Brake Adjustments and Modifications to Minimize Drag
Jim Hand, July, 1998
The last thing we want on a car at the drag strip is brake drag, yet we want the brakes to work reliably. Disc brakes, when working properly, should not cause drag. You should be able to spin the front wheel with your hand and have it turn at least part of a turn by itself. If it does not, the most likely cause of the turning resistance is the caliper assembly. Although rebuild parts for calipers are available, they do not always eliminate the drag caused by warped or misalign cylinders. You usually are wise to buy new or rebuilt caliper assemblies. The self-adjusting feature of drum brakes should be retained to assure that the brakes stay properly adjusted. However, it is possible for the adjusters to tighten the brakes too tight thus causing drag. To eliminate this possibility, bend the "adjuster lever" such that the lower part just contacts the star wheel at the outermost tooth when the lever is forced down. Normally, the lever contacts the star wheel several teeth higher on its periphery, which causes the brakes to be adjusted tighter. This simple modification allows the retention of the self-adjusting feature without the risk of brake drag caused by over tightening. The return springs should be checked periodically and replaced as needed. The easiest method of checking return springs? Simply drop them on a concrete surface. A good spring will hit with a dull thud and have very little bounce. A bad spring will ring like a bell and bounce off the floor. No, I didn't say it backward. The bad spring has crystallized from the heat build-up and constant stretching. That, in turn, causes the ringing noise and erratic bouncing when striking a hard surface. A good functional indicator of a bad return spring is the tendency of one wheel to try to lock-up with light brake application after several miles of driving. The bad spring allows the linings to drag causing them to heat and expand - upon light application, they grab.
FRONT WHEEL BEARINGS:
Wheel bearings are not normally considered part of the brake system but they should be carefully adjusted during brake service. The bearings should be packed with a non-fibrous, high temperature wheel bearing grease and the spindle should be lightly coated with the same grease. I have read that oil or other thin lubricant in the bearings will decrease friction. That is theoretically true but it is highly unlikely that a 3000/4000# car will run measurably quicker with oil on the bearings rather than wheel bearing grease. It is likely that the bearings will be quickly damaged if oil is used. What is more important is proper bearing adjustment. Too tight and both drag and premature bearing wear can be expected. Too loose and wheel wobble and bearing wear will result. Wheel wobble will cause both drag and suspension wear.
Pontiac states that the bearings should be adjusted for .00l-.005 inches end play (Looseness). To accomplish this, tighten the spindle nut (while turning the wheel) using pliers or other appropriate tools until the bearing is tight enough to cause the wheel to slow down due to bearing drag. Loosen the nut and repeat the procedure several times to assure the spindle/nut threads are smooth and not binding. Finally, tighten the nut with your thumb and finger as snug as possible with the wheel turning. Then back off just enough to allow the cotter key to be inserted. If you have to back off almost 90 degrees to align the holes, try another washer, or insert an additional hardened washer between the original washer and the adjusting nut. You should get a close to 0 clearance as possible without over tightening the nut.Jim Hand, July, 1998
Thanks to Jim Hand for sending this to me.