someone please tell me this guy is full of BS

[1979,GMC,1ton-addict]

(portaining to the first part) that guy is full of **** i have a 1976 dodge ram and until i owned it the fluid had never been changed i had trouble finding the fluid but once i did i changed it and it opend the trucks speed not to much but u could deff. tell the difference much smoother and not as held back as the 33 year old fluid was doing lol and i live in canada so its cold even in summer and everything cured fine so i hope i helped at least a littel man good luck

[3r!c84]

Originally Posted by Mr.Scary

so i can just go ahead and use tha limited slip additive wit out hurting anything? cause i dont really kno much bout axel's or rearends 4 that matter, as a matter of fact i didnt even kno there was a special additive u had 2 add 4 limited silp diff's i thought u just buy tha gasket and tha diff fluid and drain tha old stuff out pop tha gasket and cover back on and add tha fluid back. maybe i should do a bit more researching on this b4 i change tha fluid??????

wait you didnt have to buy a gasket. just get some RTV Silicone

[pat386]

I changed my rear diff fluid and it made the left seal leak like crazy. The fluid wasn't changed in the 12 year/20kmile span the previous owner had it as far as I know..

[hatzie]

Originally Posted by Mr.Scary

so i can just go ahead and use tha limited slip additive wit out hurting anything? cause i dont really kno much bout axel's or rearends 4 that matter, as a matter of fact i didnt even kno there was a special additive u had 2 add 4 limited silp diff's i thought u just buy tha gasket and tha diff fluid and drain tha old stuff out pop tha gasket and cover back on and add tha fluid back. maybe i should do a bit more researching on this b4 i change tha fluid??????

The Limited Slip Additive will not hurt a non Limited Slip axle. I just use it when I'm not sure what I have.

I use Synthetic 75W-90 and a bottle of GM Performance #1052358 Limited Slip Lubricant Additive. The little bottle should be 10-15 bucks right from your GM dealer.
I've heard that with synthetic oil you don't need additive but I don't believe it.

The RPO code for limited slip is G80 ( I don't think G85 & G86 apply to our trucks). Should be on your option tag in the glovebox. If it's still there... and if you still have the original axle.

[cableguy0]

the synthetic oil already has the additive in it. you do not need the additive its a waste of money

[hatzie]

Originally Posted by cableguy0

the synthetic oil already has the additive in it. you do not need the additive its a waste of money

I'd check the label. I don't think it said it had limited slip additive.

[87 STEPPER]

Im guessin you changed the diff fluid and you allready know the guy didn't know what he was talkin about. But i just wanted to tell ya i use wall marts brand called super tech W85-90 it's the same thing as any big name brand but cheaper! I also use there Oil, ATF,Break fluid,PS steering, pretty much everything they have is produced by one of the big brand guys for them.

Also FWIW changing the fluid in a high milage auto tran's that hasn't had regular service through out it's life WILL cause the trans to fail i know it's happened to me!

[BIG-AL]

Rvt / and royal purple.

First thing i do when i buy a used truck. Change all fluids.

[cableguy0]

read http://www.royalpurple.com/gear-oil.html http://www.mobiloil.com/USA-English/..._75W-90LS.aspx http://www.amsoil.com/StoreFront/fgr.aspx that should about cover it

[BIG-AL]

Right on man...............

[87 STEPPER]

Well thoes are synthetics i dont use them there viscosities are too thin and promote leaks in older vehicles that were never ment to use them in the first place.

But everyone has there own thoughts on whats good and whats not

[68Timber]

Bud, these are absolute truths. The rear gear oil needs changing at regular intervals. Not as often as the engine, but that doesn't mean the pumpkin lube will last forever.

Second, and this one will draw fire and I can't back it up right now - the G80 only needs regular 90 wt gear oil. IT IS NOT A POSI AND ANY POSI LUBE WILL CAUSE IT TO CHATTER AND OTHERWISE BEHAVE ERRATICALLY.

It's a locker, not a posi. I have the tech bulletin on my other PC about putting posi additives in a G80 axle. I'd copy it over to this PC and post it but I gave that PC to my kids and it's virus infested and I'm not copying anything from it to this computer.

I did a quick search and couldn't find the tech bulletin. If you need the proof, I'll do some more searching for the tech bulletin.

That's the skinny the way I know it. If you want me to back it up with a GM link I'll do my best to find it.

[68Timber]

A quick search:

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.
VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
� Copyright General Motors Corporation. All Rights Reserved

[Tex_50613]

I personally use Mystic 80-90 gear lube (red 5 gal Bucket) for my diffs, trans and t-case. 1 it helps see if you have any leakes and 2 I change my fluids in those items atleast 3 times a year to insure my bearing life after submerging and possably contaminating them with mud and water

[68 TT]

I put over 100k miles on my 95 Blazer gov-lock posi with Mobil 1 synthetic in it without any problems.

I also put 70k on my 91 Z/28 that had a clutch type posi with the same Mobil 1 synthetic gear oil with no additional additives and had no issues at all.

When I worked at a Corvette repair shop before the synthetic oils were popular I rebuilt quite a few clutch type posi carriers. Vettes tend to sit a lot and the gear oil settles out of the clutches then they get overheated just turning corners until the oil re-infiltrates the clutch packs. We always used the GM posi additive as an assembly lube on the new clutch plates when putting the posi together then poured the rest of the tube in the diff when done. Not cheap stuff but worth it in quieter clutches when using dino gear oil.

[pat386]

we just did rear bearings and seals in mine (and found it's a posi rear end) and we refilled it with lucas. good idea or bad?

[Mr.Scary]

man this thread turned in2 a snowbal effect, just FYIi havent changed my diff oil just yet cause tha good oil cost an arm and a leg but i did get tha "the right stuff" gasket maker stuff tha other day from o'reillys they carry that stuff there 4 pretty cheap and some1 on here said it was really good stuff so ima just use that stuff wit no gasket and some mobile 1 or royal purple or something. hopefully get started on this sat of next week. wish me luck guys!!!!!!!!!

[hatzie]

John
Thank you for the tsb. I had no idea that the eaton gov loc could operate erratically from lsd additive. Open diffs don't care. Guys that are willing to share that kind of info make this board what it is.

[Mr.Scary]

[68Timber]

Originally Posted by hatzie

John
Thank you for the tsb. I had no idea that the eaton gov loc could operate erratically from lsd additive. Open diffs don't care. Guys that are willing to share that kind of info make this board what it is.

Thanks, but I got the info the same way you did. The topic came up on another forum and someone posted the TSB. I don't know why I saved it, but it is useful info.