GM rear differential lube - synthetic 75W-90...

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NewGuy,

Try a parts store for the gasket, or maybe use a Mityvac so you do not have to remove the rear cover. However, you will not be able to remove the debris from the magnet.

I changed the fluid on my rear diffy at 30k and it was pitch black.

I have been thinking about whether the overfilling will allow the diffy to dissapate heat faster or not. Hmm. The heat will only be transfered to the metal casing where the fluid contacts the metal on the inside of the diffy. So at first I thought that overfilling would cause quicker heat transfer since there is more area of fluid in contact with the diffy casing. However, when driving, the fluid will splash all over, so i dont think it will really matter much.
 
Overfilling does increase heat. In your case the manufacturer made several errors, apparently including having the wrong fill specification. Truly overfilling, beyond what the differential needs, has no benefit. What you've done is "proven" nothing regarding the differential in most vehicles, much less a late-model Tahoe.
 
Respond back if you wish, I'm done. You believe what you believe, and I don't. If I run across any legitimate testing in this regard, I will post it. Otherwise, I stand behind my premise that truly overfilling a differential serves no benefit at all and may have detrimental effects.
 
I have mobil-1 75-90 synthetic in my Town Car diff
90k miles/3 yrs with the cover sealed with RTV--
I have no leaks
 
Just so everyone knows if ever you add a gear lube to a limited slip diff. and it chatters you are not up a creek. Most part stores like AUtozone cary tubes of limited slip additive and are open late. I mentioned this because the dealership is normaly closed when you find out you need some limited slip additive!Some rear ends are really picky while others are easy to please.Most of the staff at most parts store have no clue that they carry it or what it is for! It is usualy close to the gear lube.

Specialty Formulations has a kick put gear lube. I belive it is semi-synthetic but the additive chemistry is spot on!!!Molakule has worked wounder with some of his other fluids for manual transmissions!
 
RTV is fine if you use it properly. I prefer to use a product called The Right Stuff it is awesome. It is cured and ready to put back into service within 1 minute after assembly. You only have a 5 minute work time from when you start to apply it to the part until you have to have it on. It is not like most RTV's were you can let them sit on the work bench up to 15 minutes before assembly.
 
Quote:


..if ever you add a gear lube to a limited slip diff. and it chatters you are not up a creek. Most part stores like AUtozone cary tubes of limited slip additive and are open late...




The G80 4.10 rear in my 2002 isuzu rodeo was like that. It had the clutch pack limited slip. Those will chatter like crazy w/out the additive!
crazy.gif


Joel
 
Some gear oils have enough additive in them for most limited slips but some are marginal.When I did this type of work for a liveing I always kept a couple of tubes of additive in the shop. You might do 12 rear ends and not have a problem then have one or two in a row that simply needed more additive then the gear lube contained. Most gear lubes say something like "limited slip approved", "with limited slip additive", "compatible with limited slips" etc.....Amsoil gear lube for example claims that you do not have to add any additive for limited slip use but it is just like the other brands it is hit or miss.
 
Here's my email to Eaton performance products from the link provided above:
-----------------------------------------------------------
1. Does G-80 Locker have clutch packs that wear out?

2. Is a normal 75w-90 synthetic gear oil (like Mobil 1 75w-90)acceptable? Subject to your answer above, does this gear oil need a friction modifier?

I have this rear end option in my 2004 Chevrolet Avalanche and do not want to use the factory specified synthetic gear lube because it costs $28/qt.

----------------------------------------------------------

Response from Eaton:

"Jim,

Yes, the G80 locker has clutch disks in them that may eventually ware out over time. As for as the fluid recommendations, please reference an owners maintenance manual to verify, but I have always used the straight
80w90, GL5 mineral axle oil with no issues.

I hope this helps.

Regards,

Barney Gwozdz
Sales Administrator
Eaton Performance Products
Phone# (248)226-****
Fax# (248)226-****"

[I will provide his phone number to anyone who PM's me. I just don't want him to start getting phone calls from telemarketers and such.]


So......I guess it's really a limited slip, and not a locker like it's described in the option sheet.
 
A good replacement for the expensive GM gear oil is the synthetic gear oil heavy trucks use in Eaton differentials that qualify for their 750,000 mile warranty. Take your own gallon jug to a truck repair shop and buy a gallon from their drum.


Ken
 
This thread has me really interested.

My 2005 Silverado 2500HD Crew Cab short bed has 20K.

Very little towing so far, easy break-in, changed tranny filter twice and used Dexron III-H.

I'm thinking of switching to Amsoil SVG or Redline 75W-90 in the front and rear diffs.

Dexron VI in the Allison. AllTrac II in the transfer case.

Delvac 1 5w-40 in the engine and OCI by OLM. So far the engine has had frequent 2K to 3K changes with dealership Valvoline 15W-40 and I use Delo 400 15W-50 and change at 40% left on the OLM.
 
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