350 groundpounder

iTrader: (5)

96 Lt1 M6

I was wondering which oil to use in my rear end, I was thinking of going with synthetic but not sure if it is advised? Do I need to use GM additive?

I heard with royal purple that you don't need the additive? Lots of questions!

Also I hear a slight whining from the rear end in six gear. Would synthetic help that?

Purple Poncho

iTrader: (1)

2 quarts of non synthetic and a bottle of GM diff. Additive.

leadfoot4

iTrader: (1)

Maybe......



GM, through SLP, offered a full synthetic oil package, on the SS/Firehawk models they did the conversions on. This included the rear end lube. I have a '96 Z-28 that I purchased brand new. I changed the rear end oil twice, on an annual basis, the first two years I had the car. On the third year, I filled the rear end with Valvoline syn gear oil and a bottle of the Positraction additive. It's been in there for 15 years now, without issue.

My only concern with adding syn oil to an older car, is based on what a Tech Rep for one of the oil companies told me about 16-17 years ago. He said that if a rear end has had "dino" oil in it for more than 5-6 years, the seals have "acclimated" to it, and switching it to syn oil might cause leaks, due to the different chemical make up of the syn oil. Take that for what it's worth...

speed_demon24

iTrader: (6)

Or ford additive if you dont want to get raped by gm's prices.

Paul Bell

iTrader: (9)

I like the Lucas non-synthetic gear lube. And a bottle of Redline posi modifier.

Catmaigne

iTrader: (6)

Walmart brand conventional 80w90 and a bottle of equatorque from the Pep Boys next door. My 10 bolt and I weren't friends.

fleetmgr

Use a full synthetic 75w-140 that either has friction modifier in it, or add the modifier. Why full synth? Quite simply because it does a better job at lubrication, in any and all conditions. It's more temperature stable (especially with a broad viscosity index), it's less affected by oxidation, it has greater shear strength, it holds it's viscosity over time. There are zero negatives.

Wheelman916

This.

Synthetic beats conventional in pretty much every way, except for price. Royal Purple makes a good gear oil. Is it the best? That's a matter of opinion and debate. I would say no. But it's good gear lube. Much like motor oil, any gear lube, conventional or synthetic, will get the job done if changed out regularly.

Pretty sure in '96 & '97, SLP offered an optional Torsen dif in the SS and Firehawk... which came with the upgrade to synthetic gear lube.

Switching to synthetic after running conventional for so long can lead to leaks, but it has nothing to do with the seals acclimating to the conventional. The seals have long since developed the leaks, but the sludge left behind by conventional clogs the holes. After switching to synthetic, the sludge gets cleaned out and reveals the leaks that were already there. Same thing can happen in engines.

fujitashi

I filled the rear end with Valvoline syn gear oil and a bottle of the Positraction additive.

nitrous2fast

iTrader: (2)

I put ground up hopes and dreams in my ten bolt.....

Paul Bell

iTrader: (9)

Some differential manufacturers specify to NOT use a synthetic gear oil.

http://www.eaton.com/Eaton/ProductsS...ials/index.htm

While I'm sure we all agree that synthetic lubricants have advantages over petroleum based lubricants (as posted above) the stresses and harsh environment of an engine are far greater than that of a rear end. The rear end is one area that the advantages of a synthetic lubricant are simply not needed.

Use what you think is best for your application but be aware that the above post about changing to a synthetic may cause seals to leak is accurate.

This is a topic that pops up every year or so.

guppymech

iTrader: (7)

Auburn as well specifies NOT to use synthetic lube. Ford friction modifier works good and is way less expensive than GM, Summit Racing has it.
http://aftermarket.auburngear.com/ma..._and_warranty/

Paul Bell

iTrader: (9)

An interesting fact is that friction modifiers used to be made from whale oil, it's the long alkyl chains that make it work. That's why when opening some rear ends the fluid stinks.

speed_demon24

iTrader: (6)

Everything Lucas makes is complete garbage.

Paul Bell

iTrader: (9)

While I'd agree their synthetic oil stabilizer is crap and should be pulled off the market, I do believe the rest of their products are pretty decent. I've never heard anything anywhere that it's all garbage.

If you have some info or facts about this, please share them so we can all be a bit more educated. If Lucas products are all in fact garbage, we should know why.

leadfoot4

iTrader: (1)

Yes, SLP did offer the Torsen differential as an option, however, I don't think the syn gear oil option was offered just for that diff.

With respect to the comments about seal compatibility, I'm simply restating what I was told by the oil company's tech rep....

fex77k

iTrader: (2)

I don't ever use synthetic for the rear.