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71 350 auto trans leak


ejw71

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My '71 sat up in an unheated garage over the winter. Auto trans fluid leaked out. I was unable to find the source of the leak. This happened twice. I cleaned up the first leak but another appeared in about two weeks. This same problem happen to my '79

El Camino. It also has a 350 auto trans. And believe it or not it happened to my '63 Corvette. Which has a two speed powerglide. Yep, it all sounds weird. But it happened to all three cars in the same fashion. Thanks for any assistance in helping me determine the cause. None of the trans were over filled with A/T fluid. Ed

 

 

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Mine did the same thing and I had all the seals replaced so far so good. If it is shifting ok, I would look at the seals. The new type of seals last a lot longer and I run the car every couple of weeks. I am not a tranny person just adding info hope it helps.

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I have heard this is common with the powerglide, but don't know about the others. They said if they sit for an extended period, the fluid in the torque converter settles into the pan, which raises the level and causes the trans to leak from its vent tube.

They made it sound perfectly normal.

I don't know if this could be your mystery leak, but it's something to consider.

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I have a 350 turbo hydramatic and had that happen to me twice, after the car sat for about 8 months or more. During a 6 month winter storage or driving it once in a while, it is pretty much fine. The theory is similar to wallaby's explanation. Over an extended period of time, all of the fluid ends up draining in the pan and the level reaches areas which don't typically bathe in fluid and/or apply more pressure to other areas. If these areas include seals and gaskets that are not in prime condition, it leaks out until the level gets back to its regular height (in my case losing about 1L or so). I have found it impossible to determine exactly where it was leaking from.

 

One interesting point is that mine only started doing this after I had the transmission flushed and filled by one of those tranny shops offering this specialized service. What a mechanic friend of mine said that with these old trannies, the seals/gaskets get old but dirt and debris accumulate in these areas helping them seal. When you have it flushed out vigorously as these processes tend to do, you remove all of this debris and the tranny is more prone to leakage as the seals/gaskets are old.

 

The cheapest solution, is to drive it more and not let it sit for so long. It has worked for me. shifter

 

Hope this helps a bit.

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  • 4 weeks later...

I have the same problem with my car, a 350 motor and th350 tranny. The car sat for along time in the previous owners driveway. When I was considering the car, it would not go into gear untill we added about two qts of fluid.

I bought the car and after it sat in my garage for a month or so, I noticed a large puddle of tranny fluid under it.

The weird thing is I know its not from the rear seal and I am not 100% positive it from the pan gasket. So now I am wondering if its from seals or vents too. I hope I don't have a leak in the case.

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  • 4 weeks later...

Thought I was going mad thinking that nothing happened to the car and the b...h starts to leak right when I have other things to fix. Finally decided that the oil draining down reaches areas where it can leak out. Suspect it leaks out at the filler tube case junction. Ok what's the next problem. Motto: If you have one car you'll have X problems. If you have N cars you'll have NX problems. Yep, that simple. Of course, this is independent of the brand. Thanks for the help. Ed

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Didn't Nissan have an NX? Just kidding, mine leaks a little too.

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TH350's leak when they sit for a long time. every TH350 we have at leo's leaks. even some of the 400's do too.

 

simple solution is to drive them more often!!!

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most 350s and 400 leak from the selector shaft seal or shift shaft seal.

i have found that putting 2 seals in there bore solves the problem.

even my tci trans leaked from there before i did the second seal

just something that was not mentioned yet.

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