Project "Fix that damn 5th/6th gear high speed vibration".
12-04-2010, 04:11 PM
#1
Project "Fix that damn 5th/6th gear high speed vibration". Quick recap.
I have a vibration that starts at 80MPH in 5th and 6th gears only, 4th gear at 80MPH is smooth as silk. It is entirely speed related and not RPM, and I have troubleshooted every damn thing imaginable over and over and have determined that the source of the vibe is in the T56 transmission. No chance its the driveshaft or pinion angles.
After talking to Jason at Texas Drivetrain Performance, he is convinced that the problem is the 5th/6th driven gear which is supposed to be pressed tightly on the main shaft. He claims that the 5th/6th driven gear loses its tight pressed fit and it starts to flutter at high speed. After searching the net, I found others that had the same problem and have also blamed this gear or the main shaft.
So I have pulled the transmission and started the disassembly to check this gear and guess what? The 5th/6th driven gear was easily removed from the main shaft by hand with absolutely no effort. Normally, it should take a sophisticated puller to pull this gear off the main shaft. I also saw that the small end which is 6th gear, had the most slop on the main shaft. This is consistent with the fact that 6th gears vibrates more than 5th.
I have already purchased a repaired main shaft from Jason at TDP and have quickly verified that the 5th/6th driven gear will fit tightly on the repaired shaft. There does not appear to be any damage to the gear. I am feeling very confident that this is the root cause for my high speed related vibrations. Clearly I have found a smoking gun with this loose gear.
Click the video below to see the loose gear:
I will keep this thread updated with my findings. I know there are several that are fighting the same problem so hopefully they will see this.
I have a vibration that starts at 80MPH in 5th and 6th gears only, 4th gear at 80MPH is smooth as silk. It is entirely speed related and not RPM, and I have troubleshooted every damn thing imaginable over and over and have determined that the source of the vibe is in the T56 transmission. No chance its the driveshaft or pinion angles.
After talking to Jason at Texas Drivetrain Performance, he is convinced that the problem is the 5th/6th driven gear which is supposed to be pressed tightly on the main shaft. He claims that the 5th/6th driven gear loses its tight pressed fit and it starts to flutter at high speed. After searching the net, I found others that had the same problem and have also blamed this gear or the main shaft.
So I have pulled the transmission and started the disassembly to check this gear and guess what? The 5th/6th driven gear was easily removed from the main shaft by hand with absolutely no effort. Normally, it should take a sophisticated puller to pull this gear off the main shaft. I also saw that the small end which is 6th gear, had the most slop on the main shaft. This is consistent with the fact that 6th gears vibrates more than 5th.
I have already purchased a repaired main shaft from Jason at TDP and have quickly verified that the 5th/6th driven gear will fit tightly on the repaired shaft. There does not appear to be any damage to the gear. I am feeling very confident that this is the root cause for my high speed related vibrations. Clearly I have found a smoking gun with this loose gear.
Click the video below to see the loose gear:
I will keep this thread updated with my findings. I know there are several that are fighting the same problem so hopefully they will see this.
Last edited by wrd1972; 12-06-2010 at 10:54 AM.
12-04-2010, 04:53 PM
#3
Yeah the gear could be sleeved and the overall repair would be much easier comapred to replacing the main shaft. However TDP sells the repaired main shaft for $80.00 and he has history of the the repaired shaft resolving the issue. This will be the best $80.00 I have spent on the car considering it has had high speed vibes since it was nearly new.
12-04-2010, 09:29 PM
#6
About an hour to get the tranny out. Done it many times so I am a pro at it now. Doing the clutch while I am at it to.
Took about an hour to get to ultimately get to the 5/6 driven gear and for the most part, it was rather intuitive. Took much too long (and lots of foul lenguage) to get several thick c-clips off due to not having the correct pliers for the job. I am going to purchase the correct pliers tomorrow.
Planning on pulling the main case off tomorrow and hopefully getting the main shaft switched out. I have been using the "sticky" thats posted in the manual transmission board for reference material.
Took about an hour to get to ultimately get to the 5/6 driven gear and for the most part, it was rather intuitive. Took much too long (and lots of foul lenguage) to get several thick c-clips off due to not having the correct pliers for the job. I am going to purchase the correct pliers tomorrow.
Planning on pulling the main case off tomorrow and hopefully getting the main shaft switched out. I have been using the "sticky" thats posted in the manual transmission board for reference material.
12-05-2010, 04:20 AM
#7
Wasnt there a thread on this not too long ago and the culprit ended up being some sort of a plate that was too small in the M6? I dont remember the exact details but someone was providing/making a thicker plate that eliminated the problem
cant remember the act detials, someone help me out here...
cant remember the act detials, someone help me out here...
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12-05-2010, 05:14 AM
#8
Wasnt there a thread on this not too long ago and the culprit ended up being some sort of a plate that was too small in the M6? I dont remember the exact details but someone was providing/making a thicker plate that eliminated the problem
cant remember the act detials, someone help me out here...
cant remember the act detials, someone help me out here...
12-05-2010, 05:56 AM
#9
I remember those days back when i rebuilt mine in the basement over the winter lol. Luckily for me not much was wrong with the trans i bought it to swap my a4-m6 and wanted to go through it before i put it in the car for my own piece of mind. All the forward gears and syncos turned out fine it was just reverse which i assumed would be worn or bad. Luckily its reversable and flipped it over and replaced the fork pads with bronze ones, 3-4 steel shift fork, and all new seals. Those gears definetly didnt come out that easy for me thats for sure
12-05-2010, 12:19 PM
#12
Update:
I have the entire mainshaft completely out of the transmission. I still need to completely disassemble it and swap all those parts to the repaired shaft. The job thus far still has not overwelming to take apart but I am taking plenty of photos. The shifting shaft and internal mechanisms were a little tricky but I got through it.
There are two worn journals that are concealed by the 5/6 driven gear. I believe these were intended to provide some interference fit when new but now they both measure ~1.495".
There is evidence that these two journals used to be 1.498" because there is a 1/4" area on the front most journal that has not been worn away by the gear. It is just totally obvious that metal has worn off these two journals of the shaft (area concealed by the gear) because there is now a leather like surface which is the scarring of the metal. Anyway, the size of the repaired journal on the repaired main shaft measures 1.500" which will hopefully result in the 5/6 driven being captured much tighter.
Time to start taking the main shaft apart.
I have the entire mainshaft completely out of the transmission. I still need to completely disassemble it and swap all those parts to the repaired shaft. The job thus far still has not overwelming to take apart but I am taking plenty of photos. The shifting shaft and internal mechanisms were a little tricky but I got through it.
There are two worn journals that are concealed by the 5/6 driven gear. I believe these were intended to provide some interference fit when new but now they both measure ~1.495".
There is evidence that these two journals used to be 1.498" because there is a 1/4" area on the front most journal that has not been worn away by the gear. It is just totally obvious that metal has worn off these two journals of the shaft (area concealed by the gear) because there is now a leather like surface which is the scarring of the metal. Anyway, the size of the repaired journal on the repaired main shaft measures 1.500" which will hopefully result in the 5/6 driven being captured much tighter.
Time to start taking the main shaft apart.
Last edited by wrd1972; 12-19-2010 at 04:13 PM.
12-06-2010, 10:30 PM
#13
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We swapped my son's A4 to a M6 2 years ago. We bought a wrecked 120,000 mi. donor car for the parts. Soon after we completed it we discovered it needed 3-4 synchros. When the shop got it apart they discovered damaged splines on the main shaft for 5-6. They said they had seen the same thing on other Tremec trannys and suspected vibration from the driveshaft. We had ours checked and it was straight and balanced but I have seen posts saying that f-body steel driveshafts are less than rigid. We plan on switching to aluminum in the future.
01-05-2011, 01:44 PM
#16
Update:
Finally after all these years, I can honestly claim some real progress at resolving the high speed vibes. I got the car all back together and went for a test drive for about 10 miles on the interstate. During the drive, I detected absolutely no vibrations at all at speeds up to 90MPH. Before the vibes started at 80MPH and quickly got more intense at 85MPH. Everything felt smooth as silk in 5th and 6th gears plus the car just sounded differently overall due to the absence of the noise and rumble that was produced when the vibrations were occuring.
Their is definitely a lot less "clunking" now especially in 5th and 6th gears plus all the gears engage and switch buttery smooth just like when the car was new.
Anyone that seems to have this problem I have illustrated in this thread ought to look at the 5/6 driven gear and the main shaft for wear. I think its safe to say that the new 5/6 driven gear is attached to the repaired main shaft much better and tighter than when the tranny rolled off of the assembly line. I really want to give a big time thanks to Jason at TDP (Texas Drive train Performance) for all the assistance.
Just to be on the safe side, I want to get some more miles on it before calling it 100% fixed. But as of right now, its looking very likely that it is.
Finally after all these years, I can honestly claim some real progress at resolving the high speed vibes. I got the car all back together and went for a test drive for about 10 miles on the interstate. During the drive, I detected absolutely no vibrations at all at speeds up to 90MPH. Before the vibes started at 80MPH and quickly got more intense at 85MPH. Everything felt smooth as silk in 5th and 6th gears plus the car just sounded differently overall due to the absence of the noise and rumble that was produced when the vibrations were occuring.
Their is definitely a lot less "clunking" now especially in 5th and 6th gears plus all the gears engage and switch buttery smooth just like when the car was new.
Anyone that seems to have this problem I have illustrated in this thread ought to look at the 5/6 driven gear and the main shaft for wear. I think its safe to say that the new 5/6 driven gear is attached to the repaired main shaft much better and tighter than when the tranny rolled off of the assembly line. I really want to give a big time thanks to Jason at TDP (Texas Drive train Performance) for all the assistance.
Just to be on the safe side, I want to get some more miles on it before calling it 100% fixed. But as of right now, its looking very likely that it is.
01-05-2011, 10:13 PM
#17
I get a little vibration from 80+ too...never really thought much about it but I had a real bad vibe from the stock lt1 driveshaft then i upgraded to ls1 and it got way better but still some vibes and now w/ my s60 and chromoly driveshaft its still there a little bit. Seems to get worse if im going 80-90 and i go from being on the throttle to off and the vibes get worse...ill have to look into it.
03-01-2012, 08:39 AM
#19
It has been 100% vibe free for over a year now and I am 100% confident the root problem was a shitty design specific to the 5/6 driven cluster gear and the way it press fits on the main shaft.
Jason at TDP sold me the repaired main shaft for a very reasnable cost which has a tad more "build" in the problem area which will make for a tighter fit. I also purchased a brand new 5/6 gear and did a typical rebuild including new blocker rings and a new 1/2 syncro. Could not be more happy with the way its now working.
Lastly if you take your tranny apart and you can remove the 5/6 cluster gear by hand, you will have found the source of the 80MPH vibe assuminig everything else has been ruled out.
Jason at TDP sold me the repaired main shaft for a very reasnable cost which has a tad more "build" in the problem area which will make for a tighter fit. I also purchased a brand new 5/6 gear and did a typical rebuild including new blocker rings and a new 1/2 syncro. Could not be more happy with the way its now working.
Lastly if you take your tranny apart and you can remove the 5/6 cluster gear by hand, you will have found the source of the 80MPH vibe assuminig everything else has been ruled out.
