C5 Auto gearbox fluid leak?

[Brads]

Hi everyone,
I have a C5 that seems to leak transmission fluid if it’s sat for a few weeks without moving. If I drive it weekly it seems ok, but if it’s garaged for a couple of months, I start it up every few days but it seems to have a small amount of fluid underneath. It’s about 50ml or so but looks more with it being on the floor.
Anyone else have any similar issues or solutions to the problem?
Many thanks

 

[62 C1]

First thing to do is the obvious and check that the drain plug bolt and fill bolt are tight plus look for signs of leakage around them. A minor leak here might only be noticeable after a few weeks of being stationary. I think the drain plug will take the square end (with no socket on it!) of a 3/8th ratchet or a short extension bar. The fill bolt has a temperature sensor wire which you can remove to stop you damaging it and get an adjustable or ring spanner on the bolt. Not sure of the size.

If that doesn't do it, the next simple check is that the gear box hasn't been over filled. Make sure you have the car level when you remove the fill bolt. if fluid comes out let it flow until it stops and then replace the bolt. Usually they are difficult to over fill but is can happen if the car wasn't level last time it was done.

You can also so the same procedure with the differential which uses a 10mm hex on the drain and filler.

 

[Stingray]

C5s had a habit of leaking from the drive shaft seals. Are you sure it's auto fluid and not the diff'?

 

[teamzr1]

As mentioned, check to see if the A4 fill or drain plug loose or that it is not overfilled as when A4 gets hot the fluid expands and is blown out
the vent plug at the top of A4

Also were issues with the gasket between A4 and transaxle which is tough as to replace the transaxle has to be removed to replace the gasket
You need to determine by color, smell and feel if the leak is from A4 or transaxle
Place some light color paper or cardboard on floor area of leak so the fluid leaks onto it and then easier to tell which fluid/oil it is

Common was a transaxle leak due to a bad O ring on the left halfshaft :

GM TSB-
Fluid Leak at Rear Axle (Replace Left Differential SIde Cover O-Ring and Left Axle Shaft Seal, Add Sealant to Side Cover Flange) #03-04-20-006

Raise and support the vehicle.
Remove the left rear tire and wheel assembly.
Install J 33432-A Transverse Spring Compressor to the rear transverse spring and compress the spring.
Disconnect the electrical connector from the left wheel speed sensor.
Disconnect the electronic suspension control (ESC) position sensor link, if equipped.
Disconnect the shock absorber solenoid electrical connector, if equipped.
Remove the outer tie rod end nut.
Disconnect the outer tie rod end stud from the rear suspension knuckle.
Disconnect the park brake cable from the park brake apply lever and bracket.
Remove the bolts securing the upper control arms to the frame.
Remove the spindle nut retaining the rear wheel axle shaft to the hub.
Rotate the suspension knuckle until the axle shaft clears the hub.
Release and remove the rear wheel axle shaft from the differential.
Remove the left muffler.
Drain the rear differential fluid. Refer to the Lubricant Change procedure in the Rear Axle sub-section of the Service Manual (SI Document ID #675189).
Remove the retaining bolts and the damper/tuned absorber from the differential.
Loosen the nut retaining the transmission to the transmission LH mounting stud.
Install a second nut onto the stud.
Remove the stud from the differential cover.
Clean any dirt or debris from around the differential cover.
Remove the bolts retaining the differential cover.
Remove the differential cover from the differential.
Remove and discard the O-ring seal and the axle seal from the differential cover.
Clean the O-ring sealing surface on the differential cover and the differential housing.
Install new O-ring, P/N 89047953, to the differential cover.
Apply a continuous 3 mm (0.125 in) bead of sealant, P/N 1052942 (Canadian P/N 10953466), or equivalent, to the cover flange.
Apply sealant around the bolt holes. Keep sealant away from the O-ring.
Install the differential cover to the differential.
Install the differential cover retaining bolts. Tighten
Tighten the bolts to 28 N·m(20 lb ft).

Clean the excess sealant from the left cover/housing splitline.
Using two nuts installed on the stud, install the transmission mounting stud to the differential cover. Tighten
Tighten the stud to 42 N·m(31 lb ft).

Remove the second nut from the transmission mounting stud.
Tighten the nut retaining the transmission to the transmission LH mounting stud. Tighten
Tighten the nut to 50 N·m(37 lb ft).

Install the damper/tuned absorber and bolts to the differential. Tighten
Tighten the bolts to 25 N·m(18 lb ft).

Install the new axle seal, PN 88996703, into the differential cover using J 46405.
Install the left muffler.
Install the rear wheel axle shaft to the differential.
Install the spindle nut retaining the rear wheel axle shaft to the hub. Tighten
Tighten the spindle nuts to 160 N·m(118 lb ft).

Install the bolts securing the upper control arms to the frame. Tighten
Tighten the upper control arm bolts to 110 N·m(81 lb ft).

Connect the park brake cable to the park brake apply lever and bracket.
Connect the outer tie rod end stud to the rear suspension knuckle.
Install the outer tie rod end nut. Tighten
Tighten the outer tie rod end nut to 20 N·m(15 lb ft) to seat the outer tie rod stud.
Turn the nut additional 160 degrees.
Check the outer tie rod end nut for a minimum torque of 45 N·m(33 lb ft).
Connect the shock absorber solenoid electrical connector, if equipped.
Connect the electronic suspension control (ESC) position sensor link, if equipped.
Connect the electrical connector to the left wheel speed sensor.
Remove J 33432-A Transverse Spring Compressor from the rear transverse spring.
Install the left rear tire and wheel assembly.
Refill the rear differential fluid. Refer to the Lubricant Change procedure in the Rear Axle sub-section of the Service Manual (SI Document ID #675189).
Lower the vehicle.

88996703 Seal, Output Shaft Oil

89047953 O-Ring, Differential Side Cover

 

[Robert Craske]

If it is the differential you can see it from under the back of the car and this can easily be regularly topped up. But if it is the transmission , do keep a regular eye on it but you need the car on ramp to check and top it up . If the oil is reddish then it is the transmission.

 

[Krusty]

A bit late to this discussion as I've only just became a member. Maybe my input might hopefully help someone else in the future?
My 2001 C5 Targa Auto does the same if I don't drive the car for a long period of time.
Same as Brads. When I start it, I get a small amount of fluid on the floor. Not all the time though! It only does it if I put my car in Drive or Reverse within a minute or 2 of starting it up (because I'm usually just moving the car around on my driveway). It will leave a small little pool of oil around 50ml or so.
I recently had it up on a 4 post ramp to trace this issue and found the gearbox, diff and driveshafts are all dry.
I did have a lot of oil covering the rear leaf spring and managed to trace it right up to the gearbox breather pipe located above the spring.

My theory (being a motorcycle mechanic and quite handy with cars/vans also) is the following:
The oil level for the gearbox should be checked on a 2 or 4 post ramp, with the vehicle flat and the engine running.
The fill hole is on the side of the gearbox sump and the oil capacity level is basically fill the gearbox through that hole, until oil comes out of it and you can't get any more in.
You then wait until the gearbox oil stops dribbling out, select the gearbox through its gear selections a few times (car still running), back in to Park, double check the level and top it up if required... it is then full. Fill plug back in. Winner
Now when the car has sat for a while, you have to remember that the gearbox oil cooler is located right at the front of the car and it sits slightly higher than the height of the gearbox itself. So when you leave the car for a long period of time, the oil that is pumped from the gearbox, all the way up to the front of the car, through the oil cooler and all the way back will in theory drain back to the gearbox itself (gravity fed basically).
This then makes the oil in the gearbox OVER its capacity! BUT DON'T WORRY!!!!! I have kept an eye on mine for a while now and found that when you start your car again, the gearbox will slowly pump the oil back through to the cooler as it should and then your level will be correct.
As mentioned before, if you start your car after leaving it a long time and then put it pretty much straight in to gear without giving it time to circulate the gearbox oil back up to the cooler, then it will assume it is overfilled and chuck out the excess through the breather... obviously this doesn't happen when the car is being used every day or at least in occasional use (I have noticed) as it takes a long time for that oil to drain back from the cooler, to the gearbox when it isn't in regular use.

All I can say on the matter is (and feel free to correct me if I'm wrong, but this is just MY personal experience and MY findings, on MY car) if you've left your C5 sat for anything over let's say, 2 weeks? then give the car around 10 minutes or so after starting it to just sort itself out before driving it or even putting it in a gear. You should find that no oil will be on the floor
Temperatures and Pressures as they say.

If you're concerned about the oil level being too low already and don't have the means to get under the car yourself then drive it to your local trusted garage where they can put it on a 2 or 4 post ramp (because the car needs to be perfectly level remember), ask them to leave the car running in Park, take the fill plug off the gearbox and top it up if necessary. You won't need to run it through the gear cycles as you're only topping it up... but it won't be anywhere near as much as you think.

Sorry for my LOOOOONG and probably boring first post, but I hope it's informative and clear enough to anyone suffering the same issue.
This is only what I have found in regards to my own C5 Vette