Transmission Fluid Dripping From Front U-Joint

[ram1220]

Guys I am sorry if this has been asked. I am not having any luck with search function and no response in the tranny section.Truck is a 1990 GMC Sierra 5.7l auto with 157,000 miles. 2x4. Truck has been sitting for a while which I know is not good for it. But it has been sitting. Talking 8 to 9 months. Anyway I have 2 questions. How do I know which tranny is in the truck? Any search I do only results in places wanting to sell me stuff. Is there a label with a code somewhere that could tell me? This would help me in finding the right part.
Second question is from experience or knowledge in this forum. What would be a good guess as to what seal needs to be changed? I have tranny fluid dripping off the front U-joint onto the ground. Surrounding areas are clean and dry. Just dripping from u-joint. I'm sure I can fix this but I need to get some ideas. Thanks.

 

[Curt]

How do I know which tranny is in the truck?

From page 8 of LMC Truck’s catalog

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Or you could take a look at the RPO code in the glove box and look for any of these:

MD8 - TH700-R4
M30 - 4l60e
MT1 - 4l80e
M40 - TH400

Is there a label with a code somewhere that could tell me?

The RPO codes should be in the glovebox. Make sure the VIN on the RPO code matches your truck. It is the sticker in the glovebox with a bunch of three letter/digit codes on it labeled “Service Parts Identification”



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[ram1220]

Thank you very much. I have an MD8 in the codes so I have a TH700-R4. At least I can order the part that I believe I need.

 

[delta_p]

I'm guess the transmission rear output shaft seal. on this picture of 4l60e would be the one that says 691. The outside diameter of the drive shaft yoke rides on this seal and the rear oil seal so if 691 leaked would allow oil to the inside of the drive shaft yoke. Since there is probably a breather hole or something in the yoke to allow the shaft/splines to slip without compression, the oil would get the ujoint area. Takeing off the extension housing would allow access to this seal.

picture of the th700-r4 looks to have the seal too.
http://sbcv8.com/wp-content/uploads/2016/01/20160111_210039.jpg

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[BubbaGump]

If the new rear seal doesn't fix the problem, it's worn splines on the driveshaft yoke letting fluid past them back to the weep hole in the rear center of the yoke. Quick and dirty repair is to squirt some RTV or "right stuff" into the weep hole to seal it up. Correct way is to replace the yoke.

 

[delta_p]

Everything a grown man needs for the butt end of his transmission.

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[ram1220]

Thanks for all the replies. The part I was sold looks like #34 in post #4. But I went out yesterday to fix the truck and the part is too big. It's just too big around to fit. Right now I am extremely frustrated. I have a bad back, shoulder, and neck and can not keep getting under this truck. I am putting the truck up for sale this morning. I just don't want to deal with it anymore. It's a 90 with only 158k miles on it. Engine and tranny are strong so I should get a good price for it. Thanks for all the help but I just don't want to deal with it.

 

[ram1220]

Delta that's exactly the one I bought but it's too big. I checked with Amazon and they say it will not fit my truck. OReilly said it would. Auto Zone had no idea. This is the problem I have been running into. Every place I go to tells me I need a different part. When I finally think I bought the right one it was too big. Extremely frustrating.

 

[ram1220]

I'm guess the transmission rear output shaft seal. on this picture of 4l60e would be the one that says 691. The outside diameter of the drive shaft yoke rides on this seal and the rear oil seal so if 691 leaked would allow oil to the inside of the drive shaft yoke. Since there is probably a breather hole or something in the yoke to allow the shaft/splines to slip without compression, the oil would get the ujoint area. Takeing off the extension housing would allow access to this seal.

picture of the th700-r4 looks to have the seal too.
http://sbcv8.com/wp-content/uploads/2016/01/20160111_210039.jpg

You must be registered for see images attach

Ok sorry I have no idea how but I missed your message. I saw the pic but didn't see the message. Tough weekend. Lol That gives me something to try. It's definitely leaking from the U-joint. The outer seal is dry. I'm pretty good at fixing this truck. But I have had so many places tell me I needed this or that part I am just frustrated. Any idea why #34 in your pic and your Amazon pic are not the right size? I bought a seal that looks just like that and it's too big. I definitely have the MD8 code in the glove box and the sticker matches the VIN on the truck. So I am sure I have the TH700-R4.

 

[delta_p]

On the oil seal #34 i had a similar problem on my '96 C1500 at the rear pinion oil seal at the differential where the drive shaft yoke is. If i have someone look up the part number it is the wrong seal and while it will press in to the differential, the seal id is too small for the drive shaft yoke.
I ended up taking measurements and going onto Oreilly auto web page and looking backwards '95 and back, and forwards '97 on until i found the different part. since i had already pried mine out I checked the dimensions with those on the webpage and back to auto store and bought it. I was frustrated too while i was at it but once i found the part it was all down hill and smooth sailing. Make sure you check OD and ID for the right fit. I hope you decide to fix this and keep your GMT400.

Again, the one you may need to replace is the O-ring inside the extention housing. Also not that difficult to remove. Here is also a good description of this. http://www.73-87.com/7387garage/drivetrain/yokeleak.htm

In a worst case you could check dimensions using National Oil seal catalog http://www.timken.com/pdf/7707_National Indust Seals Catalog.pdf
That's the same catalog the guy that designed the transmission would have used.