Leaking differential?

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Mogordo
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My tercel:: 1983 SR5 Wagon

Leaking differential?

Post by Mogordo »

Hi, I'm looking for help figuring out the seriousness of a leak. I think it is from the front differential somewhere but I am still getting the hang of what pieces are called what so I may be wrong. I attached photos to show where it looks to me like it is coming from and how much is on the bottom of the transmission/differential/transaxle (again not sure appropriate names).It is fairly recently started as I was checking that area often for a while after changing gear oil a few weeks ago. There was a leak from a drain plug that I got stopped maybe a week and a half ago and I stopped looking after that but I thought I was smelling gear oil the last couple days and I just jacked the car up for something else and there is evidently a leak from above and to the right (looking from driver's side) of the front filler plug. If I have this correct it is more from what is called the differential carrier or transaxle case I think. I am wanting to know your opinions on if I can keep filling it and keep driving it for now without there likely being a much bigger issue to result or soon follow. I have another car that if all goes well I can perhaps have driving again soon but I won't know until I get it all back together.
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SirFoxx
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Re: Leaking differential?

Post by SirFoxx »

its hard to tell wheres its leaking from those pics. honestly, that doesnt look like a whole lot. as long as its not leaving considerable amounts of oil on the ground, i wouldnt pay much attention to it.

the second pic is the flexplate that goes between the engine and trans. theres a good chance that may just be engine oil from a tired rear main seal.
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dlb
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Re: Leaking differential?

Post by dlb »

If it's coming from up there, it seems like it would have to be the seal for the input shaft. That's the only thing in the bell housing I can think of where gear oil could leak through. I hope someone else can chime in on this though. If that's the case, it shouldn't leak too quickly because the gear oil level is quite a ways below that, but you definitely will want to keep an eye on it because running low on gear oil will trash the trans fast.

I actually just removed an al25 transmission for the first time a few months ago. I used xirdneh's write up on the process, and was surprised how easy it was. I was working on a concrete floor though, with a big low profile/high max height jack. Those details definitely made the job a lot easier.
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dlb
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Re: Leaking differential?

Post by dlb »

SirFoxx wrote: Fri Oct 28, 2022 9:11 am the second pic is the flexplate that goes between the engine and trans. theres a good chance that may just be engine oil from a tired rear main seal.
Mogordo wrote: Fri Oct 28, 2022 8:33 am I thought I was smelling gear oil the last couple days
It could definitely be engine oil. I find the easiest way to tell the difference between engine and gear oil is the smell -- engine oil doesn't have much smell, while gear oil has an intense onion odor. It's unmistakable. So maybe confirm the smell and then go from there.
Mogordo
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Re: Leaking differential?

Post by Mogordo »

It's hard for me to tell. I wiped onto my finger some of what was dripping and with that little bit I didn't smell much, thought it smelled a little of gasoline actually which I wasn't expecting. I then wiped about the same amount of confirmed gear oil on another finger and could smell a faint gear oil smell. So it seems it is just as likely engine oil. I spilled gear oil on various places when I was filling it and tubes didn't go where I wanted and I don't know if I could still be catching whiffs of that stuff. And it really looks to me like it is coming from behind that flexplate (I didn't know what that was called, just looked a plastic piece). If it is really coming from there could it still be input shaft? Or just rear main seal? The engine oil up to this point since I got it has maintained it's level pretty well so if that changes that will indicate engine oil as well. Will either seal leaking be more noticeable right after driving than when it has been sitting for hours? I'm thinking at this point I will put cardboard under it while it sits at home and see how much ends up on it. And see about smelling it again. I really do not want to ruin the transmission. It has signs of wear as it is but is still quite functional. If I get my other car back on the road I would be more willing to pull this one further apart. I had an '85 VW Golf years ago and the clutch started slipping when the rear main seal got too bad. Is that pretty likely to happen with any car? Thank-you both for your help :)
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Petros
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Re: Leaking differential?

Post by Petros »

if it is on the bottom of the trans case, almost certainly it is coming down from somewhere else. If it is not a lot, I would just check and top up periodically.

the most common sourse of gear oil leaks on the trans axle, in descending order, is as follows:

the CV axle output shaft to diff housing seal. make sure you replace with the type that has the dust shield, they should be available (but some suppliers will sell you a seal that will fit but does not have the built in dust shield, and it will not last up as long since dirt and grit from the tires will get all over it). It is not to difficult to replace, but setting the depth is important so read up on how to do it in the repair guides section.

the Transmission tail shaft seal, where the rear drive shaft plugs into the back of the trans. also not too difficult, but if the gear oil is topped up it can leak out the back when you unplug the drive shaft. be ready to catch it in an oil pan. there is a metal dust shield over the tail shaft, that will just slip off by gently tapping it back and forth, it will give you the access to remove the old seal. the dust shield is held in place by simple transition fit between the steel sleeve and the rear aluminum housing. That seal should still be available since it is a common type of seal.

the 4wd/fwd selector lever shaft seal, in the side of the gear box, is also a common source of leak. it is a seal about the diameter of a dime, it is a standard seal so it too should still be available. it is a bit of a PIA to each, but unbolting the rear cross member and lowering the back of the trans a few inches is a big help (you should not have to remove anything else, but watch you do not put pressure on the wire connectors when they pull tight).

It is very rare that the trans input shaft goes bad, usually if it does it means your input shaft bearing is also bad and the shaft is rattling around and took out the seal. if that is the case your trans has to be removed anyway to fix it.

the rear main seal can leak and drip down to the bottom of the trans. you must verify that it is motor oil, and not gear lube from the trans. you have to drop the trans to replace it, a big job and if not too bad you might add oil stop leak (and top up your engine oil regularly) until you can replace it. When you do replace it, while you are at it, replace the clutch, disk, throw out bearing and pilot bearing (and resurface the flywheel if necessary). it is a big job and if you have to pull the trans you might as well replace everything else in there while it is out (unless you know the clutch is fairly new, it is well worth replacing it...use ONLY Aisin clutch and quality Japanese or American made T/O and pilot bearings).

Do not despair however if it is engine oil, the rear of the valve cover gasket, and the half moon rubber plug under it, are a common source of engine oil leaks that can run down the back of the engine and fool you into thinking it is the rear main seal. so check that out first.

Another common source of oil leak is the o-ring round the distributor, and also the fuel pump gasket. As well as the oil pressure sending unit (behind the alternator). Any of those can run down the block and get blow back on to the trans housing, fooling you into thinking it is the trans leaking.

Your action should be to first steam clean off the engine and trans to allow you to better trace the source of oil leak. Than go from the easy to check/fix items, and than move to the more costly/difficult sources.

Do not just randomly replace parts/seals hoping it will help, find the source and fix it.

ALWAYS diagnose the problem BEFORE you try to fix it!

Good luck.
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Mogordo
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Re: Leaking differential?

Post by Mogordo »

Thanks. That is a good guide with information that could be helpful for other questions too. I didn't see the oil after that one day so though I still don't know where it came from I felt better about it then. I plan to change cv axles soon but seals for where those go in are good. The lower part of the engine and surrounding components could use a cleaning for sure, I considered that before because I think there are/were other leaks and it is it hard to tell what is old and what is new and follow the leak paths. I'm not sure how to go about it and with it getting cold outside here (not as cold as it is where some live I'm sure) I'll probably not want to do it until after winter. There is some I can probably just scrape off though with how thick it is.
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Petros
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Re: Leaking differential?

Post by Petros »

I have found the cv axles seals last a long time, usually if they leak it is because someone damaged it when they replaced an axle during other maintenance. if your axle seals are not leaky, when you pull the old axle shaft out, check that it is still soft and flexible (with just finger pressure), and not visibly damaged, they are good to leave in place and reuse them.

Just take precautions when removing the shaft, and especially when replacing it so you do not damage the existing seals. When installing the axle shafts, clean off the spline shaft on the axle stub good, and put some clean axle grease on the seal land (where the seal rides, this will lubricate the seal before it gets splash lubricated once it is back on the road) and on the spline shaft, and wet it all with some clean gear oil. Carefully guide it into the side of the diff, not allowing it to rest on the seal. Once it is far enough into the diff assembly the splines will engage and none of it will touch the seal. Not difficult, it just takes some awareness to be careful when you install the spline shaft.

if you should accidentally drop the axle, or allow it touch a dirty part of the trans or suspension as you install it, it must be cleaned off again, and lubricated. wipe it all off with a clean wipe or rag and reapply the grease and gear oil. getting any grit into the diff will slowly grind away the internal parts (that are impossible to find new any more), so take care of all the parts of the transmission. keeping up on the maintenance, fixing leaks and changing the gear lub every year (or30k miles) will go a long way to make it last indefinitely, no need to take risks by being careless while doing maintenance. You may regret it later.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
Mogordo
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Re: Leaking differential?

Post by Mogordo »

Thanks. I already tried an axle that isn't good and I was easy on it but had trouble with it going in at first. Fortunately I called my dad when it did not easily go in, to see if I was missing something important, and he told me to grease some part of it, might have just been the end of the spline shaft, and it went in after that. It sounds like I can be more liberal with the grease or gear oil than I was though.
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