Tranny fluid leak

WhiteThunder

Registered User
The automatic transmission on our stock '90 SC is leaking. Overnight it leaves a four to five inch thin puddle on the driveway. But it only leaks when the transmission dipstick is in the dipstick tube. If I pull the transmission dipstick out of the tube and leave it out, there's no leak overnight. Anyone else have this happen?

It's my understanding there's an o-ring where the dipstick tube goes into the transmission. Anyone change one of those? And is that o-ring a dealer item?

Eddie
'90 5-speed SC modified
'90 automatic SC stock (except for double intercooler)
 
You may have a cracked tube that is being levered when the dipstick is present.

Best to remove it for inspection. Any auto parts store can furnish a replacement 0-ring - just ask if it's ATF compatible:

ACM or simply acrylate rubber consists of a polymerized ester and a curing monomer. Ethyl acrylate rubber has a good resistance to heat and mineral oil; on the other hand butyl acrylate has a better cold flexibility. Polyacrylate has a good resistance to mineral oil, oxygen and ozone even at high temperatures. The water compatibility and cold flexibility of ACM are significantly worse than with NBR.

Chemical resistance
• Mineral oil (engine, gear box, ATF oil)
 
The trans may have a plugged up vent. By removing the dipstick you release the pressure and stop it from pushing fluid past the o-ring seal. just a thought.
 
Sitting still ...

I'm not sure if it's leaking while the car is running. But I know it leaks when the transmission dipstick is in and the car just sits overnight. If the dipstick is out and the car is sitting still, there's a very small leak overnight as in the size of a one dollar coin.

Eddie
'90 5-speed modified
'90 automatic stock (except for double intercooler)
 
If the dipstick is out and the car is sitting still, there's a very small leak overnight as in the size of a one dollar coin.

Besides spotting a puddle (just one?) near where the tube enters the trans, what else have you checked? Did you confirm the fill level with engine hot and running? Added how much lately? Added any kind of treatment or changed the filter lately, or?
 
The level of fluid will raise when the engine is not running, thus the leak from the dipstick area. by removing the dip stick from the tube you release any pressure and stop the leak. I think that checking the vent is worth the time it would take. Also it would be prudent to change the o-ring. Once a guy had a trans leak on his sportster and wanted me to change out the trans gaskets, well lo and behold i took his vent tube loose and blew into it with just my own lung power and out pops a spider nest. No more leak. Seems like the filter for the tube was missing. Now i could have made 200 bucks by letting the bike set at my garage for a week but i'm not that way. Just sayin
 
The AOD vent is on the top side of the trans back by where the extension housing meets the main case. There is no filter for it as far as I know. I would imagine if the vent was blocked it would leak worse when the trans heats up and builds pressure as the fluid and everything else expands. My vote is for just an old worn out dip stick tube "O" ring. Replace it, clean up the area with a good degreaser, and see if the leak reoccurs. If you have any additional questions, visit www.clickclickracing.com. They most certainly can answer you AOD questions there.

Good luck!

Bryan
 
While your under the car replacing the O ring, snug up the pan bolts while your at it. Have had a similar issue before and pan bolts worked a little loose.
 
I'm pretty sure you know the location of the trans end of the dipstick tube :) This is the location of the vent on an AOD:

AOD_Vent.jpg
 
Not uncommon for the dipstick tube o-ring to leak. Check to make sure the dipstick tube retaining tab is bolted to back of transmission securely and that the mounting tab isn't bent. Sounds like you just need a new o-ring.

David
 
Thanks!

Thanks for the replies everyone. I'll let you know what I find when I get the car up on lift later this week.

The previous owner of the car had the transmission fluid changed just before we purchased the car. He told me that the pan leaked after it had it serviced and had to take it to another shop for a do over.

After it started leaking, I checked the fluid. It was a quart down. Added a quart. Also, when I jacked it up in the driveway, most of the pan bolts were loose. I was told that cork gaskets tend to shrink over time. I snugged up all the pan bolts.

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
Worst than I thought

Got it up on a lift today. It's leaking out of the front seal. It's gotta come out and be rebuilt.

Eddie
'90 5-speed SC modified
'90 automatic SC stock (except for double intercooler.)
 
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