Transmission leak - ClassicOldsmobile.com

Transmission leak

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Old March 9th, 2018, 05:23 PM
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Transmission leak

Question from an old guy that can't get under and crawl around any more.
I have a 73 Cutlass with about 72K miles on it...just like a new car and runs great....it's got the 350 engine and the 350 transmission....

I drive the car about every 2 weeks except more often in the summer for cruise nights, etc...It drives and shifts perfectly and we are gentle with it.
I've noticed I can drive it for 20 or 30 miles and bring it home and just set in in the driveway for a while while I work in the garage....it might sit for 3 or 4 hours before I put it away....it's never leaked a drop of anything but if I let it sit in the garage for a couple of weeks or a bit more...I'm getting a transmission fluid leak..maybe 1/2oz to an ounce (spreads out on cardboard so not exactly sure..but looks like more than it is I'm sure..Don't seem to notice the dip stick showing much low...

Is there some seal that might act that way? there is no slip, noise, chatter or anything that acts wrong with the shifting and as I say...it's not leaking all the time..just when it sits for a significant period.

I have a bit of a trust issue when I go to a trannie shop...been burned way too many times in my 80 years...just thought I might get a lead and have someone that won't jerk me around see if what I might learn here is correct.

Thanks!!
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Old March 9th, 2018, 05:52 PM
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The common culprits are the torque converter seal, pan gasket, rear and speedo seal. I have a hate on lately for these old GM transmissions leaking somewhere no matter how many seals and the bushings are replaced.
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Old March 9th, 2018, 05:59 PM
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Old cars don't leak, they just ooze character! Others can confirm, but I believe when they sit more fluid works its' way down to the pan and causes leaks you don't see when it is driven regularly. Personally, I don't worry about it unless I find it at a low level frequently, or smell it when shut down after driving. If it bugs you, park it on stands keeping it level over fresh cardboard and have a look.
A small amount can look like a lot on the floor. A teaspoon makes a small puddle.
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Old March 9th, 2018, 06:06 PM
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I had a persistent leak on my 71 Cutlass with the 350 transmission and I changed the pan gasket a number of times with no success. I finally changed the shift shaft seal and that was the sorce of leaks all along! Simple fix under $5.00
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Old March 9th, 2018, 07:27 PM
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Since there are so many places that can leak, you need to try to narrow down where the drips are coming from. Use a clean piece of cardboard and see if the leak is near the front, back, drivers side, or passengers side of the trans. That will help localize the problem site.
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Old March 10th, 2018, 05:58 AM
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If you know of someone that has a lift ( a muffler shop ,tire shop ,or oil change place) it would sure be nice to get it up in the air where you could be under it long enough to locate the source of the leak,and it should take no more than 5-10 minutes.With luck maybe it will not be the front transmission seal,and if it is I would try some transmission oil leak additive since it seems to be very minor. Larry
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Old March 10th, 2018, 07:07 AM
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Thanks for the input...My guess is it's a seal and maybe even the dip stick...I'll have the oil changed and get the car serviced (it's about due) and have a good look....I'm one of those old farts that hates drips on the drive way and when I see a leak (like on the cardboard in the garage, I get frustrated...I got to remember this is our "go get ice cream car" and doesn't get driven a bunch and doesn't seem to leak when it running along nor when it sits for a while...only after a lengthy period of sitting....I'll try and pinpoint the location with a fresh hunk of cardboard and keep an eye on the dip stick...I know this...a few bucks for a quart of fluid (probably last a year or more) is a heck of a lot cheaper than a trannie rebuild and tossing a chunk of cardboard every few months is "recycling" at it's best....Love the old car and have had a number of old cars that all dripped and drooped now and then..think I'm frustrated that my age now prevents me from crawling around under and "solving" my issues..

Thanks again..
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Old March 10th, 2018, 11:31 AM
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I am with you on not liking to crawl under them ,but if you are having the oil changed, that would be the perfect time to locate the leak ,and especially if it happens to be the speedometer seal its a cheap fix.. It's not just 50- 60 year old cars that leak either, just look at the parking spaces in any parking lot and there are oil spots in every one. Good luck,Larry
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Old March 10th, 2018, 06:04 PM
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If you can't completely stop the leak an old scrap of dark colored carpet placed directly under the leak,will make it easy to take care of. Larry
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Old March 12th, 2018, 06:29 PM
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The leak is at the speedometer cable connection seal...got the guy at the garage where I do business going to put one in later this week..He likes to fish and I got a bunch of old lures I never use so we both win...

Thanks for all the input...especially the dark carpet..heck I was going to use white wool carpet to be fancy.
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Old March 12th, 2018, 06:47 PM
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Wool carpet attracts moths.
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Old March 12th, 2018, 08:55 PM
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Originally Posted by opos View Post
got the guy at the garage where I do business going to put one in later this week..He likes to fish and I got a bunch of old lures I never use so we both win...
Old fashioned helping each other. I love it.
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Old March 13th, 2018, 06:27 AM
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Originally Posted by opos View Post
The leak is at the speedometer cable connection seal...got the guy at the garage where I do business going to put one in later this week..He likes to fish and I got a bunch of old lures I never use so we both win...

Thanks for all the input...especially the dark carpet..heck I was going to use white wool carpet to be fancy.
This is a very common one and can be a pain, it can travel up the inner cable as well.
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Old March 13th, 2018, 07:48 AM
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Glad you found the leak and that is the easiest source that it could be to repair.Yeah,white carpet would not be a good idea! Larry
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Old June 13th, 2018, 10:55 AM
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I have the same leak on my dad's 1970 Cutlass Supreme.. My mechanic is afraid of removing the speed sensor to replace the seals, afraid it might fall apart or something. Anyhow, I can't seem to find a replacement transmission speed sensor online. Does anyone know where I should try? I'm new here, and soon to be owner of this nice machine.... Thanks!
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Old June 14th, 2018, 05:46 AM
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They are pretty durable. TCI and others sell speedometer gears but there are different size speedometer bullet's, so certain gears fit certain housings.
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