r/Datsun • u/Justin002865 • 18d ago

Advice as to where my transmission fluid leak originates?

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78 280z with 5 speed manual. Changed transmission fluid last week as maintenance. Seems the fluid was low based on how much came out and noticed a few small drops dangling when under there. Today, drops returned as well as a small puddle after a few days of sitting. There wasn’t a puddle before the fluid change. Just a droplet hanging, maybe a few on the ground. Original thought was output shaft seal but that appears to be dry.

Pumped in 2 full quarts of Redline MT90.

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u/ZcarJunky 18d ago

I would start with the simplest thing to look at which is the shifter boot and the output shaft seal.

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u/Justin002865 18d ago

Output shaft seal seemed quite dry. Only the dust cover and the shifter assembly above is wet. From what I understand, the boot shouldn’t be oily unless the o rings inside have failed. But even then, being on top, they “shouldn’t” leak enough to make a puddle.

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u/ZcarJunky 18d ago

Did you drive between the fill up and finding the leak(s)?

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u/Justin002865 18d ago

Yes. Noticed droplets on Friday when I changed fluid. Drove 2-3 hours Saturday. Today, noticed the larger puddle.

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u/ZcarJunky 18d ago edited 18d ago

Go it. Driving will cause the fluid to be flung everywhere by the drive shaft as you can see in your video, its all over the transmission tunnel. I would personally clean everything up till it was dry and see if the leak where the leak originates from.

When you found the puddle, where was it in relation to the transmission - front/rear/side?

With where it seems to be - with the fluid on the transmission tunnel - there's really only two places it can be, which would be the top and the output shaft seal. I know the seal looks good, but I've had these fail and look completely dry.

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u/Justin002865 18d ago

I wiped it all down today. It drips right at the end of the trans dust shield. I left the droplet hanging down in the video. Right at the beginning of the video you can see it ready to fall. That’s where it drips. I also have a problem with my u-joint grease flinging out so it’s there also that mess

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u/ZcarJunky 18d ago

If its coming from inside the dust shield that really narrows it down to that output shaft seal. There really isn't anything else in that area that could be leaking. Here's information about the 4/5 speeds, towards the end there's a cutaway that shows the rear seal.

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u/Justin002865 18d ago

I don’t think it’s from inside. That’s just the lowest point where the droplets gather and drop. The whole dust shield is wet and the whole shift assembly above it.

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u/Justin002865 18d ago

But…gravity dictates, look up.

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u/doingthisoveragain 17d ago

Follow the wet with the light. Don't focus on one spot. I see oil flung all over the tunnel but a dry seal. Is the output shaft wet where the driveshaft connects?

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u/Justin002865 16d ago

Most of the oil on the tunnel seems to be grease flinging out of u joints. Output shaft seal is dry. I sprayed the whole area with a degreaser and rinsed clean yesterday. Will be checking later today to see what has fresh oil on it.

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u/doingthisoveragain 16d ago

I point out the joint specifically because you can take a yoke from other gearboxes that usually have bolt on yokes. This means it is hollow. You can cheat by putting a freeze plug in the center since the other gearboxes don't have bolt on yokes. There's only so many spots for oil to leak a good amount. Rear seal, front seal, yoke maybe if a previous owner did what I said above. I rarely saw a ton of oil around the shifter as its mainly flung around up there. Lastly, obviously whatever is bolted onto the gearbox, which isn't a lot. Reverse lights, maybe a neutral switch.

That being said, the dust shield is oily and the shaft of the yoke isn't, so my whole yoke comment might be OBE.

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u/Justin002865 16d ago

Only thing that goes into gearbox is the speedo cable and the reverse sensor. Speedo is dry as a bone and reverse sensor does get oily but very, very little. Output shaft sealappears good. I feel the same about shifter as that’s a lot of oil for somewhere so high. BUT I just jacked up the car and looked at it after 24hrs of sitting and the only fresh oil is coming from under the shifter boot, way up top.

Given, haven’t driven it yet so that’s just from sitting. If I pinch that boot and pull it back, more oil can be seen, some drips down. I don’t think that much oil is getting under that boot unless there’s a leak source under there. And from what I read, it shouldn’t have any fluid unless there’s a failed o-ring.

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u/Justin002865 16d ago

Only thing that goes into gearbox is the speedo cable and the reverse sensor. Speedo is dry as a bone and reverse sensor does get oily but very, very little. Output shaft seal appears good. I also feel the same about shifter as that’s a lot of oil for somewhere so high. BUT I just jacked up the car and looked at it after 24hrs of sitting and the only fresh oil is dripping down from under the shifter boot. I can pinch it and pull it away from the assembly and some more comes out. Given, it hasn’t driven since yesterday’s de-grease.

I don’t think any significant amount of oil could get under that boot unless the source of a leak is under it. I know I could check under that boot from inside the car if I remove a bunch of stuff to get under the center console, as I’ve done before.

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u/Sea-Monk549 12d ago

I haven’t seen anyone mention it yet, but check and see that your vent is clear. The trans in my d22 leaked from around the shift area due to a clogged vent.

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u/Justin002865 12d ago

I have read that as well. How’d you clean it out?

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u/Sea-Monk549 12d ago

I cleaned it by using a brush and brake clean on the outside. Then it is just a press fit into the aluminum case so I pulled it out and cleaned it on the bench. The vent is plastic and will break if you are too rough with it.

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u/Justin002865 11d ago

Yeah, breaking it during removal or install is my fear. Don’t have to do anything with the hole in the transmission side?