Never use Teflon tape on a brake fitting
Dear Mike: I screwed up. I wanted to bleed the brakes on my old pickup, but I broke off the bleeder bolt flush with the caliper casting. I tried to drill out the old bolt nub and install a Helicoil in the hole, but now it leaks — badly.
How can I fix this? Teflon tape didn’t help.
— J.T., via e-mail
A: Rule One: Never use Teflon tape on any brake fitting. It won’t help and it might screw something up. Think about little pieces of tape inside the ABS controller holding the poppet valves off their seats. The ABS controller can’t deal with even the tiniest internal leak, so it’s not a pretty picture.
The best solution is to buy a rebuilt caliper at the auto-parts store. If you have a classic or rare vehicle and no replacement caliper is available, however, you might try to fix it properly.
The bleeder bolt seals at the tapered seat at the base of the hole, not along the threads, so Teflon tape can’t possibly be effective. If you managed to get the Helicoil installed correctly, you probably damaged the seat at the bottom of the bore with your drill bit, making a good seal impossible.
Get a repair fitting. This will have tapered pipe threads on the caliper side and a proper bleeder-bolt drilling on the outside. Remove the caliper and pull out the piston or pistons. Drill and tap the caliper casting for pipe threads, then carefully clean it to remove any debris from the drilling and tapping operation. Thread in the repair fitting, rebuild the caliper with new seals and install and bleed it normally.
I predict that the repair fitting and the rebuild kit will cost about as much as a rebuilt caliper, which is why I suggest simply replacing it if at all possible.
By the way, if you bleed your brakes every year or so, the bleeder bolts probably won’t seize and break off.
Dear Mike: I bought a new GMC pickup recently. I feel that there is a problem with the brakes. The pedal is very spongy and, when I’m in gear with the engine running, it doesn’t take much pressure to depress the brake pedal all the way to what feels like a mechanical stop.
The dealer’s service department tells me that this is normal. I suspect a defective vacuum booster or soft flexible lines.
Mind you, the truck stops OK, but the pedal travel really seems excessive.
— B.S., via e-mail
A: GM brakes are notorious for that spongy feeling. First off, if the master cylinder is bottoming out — if that’s the mechanical stop you’re feeling — you run the risk of damaging it internally. Insist that the service manager let you drive at least two other trucks from the same year to compare. If those trucks have better-feeling brakes, he’ll have to take corrective action.
Begin by having him perform a thorough brake bleed according to the service-manual procedures. This may involve using an ABS tester to cycle the valves in the antilock pump to purge any hidden air. Bleeding ABS systems is not trivial: The traditional “pump the pedal, hold it down, open the bleeder, close the bleeder and pump some more” litany won’t always collect the last bit of air lurking inside the ABS pump.
Pressure-bleeding the system may only froth up the entrained air into foam that will be impossible to bleed by any means, so it’s important to follow the factory-manual recommendation.
If this procedure doesn’t give you good pedal feel and appropriate travel, look for a misadjusted brake pushrod or a cranky vacuum booster.
Still stepping on a sponge? Upgrade to Teflon-lined, braided, stainless-steel flexible lines. Easily done, but certainly not cheap. Even so, they will help a great deal.