| Author | Message | ||
     Anders Nilsson New User Username: nilssan Post Number: 4 Registered: 4-2013 |
Hi all, I have been restoring a 1981 R-R Corniche at slow pace since 2011. Now, when everyting was supposed to be ready, I started the engine with the car still on stands. However, as I select any gear, there is a loud knocking sound in frequency proportional to the propshaft rotation speed (one knock per revolution). Transmission is at the correct level. The transmission has not been in use since 2011 and not separated from the engine. Oil and filter have been renewed at 3 years' interval. Any suggestion in addition to replacing the whole gearbox would be highly appreciated. Best Regards, Anders Nilsson | ||
| Robert J. Sprauer Grand Master Username: wraithman Post Number: 320 Registered: 11-2017 |
Perhaps a process of elimination. Does it produce a sound in neutral? Note the torque converter is rotating in neutral pumping away. To test the rest of the trans, disconnect the drive shaft at the transmission extension. This will eliminate the prop and everything after it. Now your trans is isolated and run thru the gears and see what happens. | ||
| Mark Herbstreit Prolific User Username: mark_herbstreit Post Number: 197 Registered: 5-2005 |
If the car is on stands, I assume the driveshafts are hanging at full extension. I have heard them clunk if rear jacked up running at that extreme angle but dead quiet when everything on the ground. | ||
| Robert J. Sprauer Grand Master Username: wraithman Post Number: 329 Registered: 11-2017 |
Mark that is also a strong possibility. They are at a steep angle, so you could raise them or drop the car and test in the driveway? | ||
| Larry Kavanagh Grand Master Username: shadow_11 Post Number: 419 Registered: 5-2016 |
Hopefully putting the car on the level will solve the problem but I would also advise you to check the oil level in the trunnions and top up if you haven't already done so. | ||
| Robert J. Sprauer Grand Master Username: wraithman Post Number: 331 Registered: 11-2017 |
I recall 150ml go in the trunnions--SAE80/90 thru the small fill bolt on each housing. Note: They also wear and each has to be measured and shimmed accordingly. Did mine almost 2 yrs ago with new boots. | ||
| Mark Herbstreit Prolific User Username: mark_herbstreit Post Number: 198 Registered: 5-2005 |
An 81 Corniche will have CV style sealed driveshafts not Shadow style trunnions. | ||
| Robert J. Sprauer Grand Master Username: wraithman Post Number: 332 Registered: 11-2017 |
Thanks for the info | ||
| Anders Nilsson New User Username: nilssan Post Number: 5 Registered: 4-2013 |
Hi all and thanks a lot for all kind advice. Problem is now solved. I lifted the brackets for the rear engine mounts approx. 3 mm to the upper position along their oval mounting holes, and no more noise. Didn't realize there is such a tight clearance around the prop shaft and the prop shaft tunnel. Apparently there is balance weight(s) on the prop shaft that cannot easily be seen form its fwd aperture. Best Regards, Anders | ||
| Larry Kavanagh Grand Master Username: shadow_11 Post Number: 426 Registered: 5-2016 |
Good result Anders, the engineers at RR were devious rascals when they added hidden obstacles to baffle DIY enthusiasts. |
