...Or How a Simple O-Ring Can Drive You Crazy.....
Backstory - about 11K miles ago the torque converter in our 6.0/6L90E equipped Roadtrek failed as we rolled into Trinidad CO. We were blessed that a local shop stepped up to handle the rebuild, including horsing that transmission out with the crossmember in place since the RT tanks block the crossmember attachment bolts. Great work RT.
Anyway, the unit has worked perfectly since, including dealing with grades in CO and UT. Sidenote - if you have one of these 6-speeds just put it in Tow Mode for any sort of inclines. Substantially better for the transmission.
We're planning a 6-week road trip after labor day to the northern US after Labor Day, so among my get-ready list was to change out the transmission fluid/filter, mainly to see what the inside of the pan looked like. Speaking of the pan, I also bought a new OEM pan and gasket.
Fluid looked/smelled good without a lot of debris, so I was happy. That happiness soon ended.
I install the new pan/gasket, torqued to spec in the correct sequence. Add fluid, start it up, look underneath, and I see fluid dripping. The oem gasket is quite good, with metal core covered with rubber gasket - it's actually reusable. It looked like the fluid was dripping at a bolt location and with the bolts correctly torqued, nothing else to do but pull it apart.
I verify that the new pan is straight and I even install another new oem gasket, everything torqued to spec. This time I didn't even start it and saw fluid dripping. What the heck.....
I start examining everything under there, couldn't see anything else leaking except for that same spot. I kept looking and noticed that the portion of the dipstick tube that was visible (heat shield in front of it) was wet. This is all on the passenger side.
Heat shield in place, the black tube is the dipstick tube.
Heat shield removed
With the heat shield removed I could now trace fluid coming off the tube and finding its way to the pan. So the pan was fine, all sealed, but the "leak" I was chasing was coming off the tube while I was filling the transmission. I thought how could that be? Was the tube broken or cracked?
The answer is neither - GM decided to install a two-piece fill/dipstick tube on these Express 3500 vans. The connection between the upper and lower tubes is right behind the passenger side cylinder head, as you can see, it was seepy-looking. The reason I never saw a drip or lost fluid was that I had never needed to add any fluid since the rebuild and checking the level was just using the dipstick.
It's a poor design - the lower tube uses an o-ring and slides up into the upper section, essentially against the flow of fluid being poured. Great design feature #1. Evidently when the transmission was installed, the o-ring was damaged. The picture is of the lower tube with upper tube removed.
I figured, ok, things happen. I'll just replace the o-ring. I find an appropriate size, but after 2 hours I'm still trying to the get the two tube sections aligned and connected without squeezing out the o-ring. I also tried a couple of different diameters and thicknesses just to be sure. I've worked on cars/truck all my life, but this was a first. My conclusion was that one or both of the tubes may have gotten tweaked.
I order new oem tubes, not that expensive. Note the thinner end of the lower tube where it goes into the transmission - we'll get to that.
The new upper tube was indeed a bit different curve at the bell end where it connected to the lower section that didn't help alignment. I figured it got slightly twisted at some point. I installed that upper tube loosely in place, then headed below to swap out the lower tube. Remember this picture?
This is the lower end of that tube that extends through the seal into the transmission, it's about 3 or 3.5 inches long.
But the problem is that you can't remove that lower tube from the transmission - there's not enough room between the seal and the body! Great design feature #2. You have to lower the transmission slightly (or cut that skinny part down a couple of inches). But you can't lower the transmission because the crossmember isn't removable. At this point we're down the rabbit trail.
So I decide to leave the lower tube in place - the top hat seal at the transmission is virtually new, no leakage there. I swap out the supplied o-ring from the new lower tube onto the original lower tube and connect the new upper tube to it. It still took a number of tries and a mirror to be sure that o-ring seated correctly.
Finally, success. All is dry, no leaks. The reason I posted all my nonsense was just in case somebody sees a leak from their 6-speed that they can't easily find, check that two-piece tube. And about that non-removable crossmember - after this road trip, my winter project will be to modify the crossmember so the center of it is removable while remaining structurally sound when re-connected.
Backstory - about 11K miles ago the torque converter in our 6.0/6L90E equipped Roadtrek failed as we rolled into Trinidad CO. We were blessed that a local shop stepped up to handle the rebuild, including horsing that transmission out with the crossmember in place since the RT tanks block the crossmember attachment bolts. Great work RT.
Anyway, the unit has worked perfectly since, including dealing with grades in CO and UT. Sidenote - if you have one of these 6-speeds just put it in Tow Mode for any sort of inclines. Substantially better for the transmission.
We're planning a 6-week road trip after labor day to the northern US after Labor Day, so among my get-ready list was to change out the transmission fluid/filter, mainly to see what the inside of the pan looked like. Speaking of the pan, I also bought a new OEM pan and gasket.
Fluid looked/smelled good without a lot of debris, so I was happy. That happiness soon ended.
I install the new pan/gasket, torqued to spec in the correct sequence. Add fluid, start it up, look underneath, and I see fluid dripping. The oem gasket is quite good, with metal core covered with rubber gasket - it's actually reusable. It looked like the fluid was dripping at a bolt location and with the bolts correctly torqued, nothing else to do but pull it apart.
I verify that the new pan is straight and I even install another new oem gasket, everything torqued to spec. This time I didn't even start it and saw fluid dripping. What the heck.....
I start examining everything under there, couldn't see anything else leaking except for that same spot. I kept looking and noticed that the portion of the dipstick tube that was visible (heat shield in front of it) was wet. This is all on the passenger side.
Heat shield in place, the black tube is the dipstick tube.
Heat shield removed
With the heat shield removed I could now trace fluid coming off the tube and finding its way to the pan. So the pan was fine, all sealed, but the "leak" I was chasing was coming off the tube while I was filling the transmission. I thought how could that be? Was the tube broken or cracked?
The answer is neither - GM decided to install a two-piece fill/dipstick tube on these Express 3500 vans. The connection between the upper and lower tubes is right behind the passenger side cylinder head, as you can see, it was seepy-looking. The reason I never saw a drip or lost fluid was that I had never needed to add any fluid since the rebuild and checking the level was just using the dipstick.
It's a poor design - the lower tube uses an o-ring and slides up into the upper section, essentially against the flow of fluid being poured. Great design feature #1. Evidently when the transmission was installed, the o-ring was damaged. The picture is of the lower tube with upper tube removed.
I figured, ok, things happen. I'll just replace the o-ring. I find an appropriate size, but after 2 hours I'm still trying to the get the two tube sections aligned and connected without squeezing out the o-ring. I also tried a couple of different diameters and thicknesses just to be sure. I've worked on cars/truck all my life, but this was a first. My conclusion was that one or both of the tubes may have gotten tweaked.
I order new oem tubes, not that expensive. Note the thinner end of the lower tube where it goes into the transmission - we'll get to that.
The new upper tube was indeed a bit different curve at the bell end where it connected to the lower section that didn't help alignment. I figured it got slightly twisted at some point. I installed that upper tube loosely in place, then headed below to swap out the lower tube. Remember this picture?
This is the lower end of that tube that extends through the seal into the transmission, it's about 3 or 3.5 inches long.
But the problem is that you can't remove that lower tube from the transmission - there's not enough room between the seal and the body! Great design feature #2. You have to lower the transmission slightly (or cut that skinny part down a couple of inches). But you can't lower the transmission because the crossmember isn't removable. At this point we're down the rabbit trail.
So I decide to leave the lower tube in place - the top hat seal at the transmission is virtually new, no leakage there. I swap out the supplied o-ring from the new lower tube onto the original lower tube and connect the new upper tube to it. It still took a number of tries and a mirror to be sure that o-ring seated correctly.
Finally, success. All is dry, no leaks. The reason I posted all my nonsense was just in case somebody sees a leak from their 6-speed that they can't easily find, check that two-piece tube. And about that non-removable crossmember - after this road trip, my winter project will be to modify the crossmember so the center of it is removable while remaining structurally sound when re-connected.
