Transmission noise

[crannyr]

We just completed the replacement of the exhaust and muffler on my friends Plus 2. The pipe and muffler are upgraded to 2"od to accommodate the engine which is 1885cc with fuel injection. Almost immediately after completion of the work we noticed a distinct vibration/noise from the car but only while on the upper end of acceleration thru 2 or 3 gears. There appears to be no noise in either 1st or 4th gears, shifting gears is normal, and there is no change in noise or performance from clutch engagement or disengagement. There is no obvious point of contact anywhere in the exhaust system other than the standard hanger brackets.
Would appreciate any suggestions for testing or past history of similar problems before I get into pulling engine and transmission for repair.
thanks
Rick

[types26/36]

Just a suggestion, make sure the diff is not touching the chassis (it must have clearance under it) although I cannot explain why the vibration is not there in 1st gear or why it has suddenly appeared you did not jack it up on the chassis under the diff did you?....it could bend it up slightly making it touch the diff

[crannyr]

Brian thanks for the imput. Did not jack on the chassis such that the frame would have moved. In addition it has a Spyder chassis so it is pretty stiff back there.

[Panda]

Hi Rick,
Is it possible the new exhaust has a loose or broken interior baffle. This could set up an odd vibration at certain combinations of load or revs. Try tapping the system with a soft hammer to see if you can hear any odd noises.
If you can jack up and support the car securely on all wheels, try running the engine in all the gears, driving the wheels with someone underneath listening and trying to locate area the noise is coming from.
Good luck
Alan P.

[crannyr]

Many thanks Alan will give it a try.

[MartinH]

Almost immediately after completion of the work we noticed a distinct vibration/noise from the car but only while on the upper end of acceleration thru 2 or 3 gears. There appears to be no noise in either 1st or 4th gears, shifting gears is normal, and there is no change in noise or performance from clutch engagement or disengagement. There is no obvious point of contact anywhere in the exhaust system other than the standard hanger brackets.

Rick what was the eventual cure for your 2nd and 3rd gear noise? I have the same problem on my S3 following replacing the inboard drive shafts. There was no noise before and now the noise in 2nd and 3rd only. I've tried everything with the set up of the diff mountings, exhaust location but cant get rid of it. Am beginning to think it is a sudden gearbox bearing failure. The archive suggests main-shaft spigot bearing but it would seem unusual for this to go suddenly.

Martin

[crannyr]

I wish I was sure what the "cure" was. I ended up pulling the transmission out and replacing it with another that I knew to be good. Unfortunately at the same time I addressed other problems like worn motor mounts, some light weight heat shields, and driveshaft universals all of which might have been contributors. The end result was that the noise went away but I can not say which was the cure. If I had it to do again, I would have rebuilt the drive shaft before pulling the entire drive train out ( suggestion came from 2 very knowledgeable "old wrenches" only after the car was apart). Hope that helps. By the way when I did open the original trans I could find no obvious problem.

Rick