Very small transmission leak

[Pryme]

So I noticed a very small (3/8”) drop of transmission fluid under the truck today before I left. Upon closer inspection it looks like it has made 4 of these tiny drips different days and then kind of dried up or wore off but I can see the small stains. Anyway it is pretty far forward. I’d say 15-18” from front of truck and slightly off center but towards the pass side. 
 

I will have to crawl under the truck to see where it’s coming from. Any ideas?

a trans line maybe?

 

kind of a bummer. 

[davester]

Yes, trans lines commonly run up to the radiator to do a heat exchange there, possibly w the option of a second cooler up front.

[Pryme]

So I got under the truck this evening and if it is trans fluid it would have to be coming from the lines directly over the idler arm as there was a red drip hanging from idler arm. But here’s the thing? I not too long ago greased all the fittings with Lucas red and tacky and the drip on the ground seemed more viscous than tranny fluid. So I’m wondering if a good amount was sitting on top the idler and melted down some??

 

I read the drop point(melting) for red and tacky is like 540deg so that doesn’t seem likely. 
 

i throughly cleaned the idler and all around that area and will watch it. 

[AndrewF]

9 hours ago, Pryme said:

So I got under the truck this evening and if it is trans fluid it would have to be coming from the lines directly over the idler arm as there was a red drip hanging from idler arm. But here’s the thing? I not too long ago greased all the fittings with Lucas red and tacky and the drip on the ground seemed more viscous than tranny fluid. So I’m wondering if a good amount was sitting on top the idler and melted down some??

 

I read the drop point(melting) for red and tacky is like 540deg so that doesn’t seem likely. 
 

i throughly cleaned the idler and all around that area and will watch it. 

I have noticed the same thing on my truck. I use black severe duty grease but last time I greased it some had liquified and the idler arm was coated and had a few black drips about to fall from it. 
 

I don’t recall seeing something like this happen with any other vehicle I’ve had to grease. I cleaned up the idler as best I could and will keep an eye on it. It is definitely strange. 

Edited November 21, 2025 by AndrewF

[Pryme]

2 hours ago, AndrewF said:

I have noticed the same thing on my truck. I use black severe duty grease but last time I greased it some had liquified and the idler arm was coated and had a few black drips about to fall from it. 
 

I don’t recall seeing something like this happen with any other vehicle I’ve had to grease. I cleaned up the idler as best I could and will keep an eye on it. It is definitely strange. 

I will be letting it idle in the garage awhile this am and again when I come home as if it is trans fluid it wouldn’t or doesn’t drip with it’s not running. I hope it’s grease though. 
just seemed very viscous for trans fluid so we shall see. 
 

I’ve read a lot of other comments on forums saying trans cooler lines are common leak points though for GM. This is my first GM truck in over 25 years so I’m not sure. 

[bruceb58]

I use Mobil 1 grease. The tubes I have stored in my cabinets always leak some red oil. That's just the nature of grease. Maybe that is your issue. Is it near a zerk?

[Another JR]

In my experience with GM oil, steering, and transmission cooler lines over the years, once they start leaking at a swage between the hard and flexible sections, the leak increases to be very noticeable pretty fast. 

[Pryme]

4 hours ago, bruceb58 said:

I use Mobil 1 grease. The tubes I have stored in my cabinets always leak some red oil. That's just the nature of grease. Maybe that is your issue. Is it near a zerk?

Yeah it was just below the really annoying idler zerk that I was having issues greasing last month. And now after driving the truck all over town today I went under there are no sign of any red fluid, grease or anything. 
 

im thinking because of many attempts to get that zerk greased without actually seeing the top of where that zerk is, I had a good amount of grease sitting up on top of that idler and some made its way down to the ground a couple times. 
the idler and those lines above were all dry. The ones with that black mesh material over them. 
 

I will keep watching it for a bit. 
 

 

Edited November 21, 2025 by Pryme

[Chuck FB]

I had a look at mine for the fun of it but already expected to see what I did and that is a red colored droplet hanging there at the lowest point of the curvature of the idler arm as well as on the tie rod center assembly that the idler arm slips into, and going over to the pitman arm basically the same thing with a droplet formed on the underside of the arm there as well. When I sprayed fluid film under my truck I purposely tried to get some on the center tie rod link and some is on the idler and pitman arms as well so that has mingled with what I presume is the oil from the grease having dropped out of the grease carrier. I also use red Mobil grease and it seems to have a really bad habit of the oil oozing out of the grease, I never used to have that happen with the older Esso Unirex ( blue dye ) grease or the Mobil grease I used that had a bit of moly content which made the grease look grey/black. There may be one drip onto the cement but nothing of consequence.  The trans lines or I assume that is them where they swag into the flex line right above the idler arm, they look completely clean. It certainly can make a guy wonder though simply because of the color of the dye in the grease and hard to distinguish between it and trans fluid. 

 

When you notice speckles of oil mist on your rear bumper and tailgate and then look under the truck at the front of the rear diff axle housing and see it dotted up if not covered with a wet substance, that's when you know a trans or engine oil cooler line is leaking rather excessively !.