Help ! Sudden No Auto Gear Shift
#76
Rennlist Member
MainePorsche
with both rear wheels off the ground turning one in P N D 3 2 should always result in the other turning (unless you have LSD). Try turning one wheel with other on the ground. In theory this should not work in P. If you can turn the one wheel in any gear other than P then it would indicate that the diff and P are still both OK.
This should also give you an opportunity to feel if there are any hard, rough or irregular spots.
Myles
with both rear wheels off the ground turning one in P N D 3 2 should always result in the other turning (unless you have LSD). Try turning one wheel with other on the ground. In theory this should not work in P. If you can turn the one wheel in any gear other than P then it would indicate that the diff and P are still both OK.
This should also give you an opportunity to feel if there are any hard, rough or irregular spots.
Myles
#77
Nordschleife Master
Thread Starter
The first time I had it on stands when I got it home, there was a 2 - 3 inch forward rotation when I engaged it in Drive while running. Nothing since. No odd sounds as well.
#81
Nordschleife Master
Thread Starter
Thanks Simon. I was hoping that my reporting did not get read over to rapidly, and that if this were an anomaly, it was missed by the more knowledgable.
#82
Rennlist Member
in anything but park there is no guarentee that the other wheel will rotate the opposite way. it all depends on friction. if it is easier for the output shaft of the trans to rotate than the other wheel (say if a brake is dragging) then when you rotate the wheel the other may stay stationary and the trans shaft will rotate. park is the exception as the parking paw locks the trans shaft from rotating and therefore the rotation has to occur at the other wheel.
#83
Rennlist Member
I don't know how much visibility you have through the drain and fill plugs for the diff but if you can see the diff carrier, get someone to watch it when you rotate a rear wheel with the car in park. the diff carrier should not rotate. the differential should transfer the rotation to the opposite wheel. if the opposite wheel rotates inthe opposite dirrection see if you can get another assistant to try to hold it from rotating. try this from each rear wheel. if it is a half shaft issue this may help determine where the problem is.
#84
Nordschleife Master
Thread Starter
in anything but park there is no guarentee that the other wheel will rotate the opposite way. it all depends on friction. if it is easier for the output shaft of the trans to rotate than the other wheel (say if a brake is dragging) then when you rotate the wheel the other may stay stationary and the trans shaft will rotate. park is the exception as the parking paw locks the trans shaft from rotating and therefore the rotation has to occur at the other wheel.
So my findings on hand turning are not anomalous.
I just wonder what it's going to take to diagnose my issue.
Last edited by MainePorsche; 10-15-2012 at 11:52 PM.
#85
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Greg,
When the event first occurred I had just started the car up to pull away. Obvious it wouldn't go into Drive. I then put it into Park and I began to roll forward on the slight grade I was on. Attempted to back up - nothing. Had to use the E brake to keep from moving.
When the event first occurred I had just started the car up to pull away. Obvious it wouldn't go into Drive. I then put it into Park and I began to roll forward on the slight grade I was on. Attempted to back up - nothing. Had to use the E brake to keep from moving.
#87
Rennlist Member
basically as you look at the differential system there are three shafts. Trans output shaft, right half shaft and left half shaft. the way the system is designed (functioning correctly) you should never be able to rotate just a single shaft. if one is held stationary and one is turned by design the third shaft must rotate. It seems to me the place to start is witht the failure of the park position. you should be able to place the car in park and observe several items. the right and left wheels and through the diff fill hole the diff carrier (wich should correspond with the trans output throught the ring and pinion). by observing these three you should be able to determine the dis connect. first with car in park and one wheel held stationary rotate the other. if diff carrier rotates the trans Park position is not functioning correctly (the problem is in the trans). if the diff carrier does not turn the trans is OK and the failure is in the final drive.
#88
Rennlist Member
If you determine the failure to be in the final drive, try to to see if you can get the diff positioned so you can see the spider gears. if you can then you should be able to determine which side the failure is on as follows. place the trans in Park watch the spider gears and have someone rotate one rear while the other is held stationary. if the spider gears rotate the failure is on the stationary wheel side, but idf they do not rotate the failure is on the side being rotated. you can switch which wheel is being rotated to confirm.
#89
Former Vendor
Greg,
When the event first occurred I had just started the car up to pull away. Obvious it wouldn't go into Drive. I then put it into Park and I began to roll forward on the slight grade I was on. Attempted to back up - nothing. Had to use the E brake to keep from moving.
When the event first occurred I had just started the car up to pull away. Obvious it wouldn't go into Drive. I then put it into Park and I began to roll forward on the slight grade I was on. Attempted to back up - nothing. Had to use the E brake to keep from moving.
If the car is off the ground, put it into park. Then rotate both rear wheels, in the same direction, with your hands. Sometimes there will be an audible "clunk" as the park pawl engages into the teeth. Sometimes not, as the "teeth" may line up with the pawl when shifted into park.
Once both wheels, turning in the same direction will not turn, go up and take it out of park and put it into neutral. Then see if both wheels can be turned in the same direction.
This test should tell us if the differential is properly connected to the output shaft of the transmission.