gear oils need changing,need info on correct oil/type

[73GMC10]

Hi all, that's all this forum needs is another oil question, I have researched for about over an hour and I think im going to go with 80w90 for my dana44,sm465/np205,14bolt ff rear end, now as everyone has diff types of oil recommendations I just want to be clear that from the d44 front,tranny/tcase/rear end 80w90 is fine.
But what is not answered though is positive and negative talk about GL-5 oil, people are saying use it, its recommended and others are saying no don't it'l eat /do harm to your parts inside especially the tranny and tcase, so just want to know if anyone can help me on this gl-5 thing or do I need to find just regular 80w90 if there is just that without the gl-5 numbering, thanks in advance I just don't want to hurt anything.

[73GMC10]

after some much deeper searching I found this posting so GL-5 is definatly out for me ill try find a regular 80w90 without the additives.

SWHEATONJun 5th, 06,
GUYS/GAL'S?,I know this is the wrong forum for this but i am trying to get the word out to ALL T/C's that run muncie's about this info i just learned that i am sure others are not aware of either.

I was not aware the GL5 & Hypoid additives that contains sulphur & is very slick was harmfull to the syncros in our muncie's that are rated for 80/90 LUBE ONLY. I was unknowingly running GL5 lube in my muncie for 4+ yrs and it has been shifting harder even though clutch is adj correctly. Now i know why after reading the info from the Redline Oil Site which i have LISTED BELOW FOR YOU ALL TO READ TO AVOID DAMAGE TO YOUR MUNCIE'S.

Also,i checked approx 9 auto parts stores in my area and not one of them sells or stocks any 80/90 std trans lube that not rated for GL5/Hypoid,they are all rated for GL5/hypoid use . None of the 9 stores i checked stock the lower rated GL4 80/90 lube thats rated for our older muncie std trans so beware of this as i am sure many of you are running the wrong GL5 rated lube that will eventually tear up your syncro's AND DONT EVEN KNOW IT'S HAPPENING.

I just drilled and tapped my muncie for a drain plug so i could drain the wrong GL5 lube out and replaced it with redilnes MT-90 gearlube thats specifically desigend for our trans but i think it's too late for me but i hope i can save some of your trany's if you take the time to read this great info from Redline oils listed below.

[hatzie]

SM465, NP205, Dana 44, & 14 Bolt all call for 80W90 GL5 Gear Oil in the GM service manual. Download one for your year and take a gander. I use a Synthetic 75W90 GL5 in all three of my pickup axles with no additives.
GL5 will not hurt the stock 73-91 Squarebody light truck transmissions. Also. Modern GL5 oils will not attack yellow metal synchros as it has been re-formulated to avoid this problem.

Limited Slip Additives are to be avoided unless your Aftermarket diff specifically calls for it and never in a transmission.
None of the stock 3/4Ton and larger light truck axles need a Limited Slip Additive regardless of G80 option. See the GM TSB below...

-------------
SERVICE BULLETIN: 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.
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[73GMC10]

wich is weird why GL-5 is recommended when muncies have brass syncros and gl5 is harmfull to brass.




[QUOTE=hatzie;6906446]SM465, NP205, Dana 44, & 14 Bolt all call for 80W90 GL5 Gear Oil in the GM service manual. Download one for your year and take a gander.
I use a Synthetic 75W90 GL5 in all three of my pickup axles.

None of the stock 3/4Ton and larger light truck axles need a Limited Slip Additive regardless of G80 option. See the GM TSB below...

[hatzie]

The Muncie referenced in your article is the M21 or M22 used in automobiles.
Very different transmissions.
Not even in the same class as the SM465. The NP205 doesn't have synchros...

Use what GM called for in the service and parts manuals or something similar off the shelf. GM 10950849 is 80W90 GL5 gear oil. If you're worried stay away from the synthetics but otherwise...

I had an SM465 in my 73, 75, 83, 85, & 86 3/4 ton trucks. I always used 75W90 & 80W90 GL5 dinosaur juice in everything after the engines except the the NP203 & NP208 transfer cases. No issues.

My trucks have NV4500 & TH400 trannys with NP208 transfer cases now so the only things onboard that use gear oil now are the axles.

[73GMC10]

Thanks hatzie for clearing that up for me on the difference in the muncies internals from autos to trucks,so besides the engine from from axle through trans ,tcase,diff GL-5 80w90 will work on all 4 correct?then I can put this thread to bed.

*edit, I actually found my manual go figure I thought I lost the darn thing, sure enough there it is about GL-5 oil*

[hatzie]

The owners manual works...
You can get a searchable PDF of the 1973-91 CK & RV squarebody service manuals and parts books from the RTFM link in my signature.

SM465, NP205, Dana44, and GM Corporate 14bolt... in 1973 GM calls for 80W or 90W GL-5 gear oil. By 1977 they called for 80W-90 GL-5. I use 75W-90 GL-5. It flows better at low temps and is 90W at operating temp.