Rear end breakin Procedure

[turbo Al]

NeedsbigTruck:

Written by "Shawn Spickler" of Off-Road.com

The greatest damage to a new gear set results when it has been run for ten minutes or more during the first 500 miles and the oil is very hot. Any heavy use or overloading while the oil is extremely hot will cause it to break down and allow irreversible damage to the ring & pinion. In order to make them run cooler and quieter, new gears are lapped at the factory. However, they are not lapped under the same pressures that driving creates. These loads generated while driving, force any microscopic high spots on the gear teeth back into the surface of the metal. This is called "work hardening". Work hardening is similar to forging in the way that it compresses the metal molecules into a very compact and hard formation. This can only be accomplished if the metal surfaces are lubricated and the gear temperature stays cool enough that the molecular structure does not change. If the temperature of the metal gets hot enough to change the molecular structure, it will soften the surface instead of hardening it. This may seem like a balancing act but it all happens easily & passively as long as the oil keeps the gear cool while it is breaking in. Some of the synthetic oils on the market today can help a gear set live longer. Theses oils will continue to lubricate at temperatures where many crude oils break down. Even with synthetic oils, you should still follow the procedure for
BREAKING IN A NEW GEAR SET:
After driving the first 15 to 20 miles it is best to stop and let the differential cool before proceeding. Keep the vehicle at speeds below 60 mph for the first 100 miles. You should put at least 500 miles on the new gear set before heavy use or towing. During the first 45 miles of towing it helps to go about 15 miles at a time before stopping to let the differential cool for 15 minutes before continuing. This is necessary because not all of the gear tooth is making contact until it is heavily loaded. When towing, the teeth flex to contact completely, and cause the previously unloaded portion of the teeth to touch and work harden. All of this may seem like paranoia, but it is very easy to damage the ring & pinion by overloading before the teeth are broken in. It is a good idea to change the gear oil after the first 500 miles in order to remove any metal particles or phosphorus coating that has come from the new gear set. This is cheap insurance and a good time to discover any problems before they grow to disastrous proportions.
Again thankyou Shawn Spickler

Turbo Al Member #750

[DURASAM]

I changed the oil in the rear end of my truck yesterday and the oil that came out of it looked like it had lapping compound in it. Both plugs had a build up of a gray compound on them and the bottom plug also had little bitty tiny metal flakes on it.

[mulerose]

Nice discussion on break in-makes sense. Makes you think about buying one off the lot that has a couple of hundred miles of "test driving" First thing most guys do is punch it...

[needbigtruck]

Thanks Turbo Al this is the info I was looking for. Now as soon as I get my truck I will apply this very simple procedure to properly break in the rear end (I suppose it also will break in everything else).

[turbo Al]

You are all welcome but the credit goes to Shawn Spickler for such a detailed article. I did not type the whole article just what I thought you wanted Needsbigtruck.
Mulerose: YES I just hate it when a "Dealer" lets every pilot in town Test Fly new trucks.
Turbo AL

[Bad Dawg]

I've been looking through the owners manual trying to find any info for the rear locking differential and can't find anything. With my last truck (97 3/4ton 4x4 with limited slip)the owner's book said to change out the rear oil after either 500 or 5000 mile (can't remember which now)for the same reasons listed on this site. This time around I can't find any mention of doing this.

I had loud clanks coming from my last trucks rear before we found out about the first oil change and found out that the rear needed TWO bottles of limited slip oil added and not just one. Does anyone know if this new locking differential takes any extra additives and if the locker takes any different oil than a standard rear end?

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2001 Silverado LS 3500 4WD Crew Cab D/A Dually, Med. Charcoal Gray.

[DeepVee]

I just changed mine after 500 miles of heavy towing. I checked the fluid before I left(500 miles on truck), it was clear and looked new. When I drained it after the tow it was solid black and no longer clear. I replaced it with the GM Synthetic stuff even though it cost me $112 for 4 quarts. As far as I know it does not require the limited slip additive. My co-worker also changed his last weekend after towing and had the same black oil.

[This message has been edited by DeepVee (edited 05-04-2001).]

[happy can]

Thanks Turbo Al. That article was so good and explained exactly what I needed. I did the search on "breakin" as the one person suggested, but I didn't find that detailed article you sent. I now know what to do to break it in, and yes, I might be paranoid, but I like to eliminate those potential problems in life that I can, and this is certainly one of them. Thanks again.

[Turbo Al]

Happy Can: Glad to help, Paranoid is when you change the rear diff oil at 500 miles then remove the diff cover to see if it all came out http://www.62-65-dieselpage.com/ubb/biggrin.gif
Yes it is a well written article -- thanks goes to "Shawn Spickler" of OFF-Road.com

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2001 Ext Cab LB 4x4 Duramax/Allison, Victory Red, K & N
1993 6.5 TD 4x4 reg cab LB, 5 speed
1972 Pontiac Lemans

[Tractorhauler]

Thanks again Turbo Al,
Excellent article, BTW is hydrotex gear oil a satisfactory replacement after 500 mile Break in?
Also, is the search engine on this site having some problems?



------------------
Tractor Hauler

[ralphrah]

After breaking the gear set in I towed my 30ft fiver a few times with the lube that came with the truck.

At about 1500 miles I changed the lube out with Amsoil 75/90 gear lube. The original lube was black and there was a large amount of metal attached to the magnet.

Since then I have change the lube out at 45K and the amount of metal was very little and the gear lube was clear. Didn't look like it needed to be changed.

If you make sure that the lube you are putting in the truck is GL-5 rated, which Amsoil is, there is no need for limited slip adative.



------------------
A=R+P (ADVENTURE=RISK WITH A PURPOSE)

Late 96
HD Xtended cab 2500
6.5 TD HO
Factory 97 cooling mods
Factory HD trans oil cooler
Factory HD engine oil cooler
4L80E
Derale remote trans oil cooler with a 1K cfm fan.
4:10 Locker
Amsoil air filter and ATF

[Turbo Al]

Tractor Hauler: Your welcome -- hope it gets fixed soon. Sorry never heard of hydrotex oil, I went with the Castrol with the GL5 rating.
Ralphrah: I changed out the rear diff. right at 500 miles (no towing) and it was full of metal flakes, going to drain again on my Holiday's after towing 500 miles. I did pull the cover off just to see inside and all the oil & metal flakes had drained out via the drain plug.

[ 07-19-2002: Message edited by: More Power ]</p>

[DmaxMaverick]

In regards to the limited slip additives:

The G80 rear end IS NOT limited slip. It has a Gov-Lock carrier. Meaning it does not rely on clutch friction for torque transfer and does not require friction modifiers. The use of friction modifiers in rear ends and gear boxes that do not recommend them can damage them by causing metallic erosion/corrosion and react with some elements.

The GL-X requirement is not just for addressing limited slip issues. The additive package recommendation addresses the system as a whole according to its components.

Although the G80 requires a GL-5 class lube, not all GL-5 rated lubes will be compatible. None of the mineral based GL-5 lubes are acceptable, according to the manufacturer.

I'm not making a lube recommendation here, just offering info. I replaced mine with Amsoil Series 2000 75-90 synthetic, as recommended and supported by Amsoil to be a correct replacement for the OEM.

------------------
2001 GMC 2500HD SLT 4X4 E/C SB loaded -D/A- Indigo Blue - Amsoiled bumper to bumper - Delivered November 2000

1985 K Blazer 6.2L N/A 500K+ original miles on Engine/Tranny (2 transfer cases, 1 pump, and a few rear ends)
Synthetic Oil!!

[Kennedy]

Ok, here's a question:

Who has had the rear cover off??? GM typically has a large round magnet glued into the case on the 14 bolt FF axles. I hear talk of the magnet being on the drain plug, but wonder if there may still be a large magnet inside???

With all the filings coming out...

Another note worth mentioning:

The hubs are not drained with the center section as they are below axle tube level. For those EXTREMELY particular about maintenance, it isn't that difficult to slide out the axle shaft and drain the hubs along with whatever contaminants are in the oil. I generally tip up one side at a time while draining AND filling. Hoy oil of course will drain better, and Brakleen can be used to expedite the process so long as it is all evaporated out prior to closing up. I haven't seen the fluid level, but generally it is below tube level, so if you have dry hubs, you should tip axle to distribute clean oil to the hubs, and recheck level when done. Typiclly they have used an aluminum? gasket ring behind the axle hub wich I have had good success in reusing.

NOTE: I have NOT had one of these new monsters apart yet, only conveying past experiences

------------------
John Kennedy
www.kennedydiesel.com (http://www.kennedydiesel.com)
John@kennedydiesel.com
1996 K2500HD 6.5TD Ex.Cab LWB 258 Rw H.P.
1984 K30 SRW 6.2NA Headers and custom 2 into 1 exhaust FOR SALE
'01 FXDWG Black/Chrome Yellow (2 into 1 Thunderheader &lt;naturally&gt;) (98RwHP going for 103!)
"If I had to explain, you wouldn't understand"

[Turbo Al]

John: Took my cover off at 500 miles and didn't see a magnet in there. Really not a lot of room in there anyway, the Locker takes up most of the room.
Good point on the hubs retaining oil but even I am not that http://www.62-65-dieselpage.com/ubb/biggrin.gif paticular http://www.62-65-dieselpage.com/ubb/biggrin.gif (yet)
I admit I do service things a little much, but if we can get the Members educated into doing a little "extra" at the beginning then these units will remain (for the most part) trouble free untill they just plain wear out.


------------------
Member #750
2001 Ext Cab LB 4x4 Duramax/Allison, Victory Red, K & N
1993 6.5 TD 4x4 reg cab LB, 5 speed
1972 Pontiac Lemans

[JimWilson]

Wonder if I got the "special" locker form Eaton... :D

My 02 2500HD CC has the G80 rear. I changed the fluid this past weekend, when she had just a hair under 3K on the odo. I waited that long because I haven't towed yet, and I wanted all the manufacturing crap to have broken free completely so it would drain out. Refilled it with Amsoil 75/90. The reason I say maybe I have the special locker is that my drain plug had no metal shavings on it; nothing, nada, zilch. The fluid appeared to be mostly black, with some type of tannish, milky substance that didn't appear to mix well with the oil -- they seemed to stay separate. And it stunk! Smelled like raw sewage.

With all this talk about massive amounts of metal shavings on the drain plug I'm wondering if I got a marvel from Eaton or if I didn't wait long enough to change the fluid.

[odoh]

JK ~ Good point. Explains the factory fill being a lil' short/below the fill hole. Some of the oil is out in the back forty ;) ~ odoh

[D-n-Tyke]

So when is the fluid in the front diff. due to be changed? For us with 4X4.

[oneton]

Well, I just changed the rear end fluid and found a very small amount of shavings and casting junks. The truck has 1500 miles on her in 7 days. I was hoping to change out the fluid as soon as I got back from OH but it didn't happen. It did have a real mild sewage smell according to the wife. ( I have no sense of smell at all, yep, natta!!) Next is the oil, and I hope I have better luck with the oil filter that some of you.

JK, thanks for the info on the testing the oil. Is the first oil change used as a base line or should you use one from a later oil change?

&lt;on edit&gt;
BTW, I used a flex funnel to fill the rear. It worked perfect and fit between the spare and the pumpkin. I laid on the creeper in front of the axle so I could reach the top of the funnel easily. Plenty of room on the front side to do this. Just make sure the muffer is cool first ;)

Thanks


opps wrong post sorry for the intrusion one ton

Turbo Al

[ 07-20-2002: Message edited by: Turbo Al ]</p>

[D MAXIMUS]

This information is from the Eaton website.

What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?

Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford).

See http://www.torquecontrol.eaton.com/prod6.htm

Therefore, it seems that a previous post that states that the additive is not needed is incorrect.

John

[oneton]

D Maximus, the locking rear(G80) is not a limited slip rear end. The question posted on the Eaton site was refering specificly to the Limited Slip rear end.

[D MAXIMUS]

oneton,
You were right. I did email Eaton to get their recommendation on oil type and maintenance schedule. Here is their reply:

"The newer GM trucks use synthetic oil that is considered lube for life in most cases. Depending on the year /make of your truck the GM manual may require you to change the lube after 500 miles of aggressive towing , as
this condition works the axle (generates heat) the hardest. After initial
towing the axle temperatures will no longer peak, and the new synthetic lube will last a long time.

You should stay with the lube GM recommends as other lubes, especially synthetics may cause G80 to lose capability. Some of these oils reduce the friction characteristics of the G80 clutch packs, increasing the slip
between clutch discs, which will prevent the axle from locking. Never
use friction modifier (additives) in combination with the G80 as they also
increase slip between the discs."

John

[TxDoc]

Here is some info Eaton sent me in the past:

"GM introduced the new body style in 1998. At the same time they upgraded
the differential and changed to a synthetic lube. The G80 is specifically
designed to give ultimate performance with this lube, and the lube contains
special additives that help reduce slip stick that occurs between the
clutches. the GM synthetic lube typically runs about 100+ degrees cooler
than mineral base lube, which is better if you do allot of towing or heavy
hauling. I would recommend that you stay with the GM synthetic, not Mobil 1.
If you don't tow or haul you could use the pre 1998 mineral lube without
degrading performance of the differential. this would be a cheaper option
but require more lube changes. "
"Axle tolerances of the 1/2 ton trucks are very tight. The recommended
procedure was to change lube after 500 miles of heavy towing, which would is
considered a break in period. This breaking period generates high heat
conditions in the axle which was found to degrade the synthetic beyond the
point of mineral lube. After the 500 mile lube change, the axle is broke
in and does not generate the high heat. If you use GM synthetic after the
break-in period, it can be considered "lube for life", although some say to
change it at 40,000 - 50,000 mile intervals."

"If you don't tow, don't worry about the oil change as it a waste of money."


"If your truck is pre 1998 or the old style, it comes with mineral lube. IN
that case you need to stay with mineral because the seals are designed to
work with it. If you changed from mineral to synthetic you'll cause your
seals to swell and eventually leak. It's ok to go from synthetic to
mineral because you won't cause swelling. many of your stop leak
chemicals effect seals in this manner, resulting in a short term fix but a
long term problem."

Back in November, I received the following:
"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:
"The maintenance schedule for the rear axle was developed by American Axle &
Manufacturing and GM truck based on multiple tests. The Eaton locker does
not require additional maintenance nor does it add heat to the lube. The
lube will darken due to the carbon wear on the clutch surfaces, much the
same as a disc brake pad & rotor. This does not damage axle components such
as seals or bearings. However, a new axle can produce excessive
temperatures (plus 350 degrees F) due to the ring & pinion breaking in that
will break the lube additives down. Avoid high loads, trailer towing and
high speed extended driving during the initial break in of the vehicle.
After the break in period axle temps will level at a much lower figure.
Lube changes are a good idea because the additives are replenished and
contaminates such as casting sand are eliminated. The axle is filled at the
factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.
The GM service # is 12378261. This is the only lube we have done extensive
testing with to insure locker compatibility. The only negative to using one
of these other lubes is an increased potential for clutch chatter. This
really doesn't hurt anything and can be corrected by changing the lube. I
noticed in the latest GM owners manual the term "or equivalent" when
referring to the lube specification. Look for a GL5 rating on the bottle to
make sure the ring & pinion, seals & bearings are protected. Limited slip
additive is not needed."
The following information outlines the type of
rear axle lubrication utilized in GM Truck axles.
I. Fluid Type
II. The 1500, 2500 and 3500 GMT 800 Trucks utilize SAE 75W-90 Synthetic Axle Lubricant. The GM part number is 12378261 and the specification is 9986115.

[D MAXIMUS]

TxDoc,
That is the kind of information I was looking for. Thanks.

John

[Turbo Al]

BTT

[Turbo Al]

BTT for the newer members

[Turbo Al]

BTT

[HDV-rod]

46K with the original fluid front and rear. No noises, no problems.

Will change with the tranny fluid at 50K. No need to do it sooner.

[Turbo Al]

O.K. I think it goes something like "You can lead a horse to water but you can't make him drink"
Al

[byronlj]

If they(GM) want us to break the rear end in properly to avoid too much heat, then why do they significantly under fill the differential at the factory? On my 2001 HD the paint was burned on the outside of the case when I changed it at 7,500 miles. I wanted to avoid this on my 04 HD so I changed the fluid @ 1,600 miles. Both differentials were very low so I checked how much when I drained the 04. It was more than 2 quarts low. BTW, I did break both in according to GM recommendations.
Dave

[Kennedy]

I saw my 2005 on the hoist during dealer prep. The Tech had the fill plug out and was topping it off. I also believe that the proper fil level is approx 1/2" below the opening isn't it?


I want to clarify on the magnet thing. The ring magnet is typically on the floor of the housing, and resembles the one inside Allison spin on. The old 14 bolters had this, but no drain plug...

[MaxACL]

Two dealer techs said the new trucks fresh off the delivery truck are always low on all fluids. Nobody knows why, they just are. My transfer case was run dry and cost me $3200 to replace it.

Turbo Al:
"You can lead a horse to water but you can't make him drink" YES you can, at least here in Texas we can. Takes two people. One in the front to hold his head under water and another around the back side to lift his tail and create a low pressure area in the animals insides (use your imagination here with this).

The elevation of the head can be monitored by the presents of air (head too high) or mud (head too low).

Gads... It's good to be home for a while:)

Mike

[Turbo Al]

:eek:
Thanks for the Morning laugh!

[More Power]

While I was at Randy's R&P this past September, I snapped a couple photos of an AAM1150 rear diff out of a 2500HD that was in for service.

http://www.thedieselpage.com/images/2500hdrear01.jpg
http://www.thedieselpage.com/images/2500hdrear02.jpg
http://www.thedieselpage.com/images/2500hdrear03.jpg

MP

[DMax Farmer]

Great info, but
Does cold weather affect break-in proceedure?
It's been between 10-20 degrees here with the new trk. I've been running 40 mile junts to compensate for the cooler temps. Does that make sense? You thoughts?

[Turbo Al]

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[Turbo Al]

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