Rear differential drain plug broke - please help

bluedevilsbluedevils Member Posts: 2,554
edited March 2014 in Isuzu
ear differential drain plug on our 98 Isuzu Trooper broke off last night while I was trying to tighten it. I'm not sure if it was worn out (long story) or if I cross-threaded it (I don't think so, but possible).

I need advice/suggestions/info please - what is the likely fix, what should it cost, where should I go (dealer or not), etc.

The drain plug appears to be a 24mm unit. It's "hollow" in that there's a small round/cylindrical magnet in the center, with the threads around the outside of the bolt. While trying to tighten the plug last night, it broke off. Approximately the top half of the threads are stuck in the hole and the rest of the threads are still on the bolt/drain plug.

The drain hole is 99% open (the drain plug head did NOT break off in the hole), so the fluid drained out.

I'm out of town now (Grand Rapids, Mich.) and only local Isuzu dealer is closed today. I want to acquire the part ASAP even though I cannot pursue a repair until tomorrow at the earliest.

I'm hoping that the broken-off threads can be removed from the hole (by some "tapping" procedure my dad described) and that the entire rear differential housing/drain pan/whatever the thing is called that the drain and fill plugs thread into does not need to be replaced.

Your help advice is appreciated.


  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Well, now......presuming that the bolt is not cross-threaded and you weren't jamming it in there will superhuman force, you should be able to extract it with an "easy-out", which is sometimes not so easy. what it is is a small shaft with 4 sharps edges...a square-ish shaft if you will, and it is machined so that it is also somewhat conical in shape. It is thinner diameter at the tip and gets fatter towards the bottom.

    So you insert it in the hole, jam it up in there, maybe tap it with a hammer so it locks up in there, and then unscrew it with the bolt-head or socket head provided. The sharp edges jam against the inside of the broken hollow bolt and remove it.

    If you can't get an easy out inside the hollow part of the broken bolt (man, are you ever lucky it is a hollow bolt), then you'll have to drill it out very carefully so as not to damage the threads in the differential housing. You will need a very good set of drill bits for this, as cheapos may not cut through machined bolt stock.

    There are also various expanding plugs you can put in there but that would only be for a dire emergency use IMO.

    If the threads are damaged in the differential housing, they will have to be tapped out or at least cleaned with a tap and die set. This may have to be done at the dealer, but a skilled amateur certainly can do this in their garage.

    If you tap the threads or enlarge them a bit (hopefully all you need do is clean them up), you may want to flush the differential with some kind of spray (wear goggles!) to get the little bits of metal out.

    Good luck---this may all turn out to be easier than you think.
  • jgmilbergjgmilberg Member Posts: 872
    If possible the easy out is the best way. Hopefully the ring gear is not in the way. If you have enough of it sticking OUT of the housing, try caveing it in with a screwdriver and a hammer. If you can knock a chunk of it out the rest will either move freely, or fall out. It the remaining part of the plug is inside DO NOT try this, you will for sure mess up the threads. A drill is the only other alternative, but you must be careful not to damage the existing threads, unless you can drill larger and tap it out to a larger size.

    In either event you will need to flush the rear end out and refill with new fluid.

    How do you wear out a diff plug anyway?!
  • bluedevilsbluedevils Member Posts: 2,554
    I will NOT be trying to fix this myself-- I'll be taking it to a shop. Any reason to think a dealer would be more knowledgeable/skilled/capable than a "regular" shop?

    Drain plug was worn out because I tightened and removed it several times in the last week (used wrong fluid and flushed it several times to get the bad fluid out).

    Actually, I'm not sure if the plug was worn out or if I crossthreaded it. I didn't think I crossthreaded it, but I guess I might have.
  • bluedevilsbluedevils Member Posts: 2,554
    I took another look at the differential housing last night and realized that the threads that broke off from the bolt twisted right out of the housing. I had assumed that they were stuck/jammed in there, but was very pleased that they came right out.

    The 2 pieces fit together to make basically the whole bolt, so if there are any metal particles still in the housing I doubt there is very much.

    The replacement bolt I receive tomorrow should have the same magnet on the bottom as the original one.

    One question: what's the best way to ensure that any metal particles are removed from the housing? I plan to fill the rear differential with fluid and drain it, then refill with the final fluid I plan to keep in there. Once I fill with the first round of fluid, should I drive the truck around or just drain it out as soon as I fill it?

    Are there any other ways to remove any metal debris?
  • adc100adc100 Member Posts: 1,521
    There is no reason for those chips to have left the plug area. I would first make every effort to remove any residue around the hole by using my little finger to clean around the inside of the hole. Be very careful not to cut yourself. I just think you get a better feel with the "naked" skin. then put a rag around finger and repeat. Only after you feel you got everything then flush. Probably twice. I don't think I would drive it and then flush. You may just drive particles in the gears. You must have almost 100% conficence you can get all the chips first without flushing. If not 100% sure remove the rear cover. Don't take chances.
  • bluedevilsbluedevils Member Posts: 2,554
    Thanks for your suggestions. No, the truck has NOT been driven since the plug broke off. I'll probably feel around w/my bare finger for metal debris, and also stick a magnet in there.

    When flushing, should I leave the drain plug out or put it back in? Seems it might be better to leave it out-- that way any metal debris near the drain plug at the bottom of the reservoir will stay down there and flow out with the fluid as the fluid flows through.
  • adc100adc100 Member Posts: 1,521
    I agree with you on that. You must be an engineer? I can usually tell. Let me know how you make out.

  • bluedevilsbluedevils Member Posts: 2,554
    But extremely detail-oriented, often to a fault.
  • bluedevilsbluedevils Member Posts: 2,554
    Just thought you guys (gals?) might be curious to know how my ordeal worked out.

    Two days after breaking the drain plug, I looked again at the housing and realized the broken-off threads weren't jammed in there. I was able to twist them right out. The 2 broken bolt pieces formed what looked like a whole bolt, and I saw no evidence of metal debris.

    I poured 1/4 qt. of leftover motor oil through w/drain plug still removed, then added 3 qts. Valvoline 80W90 gear oil. Drove around 3 days, no observable problems. Yesterday I drained that stuff and put in Mobil1 gear lube and a bottle of GM/Isuzu limited slip additive.

    Even though I wasted quite a bit on fluids (probably $100) and $30 on a rush order for a drain plug and a couple other things, the damage could have been much worse.

    Thanks for your help.
  • adc100adc100 Member Posts: 1,521
    I really don't think you wasted money. I have found that over the years that money spent on doing the right thing is a good investment.
  • wtd44wtd44 Member Posts: 1,208
    A friend of mine strip-threaded a transmission plug in a Harley Sportster. I helped him solve the problem. We went to a top quality local automotive parts store and purchased an oversize adapter. We followed the directions and used an electric drill to bore the damaged hole out. We used techniques similar to those described above to get the particles of metallic debris out of the case interior, and then carefully installed the self threading adapter into the fresh hole. that adapter had a threaded hole through its center, and a plug for it. That covers the story! Any questions? I hope I described enough to get the "image" of this procedure across.
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