Differential issue, wear/damage limits
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Senior User
Joined: Sep 2006
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From: West Point, UT
Differential issue, wear/damage limits
A couple days ago I was driving my truck home and I heard a howling noise coming from the rear end, but only on decell. It's a 1976 highboy. I was about 3 miles from the house so I continued driving it figuring I could make it home. The rear end locks up and I come to a stop. I was going about 25 mph so I guided it off to the side of the road. The wife was following me so we went home got a few tools and came back. I pulled the rear axles out and put it in 4wd. I made it about a 1/4 mile down the road and the drive shaft falls out of the differential. I seperated it from the transfer case and it drives just fine to the house. Apparently the nut that holds the driveshaft to the pinion gear backed all the way off. I just finished pulling the interals of the diff out and posted a few pictures in my gallery. I'm not sure if there are any limits to nicked teeth but I was just wondering if anyone could take a look and give a guess. On a side note the first thing I noticed when I pulled the diff cover off was Timken bearings. They make the wheel bearings for the F16.
Diff pictures
-Destin
Diff pictures
-Destin
Post Fiend
Joined: Jul 2006
Posts: 6,948
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Pretty sure I don't even need to look. If your description is regarding chipped teeth, then they are shot in my opinion.
Things like "broken", or "pregnant", or "in trouble with you mother in law", all are cut, and dry, wothout any degree of speration.
If a part is broken, it is broke, and not a little bit broken, just like, a little bit pregnant, (can't be done) and only being in a little bit of trouble with the in law, is as close to impossible as the first two.
Looks like a black, and white issue with no gray area.
Some may suggest that re-using a gear that has teeth chipped might survive, but I would hate to repair anything as important as the diff, and have a failure prematurely, because I tried to take a short cut. It usually costs twice as much that way.
"Murphey" rides shotgun in my truck, and all of his laws apply. I just don't have good enough luck to try to re-use some busted parts.
Things like "broken", or "pregnant", or "in trouble with you mother in law", all are cut, and dry, wothout any degree of speration.
If a part is broken, it is broke, and not a little bit broken, just like, a little bit pregnant, (can't be done) and only being in a little bit of trouble with the in law, is as close to impossible as the first two.
Looks like a black, and white issue with no gray area.
Some may suggest that re-using a gear that has teeth chipped might survive, but I would hate to repair anything as important as the diff, and have a failure prematurely, because I tried to take a short cut. It usually costs twice as much that way.
"Murphey" rides shotgun in my truck, and all of his laws apply. I just don't have good enough luck to try to re-use some busted parts.
Elder User
Joined: Feb 2004
Posts: 909
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From: San Luis Obispo, CA
Destin,
I looked at your pictures and did not see anything that I think would cause you problems. In general, gears do not use the tips of their teeth, but hypoid gears only use a long oval area in the center of their faces. They use a sliding action rather than the rolling action of "normal" gears. After a rings & pinions are machined, a R&P pair is put into a lapping machine in exactly the relationship to each other that they will have in your axle housing. They are then lapped to match each other, with the oval pattern mentioned above. When R&P's are set up, the mechanic uses a marking compound to duplicate this contact pattern. Bottom line: the edges & corners do not normally make contact. With the bearings coming loose, the pinion moved out of position and eventually jammed.
Do inspect the R&P carefully to see if any of your chipped places have a crack starting. Any chip that has not fallen off by itself should be removed - you do not want it coming off later and mucking things up. Look most carefully for cracks near the bottom of the gash between the teeth - this is where the load is carried. (You could have a magnetic particle or dye penetrant inspection of the R&P done at any good automotive machine shop.) The most important thing for you to do if you choose to reassemble the the old gears (I probably would), is to clean everything out VERY thoroughly. If the heavy gear oil carries one of those pieces between the gear teeth you will have a problem. Put in magnetic plugs in both drain & fill positions to pick up any small piece of steel that comes their way. When you check the oil, you can see what the magnet has collected.
Put it together with a new seal and NEW pinion nut - maybe Locktite as well. As long as you have not mixed up any shims you should be able to reassemble it without much trouble. Once together, you should double-check the backlash and take a quick look at the pattern with a little white grease as a marking compound. Be sure to use hypoid gear oil.
P.S.: I see that two of us posted at the same time. Let me add that the BEST thing to do is to put in new gears and probably bearings while you are at it. I assumed you were not able to handle the cost of you would not be bothering to post pictures. As I said: IF the damage is no worse than that shown in your pictures and if you have a shop do a crack inspection, the corners of the gear teeth will never be missed. You need to decide if you want to take the gamble on trying the old gears. From your description, this happened a low speed - if you had locked up out on the interstate at full speed, a lot more damage would have been done.
I looked at your pictures and did not see anything that I think would cause you problems. In general, gears do not use the tips of their teeth, but hypoid gears only use a long oval area in the center of their faces. They use a sliding action rather than the rolling action of "normal" gears. After a rings & pinions are machined, a R&P pair is put into a lapping machine in exactly the relationship to each other that they will have in your axle housing. They are then lapped to match each other, with the oval pattern mentioned above. When R&P's are set up, the mechanic uses a marking compound to duplicate this contact pattern. Bottom line: the edges & corners do not normally make contact. With the bearings coming loose, the pinion moved out of position and eventually jammed.
Do inspect the R&P carefully to see if any of your chipped places have a crack starting. Any chip that has not fallen off by itself should be removed - you do not want it coming off later and mucking things up. Look most carefully for cracks near the bottom of the gash between the teeth - this is where the load is carried. (You could have a magnetic particle or dye penetrant inspection of the R&P done at any good automotive machine shop.) The most important thing for you to do if you choose to reassemble the the old gears (I probably would), is to clean everything out VERY thoroughly. If the heavy gear oil carries one of those pieces between the gear teeth you will have a problem. Put in magnetic plugs in both drain & fill positions to pick up any small piece of steel that comes their way. When you check the oil, you can see what the magnet has collected.
Put it together with a new seal and NEW pinion nut - maybe Locktite as well. As long as you have not mixed up any shims you should be able to reassemble it without much trouble. Once together, you should double-check the backlash and take a quick look at the pattern with a little white grease as a marking compound. Be sure to use hypoid gear oil.
P.S.: I see that two of us posted at the same time. Let me add that the BEST thing to do is to put in new gears and probably bearings while you are at it. I assumed you were not able to handle the cost of you would not be bothering to post pictures. As I said: IF the damage is no worse than that shown in your pictures and if you have a shop do a crack inspection, the corners of the gear teeth will never be missed. You need to decide if you want to take the gamble on trying the old gears. From your description, this happened a low speed - if you had locked up out on the interstate at full speed, a lot more damage would have been done.
Last edited by acheda; Apr 25, 2007 at 02:01 PM. Reason: additional thoughts . . .
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From: West Point, UT
update
My dad called me earlier today and said a guy advertised a complete rear member from a 1977 3/4 ton with 4:10 gears for $100. So I'll just scrape what I have and throw this one in. There might be hope for this truck. It doesn't have a vin because the previous owner did a body swap and didn't bother swapping over the vin. If I can get a new vin without to much trouble I might keep it around for awhile.
-Destin
-Destin
