What kind of fluid should you put in a posi traction rear end. The mechanic who change my tranny mount have change my rear end fluid in the same time. He only put valvoline 80w90 GL5 oil in my posi rear end. Is it good or he should have put another lubricant additive with the GL5 oil ???

 

Does it make any noise going around corners? If not, there is probably sufficient residual additive to prevent problems. It may, however, start making noise over time, at which time the additive should be added.

The biggest problem I see with your mechanic's fill is that it is a petroleum-based lube. In this day & age, why use anything but a high-quality synthetic? Cost? Give me a break, what's $18 vs $8 in a unit that will cost $600-800 to rebuild when it wears out early? To say nothing of lost effeciency with the petroleum lube. Also, AMSOIL synthetic doesn't need that expensive additive - your $8 gear lube suddenly costs $15 - "Gee, I could have had synthetic for just $3 more!"

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. 0.030 over 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlock header mufflers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, LT MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1/95.5 @ 5800' Bandimere.

 

Definitely add some posi additive to the rear end. Don't take the risk of running w/o it. If you read my post on this board about what happened to my posi, you'll understand why i'm saying this. Like five7kid said, spend a little more now to save a lot later. Don't be penny wise and pound foolish.

BTW, I was going to use Mobil 1 gear oil in my posi but the only weight they had was 75W 90. I went with Valvoline Synthetic 80W 90 instead.

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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

Wait- I was told that synthetic wasn't good for a posi rear, because it's too slippery, and the posi won't grab well- even with the posi additive. This is false? Does it have any truth?

If not, I'll put some synthetic gear lube back there this summer!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

"Positively" false! The posi additive is there to let the friction plates SLIP against each other more smoothly - NOT to help them grip!

Go get yourself some of the good stuff!

 

i use mobil 1 and gm posi additive

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

hey 5.7 where's my amsoil so i can start plugging it instead of mobil 1?

 

I'm hoping the dog won't bite and the kids don't start crying when I get home again. I haven't forgotten, just haven't been able to get it to ya!

 

Btchin! Thanks, 5.7 kid! Do they make the same weights in synthetic? I think I'm running 75w90 right now.. should I stick with that weight, or change it?


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

I'm using synthetic Castrol 75W140 + GM additive,works fine for my posi!

 

I don't know about all brands, but I know AMSOIL makes 75W90, 80W90, 75W- & 85W140, amoung others.

I changed the '57 to 75W90 in November about 15 years ago. Going from petroleum 80W90 to synthetic 75W90 at that time of year made a SOTP difference. I've used 75W90 in everything I've had ever since.

I can't think of any good reason to run a 140 weight in a car. I've seen it used in heavy duty, lower speed applications, but it really doesn't help running it in a 3rd gen rear.

[This message has been edited by five7kid (edited June 09, 2001).]

 

75W140 is just one step up the scale,compared to 75W90.
As synthetic oil tends to be (very) slightly "thinner" compared to mineral oil of the same weight,it isn't a bad idea to change from 80W90 mineral to 75W140 synthetic,specialy when the axle has seen many miles!
Again the synthetic 140 weight has almost the same viscosity as 80 weight mineral.

 

I'm running Red Line HD synthetic. So far so good.......
bsa

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"If they do not run, Then they will die." - Stonewall Jackson
#3
'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Edelbrock Intake, Accel Runners, Comp Cam, Crane Gold rockers, Lucas 24# injectors, Edelbrock headers, Flowmaster 3'' exhaust, Mallory Ignition, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

 

I think the best place to ask is Auburn gear if you have a 10 bolt and this is from them.
2.) What kind of oil should be used with an Auburn differential?

It is important when installing Auburn differentials that a high quality, non-synthetic 80w90 GL-5 oil, treated with GM or Ford limited-slip additive (also known as friction modifier) be used. Three ounces of additive will treat one quart of oil.

synthetic is good if you want your posi to last for a good long time just don't hope for it to grip at the same time.

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92 Z28 5.7 TPI AUTO 105k factory motor and trans.

SLP headers and runners, B&M 2400 stall, shift kit,LCA brackets, EIBACH spring kit, NITTO'S, N.O.S.

best 60ft 1.84 1/4 12.48 @ 110.81

 

Not true. Lubricants are rated for viscosity at a certain temperature. Although there is a range in which it can fall, it has to fall in that range at that temp in order to meet that rating. The "W", by the way, stands for "winter", not "weight", and goes with the 1st number. So, a 80W90 and 80W140 would be the same thickness (or at least within the same range) at cold temperature, while the 90 would be thinner than the 140 at high temperature. In the examples you give, the 80 and 140 have absolutely nothing to do with each other.

However, you may notice that at ROOM temperature, a synthetic 75W90 is thinner than a 75W90 petroleum-based lube (same for 80W90 syn vs petrol). That has absolutely nothing to do with what they'll be at high temp. Or low temperature, for that matter.

Perhaps it's time for a lubricant FAQ section to get some of the misinformation out there cleared up.

[This message has been edited by five7kid (edited June 09, 2001).]

 

I know that's what Auburn says, but do you have back-to-back evidence of synthetic causing slippage when petroleum doesn't? (The real test would be; slips with synthetic, doesn't when changed to petroleum with no other changes) It doesn't make any sense to me, since it is the ADDITIVE that makes (lets) the friction plates slip against each other, not the base lube. I wrote AMSOIL and asked if they knew that's what Auburn said: Their response was it was news to them, but they knew for a fact that many people have used synthetic with Auburn posi's for years with no problems whatsoever.

Perhaps it is just taking Auburn longer than others to see the light. There is no doubt that synthetic is superior for the gears and bearings.

By the way, what's the defination of "high quality" non-synthetic GL-5 80W90? If it meets the standards for GL-5 and 80W90, there aren't any other distinctions.

 

Kid,
What you're saying is absolutely true,you sure know what you're talking about,but reading isn't your strongest point!
Anyway what important is,is this:
Castrol oil UK had several complaints about axle noise AFTER changing to synthetic axle fluid with the correct viscosity,after a long investigation it is clear that synthetic axle oil CAN be slightly thinner,no matter what the numbers say!!
So,Kid,as you probably knew already,going from -W90 to -W140 axle oil, is like going from engine oil -W30 to -W40,a relative small step!
And by doing so you will end up with a synthetic -W140 that has almost the same viscosity like -W90 mineral.
It is very well posible that a lot of (noise) problems on this board are due to
wrong (to thin) synthetic axle oil!!
Just give it a thought!
I know it's a bit confusing,but I learnt it the hard way myself!

 

True, 140 is the next "weight" up from 90. But, in terms of cSt's, there can be a BIG difference! Since these ratings are a range, a 90 admittedly could be the nearly same kinematic viscosity as a 140, but they could also be very different if the 90 was at the low end of the scale and the 140 at the high.

If your diff is worn from years of mineral lube, using a thicker rated lube (even a synthetic) is at best a band-aid. Certainly the best possible situation is to have synthetic in it from the beginning (more and more factory fills are synthetic, for what that's worth).

What exactly am I missing in my reading, Dutch? If what I believe I know is wrong, I want to know about it.

 

Hopefully I'm okay in this area; when I put the axle in, I "rebuilt" it with new axleshaft bearings & seals. The only seal I didn't touch was the pinion seal; I didn't want to worry about ruining any preload. Thanks for the weight info; I'll run with the 75w90... hopefully I can feel an SOTP difference like you did! Plus, if it winds up to be noisier, that's okay- I like a little gear whine anyway

One last question- If posi additive reduces friction, would it still be needed with a synthetic gear oil? I guess there's no harm in adding it; just curious...


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

[This message has been edited by TomP (edited June 21, 2001).]

 

Hey, one more thing- why the heck do companies make a 75w90 and an 80w90? Does the "5" difference really matter??


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Excellent discussion...I agree 57, we need an oil FAQ. A lot of false information about oil around here. The only possible downside to synthetic oil is the cost, IMO. FYI, according to powertrax, synthetic oil makes the powertrax locker louder. I'm running synthetic and the powertrax is quite as can be, so I don't know how true it is.
The rear diff is usually an 'abused' component of third gens(and other cars). The fluid isn't changed often enough and it isn't checked enough. Spend the extra few bucks and you won't have to worry about it for a long time.

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro