formula87

iTrader: (2)

I have been having a driveline vibration in my track car that I can't fig out. Car is 87 Formula w/T56. I replaced DS w/ alum one from late modle Fbody, Vib. got better but it was just absorbing the vib better then the other DS. In neutral at speed it is still there. I fabbed the Xmem off of one a friend had from Skulte Perf (sp). Rear is 10 bolt, never had problem with it before. As I can't drive it on street I can only blast down my back road but only at reserved speed, this prob comes up 4th gear at would say 80-100 mph no speedo Any suggestions? Could it be that the tranny Xmem I fabbed might need to be shimmed? The car that the DS came from is a member on here
and it was perfect when it was in his car he switched to a 9" rear and got a stonger shaft because motor was getting redone. Another racer took a ride w/ me and said it may be the DS angle?

CW00BlackTA

iTrader: (31)

The X-member might be the culprit if it affected your pinion angle in a bad way. I'd start by measuring the angle of the trans main shaft, the angle of the pinion shaft and finally the angle of the drive shaft. Make your pinion shaft parallel to the main shaft and then adjust to move the front of the pinion shaft downward until you have about -3 degrees (or whatever you run). You want your u-joint angles to be less that 1.5 degrees (under load).

TDP

iTrader: (23)

The T56 mainshaft tends to get worn at the spot where the 5-6 driven gear is pressed on. Simply put, it is a bad design from the factory. The gear starts moving back and forth as it loses its press fit. Then it wears the splines down. From that point it gets progressively worse. I've been running into this more and more with the rebuilds that I do. There is a fix that I offer. I get the mainshaft re-machined to .005" thicker than stock so the gear presses on a lot tigher, and this eliminates the problem. I wouldn't have thought that this would cure a driveline vibration until I "accidently" fixed a vibration in a customer's car. He had been chasing the vibration issue for 2 years and pretty much gave up. While rebuilding his tranny I noticed the mainshaft was worn, so I had it re-machined. At this point I did not know he even had a vibration. After he got his car back he called to tell me his vibration was gone. I'll have to post up some pics soon so its easier to understand. Anyway, I offer this service for $100 exchange. You just have to send in your mainshaft.

ThoR294

iTrader: (6)

so this vibration will happen all the time? even if the car is in gear or not

ThoR294

iTrader: (6)

also, how can i be sure that this is where the vibration is coming from? I have the SAME issue as the original poster.

Formula87, are u sure the 10bolt is good? Did you have a different trans in the car and not have the vibration?

I swapped my trans out with my clutch a while back, but i cant remember for the life of me if i had the vibration with my old transmission or not. its driving me nuts. This is because i put a detroit trutac posi unit in my stock 10bolt... so I was thinking maybe i effed something up. but idk! I really hope its not the trans mainshaft, this trans has 2k miles on it...

formula87

iTrader: (2)

^^^^ No only when car is at good rate of forward speed. motor is balanced no vib when out of gear while still. Ony when moving. 1-2nd no vibe 3rd 5000-6000 rpm and 4th-5th but again only at high speed 80-100 mph smoothes out after you cross a threshold 120-140 mph will go away, havn't really pushed it faster then that..............,
mph is estimate since no speedo...........I must have done something wrong in the build all new parts except the tranny out of a 94 z28 with 6k miles I am hoping it is the xmem I fabbed.......

ThoR294

iTrader: (6)

the vibration on my car gets bad in that same range, i stopped at 100mph because yeah... im not on a drag strip, but its real bad. and it feels like the driveshaft is out of balance... but I KNOW its not.

I was told it could be the pinion angle, axle bearing.... but i would like more info about this mainshaft thing!

Shawnzr2

Any update on the mainshaft repair pics? I was fighting a similar vibration on a customers 94 Z28 M6, the vibration started after 4.10's were installed around 80mph. I have narrowed the problem down to the trans finally but would like to give the customer a better description of what is causing the vibration. I am also noticing a loud gear clash growl type noise when coasting from 40mph to around 10mph with the trans shifted into neutral and only in neutral, any input on the noise?

formula87

iTrader: (2)

I just posted about this in another thread but here are some pics:

https://ls1tech.com/forums/gears-axl...l#post11441556