Leaking Transmision HELP!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by blazer88k5, Aug 26, 2002.

  1. blazer88k5

    blazer88k5 1/2 ton status

    Aug 23, 2002
    Likes Received:
    Modesto, Ca
    Hey New Colorado K5 member here!! I am enjoying the club so much, and look foward to getting my decals so I can represent here in Modesto Ca. (Nor Cal.... joining Nor Cal Big Dawgs to!)
    Here is my problem....88 K5, I have a leak somewhere around the transmision.. I do not know enough to attempt a repair myself. I don't want to take it to a repair shop and get charged and arm and leg. I want to learn more about my rig... so if there is anyone around the Modesto or and hour or so away I would be willing to come to you if you can give me a hand in fixing. All I can offer is pizza and beer!! LOL and of course I will buy all needed parts. I don't want this done "for me"... I want to learn with someone willing to teach.. I have basic tools and will buy what I need to get the job done. Maybe down the road I could return the favor to the next person who needs a hand! Thanks
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Feb 17, 2000
    Likes Received:
    What you need to do is figure out where the leak is coming from. It may just be the pan gasket and that's a no big deal repair. Under $25 repair. Hopefully that's it.
    It could also be the Pump seal has failed. The AFT will dribble down the front of the tranny and oftern looks like a bad pan gasket. If you don't have the tools and equipement to remove the transmission to replace the $5 seal then expect to pay about $300 in labor to have it done at a shop. Unfortunatly the front seal failing is not that uncommon on a high mile tranny.
    Welcome to CK5.
  3. Leadfoot

    Leadfoot 1/2 ton status Premium Member

    Nov 28, 2000
    Likes Received:
    Western Massachusetts
    As Grim stated the first thing you need to do is figure out where the leak, or in some cases leaks, are coming from. Some leak at the tranny pan gasket, some leak at the front pump seal, some leak where the gear selector goes into the case, some leak in the rear where the driveshaft/t-case adaptor goes, and some get wet with ATF due to fluid spitting out the breather. I have had the best luck using brake cleaner (make sure to have a drop cloth and spare rags handy) to clean all surfaces around the tranny pan, gear selector shaft, front pump area (area behind torque converter and sometimes hard to get at, but necessary to find out if front seal is shot), and tailhousing area where the tranny meets the adaptor (4WD) or where the slip yoke/yoke goes in (2WD). Once the areas are completely clean start up the truck and get under it and see if you can see where the leak is coming from. When you diagnose where it is coming from then you can tackle the problem. The pan gasket and selector gasket can easily be done by you will minimal tools and know-how, the others require a little more involvement.

    If you fluid and filter have not been changed in a while, it might be a good idea to change them while cleaning up the tranny. Slowly remove the bolts from the tranny pan (loosen all bolts a little, then remove all bolts from one corner and work you way back), and the fluid will start coming out so make sure you have a good sized catch can to catch the fluid. When putting them back in, make sure the mating surfaces are clean (again brake cleaner works real well) and straight. A lot of pans leak due to getting hit or warped. Place the tranny pan on a hard, flat, level surfaces and make sure it is straight and true. A block of wood and a rubber mallet can straighten any irregularities that exist. If the pan is good, put the new filter in, new gasket on the clean mating surfaces and criss-cross tighten the tranny pan bolts in steps to the proper torque. Fill the tranny up to the proper level and this will hopefully eliminate the tranny pan gasket as a source of the leak, and you will have successfully "serviced" your transmission. If it still leaks, hopefully it won't be from the pan gasket and you can look at other areas. The front pump seal replacement requires seperating the transmission from the motor (you can slide the tranny back but that means unbolting it from the crossmember, pulling the driveshafts, cooler lines, maybe exhaust, etc.), so you may want to leave that up to a mechanic. You can do it, but it will take some time and patience.
    Hope this helps.

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