I recently had a guy with a later 80s corvette in the shop, who complained that his transmission shifting points had recently changed, and his car has become sluggish during acceleration,his car used to shift at about 2000rpm-3000rpm when driving at about 1/4-1/3 throttle as a daily driver , but had recently started to require the engine reach about 3700rpm-4500rpm before it shifted automatically, yes he could let off the throttle a bit and it would still up-shift, when over 3500rpm, but he felt the transmission was on its way out.
now if this was a more current car pulling trouble codes would be one of the first steps in isolating the problem, but in this case there were few indicators, as the trouble codes, for some reason didn,t give much info, until you thought about what might be indicated,as it related to the transmission.
codes were,
Code #45: Rich Exhaust Indication.
Code #13: Open Oxygen Sensor Circuit.
remember not all transmission problems are directly related to the transmission itself. on many cars the computer used sensor input, to cause the transmission to shift and changing the vacuum readings changed the sensor input
checking the trans fluid and changing the fluid and trans pan filter during the inspection process did not reveal any indication the trans was at fault, checking further showed that the catalytic converter was mostly blocked and the car high exhaust back-pressure was the source of the problem.
once the cats were replaced the car shifted normally. thats because a restricted exhaust, or broken vacuum line changes the vacuum reading the transmission used to cause shift points
http://www.autoshop101.com/forms/h64.pdf
http://www.motor.com/magazine/pdfs/062008_09.pdf
http://books.google.com/books?id=buwQ8a ... &q&f=false
http://www.leemyles.com/automotive-arti ... ssion.html
viewtopic.php?f=56&t=495
viewtopic.php?f=50&t=1877&p=4935&hilit=+vacuum+gauge#p4935
viewtopic.php?f=44&t=808&p=4771&hilit=+vacuum+gauge#p4771
viewtopic.php?f=32&t=2697
now if this was a more current car pulling trouble codes would be one of the first steps in isolating the problem, but in this case there were few indicators, as the trouble codes, for some reason didn,t give much info, until you thought about what might be indicated,as it related to the transmission.
codes were,
Code #45: Rich Exhaust Indication.
Code #13: Open Oxygen Sensor Circuit.
remember not all transmission problems are directly related to the transmission itself. on many cars the computer used sensor input, to cause the transmission to shift and changing the vacuum readings changed the sensor input
checking the trans fluid and changing the fluid and trans pan filter during the inspection process did not reveal any indication the trans was at fault, checking further showed that the catalytic converter was mostly blocked and the car high exhaust back-pressure was the source of the problem.
once the cats were replaced the car shifted normally. thats because a restricted exhaust, or broken vacuum line changes the vacuum reading the transmission used to cause shift points
http://www.autoshop101.com/forms/h64.pdf
http://www.motor.com/magazine/pdfs/062008_09.pdf
http://books.google.com/books?id=buwQ8a ... &q&f=false
http://www.leemyles.com/automotive-arti ... ssion.html
viewtopic.php?f=56&t=495
viewtopic.php?f=50&t=1877&p=4935&hilit=+vacuum+gauge#p4935
viewtopic.php?f=44&t=808&p=4771&hilit=+vacuum+gauge#p4771
viewtopic.php?f=32&t=2697