Hello everyone,
I am new to this forum. I purchased a 2008 Buick Lucerne last winter with a NorthStar V8 for $800. It had a bad transmission but was in pretty good shape otherwise. From what I understand, this is similar to the Cadillac CTS and uses the same 4T80E transmission.
Anyway, I swapped the transmission out with a junkyard transmission that the junkyard claimed only had around 125K on it. At first, the junkyard transmission shifted pretty rough from 1-2 and 3-4. After driving it for awhile and adding some stop slip, it shifted much smoother, with 1-2 shifting almost flawlessly but 3-4 still a little rough. I assumed that the cause was probably a sticking valve in the VB since it had been sitting for awhile in the junkyard with no fluid, and that driving it would possibly loosen the sticking valves up.
Then a few weeks ago, I lost 4th gear completely. If I put it in "D" it will not shift into 4th gear; I don't feel anything at all. The funny thing is that the tach will still drop to around 2k on the highway if I completely let off the throttle, even though I don't feel it shifting. Any throttle at all, however, and it will go back up to around 3K RPM. The frustrating thing is that there are no diagnostic codes, even though I was driving without 4th gear for a long time.
After looking through the FSM, it looks like there are 3 possibilities for no 4th gear:
1. Bad shift solenoids, specifically solenoid "A". I was able to drop the pan and test transmission solenoids A and B today. Both of them tested ~22.5 ohms. I would assume this means that they are OK. They are cheap enough to replace, but I'd rather not drop the VB and replace them if I don't have to.
2. 4th band servo. This seems like it would be a pretty easy part to swap out since it is on the outside of the tranny. I have read some people saying that this can cause no 4th gear and no codes. I figure I might as well replace this since it is fairly easy to access.
3. 4th band itself. If this is the case, I'm debating whether I should just drive in 3rd gear until the car dies. I only have a little over $1000 into this car and it is pretty nice. If I drove it for a year or 2 in 3rd, I would for sure get my money out of it.
Some questions on the 4th band:
1. How much work is it to replace the 4th band? I saw a tear down on YouTube where the side cover has to be removed and a bunch of parts need to come out to get access to the 4th band for replacement.
2. Is it possible to do this repair with the tranny still in the car?
3. Is there any way to diagnose a bad 4th band without tearing into the transmission more than I have already?
Any feedback would be much appreciated.
Thanks
I am new to this forum. I purchased a 2008 Buick Lucerne last winter with a NorthStar V8 for $800. It had a bad transmission but was in pretty good shape otherwise. From what I understand, this is similar to the Cadillac CTS and uses the same 4T80E transmission.
Anyway, I swapped the transmission out with a junkyard transmission that the junkyard claimed only had around 125K on it. At first, the junkyard transmission shifted pretty rough from 1-2 and 3-4. After driving it for awhile and adding some stop slip, it shifted much smoother, with 1-2 shifting almost flawlessly but 3-4 still a little rough. I assumed that the cause was probably a sticking valve in the VB since it had been sitting for awhile in the junkyard with no fluid, and that driving it would possibly loosen the sticking valves up.
Then a few weeks ago, I lost 4th gear completely. If I put it in "D" it will not shift into 4th gear; I don't feel anything at all. The funny thing is that the tach will still drop to around 2k on the highway if I completely let off the throttle, even though I don't feel it shifting. Any throttle at all, however, and it will go back up to around 3K RPM. The frustrating thing is that there are no diagnostic codes, even though I was driving without 4th gear for a long time.
After looking through the FSM, it looks like there are 3 possibilities for no 4th gear:
1. Bad shift solenoids, specifically solenoid "A". I was able to drop the pan and test transmission solenoids A and B today. Both of them tested ~22.5 ohms. I would assume this means that they are OK. They are cheap enough to replace, but I'd rather not drop the VB and replace them if I don't have to.
2. 4th band servo. This seems like it would be a pretty easy part to swap out since it is on the outside of the tranny. I have read some people saying that this can cause no 4th gear and no codes. I figure I might as well replace this since it is fairly easy to access.
3. 4th band itself. If this is the case, I'm debating whether I should just drive in 3rd gear until the car dies. I only have a little over $1000 into this car and it is pretty nice. If I drove it for a year or 2 in 3rd, I would for sure get my money out of it.
Some questions on the 4th band:
1. How much work is it to replace the 4th band? I saw a tear down on YouTube where the side cover has to be removed and a bunch of parts need to come out to get access to the 4th band for replacement.
2. Is it possible to do this repair with the tranny still in the car?
3. Is there any way to diagnose a bad 4th band without tearing into the transmission more than I have already?
Any feedback would be much appreciated.
Thanks
