Triumph Repair: 77 spitfire vibration, shaft bearing, tail shaft

Question
QUESTION: "If all this is true you have a bad bearing either on the tail shaft housing or the rear main shaft bearing is bad."

I Must have described wrong- tail shaft (and bearing) is not moving when clutch is in, car still vibrates.

Main shaft bearing is in the diff right? The drive shaft is out of the car, so the rear end is disconnected. I have re-posted with a better description.
Thanks

ANSWER: There are 3 main bearings on the shafts that go through the transmission to connect to the drive shaft. The first shaft is called either the "Input shaft" or "first motion shaft" It is the shaft that supports the clutch disk and has a small bearing in the back of the flywheel/crankshaft. The other end of the First motion shaft ends just inside the Iron section of the transmission with a large bearing called the first motion shaft bearing. Inside the back of this first motion shaft are small needle bearing that supports the front of the main shaft.

The "Main shaft" runs all the way to the rear flange that the drive shaft connects to and is one piece (unless you have an over drive) At the rear of the Iron center section is a rear main bearing which supports the main shaft in it's middle. Behind the Iron center section of the transmission is an aluminum "Tail shaft housing". At the very end of the "Tail shaft housing" the main shaft extends out a short distance and has the flange to mount the front of the drive shaft. Just inside the back end of the "Tail shaft housing" is a another bearing to support the tail end of the main shaft.

Since you do have the vibration (NOT a noise BUT a vibration of the car) when the drive shaft is NOT connected to the transmission, the problem must be either in the transmission itself or the clutch. The way to check it is to Put the transmission in 4th gear and let the clutch out and run the speed up high and note any vibration.

If yes, Put the shift lever in Neutral and release the clutch and run the engine speed up again and note if the vibration is there or not.

If not, then the problem is inside the transmission. (most likely a tail shaft housing bearing or rear main shaft bearing) If the vibration is still there, then you have most likely a clutch problem.

Howard


 

---------- FOLLOW-UP ----------

QUESTION: Thanks so much for that explanation. I know nothing, and that makes sense to me !!
Since it still vibrates with the clutch depressed in gear, could i rule out the tail shaft housing bearing, since the final flange does not move with the clutch in, or could it still be that one.

Your help is so appreciated- thanks so much!!

Answer
Only if you are sure that the rear flange is truly not turning because many times a clutch will still drag the first motion shaft along at engine speed even though the clutch pedal is depressed unless there is some drag on the main shaft like a drive shaft and differential to stop the main shaft from spinning.

Howard