pilot bearing

[Noel K.]

having rebuilt the small block in my '65 roadster and installing the motor, the car developed what felt and sounded like a throw out bearing problems ( the car is obviously a 4 speed). I pulled the transmission back far enought ( could not completely remove it without also removing the bell housing so I went the short route) i installed a new throw out bearing. Result - same vibration and noise as before.

When the engine was rebuilt i had the flywheel resurfaced and balanced. There was no clutch or throw out bearing issue previously. It has now been suggested that the problem may be a pilot bearing. Would welcome any thoughts regarding this issue - should i now consider pulling the transmission completely replacing the clutch and pressure plate ? To admit my ignorance, I am not actually certain of the function of the pilot bearing. If replacement needed, how is this accomplished ?

Thanks in advance,

Noel Kendall

[Mark S. Lovejoy]

Re: pilot bearing

Noel,

The pilot bearing (or Bushing depending on application) is intended to hold the front of the transmission input shaft and prevent it from 'whipping'. It sounds as though it may be your problem as they do wear out and must be replaced. I would never replace a clutch or throw out bearing without replacing the pilot bearing as well.

Make sure you carefully measure the OD (outside diameter)of the old one as there are many out there with different OD's.

Hope this helps.

Mark

[Ron Bauer]

Re: pilot bearing

Noel, there are many items that could be causing your noise/vibration. I think it took me 3 times pulling the trany out of my 62 before I figured everything out. Here are a few things to check that I found were suspect on my car. Bellhousing face must be square with face of flywheel. Bellhousing opening must be in line with hole in pilot bushing in end of crankshaft. You can check these with a dial indicator but the trany, clutch and pressure plate will need to be removed. Pilot bushing must be installed correctly so as to not distort the opening as it is a soft bronze type of alloy. Make sure the opening fits your input shaft on the trany. I used a non-metallic one from a Napa store. You can check that it is non-metallic using a magnet at the counter. The return springs on my pressure plate when torqued to the flywheel did not seem to be flat across when laying a straight edge on the top. It appeared that more than a third of the ends of the diaphragm leaf ends had gaps underneath them where the throw-out bearing would normally contact. My remedies were to clean the bellhousing surfaces where it mounts of all old paint and or dirt. Install new pilot bushing. Install new clutch and pressure plate. Install new throw out bearing making sure you line up grooves in clutch fork. I used a tiny bit of lithium grease on the end of the input shaft to help aid the installation of the trany. I found many posts on the archives here and they were a great help reminding me of the many things to check. You can find tolerances for your bellhousing runout and face concentricity in some clutch books at the library. I made some copies of certain pages of the book that I used and could send the tolerance ranges if you need them. Good Luck, Ron.

[Tony Rogers]

Re: pilot bearing

A pilot bushing can often be removed without completely removing the transmission if you can get enough clearance to screw a tap into the pilot bearing by pushing the transmission back. Be careful to get the tap started squarely and screw it in until it contacts the back of the crank. Use oil on the threads and turn the tap until it extracts the bushing. To reinstall, use a bolt with tape around the threads and knock the bushing into place with a tie rod fork or open end wrench. If you have an experienced machinist available, so much the better.

Hope this helps.

Tony

[Mike McKown]

Re: pilot bearing

"Result - same vibration and noise as before."

Maybe if you were a little more specific or descriptive, someone here could help you with your problem.

[Noel K.]

Re: pilot bearing

the noise/vibration can be felt through the shifter - is evidenced when the clutch pedal is depressed. the car shifts fine and there doesn't seem to be any vibration. when the clutch pedal is depressed the noise begins. that being said, it is not a constant problem. it is still reasonably cool/cold in Indiana and when the car was last started at approximately 45 degrees ambient temp, the noise did not occur. i let the car warm up to operating temp in the driveway (without driving it) and could not get the noise to occur.

when evidenced, it does seem to sound just like a bad throw out bearing. i called the machine shop that rebuilt the engine. they did grind the crank .010, but did not replace the pilot bearing.

at this point our next attempt will be to try to put the car up on a hoist with me in the driver's seat - let a friend remain on the ground and try to use a stethescope to narrow down the source of the problem - either front or back of the transmission, bell housing, etc.

i'm reluctant to drive the car until i get the problem corrected with the concern that i will cause or due damage to additional items.

again thanks all for the suggestions and comments.

Noel Kendall

[Timothy B.]

Re: pilot bearing

Noel,

Did you check the clutch fork to make sure it's not wore where the throw out bearing slips in? These wear and when the clutch is depressed the spining bearing rubs the fork and can make noise.

[Clem Z.]

make sure the bearing is installed in the fork

correctly. the spring on the fork goes INSIDE the groove in the bearing

[John H.]

Re: pilot bearing

The portion of the throwout bearing that's contacted by the fork doesn't rotate; the eccentric formation in the base of the groove bears against the fork and keeps the center sleeve assembly fixed. Only the very thin front face of the bearing (that contacts the clutch fingers) is allowed to rotate.