Mystery Oil Leak From Transmission(?) (Page 1/2)
Additivewalnut FEB 28, 11:28 AM
86 muncie 4 speed, 3800sc. I have oil pooling on the top of my transmission, and oil all over the trans mount. There's oil all along the weird seam going down the middle of the trans, is that a gasket? My only guess where it could be coming from is either the shift linkage on the top, and maybe the axle seals for the oil on the mount. Is it easy to replace seals on the linkage? Do I just throw some blue devil in it and hope for the best? It's been doing this since my swap was finished but it's only now making it to the ground. Worth noting is that it's hard to get into 1st sometimes, probably due to low oil.

[This message has been edited by Additivewalnut (edited 02-28-2024).]

82-T/A [At Work] FEB 28, 11:43 AM

quote
Originally posted by Additivewalnut:

86 muncie 4 speed, 3800sc. I have oil pooling on the top of my transmission, and oil all over the trans mount. There's oil all along the weird seam going down the middle of the trans, is that a gasket? My only guess where it could be coming from is either the shift linkage on the top, and maybe the axle seals for the oil on the mount. Is it easy to replace seals on the linkage? Do I just throw some blue devil in it and hope for the best? It's been doing this since my swap was finished but it's only now making it to the ground. Worth noting is that it's hard to get into 1st sometimes, probably due to low oil.





I don't have a 3800 SC... but where is the distributor located (or is there one?). In the V6, pooling oil on top almost always means that oil has leaked from the O-Ring on the distributor shaft, and it creates a leak that cascades down the transmission, starting at the top.
Additivewalnut FEB 28, 11:49 AM

quote
Originally posted by 82-T/A [At Work]:
I don't have a 3800 SC... but where is the distributor located (or is there one?). In the V6, pooling oil on top almost always means that oil has leaked from the O-Ring on the distributor shaft, and it creates a leak that cascades down the transmission, starting at the top.



They don't have one, ECM controls the coils. Only thing that could be leaking where the 2.8's dizzy was is the lower intake, but I don't see any evidence of that.
1985 Fiero GT FEB 28, 01:23 PM
What oil are you using in the transmission, if your using regular motor oil, you should switch to synchromesh fluid, gm recommended it in a technical service bulletin, it will likely be a different color and smell, so you'll be able to tell whether the leak is from engine or transmission. I switched to Royal purple, and it was a little thinner then the old oil, and it caused the seal between the two case halves to weep oil, I put in a bottle of Lucas oil transmission stop leak, and it shifts smoother, smells better, and doesn't leak anymore. I don't know what would pool oil where it is other then something up above, on the engine.
Additivewalnut FEB 28, 03:39 PM

quote
Originally posted by 1985 Fiero GT:

What oil are you using in the transmission, if your using regular motor oil, you should switch to synchromesh fluid, gm recommended it in a technical service bulletin, it will likely be a different color and smell, so you'll be able to tell whether the leak is from engine or transmission. I switched to Royal purple, and it was a little thinner then the old oil, and it caused the seal between the two case halves to weep oil, I put in a bottle of Lucas oil transmission stop leak, and it shifts smoother, smells better, and doesn't leak anymore. I don't know what would pool oil where it is other then something up above, on the engine.



The oil in the transmission may very well be the same stuff from 1986. I haven't changed it and I have no idea if my grandpa did while he actively driving it 30 years ago. I'll switch fluid and see if I can smell test. I don't see anything that could be leaking other than the head or intake, none of which have a trail coming from them. Only thing above the trans is the TB, exhaust crossover, and the shift linkage as far as I can tell. My engine oil doesn't seem to be any lower than normal.
1985 Fiero GT FEB 28, 09:03 PM

quote
Originally posted by Additivewalnut:


The oil in the transmission may very well be the same stuff from 1986. I haven't changed it and I have no idea if my grandpa did while he actively driving it 30 years ago. I'll switch fluid and see if I can smell test. I don't see anything that could be leaking other than the head or intake, none of which have a trail coming from them. Only thing above the trans is the TB, exhaust crossover, and the shift linkage as far as I can tell. My engine oil doesn't seem to be any lower than normal.



I will say, however much oil seems to be on the trans, it likely won't impact the oil level in the engine, I had a bad distributor leak, about a bottle cap or more every time I started or drove, I ended up doing 5000km over a month on a trip to visit family, and it didn't show a difference on the dipstick. Before heading home I emptied about 500ml of spare oil I had into the engine, and it still didn't show a meaningful difference. The dipsticks are like the fuel gauge, merely a suggestion, and there is a wide range of acceptable oil level, that won't really show on the dipstick.

What color is the oil pooled in the trans, is it black and burnt/dirty, or is it relatively clean. Your old trans oil will be quite dark, noticeably more so then your engine oil would be (if the engine oil is relativity fresh)
jelly2m8 FEB 29, 02:07 AM
Best thing would be to wash it off and start keeping an eye where it is originating. The transaxle's are 2 halves with an anaerobic sealer ' gluing' them together. I've never seen one leak at the top, always at the bottom. Seeing you have a 3800, you certainly want to look at the intake manifold gasket if that is leaking on the end it will run down over the transaxle. leaking intake manifold gaskets on a 3800 is one of the very few things that will kill that engine.
sleek fiero MAR 01, 05:19 PM
Hi Guys . My 85GT muncie was leaking all over the top and dripping. I finally figured out I had overfilled by a bit and at speed it would blow oil out the vent on the top of the tranny. I drained a little out and it gave no more problem. What I had done was jack it up on axel stands and drained and refilled but on the stands it had not drained completely and I refilled and put the filler plug back in . Correct amount of new oil and a little residual old oil = overfill.
1985 Fiero GT MAR 01, 06:49 PM

quote
Originally posted by sleek fiero:

Hi Guys . My 85GT muncie was leaking all over the top and dripping. I finally figured out I had overfilled by a bit and at speed it would blow oil out the vent on the top of the tranny. I drained a little out and it gave no more problem. What I had done was jack it up on axel stands and drained and refilled but on the stands it had not drained completely and I refilled and put the filler plug back in . Correct amount of new oil and a little residual old oil = overfill.



Good point, I hadn't thought of that, op should park the Fiero on level ground, and open the fill port, any extra oil should drain out. Op should fasten some paper towel around choice components like the vent, and somewhere above the trans to maybe pinpoint the leak a bit better.
Additivewalnut MAR 01, 07:50 PM

quote
Originally posted by 1985 Fiero GT:


Good point, I hadn't thought of that, op should park the Fiero on level ground, and open the fill port, any extra oil should drain out. Op should fasten some paper towel around choice components like the vent, and somewhere above the trans to maybe pinpoint the leak a bit better.




Not a bad idea. I've never filled it myself but maybe it got topped off at some point before I owned it. I put a total of 150 miles on it before the 3800 got dropped in. Where is the vent?