Dan H.

Took my car in for an inspection and discovered a significant leak from the diff. It appears to have come out of the vent on top of the diff.

So I get home and first pull the fill plug. The level is up to the fill plug, but the first thing I notice is bubbles when I stick my finger in the hole. The second thing I notice is the fluid is water thin. It's still warm from the 25 minute drive home from the shop. Probably say for 2 hours.

I then pull the drain plug. The fluid pours out again like water and stinks badly. I grabbed most of it in old Chinese food containers to inspect it. When I swirl my finger or screwdriver in it, I get swirls.

I've used amsoil severe gear 75-90 with 2oz of amsoil slip lock for a couple years. I change the diff fluid every winter. I run about 6 track events a year for 4 years now. Car is a stock power and driveline C5Z that just turned 30k miles. I run nt01 tires. I do not have trans or diff coolers

Would like advice on what my issue could be
Thank you
Attachment 48297402

fatbillybob

of all the oils gear oil stinks! normal

C5 known to leak from driver cover. There is a TSB on it. My rec is not to use the new GM o-ring. When I ordered it new it came from china. It was lame and smaller than the old one. So I reused the old one and sealed the case with locktite 518 which is a case sealant.

I also thought the vent was leaking and I out a new one it. The vent is not the problem. They are s stupid sort of check valve and almost never fail and don't burp oil out even at race speeds. Once I sealed the driver side cover all was good. That's my story and I'm sticking to it.

Socko

I filled my diff in my c5z once at an angle and it burped out the top. It can happen. I replaced my side seals as the passenger side started leaking eventually. I never had the covers leak but it does happen. To have metal in the diff is pretty normal but only you really know how it looks from change to change. New diffs from gm were under 1600 2-3 years ago when I got mine.

argonaut

I think its pretty rare for a Corvette that sees track time not to leak. I recall putting in a brand new C5 diff and it was leaking within a matter of a few track events. As mentioned - smell is normal. Is it noisy? Any smoke? If you run magnet thru oil - it pick anything up? If No, No and No then its probably just fine. When my diff went bad the oil had lots of very fine metal particles - it 'shimmered' when stir'd.

Dan H.

Thank you for the notes so far, I appreciate it. After some searching last night it sounds like leaking from the driver side cover is pretty common. I was concerned it was leaking onto the tail pipes too. I've always had some gear noise from the diff, not super loud. I just always thought it was from the lack of insulation in these. I didn't have any smoke. I did have some smell when I arrived at the shop, guy said he could smell it, but no smoke. I'm guessing its from the oil on the tailpipe burning off.

I didn't think to run a magnet through it last night. I will try that tonight when I go out and mess with it. I am also going to check the ATF level to make sure that hasn't gone down and leaked into the diff.

I am happy to hear and read that re sealing the side diff cover can be down without removing it from the car. I don't see that happening for Summit this weekend. I can get it done before VIR in October.

Dan H.

Here's what it left on the ground where I parked it at work yesterday

Scooter70

Keep in mind that the fill capacity is less than it takes to reach the hole. If you're filling it until it comes out of the fill hole, you're overfilling it.

A few of us have had issues with the vent not working well enough when the diff gets hot so I pulled off the cap and ran a hose with a breather filter to help it.

Dan H.

This is good to know, I've been filling it until it runs out of the fill hole.

fatbillybob

Oil leaking out fill hole is the right level. That's why the fill hole is where it is. In fact most of us running coolers plumb to the hole with say 10AN or 8 line which means we over fill and have zero issues burping oil out the vent.

Socko

It really isn't a huge deal to pull it. The first time it seems daunting but outside of needing an alignment I pulled the subframe/diff+trans/ and torque tube by myself and reinstalled it in a weekend. On the ground in my garage. It will take a bit the first time, but it isn't really something to be afraid of. If you track it regularly you will be in there again.

I would imagine anyone who can use a wrench and has a reasonable set of tools can do a diff removal and reinstall on a c5 in a weekend.

Then when you decide/have to buy a new one in a year or 2 you know what you are doing! :P

Scooter70

Not according to Greg at Katech.

fatbillybob

From workshop manual also in TSB:

Check the fluid level to ensure it is even with the bottom of the fill plug hole to no lower than 6 mm (0.25 in) below the opening. Install the fill plug and washer to the differential. Tighten the differential fill plug to 35 N•m (26 lb ft).

Dan H.

I have a feeling both of you are correct. The TSB states the capacity for a C5 diff is 1.69 quarts. I only had 1.6 quarts on the shelf and its a couple millimeters from running out the fill hole. Picking up a couple quarts on the way home tonight to finish filling it.

mgarfias

Mine was leaking when it was 2-3 years old. Turns out the case was cracked. Check for that too.

Rx7Rob

I've always filled until it runs out the hole. 2000 C5 31kmi, lots of track days, zero leaks. BUT, I never do track days during the summer. I don't have trans or diff coolers and don't want to stress anything.

Yep, gear oil stinks!

I bet it will show swirls if you fill / drive around the block and drain.

Curious, how's the differential action (is it worn out)?.

Dan H.

Rob,
Thats a good question, I don't know. I haven't had any luck finding a 33mm socket. I have up to 32 and then a 36. I have been passivily looking for one at sears when I make trips for other things. Time to get serious about finding one. I have 1 5/16" I think which is almost the same size and I've read about people using these. I found that the axle sticks to far out on this socket to get it on the nut so the search continues.

Sorry for the delay in the measurements, this leak was a whammy for me. I'll get them out to you over the next couple days, I'll have a lot of idle time with the car.

mgarfias

I bought mine from snapon. Ended up being a crazy $$$$ deep socket impact.

Rx7Rob

No worries on the measurement. You got bigger fish to fry.

See if the wheel will rotate by torquing a lug nut (don't exceed the torque spec). Thats how I found my diff was toast. One wheel up, trans in neutral, 50 ft lbs on torque wrench for first pass and the tire rotated. Then I grabbed the tire with my hands and could rotate it with some effort. :-(

fatbillybob

Regardless of torque reading you get which is sort of all over the map here on CF anyone believe that if you can leave 2 black lines on the asphalt your diff works fine?

NSFW

That's certainly a good sign. But ideally (and, this being the AX&RR section...) I'd guess that most folks would want to do that test coming out of a corner, to unweight one tire.

Also look for binding when making very slow very sharp turns. No big deal for a race car but it's annoying in parking lots.