Had 4.88 Yukon gears put in June 2010 in my front Dana 30 and rear Dana 44. Rear axle just recently started groaning/whining above 30mph and I took it back into the shop that installed the gears and it should all be covered under their 12,000/12 month warranty. They ran it in the air and think from the sound it may be pinion bearings. They'll tear it down tomorrow and let me know what's failing.
I tow with my JK a lot during the summer through hills in TX (temps often 100+ degrees outside load is approx 3400lbs) and thinking about running Amsoil 75w-140 severe duty oil in the rear dif on this set of bearings/gears and adding a Mag-Hytech high capacity Dif cover to add an extra 2 quarts of fluid. Anyone have any experience with Amsoil gear oil or Mag-Hytech dif covers good or bad?. Are the high capacity dif covers worth the money for the added gear oil/heat reduction? Can these Dana 44's really handle towing 3400lbs or is this pushing the 44 too hard?
The 44 should handle the tow fine, but the 4:88 pinion is really small. It can get pretty hot. What is the shop saying? Did you tell them you tow? I am surprised they would install anything lower than 4:56 for towing. I am not saying that 4:88 won't work, but I would definitely run some kind of synthetic oil, and I wouldn't start towing till you break in the diff.
Shop is tearing it down tomorrow and I'll post back what they find. They originally put in Synthetic gear oil but it doesn't say on the invoice what brand of oil they used.
I went with the 4.88s for larger tires in the future but also for towing. Shop said they'd be fine. Place I have dong the build seems pretty knowledgable and mainly works on difs only from my little Jeep to Semi difs.
If it turns out just to be bearings I won't be too worried towing later on but if I chewed up a ring gear or pinion gear in 6 months I'll have to monitor the new setup pretty closely.
So far the shop manager left me a voicemail saying it would be ready to pick up on Thursday but he didn't leave any specific details. I'll for sure post what he found once I know. I'm very curious myself lol.
Total parts, labor and tax for both front and rear difs including a new carrier for my Dana 30 to handle the higher ratio ring gear and rebuild kits with new bearings for both axles was 1500.
Shop manager got a hold of me today and said the gears and bearings are both toast. I had about 11,000 miles on this axle which luckily is covered by the shops warranty where I had the work performed.
They said the gear oil looked very burnt which had been run about 10,500 miles. It was a synthetic 75w-140 oil but I forgot to ask what gear oil they use manufacturer wise.
I'm getting pretty lucky getting this replaced right before the warranty expires so I'm gonna try a break in on the new gears this time around with a lower weight conventional gear oil and then after 500 miles switch to the Amsoil 75w-140 and monitor the oil a little more closely.
Temps during the summer in Central Texas can hit 106+ and towing through hills prob didn't help the gears and bearings in this axle too much. I went offroading on some beaches in South Padre and Corpus Christi during the hot months too so I may just have worked the gear oil too hard.
Gears are installed but shop has shims on order from Dallas so I won't get my Jeep back until Monday. He said he has the pattern close but doesn't want to give it back until it's dead on and didn't have any more shims for a JK/44.
Yukon apparently had no problem with sending new gears under warranty. Hopefully I'll have better luck with this set. I doubt I'll be able to but I'll see if I can get some pics of the worn gears and bearings before they're sent back to Yukon.
I'll ask the shop on Mon about gear oil temps. I'd be surprised if they don't know because of the range of vehicles and equipment they work on but if they don't I'll just call Amsoil directly.
They're closed on Fri ;( Didn't know mechanics were allowed days off lol just kidding.
I did finally find an answer to diff temps and heat ranges for most gear oils. Sustained heat above the 250F range for an extended amount of time seems to be cause for concern in most cases.
Thread quote: My own criteria for the viscosity choice is whether or not the diff oil temp exceeds the 212F (100C) degree threshold significantly or long term. AYK, 212F is the point at which the hot viscosity measurement is taken. Using a temp vs viscosity chart (good ol' Widman has one on his site), I want to keep the oil at no less than about the bottom of the 90 grade range, around 14 cSt at whatever my highest sustained temp is. I don't worry about an occasional short spike unless it's well over 250F. Most oils can handle that for a few minutes. If an axle runs at a sustained 250F towing, however, a 90 grade could be down in the 75-80 grade area. That's not immediately harmful either but long term it could be, so that would dictate a 110 or 140 grade to maintain that minimum viscosity.
You have to monitor your oil temps for a while to rack up the data. I have compared mine with other guys as pedantic as me and I am surprised at both how high and how low diff temps run on various trucks. I have learned that the Mag-Hytec cover knocks an average of about 15 degrees off diff oil temp. I also learned that a good syn oil can knock an honest 10F off the same viscosity grade of mineral oil. Knowing both of these things has shown me that my truck can safely run a 90 grade for whatever increase there is in fuel economy day to day with no worries about dropping out of the 90 grade.
My overall logic is that if you tow 5 percent of the time, it makes no sense to hurt yourself MPG-wise by running a heavier grade oil than you need.... even if that hurt is only 1%. If you live in a cold climate that hit could be more in the winter. If the oil temp exceed 212F towing for five minutes going up a hill, no biggie. It will cool back down. It's possible that you might see some overly high temps towing only occasionally, so you might have to take the hit in the daily driving department and use a heavier oil to preserve the axle. I contend, however, that a diff temp gauge allows you to monitor and make adjustments to the situation to keep that temp lower. Also, a higher capacity, finned cover might be enough to maintain those lower maximum temps, though it also keeps the oil cooler longer.
Assuming demonstrated overly high temps, I've crunched the numbers a couple of ways and using 1% drop of economy, it comes out somewhat cheaper to just use the heavier oil than to spend a lot of money on covers and such, but that would depend on how much hit there truly is on fuel economy and the cost of fuel. I strongly believe the diff temp gauge is a worthwhile addition for any truck that tows.
Some general things I have learned:
1) At a given load, a larger ring gear axle will run cooler than a smaller (more tooth contact to spread the load)
2) At a given load, a lower ratio (4.10. 4.56:1 etc) will run hotter than a lower (3.23-3.55:1, etc, ... more hypoid action creating more heat)
3) At the same viscosity a syn oil will run about 10 F cooler than a mineral, EXCEPT mineral oils with special additives. I used a LE oil (LE607), which was a straight 90 but one that had lots of a proprietary moly-like additive that surprised my by running as cool as a well-known syn. The Chevron ESI oils are said to exhibit similar characteristics, though I have not seen that demonstrated personally.
Well the Jeep is back and 0 dollars out of pocket. I talked more with the service manager and the final story is the bearings probably could have been reused but he didn't want to take a chance so he installed all new bearings except for the outer axle shaft bearings. The ring and pinion didn't have any missing teeth but were extremely worn.
I'm gonna try and drive the new gears nice and easy for about 500 miles on conventional 80w-90 and then dump the diff oil and switch to Amsoil Severe Gear 75w-140. Hopefully this will be my last set of gears.
Over the weekend I'm putting in gauges for oil pressure, engine oil temp, coolant temp and rear diff temp so I should be able to monitor conditions a little closer while towing and see if I'm running things a little hot during the summer months.