Transmission shutter/leaking

[rAiN_Twist]

Hi there, so I have a 98 GMC Yukon, 4 wheel drive. It has ~262,500 miles, and I take extremely good care of it. It’s always had a slight shake to it on the highway and I replaced the entire front end trying to find the problem, and I think it came down to the hub assembly and CV’s. But after I fixed that I had an intake gasket failure, bad day, and I got that replaced. Just before getting that fixed, my brake lights stopped working. And right after I got the intake gasket fixed it started developing a shutter at about 50 or 55 mph and if I push it it will just get worse. I don’t know if the brake lights have anything to do with my transmission issues or if it’s completely separate but I figured I would give all the information I can. When I tap the brakes the lights will come on but if I push them any farther they’ll shut off. I tried pushing it on the highway passed 70 and it started spewing transmission fluid all over the exhaust and was burning, it looked like a chimney on the back of my car of white smoke. I changed the transmission fluid and filter thinking it could be a clogged filter and coming out of the vent tube but no luck. There’s transmission fluid all over the frame rails, and it drips when I park. I can’t tell where its coming from because it’s blown all over the transmission. Also the transfer case has had a leak at the output seal for a long time and I think it’s leaking out of that as well.

 

[exp500]

Possible plug in trans vent line. I think your symptoms are connected.Do you have access to a tech 2? Need to see tranmission codes. If you have a spare laptop, VX diag is a cheap way to go.

 

[rAiN_Twist]

Possible plug in trans vent line. I think your symptoms are connected.Do you have access to a tech 2? Need to see tranmission codes. If you have a spare laptop, VX diag is a cheap way to go.

I have a friend that does a lot of my car stuff that I can’t do because he has a lift. He probably has a tech 2 device, but I’m not sure. He would honestly help me with this problem and would probably know what it is instantly but he’s just too busy to look at stuff right now so I figured I would come on here to maybe get some ideas and hope it’s a simple fix. Is there a good way to see if the vent is plugged? I know that thing is kind of shoved up there, at least on mine so it would be a pain to get off of there.

 

[exp500]

Try downloading the factory service manual. It will come in handy many times over. Probably find it on a forum that I can't find the link to right now. or free files site. Search 98 tahoe service manual .pdf.
Thats a tough spot, nothing there is easy. Fingers and flashlight, mirror helps.

 

[rAiN_Twist]

Try downloading the factory service manual. It will come in handy many times over. Probably find it on a forum that I can't find the link to right now. or free files site. Search 98 tahoe service manual .pdf.
Thats a tough spot, nothing there is easy. Fingers and flashlight, mirror helps.

Yeah I’ll give that a shot, I looked it up and it makes sense, it fits a lot of my symptoms. I did get it stuck in mud last winter for quite a long time, it was bottomed out with all 4 wheels spinning. Had to get it pulled out with a winch so it might have just been accumulating in there for a while a finally clogged.

 

[exp500]

98's have a pretty good brake light switch, Worth looking at it with beeping meter connected so you can watch pedal/switch/linkage. I used huge zip ties on switches before while waiting for parts for wobbly assemblies.

 

[rAiN_Twist]

Update:
Checked the vent tube, I pulled it off and I shoved safety wire into the vent tube port that goes into the transmission. The safety wire came out clean and it went it with no problem. I check the vent tube extension that I pulled off as well. No issues there. But I did find some other problems. There’s a nut missing from the tail housing on the passenger side. So then I went back and checked the driveshaft to see if that was the shaking problem, I pushed up on it and wiggled it around and found that I can literally push up the back of the transmission with my hand. Not very far but it still moves.

 

[exp500]

Look in the service manual for troubleshooting trans. Re: Puking fluid.
Rotate tires around see if vibration follows.