Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

TH350 woes... what to start looking at...?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fredekr, Apr 14, 2003.

  1. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    So on my way home from Moab, I had a little tranny problem... went something like this:

    Thought maybe the Blazer was smoking a bit down the highway on the way to Grand Junction. Stopped to get gas but didn't look under the truck since there was no smoke at the time. Hung around GJ a bit. Headed out, started seeing serious smoke behind us. Pulled of the road in after about 5 miles, nothing smoking. Shut off the engine and look underneath; lots of ATF on the tcase, rear drive shaft, exhaust... but can't tell where it's coming from. Try to start up the engine to check the ATF level but now the engine doesn't start... hmm... poking around, looking at the batteries, starter, etc. Tow guy stops and asks if we need anything, he starts looking around and notices that a plug into the alternator is loose.... must of rattled loose in Moab /forums/images/graemlins/rolleyes.gif Gives us a jump and we start off again.

    We start to smoke some more so I stop 50 miles later in Rifle, hose off the underbody and check ATF... a bit low but still pink, so I add a pint and away we go again. Drive a bit ... starts smoking again. Now it also starts downshifting at inappropriate times. Stop after 50 miles in Gypsum and start thinking. I crawl under and start looking carefully. Tranny is very clean. Lots of ATF on tcase and everything else from there back. Look in through shifter boot, and no leaks visible on top of tranny. Hmmm...

    I pull the fill plug for the tcase and dump about 3 quarts of only slightly brown ATF on the ground. (I filled the tcase 1 week ago with 80w90.) Hmm... obviously the 1-week-old tcase/tranny seals are leaking something fierce... I drain the tcase and fill it with ATF instead of gear oil. Start driving again. No more smoking noticable. Shifting is erratic, but manageable. Check ATF level 120 miles later in Golden, it's low. Add another pint, drive home 20 miles to Boulder. Shifting is better (but not perfect) from Boulder to Golden.

    So... what should I start looking at? Why would the brand new seals between the tcase and tranny blow? Chris and I just installed the xfer case and I topped off the tranny (tranny warm, idling, in park) before I left Boulder, then drove >500 miles on it with plenty of 4wd before any problems... what gives. Also, the tranny doesn't apper to be burning the ATF; the dipstick comes up pretty pink every time.

    /forums/images/graemlins/1zhelp.gif

    cheers,
    Kevin
     
  2. fortcollinsram

    fortcollinsram 1/2 ton status

    Joined:
    Nov 8, 2001
    Posts:
    2,261
    Likes Received:
    0
    Location:
    Fort Collins, CO
    Kevin,

    If I recall correctly, there were 2 seals on the adapter, correct? One on the tranny side and one on the t-case side? this is curious...is there any visible places that the ATF is seeping out of the tranny or the adapter? Basically, where (in terms of location fore and aft on the tranny/t-case combo) is the first sign of ATF leaking out?

    Maybe the breather tube?!?!?!? My guess is that the ATF is spewing out somewhere and landing on your exhaust and making your rig smoke like a mesquito fogger /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif

    Sounds to me like that tranny is getting hot and as the ATF expands the pressure builds up (hence my hypothesis on a problem with a breather tube somewhere) the ATF has to go somewhere and it seems like that place to go was out and/or the t-case (hence the ATF fluid in the t-case) Might pull the pan off the tranny and check things out as far as debris or ANY traces of gear oil from the 205 seeping into the tranny...Let me know what you find and if you have any questions, just holla /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif

    Chris
     
  3. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    Yes, there's two seals in the adapter. I couldn't see any sign of ATF coming out of the tranny or anywhere around the adapter. I'm guessing there probably is some gear oil in the tranny, but I'll find out soon enough. I think your pressure hypothesis is correct -- I think the ATF blew past the adapter seals into the tcase, then blew out the tcase breather.

    But why did the tranny build up so much pressure? Maybe I overfilled it by not letting it warm up enough?

    And why didn't it come out of any of the various tranny holes: dipstick, vent (there is a vent on these I think?), shifter cable, kickdown cable?

    At least I know my cooler lines hold high pressure /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/tongue.gif

    cheers,
    Kevin
     
  4. Calclips

    Calclips 1/2 ton status

    Joined:
    Apr 4, 2001
    Posts:
    1,005
    Likes Received:
    0
    Location:
    Swartz Creek, Michigan/Flint while in school
    did you get it into any water? I have a buddy who got his 79 Shortbed into some deep water and his tranny pukes fluid now...
     
  5. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    Nope, totally dry... the only water that touched the tranny was when I sprayed the underside to clean off the smoking ATF!
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,982
    Likes Received:
    191
    Location:
    Roy WA
    *Might* have been getting ATF on the driveshaft, and that was flinging it onto the exhaust pipes, depending on how they are run.

    Had that problem with a car, except I didn't have an inspection cover in place, and the front seal was leaking fluid. It would get thrown onto the exhaust from the converter spinning, and smoke pretty good. More obvious at low speeds, probably due to the air rushing underneath the vehicle at higher speeds.

    Just an idea...
     
  7. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    [ QUOTE ]
    *Might* have been getting ATF on the driveshaft, and that was flinging it onto the exhaust pipes, depending on how they are run.

    [/ QUOTE ]

    Oh, I was definitely getting ATF on the rear driveshaft!!!

    Working hypothesis: the tranny built lots of pressure (why?), then blew my the adapter seals and FILLED the tcase with ATF, then started pushing it out the tcase breather, so the ATF was running off the back and sides of the tcase, including the rear driveshaft, which flung it everywhere underneath the truck, including my old dual exhaust.

    When I pulled off the tcase FILLER plug, about 2-3 quarts of somewhat brown ATF gushed out. /forums/images/graemlins/eek.gif

    But why so much pressure in the tranny??? /forums/images/graemlins/confused.gif

    The tranny itself it still very clean everywhere I can see... no leaks anywhere.

    thanks,
    Kevin
     
  8. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

    Joined:
    Jul 18, 2001
    Posts:
    5,693
    Likes Received:
    0
    Location:
    CA
    If you think the tranny is building pressure here's an easy test to do.
    Get an air nozzle and blow compressed air down the dipstick tube. Or have someone do this while you climb under the truck and feel and hear for the air to be coming out of the vent on the top of the transmission. If it is properly venting then the tranny isn't building pressure. /forums/images/graemlins/thumb.gif
     
  9. CrazyCoot

    CrazyCoot Registered Member

    Joined:
    Nov 24, 2002
    Posts:
    25
    Likes Received:
    0
    Location:
    Redding, CA
    The splines in the coupler between the trans and t-case were severely worn on my truck. The coupler wasn't running on center, so the seals leaked. Drove it like that for 3 years. Finally tore it down and changed the coupler and the input shaft on the case.
     
  10. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    Okay, so I fully believe that there's lots of causes for the adapter/coupler seals to leak... but why would the tranny build up so much pressure to cause it to KEEP pushing fluid out the back end? It seems like after pushing a couple quarts of ATF into the tcase it would have blown enough out and would be okay...

    If gear oil got sucked into the tranny at some point what kind of effects could I expect? How does gear oil react to pressure/temperature versus ATF?

    I ask because here's a hypothesis:
    Say my tranny has no vent hole (need to check). The tranny gets hotter than it ever has recently (probably true for that day), and is maybe overfilled anyway, so it pushes ATF into the tcase, compromising the seals. So some ATF comes out the breather tube on the tcase. (speculation begins here...) Maybe the extra oil in the tcase adds some load to the tranny. Anyway, I stop for a couple hours, the tranny cools down, and sucks gear oil+ATF back into the tranny from the tcase. The contaminated ATF in the tranny makes it heat up like crazy and it really starts blowing ATF. I add some ATF to the tranny but that just dilutes the contamination a bit. I drain the tcase, put ATF in there. The tranny is still contaminated so it keeps shoving stuff into the tcase, but since I drained the tcase it's got more room. Meanwhile the tranny gets low on ATF for the rest of the drive home, causing mis-shifts. But no more smoking. Then I add a pint in Golden which gives ~90% improvement for the last 20 miles, and still no more smoking but it's getting dark, so hard to tell.

    Any thoughts? I'm still wondering what caused the tranny to blow so much ATF out was... /forums/images/graemlins/confused.gif

    cheers,
    Kevin
     
  11. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

    Joined:
    Jul 18, 2001
    Posts:
    5,693
    Likes Received:
    0
    Location:
    CA
    [ QUOTE ]
    I ask because here's a hypothesis:
    Say my tranny has no vent hole.

    [/ QUOTE ]
    Your tranny will have a vent. It's just matter of if it's clear so the tranny can vent pressure. The compressed air trick to check takes 10 seconds to check, man.

    If the tranny vent is clogged it should be puking fluid out the dipstick (and catching on fire on the headers /forums/images/graemlins/ignore.gif /forums/images/graemlins/rolleyes.gif) before blowing that seal.

    Check the kickdown cable and make sure that's not the culprit of your problem with downshifting at the wrong times.

    Drain the tranny or pull the pan. Is there 90wt mixed in the transmission? That's gonna be a f'n mess. I would say 90wt in an auto would make it shift wierd and need a thorough cleaning or flush, if not a new converter and rebuild.
    You've already established that ATF is leaking into the t-case, right?! but how bout the other way around?
    In my past experiences, if you know somethings not right, don't keep pushing it, it'll only get worse and do more damage.
    That $#!+ needs to come out and get a new seal man. /forums/images/graemlins/deal.gif
     
  12. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    [ QUOTE ]
    Your tranny will have a vent.

    [/ QUOTE ]

    Check this thread, apparently not all TH350s have vent holes...?


    [ QUOTE ]
    It's just matter of if it's clear so the tranny can vent pressure. The compressed air trick to check takes 10 seconds to check, man.

    [/ QUOTE ]

    Yes, I saw your suggestion and will do that, thanks! /forums/images/graemlins/thumb.gif ... as soon as I find an air compressor /forums/images/graemlins/blush.gif

    [ QUOTE ]
    If the tranny vent is clogged it should be puking fluid out the dipstick (and catching on fire on the headers /forums/images/graemlins/ignore.gif /forums/images/graemlins/rolleyes.gif) before blowing that seal.

    [/ QUOTE ]

    That's what I would think too... maybe the unknown person who put this tranny in my 77 (it's not stock) put a waterproof dipstick in like what happened in that thread above...?


    [ QUOTE ]
    Check the kickdown cable and make sure that's not the culprit of your problem with downshifting at the wrong times.

    [/ QUOTE ]

    Yes, I'll re-check that but I adjusted it recently so it should be fine.

    [ QUOTE ]
    In my past experiences, if you know somethings not right, don't keep pushing it, it'll only get worse and do more damage.

    [/ QUOTE ]

    Yup -- I'm not driving it around right now.

    [ QUOTE ]
    get a new seal man. /forums/images/graemlins/deal.gif

    [/ QUOTE ]

    /forums/images/graemlins/frown.gif Yes, I imagine I'll have too... it's a royal PITA to take that adapter out though... /forums/images/graemlins/angryfire.gif especially since I (and Chris) just did it... so before I replace the seal I want to see if there's something that *caused* the seal to blow. I can believe that non-GM seals on a worn coupler would leak, but (ignorance here) it seems to me that a seal leak is different than the tranny pushing so much fluid out the back? My assumption is that the tranny should be okay with a "leak", but the tranny is definitely not okay with what's happening now... but maybe because there's gear oil in there... h*ll I don't know what's going on, just seems like if I flush, fill, and replace the seals, then I'll be back where I was before this mess, and odds are that it'll happen again... /forums/images/graemlins/confused.gif

    Thanks for the replies Ryan... now I'm thinking I'll check the fluid level and then drive it over to a tranny shop and see what they think, that way they can see the fluid that comes out of there when they flush it.

    thanks,
    Kevin
     
  13. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

    Joined:
    Jul 18, 2001
    Posts:
    5,693
    Likes Received:
    0
    Location:
    CA
    Wow, interesting... Ya learn something new every day.

    Thanks for posting that link. /forums/images/graemlins/thumb.gif
     
  14. fredekr

    fredekr Registered Member

    Joined:
    Jul 12, 2002
    Posts:
    92
    Likes Received:
    0
    Location:
    Colorado Springs, CO
    Well, just want to close out this thread for the benefit of future searches...

    Okay, I've come to accept that it's probably just a simple seal leak causing my problems. After many comments from CK5ers and the tranny shop's opinion, I'm willing to believe it. I went ahead and paid a shop to R+R and replace the seals (I don't have a garage), they'll guarantee their work 12 mos/12k miles so that sounds fair.

    Next long drive I'll check the tcase for ATF (should be all gear oil in there now)...

    thanks,
    Kevin
     

Share This Page