Indy_68_S

Looking for recommendations on what to use in an 'O' type posi...
I get conflicting info from what I've read & people I've talked to...

Soooo, tell me what worked for you (& what didn't & why)...

I may have screwed up by filling mine with Valvoline SynPower 75-90 Full Synth..like this



..but my bottles have a red band on the label that says "Limited Slip".

Tell me now since it'll be a lot easier to suck out this stuff & replace it with the body off the frame...!

Thanks.....

Aceshigh

I think you'll be fine. Synthetic > Conventional

I used Amsoil's Severe Gear in my 12 bolt Eaton posi.
I have a distribution warehouse near me.



Big Gear Head is a legend on several forums for being the expert on rear ends.
http://www.camaros.net/forums/showthread.php?t=97446

monzaz

Ok here we go with the gear oil controversy AGAIN....lol.

EAton and Auburn Will not warranty there limited slip diff unit with synthetic oil in the unit... That is just a fact... Auburn even goes to if you do not use their limited slip additive they will not warranty the unit either. BASICALLY NO one stands behind there products anymore...lol.

The 'O' type unit is a clutch traction lock unit just like the 1970-1987 8.5 car units... And the Auburn and eaton units. All these unit rely on some form of friction to create a locking effect under accelerated rotation.

So if you are using a synthetic oil it tends to cut down the effect of friction which it what locks the clutches and cones tightly against each other and or the cone to the machined inner conical surface.

SO the more slipping the more wear and heat build destroying the clutches and cone surfaces.

This is also why I do not recommend 800# clutch spring pack as every turn will wear posi unit clutches and cones AND with that much preload the weight of the vehicle WILL break the clutch pack loose BUT wear them excessively because of all the extra pressure. SO for a nostalgic class requiring such a posi unit YES I understand OR if you are willing to accept the fact that your clutches will wear quicker for the performance gains in a straight line.

NOW in Ford 8.8 the factory uses synthetic in there rears WHICH ARE TRACTION LOCK rears...Yes just like the 'O' type and 8.5 10 bolt.
The reason synthetic does not affect the 8.8 is that these units are Composite material glued to the clutches plates for its traction friction for lock up.
NOW that maybe the way to go you say...BUT I tell you the life of a FORD 8.8 unit is very short in a performance arena. Drag racing will whip these units out fast.

ANSWER - If you have steel clutches do not use the synthetic fluid, use mineral based fluid and use the limited slip additive as needed for chatter noise. This is what I recommend for your 'O' type steel clutch based unit.
- Composite clutches I guess you can use synthetic
-CArbon fiber...??? ANother GLUED on material... Your guess is good as mine...lol. Eaton says NO synthetic
- true trac unit can have synthetic fluid as there are NO friction based lock up clutches or cones... just sliding worm gears to lock up both side gears when they touch both at the same time.

I have personally disassemble 1000's of rears and I can tell you the old mineral base fluid is absolutely fine. 40 year rear gears and posi steel clutches are always in good shape as long AS FLUID IS IN THE REAR.

SO all in all MY opinion is WHAT EVER FLUID YOU USE PLEASE ! please just make sure you have it fill to the proper level full.

If you forget the fluid you'll have the biggest problem ever. Jim

Indy_68_S

Thanks Jim!
Great post...
That's the kind of info I was hoping for !

After I filled it with the SynPower, I heard/read more about using the older clutch types working better with conventionals. Luckily it has zero miles since I filled it, so I'll just suck out the SynPower and fill it up with some 'SureFine Dino Squeezins'....with a shot of additive...

507OLDS

Jim said all that pretty good.
I put conventional gear oil in all of my rears.No synthetics.
You "could" put synthetics in a spooled rear.No harm done there.
Good point about those Eaton 800lb springs as well.I think one of the reasons they are pushed more now is the fact that there are putting those crappy polycarbon crap clutches in them,thus needing more force to get them to work.The BEST clutches for an Eaton unit are the original GM solid knurled steel,and nothing else.Not the slotted flower petal ones either.If you shim it correctly,you can do away the the spring pack all together,& have a long-lasting unit that performs better than it ever did.I usually put them back in anyway,as you get those certain customers that like to tear everything apart & make sure they didn't get ripped-off,and you can't convince them otherwise.Either way,when I build a rear with a new Eaton unit,it comes out of the box,then comes apart,the "latest & greatest" clutches are pitched,the good clutches are put in,and the unit is tuned correctly.

monzaz

Well just remember each person is different and wants something different out of their car. Some want a very smooth operating posi others want as much hook as you can get...others want longevity at all costs.

USe the parts and fluid that will give you that desired out come. FLUID in no way will FIX any problem you are having...lol. If it is broke you need to replace the parts not try a band aid.

So for best hook and keeping your warranty on a new eaton or Auburn use the conventional DINO oil Just need to change it more often with the type of driving you do.

I think synthetic is used a lot of time as a do it and forget it oil. People think they are gonna be better off and tend to run the oil harder and longer with out changes...MAy not be so good. OIL will always collect debris and as it collects enough, it will become gritty. SO synthetic may be slippery and perform better than conventional as long as it is clean...But once they get dirty (and it WILL) the oil will still put a hurt'in on metal parts when it is full of metal. Keep it clean.

I would say every 3000-5000 miles AFTER break in gear oil is swapped out the rear does not ask for much (some cars will not get that mileage for years...lol... I have seen many vehicle NEVER get the oil in the rear changed JUST level fill performed and never had an issue...WOW!!! NOt recommending it but.... That is what I mean...it don't ask for much just give it the proper level at the VERY LEAST!

AGAIN it is your car so maintain it accordingly. Some may be more **** other not...JUST be sure you can live with your choices.

507OLDS

Yes,each person & car is different.That is why I alwasy ask each person what their plans & expectations are for the car,and I build it accordingly,but regardless,I tune the posi unit,if it has clutches.I don't make all of them the same,but all of them can use some tweaking.
I've also seen some hairy stuff directly out of the box,like one of the thrust washers missing,and one spider gear having a large amount of slop as a result. Who did quality control that day?!
As you know,if a rear would fail,the blame would not be pointed to the part,but to the person who built it,regardless,so you gotta make sure everything is right.

ROCKET VAPOR

This is what I used in my '70 type "O" limited slip differential after alot of research.



About 2 1/2 bottles of CRC Sta-Lube SAE 85W 90, API/GL-4 Hypoid Gear Oil. Your local NAPA store should be able to get it for you, and the CRC Sta-Lube part number is SL24229 for 32 fl. oz. container.

23304.jpg

One 4 fl. oz. bottle of GM Limited Slip Axle Lubricant Additive. Your local GM dealership should have it, and the GM part number is 1052358.

yb.jpg

Nilsson

Also use the Sta-lube in your manual gear boxes.

Good stuff.

stlbluesbrother

Instead of starting a new post, just going to piggyback this thread due to common topic.

Thanks to Jim (monzaz), I was able to ID the gears (limited slip) in my SX housing. Now it's time to put cover back on and fill with gear oil. Unless someone has had a bad experience with the following fluids, I'm going to use them tomorrow (March 4).

• Napa brand gear oil - SAE 80W-85W-90 - cost $4.99
• Trans-X limited slip additive - suitable for GM #1052358 per label - cost $8.49

gear oils.jpg

pcard

What is the recommended break in period for a new Eaton posi unit? Is it the same as a refurbished original O posi unit?
Do you use any special type of oil for break in?

507OLDS

I like to use the thicker 85/140 oil,but the 80/90 is fine.I use the TransX without any issues.NAPA should also have the GM bottle,with different label.

stlbluesbrother

Thanks, Brian

monzaz

Usually There is NO break in time for a POSI unit. cone clutch or other.

Just do a few turns left and right and that will be enough to circulate the fluid and additive into the clutches. It is the NEW ring and Pinion that will be a critical time period mileage and towing...

NO towing for 500 miles (usually truck issue)
4-5 heat up and cool down cycles - Complete cool down is essential
5-10 minutes is all it takes to heat up gears on a warm summer day.
YOU MUST drive the vehicle...NO jack stand heat and cool cycles as this is a false heat up and you will end up with a mess later.

You need the weight as this is what creates the good heat...weight and torque.

J D Race
JIm

pcard

Thanks Jim.