Transmission Question

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  #1  
Old 07-20-06, 11:36 AM
rav12's Avatar
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Transmission Question

Vehicle is a Chevy 2000 metro using an MX17 auto transmission. It is been venting ATF on and off over the past 3 years. It started when the transmission developed a major leak around the differential. It was fixed under warranty by the dealer was a gasket problem so they installed a new gasket. Since the repair I noticed AFT from time to time on the top but never bothered tracking it down.

About 1-1/2 years ago I lost second gear and tracked it down to a broken band. Was not happy with the expensive quotes I got so I rebuilt it at home and it has been running fine since but the venting ATF has got slightly worse. I could not figure out when it was coming from but recently tracked it down to the VSS using dye and my black light. I installed a new o-ring when I rebuilt it so I pulled out the VSS assembly under the black light and could see the rim soaked in dye. However could not see any damage to the o-ring or to the case bore felt smooth no nicks etc.

My other theory was a plugged vent but I did clean out the pipe from the vent and it seemed clear. I am unable to explain why this keeps happening any suggestions on why this may be happening. Tranny is not overheating (checked by attaching temp strips on the oil pan) and fluid level is normal.

Can someone explain how the vent system works. I have the factory manual for the car, the GM transmission unit repair manual which covers all GM trannies and the ATSG manual and none of them fully cover the vent system. Is the vent open to the outside all the time or does it only open when it is hot.
 
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  #2  
Old 07-20-06, 08:30 PM
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I don't know about the vent, but have you tried replacing the VSS? I know it looks okay, but I have a feeling it may have a crack in it. I've seen oil pressure sending units with a completely intact body, but they were blown out internally and leaking oil. I've also seen crankshaft position sensors with such small cracks in the body, that you almost needed a microscope to see the crack. If you don't want to replace it, you might try running a small bead of silicone around the mating surfaces to see if that helps.

Sorry can't help you with the vent question...
 
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Old 07-20-06, 10:54 PM
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Thanks for the reply. Yes, I guess it could be a damaged VSS. The reason I asked about the vent is that a plugged vent can also cause leaks since the expanding air cannot escape from the system as the fluid heats up and expands. Also as the transmission cools air has to get back in or you will get a low pressure situation. Normally this would be the thing to check first before replacing anything but there is not much info on how to check for obstructions in the vent. Kind of suprised at the very little info on the vent system. I have several repair books on autos as mentioned earlier including ones that cover general operation and various type of planetary gearsets etc - but no info on the vent. When I took the car for the first repair at the dealership I spoke with the guy doing the work who was a transmission specialist but even he could not tell me how the vent system worked
 
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