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Can Opeler
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Discussion Starter · #1 ·
As the title says, I have a strange issue with my GT that I’ve never seen mention on the forum. Whenever I drive my GT it leaks gear oil from the top vent (see photo with my purple gear oil pooling below the vent).

I’ve had this issue for years, but I’ve never known it was the vent until recently when my new silver spray paint allowed me to see it. (Also I just replaced all the other seals and they are dry.)

My transmission does not leak one bit in the garage while stored, but as soon as I drive it leaks everywhere. The oil pours out onto the trans mount and exhaust. The faster I go, the worse it is.

Anyone else have this problem? I guess my next step is to attempt to remove the vent and inspect it. Not much room up there now that it’s installed…

Gas Metal Machine Auto part Automotive wheel system
 
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Super Moderator
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I think this was suggested on FB, but if the lube is too high (s/b a half inch BELOW the filler hole, due to the tilt in a GT), that might cause it.

Or the lube you are using is foaming. What brand and type and weight?

Or you are driving too damn fast around corners!!!
 
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Can Opeler
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Discussion Starter · #4 · (Edited)
I think this was suggested on FB, but if the lube is too high (s/b a half inch BELOW the filler hole, due to the tilt in a GT), that might cause it.

Or the lube you are using is foaming. What brand and type and weight?

Or you are driving too damn fast around corners!!!
i don’t think it’s the oil. I’m using royal purple synthetic 75w90 that is brass safe. I run the same in my other GT and it’s dry even on the track. Of course it has the later style breather at the top.
I did lower my oil level to spec. And it’s unchanged.

no corners yet, I’ve just been doing some testing on the cam and taking it easy.

I took the vent out and it doesn’t seem clogged. I cleaned it up anyway. There was plenty of oil in the vent. I reassembled and put some sealer on the threads, but I doubt that makes a difference. I may try and do a breather extension to the engine bay for fun. Finding a barb with that strange thread pattern may be tricky.
 

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Über Genius
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This isn't a flaw or problem. It's a feature of Opel's forward thinking.
Have you ever noticed the squirter holes on the piston rods? They add some extra lube to the piston walls to help minimize wear.
The same thing goes for that "leaking" transmission cap. It's designed to lubricate the underside of the Opel to help keep it functioning properly, minimize wear, and help stave off rust.
The key, though, is that most people only drive forward in great distances so only the back half of the car gets lubed. You need to consider the front too.
Every once in a while the car should be driven a few miles in reverse to get the front lubricated too. If you do this regularly you wouldn't have a rusted out belly pan.
 

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Finding something with the same threads may be difficult. Then again, who knows?

I would just find a spare vent, take it apart and modify it to accept an extension.
 

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Opel Key Master
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I find it odd that you get any fluid out of that vent, it’s just the tail shaft that is inning back there, maybe the speedometer gear, so not really a bunch of stuff to faking oil I would think. if something is causing the fluid to foam or causing turbulence/pressure?
 

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Can Opeler
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Discussion Starter · #9 ·
I find it odd that you get any fluid out of that vent, it’s just the tail shaft that is inning back there, maybe the speedometer gear, so not really a bunch of stuff to faking oil I would think. if something is causing the fluid to foam or causing turbulence/pressure?
True. I don’t know. I’ve had the pan off before and everything looked fine except for a missing reverse tooth.

I will say that 3 out of 5 of my early spare transmissions show evidence of extensive leakage from the vent based on grime build up, while my 2 later style spares do not.
Opel may have changed the design to solve leakage.
Also one other thing. I drive differently than most opel owners. My car sees above 6000rpm every time I drive it several times. So my trans is spinning as fast as it can most the time.
 

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Can Opeler
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Discussion Starter · #10 ·
The thread pattern is m14x1.0. Not a common fitting size, but I managed to find one on eBay. I’ll install that Barb fitting and run a 3/8 emissions line to the engine bay with a 3/8” breather at the end.
It shouldn’t leak after that. If I do all of that and I still see leakage then I probably have a crack somewhere that opens under load and I’ll swap the transmission in that case.

having a vent to the engine bay will be useful though because I could use it to refill the trans too.
 

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Opeler
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It's been years since I ran a 4 speed in my GT but I never had an issue with the breather cap. I would lean more towards the oil your running. From my experience, Royal Purple tends to be more on the thin side of typical oils. It could be foaming up and causing your issue.

You may try just a generic gear/transmission oil that is safe for brass internals.
 

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Can Opeler
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Discussion Starter · #12 ·
I fixed the issue apparently. Not a drop leaked out from the vent or onto the trans mount at the track today. My guess is that vent was slightly clogged and pressure build up was forcing fluid or vapors up and out. I guess cleaning it out with compressed air worked even though it didn’t seem clogged. Or maybe enough fluid leaked out to prevent it from happening lol.

The only leak on my car now is a slow one from the speedo drive. I’ve replaced it with OGTS seals twice now. Their seals just aren’t quite right. It’s the inner cup seal that doesn’t work quite right.
 

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Opeler
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Have the same problem with my speedo drive. Dang thing always leaks even with new seals. I'm thinking about capping that nuisance off and running a GPS speedo which is way more accurate.
 

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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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I have the same slow leak with the new seals from OGTS - I remember when installing them thinking the inner seal did not look right
 

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I had some leakage due to wear on the speedo gear shaft where the seal rides. I think that installing a brand-new gear fixed it but it’s been a while and I still have a couple other nagging drips…
 

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Super Moderator
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I had some leakage due to wear on the speedo gear shaft where the seal rides. I think that installing a brand-new gear fixed it but it’s been a while and I still have a couple other nagging drips…
I believe the speedo "cup seal" is intended to seal tightly to the speedo gear shaft, and the seal spins along with the gear inside the housing. To be clear, the seal spins, and is not stationary. The cup should face towards the transmission (fluid inside the cup, not outside).

I find that packing the cup with grease helps minimize leakage. I also smear grease around the housing, especially below the O-ring.

Speaking of O-rings, I just replaced a speedo housing O-ring on Jason Selby's GT that had been purchased new from OGTS two years ago. During that time, he had to refill the transmission twice, as it leaked prolifically around the speedo cable connection. When I pulled the speedo housing, I noticed that it was actually loose in the transmission, and didn't "pop" as I pulled it out. The O-ring was noticeably too small in cross-section. I had a spare O-ring that was likely 5 or so years old (NOS!) and was at least 25% thicker in cross section. The speedo gear housing "popped" as I inserted it into the transmission.

I recall reading that OGTS had sold some "bad" speedo seals, but I thought it was the cup seal, not the O-ring. I'll ask Gil next time we chat.
 

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Opeler
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Hmm, I wonder if the o-ring I just put on mine from OPGTS was too small. When I get time I'm going to have to pull it apart again.
 
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