michelinmike

Merry Christmas to all Just became aware of this site and just joined today after Googling my ride and noticing a flurry of commentary on the Schwinn Super Sport on this forum. Also many of the posters seem to be knowledgable in-depth on the subject and that is impressive. I had a question regarding the BB on my ride. It seems but I'm not sure that the bearings may be worn. In some gears while the bike is upended there is a decided rumbling feeling if your hands are on the cranks turning them, but in other gears the rumbling is not felt. On the road all gears are smooth except the largest when I'm trying to build speed on a flat or decline course. On those I can feel a roughness to the cranks and there is a rumbling noise. I have recently upgraded to Shimano Clipless pedals and the LBS installed them carefully and they work perfectly. But I think the bike has had the rumbling characteristic for some time. If I need to replace the BB what is recommended for this bike? Any suggestions on a high quality replacement would be appreciated. Thanks for the privilege of posting here. It is appreciated.

Bike is as follows:

Serial #4I00995
Purchased 1987 new
Decal states "Made In Japan For Schwinn"
Color: Pearl White
BB Shell measures 68 mm
NGC 400 brakes
Tange Champion No.2 Extra Butted Tubing
Tange Headset
Avocet Saddle
Sugino Cranks
Suntour Cyclone M-II Derailleur
Araya Rims
Tires upgraded to Michelin Krylion 700x23 last month
Original Tire 700 x 20 lasted 20 years
Sakae Champion Bars