Transmission Oil Leak

#1

I am dripping a lot of transmission oil out of the slot (weep hole?) at the bottom of the bell housing where the trans meets the engine. I’m sure it it transmission oil because it is red (MTL) and my engine oil is green (Brad Penn). Plus, the engine oil isn’t low, but the transmission is losing oil at an alarming rate. I checked the transmission oil level before going to the track this weekend and it was WAY down. I checked it again Sunday morning and had to add a fair amount of oil after just one day.

It apparently comes out more when driving, which makes sense, but also drips slightly when the car is parked, which doesn’t (if the input shaft opening is higher than the oil level).

I pulled the engine and trans and I replaced all the seals on both after buying the car. Due to unclear instructions in the Bentley manual, I may have buggered up the housing that the input shaft seal fits into. I tried to sand off any rough spots I caused, but may not have done it well enough. I suppose it is also possible that I didn’t get the seal installed correctly. Either way, I’m afraid I will need to drop the transmission and try to reinstall the seal.

Before I do that, I thought I’d see if anybody knows whether there is another source the trans oil could be coming from? As far as I recall, the input shaft is the only opening in the front of the transmission. But, the fact that it was leaking there before I replaced the seals makes me wonder if there might be something else going on.

Any ideas?

#2

Are you sure it’s not coming from the vent tube on the top of the trans, mine was so I put a tube on it and router it to a catch tank in the engine compartment.

#3

+1, the leak is either from inside the bell housing or from the vent. If the sides of the transmission are dry, the input seal is the likely cause.

FYI: if the input seal is bad oil will continue to drip out of the bell housing for quite a while after the car is parked. I’ve also seen cracked transmission casings and seal failure where the blind plugs are.

#4

winduck wrote:

Where you able to get the hose on w/o dropping the tranny? I neglected to put hose/catch tank on mine before install. :blush:

#5

Nope, had to drop the tranny!

#6

Thanks for the suggestions.

I was looking at the Bentley manual again this morning. The manual shows a bearing shell for the lay shaft pressed into the casing just below the input shaft. I guess that could be the problem, but sure hope not. Same for a cracked casing.

I didn’t notice any oil coming down the sides of the trans, so I don’t think it is leaking around the vent.

The manual says that before assuming the oil seals are bad to check that the vent is moving freely. If the vent is clogged, it will cause high internal pressure that can force oil past the seals. I didn’t see anything in the manual about how to check the vent, other to make sure it moves up and down freely, or how to fix it if it does not.

Anybody know how you fix a stuck vent? Can you do that without dropping the trans?

If not, I guess I’ll have to bite the bullet and drop the trans. If I do that, I guess I’ll first check the the casing for cracks and the bearing shell for signs of leaks. Assuming they are good, I’ll either fix the vent or install a hose and catch can. I guess I’ll go ahead and install a new input shaft seal and housing “while I’m in there.” I sure wouldn’t want to fix the vent and then find out the oil seal/housing were also bad and have to drop the trans again.

#7

The easy way to check the vent, or to install a tube and catch tank is to cut a hole in floor pan just above the vent. Though if you remove the transmission cross member and allow the transmission to drop you can, just barely, get to the vent from under the car.

In this case I’m more suspicious of the input shaft seal. So it may make more sense to just pull the transmission.

#8

jlevie wrote:

I’ve been wondering about that. I bet if I had the defrost/air handler box still installed, it would need to be removed for access?

#9

There is a plug under the input shaft that often leaks. It is not available. So, the fix: Pull transmission. Stand transmission on output shaft flange. Get can of carb and choke cleaner, the nasty stuff with Methylethylkeytone. Get small wire brush…brass works great. Clean plug with whole can of spray while brushing the plug and surrounding area. Get tube of Permatex grey RTV and, when all is dry (blow it off with high pressure compressed air), liberally coat the plug to case interface. You cannot press enough in the area so make sure you have plenty on the interface and make a nice bead over the area. Let sit 24 hours…Must let sit 24 hours to fully cure. Should fix problem…fixed mine. CB

#10

I’m reviving this thread because I finally got around to pulling the transmission out of my car to find the cause of the oil leak.

When I pulled the trans, I inspected the inside of the bell housing. It was pretty evenly covered with black oil residue, but there were no “trails” of oil to show where the leak came from.

I tried pressurizing the trans by applying light air pressure to the trans breather opening to see if it would push out some oil. Air whistled out through the hole in the shifter shaft seal (I knew about the hole), and also around cover on the shift detent balls near the shifter shaft, but no oil came out the front which is where the major leak is.

I raised the rear of the trans and let it sit for a couple of days while I was out of town and checked it when I returned. Still no leaks at the front, not even a drop.

After replacing the shifter shaft seal and applying anerobic gasket sealer to the shift ball detent cover plate, I applied low pressure air again. The cover plate didn’t seal and is apparently warped (not unusual I understand), but still no oil out the front of the trans.

At that point, I was convinced the leak would only occur if the car was running. I spun the output flange by hand and saw maybe a slight film of oil where the oil seal met the input shaft, but nothing that would create even a drop of oil. So, I chucked the tip of the input shaft in my drill driver and spun the shaft for a few minutes. Sure enough, oil began to flow from around the input shaft at the oil seal.

Good news is I found the leak and it apparently is not due to me buggering up the seal housing the first time I replaced the seal. The seal is just not sealing around the shaft. Hopefully a new seal will fix it. I’ll pull the seal, inspect the housing and input shaft and then install a new seal and test it again with the drill driver before re-installing the trans. If the housing is really buggered, I have another I sourced from the Rev. Al, but it is a one-piece unit (oil seal housing and sleeve for throw out bearing) and mine has the two piece housing/sleeve.

After all that, I have two questions:

  1. The one-piece housing/sleeve has two bolt holes at the bottom where it mates to the transmission, and my two-piece unit has only one hole there. Otherwise it appears the one-piece unit will work. Anybody know if they are interchangeable?

  2. Any tips on how to make sure the oil seal and shaft properly mate? (I guess I could try romantic music and candles. :laugh: ) I understand it is sometimes necessary to install a new seal so it doesn’t ride in a groove left by the old seal. Any other suggestions?

#11

I reused my two piece housing. It did not appear to be messed up in any place that mattered.

I did notice that my input shaft had a rough spot on it near where the oil seal would seat. I polished that off with some fine emery paper and installed a new seal. I tested the seal by spinning the input shaft with my drill and no leaks. I hope that has fixed it.

If not, a buddy who is an engineer for Volvo Trucks told me about a product called Speedi-sleeve. It is a thin sleeve that will press onto a shaft and give the seal a new surface to ride on. It is thin enough that the original size oil seal will still fit over it. If the leaks returns, I think I’ll try the sleeve.

#12

I’m doing a followup on this topic - I don’t participate in SpecE30 but I was hoping this discussion could be of interest for all those racing in SpecE30 that might encounter this kind of problem.

I have a very strange gearbox leakage and really need expertise help!

It is a E30 323i -85 with a standard manual Getrag 260/5 gearbox.

When I drive hard on the track, it starts leaking quite badly from inside the bellhousing.

But when driving “normal” it doesn’t leak at all.

I’m really hoping that someone else recognize this problem and can help me!

My current best thinking is that the input shaft is wobbling around during certain conditions and the input shaft seal simply can’t keep up with that wobbling. If this is true, the next question would be how to prevent this from happening.

Would like to hear your experience from hard track days!

— Here is some more in-depth but important details —

I can drive “normal” without any issues.
The problem occurs when driving hard on the track.
The first stint (20 min of hard driving) is usually not a problem.
Halfway through the second stint (usually you rest for 20 min between stints), it starts to leak really bad.

I tried with the original gearbox two times and then I also tried with a spare gearbox - same result.

It is 100% confirmed it is gearbox oil and not engine oil or brake fluid.
It is 100% confirmed it is coming from within the bellhousing.

I verified the vent hole is not clogged (goes for both gearboxes).

I use ordinary ATF “Dexron III” transmission oil (goes for both gearboxes).

I verified the fill level is according to specifications (goes for both gearboxes).
Means that I fill up to the fill plug level with the car level.

On all occasions it’s been basically bone dry around the vent hole (so nothing comes out from that one).

On the original gearbox I

On the spare gearbox I

On the spare gearbox I

I pressure tested (around 1 bar) the spare gearbox and nothing…
Not the slighest indication of a leak (checked by listening as well with soapy water)…

#13

Normal operation. Add a vent hose to the vent on top of the trans and run it up into the engine compartment. Add small filter.

#14

Very thorough description. I do not have anything to add that might help you. You have covered the basics.

Here is something to double check: Early gearboxes had a different shifter holder/plate on the top. If those boxes are used on later (perhaps '87-newer) with the revised shifter, you will have to plug the bolt holes on top of the gearbox that held the plate in place, or fluid will find its way out.

RP

#15

I agree this is a good thing to do :slight_smile: And I will most probably do it in the near future.

But this will not help for this particular leakage issue I’m afraid (although would have been sweet if it was that easy).

The reason is that the oil didn’t originate from the vent hole.
On all occasions it’s been basically bone dry around the vent hole (as well as the top half of the gearbox).

It is coming from within the bellhousing - see pictures below.
The first picture is the original gearbox, the second picture is the spare gearbox.

#16

[quote=“Patton” post=83319]Very thorough description. I do not have anything to add that might help you. You have covered the basics.

Here is something to double check: Early gearboxes had a different shifter holder/plate on the top. If those boxes are used on later (perhaps '87-newer) with the revised shifter, you will have to plug the bolt holes on top of the gearbox that held the plate in place, or fluid will find its way out.

RP[/quote]

Yeah, a lot of details so fully understandable it is somewhat time consuming to “soak in” all information and the history - so all feedback is welcome!

Good point about the shifter holder - I think many forget that (but not in this case).

It is actually only the left bolt that is a through-bolt (the right one is a blind hole and can not leak).

But on all occasions both bolts got oil resistant thread sealant from Loctite.
And the rear has always been bone dry (absolutely dry around all the usual suspects back there).
And if it was leaking, it’s basically impossible to fill the bellhousing with that much ATF oil (see pictures above).

Just a side note about the shifter holders.

My original gearbox had the old style of shifter holder.

But my spare gearbox was of the new type, so I had to convert it to accept old style.
See the picture below, you can see the casting at the top for new style but I have mounted the old style.


#17

What engine oil? Check the seals on the back of the head…will do the same thing. Usually not a trans leak. Oil from the motor will get in there.

#18

It’s ordinary 5W-50, API SL, ACEA A3.

Understand your thought logic, that’s really common and older vehicles will do leak from there at at some point - and it will look very similar (been through that on my E34 535i for example). So good point!

However on a confidence scale from 0-10 it is with a confidence of 11 it is ATF oil in the bellhousing.

Crank rear seal was also replaced for about 200 miles ago when the engine was “refurbished”.

And every time I have removed the gearbox (maaany times now :frowning: ) I have always double-checked that the crank rear seal was leaking (since I know it is a common problem).

So it is 100% (or actually 11 on a scale between 0-10) it is ATF oil and it’s coming from within the bellhousing.

#19

From the amount pictured: as long as it doesn’t get on the clutch facings, don’t worry, be happy.

Wipe down after every event. Some things cannot be explained, however with stiff motor mounts, trans bushings, diff bushings, etc., all of the movement of the components takes its toll somewhere.

That’s my story and I’m sticking to it.

RP

#20

[quote=“Patton” post=83327]From the amount pictured: as long as it doesn’t get on the clutch facings, don’t worry, be happy.

Wipe down after every event. Some things cannot be explained, however with stiff motor mounts, trans bushings, diff bushings, etc., all of the movement of the components takes its toll somewhere.

That’s my story and I’m sticking to it.

RP[/quote]

:slight_smile:

I do worry! I’m being “meat-balled” (mechanical black flag), running a risk of getting a reprimand (environmental hazard in the pits), last time it was smoking like crazy behind me and finally running a major risk of dropping oil on the track for my fellow track friends!

So I do worry! :ohmy:

Maybe my phrasing and the pictures gave a somewhat incorrect and less troublesome view of it - but I can assure you all that it is leaking as hell! It’s pouring out on the track once it started!

So I would actually gone for your suggestion (at least for this season) if it only was minor, but it isn’t. It’s major leakage!