions because they do not require the extreem hypoid angles, making "EP" additives less critical.

 

[MolaKule]

The Disclaimer is there to let the prospective customer know these fluids should NOT be used a Hypoid differential, since neither the viscosity nor EP add pack is Hypoid rated.

That's why we developed the HDS-5 75W90 and 75W140 series specifically for differentials with hypoid drives.

All of our MT fluids are GL4 rated, unless the customer requests a GL5 addpack, then it becomes a GL4/GL5 dual-rated fluid.

All the gear lurbicants are safe for brass components and components with other copper-alloys.

 

[kreigle]

quote:

---

Originally posted by MolaKule:
The Disclaimer is there to let the prospective customer know these fluids should NOT be used a Hypoid differential, since neither the viscosity nor EP add pack is Hypoid rated.

That's why we developed the HDS-5 75W90 and 75W140 series specifically for differentials with hypoid drives.

All of our MT fluids are GL4 rated, unless the customer requests a GL5 addpack, then it becomes a GL4/GL5 dual-rated fluid.

All the gear lurbicants are safe for brass components and components with other copper-alloys.

---

Thanks.

I'm still confused on the hypoid to me, because I have read that the diff. gears in the old Saab transaxles are hypoid (as in this article: TSN: Alt.Autos.Saab: Re: 75W Gear Lube ). I have had a couple apart and the pinion has a very definite spiral on it (it looks like a screw).

How would I tell the difference between a spiral-cut transaxle pinion vs. a hypoid pinion? And does it even matter?

I thought that as long as the oil has the GL-4 rating, and the proper viscosity range, then that is all that matters.

 

[kreigle]

Someone please educate me on the difference between hypoid and non-hypoid?

Here are some pictures from the Haynes service manual I have for this car.
Saab 95/96/Sonett differential

Sorry about the quality, they are small in the manual and I don't have a case currently disassembled to get better.

 

[mechtech]

kreigle - That picture shows helical trans gears with a Hypoid final drive. Hypoid gears slide against each other, vs. rolling against each other like helical gears [the face of the gears]. That's why hypoid needs a 'slippery ' fluid, with extreme pressure agents.
Hypoid gears are generally used when changing the power flow 90 degrees, and are not quite as efficient as helical.
It looks like you have to balance good synchro action [not too slick], with protection for those hypoid gears.
Better discuss this with Dr. Molekule, as I'm sure he has a suitable sauce.

 

[Kestas]

Hypoid refers to gears on shafts that have non-intersecting axes. On rear-wheel-drive vehicles this is commonly done to package the components so the prop shaft isn't high up into the car's body.

 

[mechtech]

Those final drive gears are sliding, not rolling, in your application.
The more protection the better [for them].
Slippery is not so good for synchro braking/shifting.

 

[MolaKule]

Kriegle,

Our disclaimer and warning infers that 75W90 and 75W140 fluids are to be used in Heavy Duty final drive hypoid differentials such as for 2X4's and 4X4's, etc.

If you need a fluid of approx. SAE gear oil in 80 weight, then our MTL-P 75W85 with a GL4/GL5 will work.

Just remember,

"Your Brass is Safe with US."

 

[kreigle]

quote:

---

Originally posted by Kestas:
Hypoid refers to gears on shafts that have non-intersecting axes. On rear-wheel-drive vehicles this is commonly done to package the components so the prop shaft isn't high up into the car's body.

---

If I understand you correctly, since my pinion is more-or-less on the centerline of the dff. housing, that it is not truly hypoid? I beleive what you're saying is that the extra additives are required for a situation where the pinion is, say, on the bottom edge of the ring:

My setup: -O
Hypoid: _O


I know that there is a fair bit of 'sliding' going on there, but maybe that is the reason for the 'EP' spec on the oil.

There is a lot of (dis)information out there on this transmission, and over the last 30 years a lot of 'mechanics' have voiced opinions over it.

Back in the '80s, I used to read "doom-and-gloom" statements about how anything other than the factory EP80 would cause the transmission to self-destruct due to insufficient lubrication to the ball bearings on the shafts. Now I see recommendations for everything from RedLine MTL to Amsoil 75w90 and how in the Northern US you can run as low as 70 weight and as high as 90 weight in the Southern US.

Add to that the fact the car will be hardly driven at all, and we have to worry about corrosion protection over long periods of non-use.