M1028A2 differential additive

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sgms18

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After going over the LO I'm still confused about the differential additive. It says use the additive in the front but not the rear. Dosen't my truck have lockers in both ends? I have the dullay w/the dana 70 rear. Is it the same additive for the D60, D70 & 14 bolt or is it axle specific. Sorry for showing my ignorance but I've only had the truck a few months. I'm going through everything & the rear diff cover is leaking so I'm going to do new fluid front & rear.
 

v12venator

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So, the LO does not really cover this, but your front Dana 60 differential is a limited slip diff with clutch plates in the carrier. Some modern age fluids have the specs covered for limited slip differentials, but not all of them do. Your rear axle/diff should be a detroit locker and thus does not have the limited slip diff with the clutches that require the additive. The basic, run of the mill 80W-90 from the parts store will need the 4 ounces of LSD additive, whereas some of the higher end gear oils, such as the royal purple 80W-90 has the additive already covered. Most of the gear oils you can find at the parts stores are GL-5 spec but not all GL-5 spec fluids meet the requirements for limited slip clutches. If you don't feel like spending the money on the Royal Purple fluid, then the O'reillys should have a 4 oz bottle of additive that you shove in the fill port before you fill the front axle the rest of the way with 80W-90. Hope this helps.
 

sgms18

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Ok. Thanks for that. So I only need the additive for my front axle. Does it matter which additive or are they all the same. So far I've seen Acdelco, Spicer & Motorcraft. I'm sure there are probably more.
 

v12venator

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I personally wouldn't mix GM and Ford products like that just because I know their fluid specs and requirements for fluids don't match and certainly don't mix well, so that knocks Motorcraft off the list from me. The Oreillys has one bottle available that's the perfect amount for a change so that's why I got it, called "Lubegard" that is good for dump and forget. ACDelco would probably be the best if you can find it in a small 4 oz bottle so that you can dump and forget when you do the change as well, since that was probably the manufacturer of the additive back in the 80's when these vehicles were produced and sold to the military. That's just my opinion, though.

EDIT: Looking up the Spicer additive, I realize now that they are part of Dana, and I'm sure that also wouldn't be a bad product to put into a Dana axle anyway, so that option is also on the table. At this point, at most reputable stores, you're probably not going to get anything that is going to blow your vehicle up so long as you use it properly. If you have any attachment to a specific brand and you really want to stick with them, that's up to you.
 
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sgms18

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I agree about not using Motorcraft but mostly because it seems like sacrilege being a die hard bow tie man. Just wondering if they were all the same stuff just branded differently. If I use something like Lucas 80w90 that is already limited slip compatible am I gaining anything by using the additive on top of that or just wasting money?
 

v12venator

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At that point you're just wasting money. Since the Lucas already meets the requirements for the LSD clutch packs, you won't be gaining anything by adding it to gear oil that already covers it. Just make sure that it specifically states that it meets those requirements before you dump the old out and new in.
 

sgms18

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10-4 Thanks for taking the time to answer my questions. I've had a few square bodys but never had one w/lockers before.
 

v12venator

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No worries, we're all here to help. Speaking of helping, can I interest you in a spare hub for your dually rear axle? I ordered a replacement one for my 1031 not knowing my hubs were the single rears instead of the duals. I know it won't fit on my truck, but if it can help you out, I can send it to ya.
 

swinters

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Just an FYI, I had an 84 square body 1 ton dually crewcab that had a 4 speed and it would wear you out shifting. I had it in and out of the shop under warranty and they couldn't do anything about it. I had bought the Helm manual for the truck and while on a trip I was paging through it and saw a note on hard shifting and it said to add a 4 ounce bottle of the limited slip additive to the transmission. I gave it a try and it was like a miracle. I couldn't believe the difference. So, if you have a manual gearbox and want to improve its shifting, it's something worth remembering.
 

sgms18

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Just an FYI, I had an 84 square body 1 ton dually crewcab that had a 4 speed and it would wear you out shifting. I had it in and out of the shop under warranty and they couldn't do anything about it. I had bought the Helm manual for the truck and while on a trip I was paging through it and saw a note on hard shifting and it said to add a 4 ounce bottle of the limited slip additive to the transmission. I gave it a try and it was like a miracle. I couldn't believe the difference. So, if you have a manual gearbox and want to improve its shifting, it's something worth remembering.
Thats good to know. It just so happens that my truck has a sm465/np205 in it. They are also on the short list for a fluid change. Hell I may just buy a bucket of Lucas or the like & go on & do the whole truck.
 

sgms18

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Ok so a buddy of mine is a diesel mechanic (& a damn good one) & he builds differentials so i trust his judgment. He said if it was his truck he would use 75w140 synthetic in everything, diffs, trans & t-case. Says it has the friction modifiers i need & will be better in high heat situations. The LO says 80w90. Thoughts? Opinions?
 

v12venator

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Ok so a buddy of mine is a diesel mechanic (& a damn good one) & he builds differentials so i trust his judgment. He said if it was his truck he would use 75w140 synthetic in everything, diffs, trans & t-case. Says it has the friction modifiers i need & will be better in high heat situations. The LO says 80w90. Thoughts? Opinions?
So, this is kind of a tricky one. I wouldn't say it's necessarily a bad idea, but it's a specific use case, really. Not to negate or insult your buddy's knowledge and experiences with this, just providing my own based off what I've done with my trucks.

75w-140 is a good recommendation for gear oil in the differential instead of the 80w-90 from the LO if you plan on towing a lot with the vehicle. I say this because I towed a camper 4 hours back and forth one weekend a month for my reserve time and I grenaded a diff that had the factory spec 80w-90 gear oil in it. This is because the 75w-140 has a higher resistance to thinning out at higher loads and temperatures that towing would apply to your vehicle. Unlike the 80w-90 which is a more of an on-road gear oil rated for light towing and automobile use IIRC. 75w-140 also has a much shorter lifespan than 80w-90 because it moves up and down in temperature more broadly and wears out the additives from the factory whereas 80w-90, when it stays in it's operating temperature range, lasts much longer because it doesn't change that drastically in temperature. I now don't tow with the truck that I grenaded the diff on, even though I replaced the rear axle.

In the case of the trans and the t-case, I would still recommend the factory spec of GM DEX2 or 3, but not DEX 6. The DEX fluids being hydraulic fluid instead of gear oil have a higher resistance to foaming and aeration while at operating temperature with the gears moving in and out of the fluid at rapid speeds, whereas gear oil is kind of quick to foam even in a differential. I'll link Banks' video of "what is going on behind your stock diff cover" here for viewing that goes more in depth into the practice more than the theory.

Is your trans in the 1028 the THM 400 or do you have a manual gearbox in the truck? I would recommend manufacturer fluid for the trans regardless of what the make of the transmission is. An 86 Chevy NV4500 may have a tendency to splinter gears more often without GM manual trans fluid from that era that had say a higher concentration of copper for instance that would fill in the chips and nicks of the gears of the transmission.

These are just my thoughts and experiences, though. I would also throw in my recommendation of going synthetic whenever possible, since there are more additive protectants and detergents usually. Synthetic also has a longer lifespan than conventional fluids in almost every application. I hope this helps.
 

swinters

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I really like synthetics too but when the Army looked into changing to synthetics Eaton was adamant that synthetics not be used in their differentials. I've done some digging and it looks like they still maintain that position: https://www.eaton.com/Eaton/ProductsServices/Vehicle/Differentials/FAQforDifferentials/index.htm. I don't find much on why but I'm going to contact them and find out. Maybe they want to sell ore repair parts?
Anyway, I've stuck with the LO and have never had differential problems and my CUCV sees some rugged use. I've tried using the gear oils that are not supposed to need the friction modifier added and have had mixed results so when I drain and refill I just go ahead and add it. You're probably fine with synthetics and possibly even better off but I'd want to be sure. I take my CUCV into some pretty remote places doing gold panning and photography and if I grenade a differential I'll probably have a long, difficult walk and need a dozer to get me back to a road so do try to take good care of my trucks running gear. Not to mention that I'm getting too old for long hikes lol.
 

sgms18

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Ok. Thanks yall. By the way, my 1028 has a SM465 4 speed manual & NP205 t-case. I love the sm465 & hate it at the same time. Been thinking about a NV4500 or 700r4 for some top end but thats way down the road.
 
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