High speed braking shutter/vibration
 

67 Firebird 400 conv. , auto, low mileage car., bone stock.

I seem to have a shutter/vibration that only occurs during high speed braking (roughly 55mph+.). When exiting the highway, the car shutters during hard braking. The shutter is not there when braking at lower speeds. Also, there isn’t any vibration when normally driving. When braking at high speeds, I can feel the shutter in the steering wheel and brake pedal.

The prior owner (dealer) replaced the lower ball joints, brakes and also turned the original drums. They also installed new tires and aligned the car before I purchased. When driving the car home after purchase, the car did pulled to the right. I found that they did not tighten the spindle nuts enough, so I tightened and adjusted the brakes to help resolve this and it doesn’t seem to pull much anymore at low speed braking. Car seems to do down the road pretty straight and quiet (except when hard braking at highway speeds).

I went ahead and replaced the front wheel bearings just as a preventive measure. But the old ones did not look bad. Wheel cylinders and brake hoses seem to be working fine….especially since the car stops fine when braking at low speeds.

I also lifted the car and shook the wheels to see if It might be a ball joint, tie rod, etc. but can’t seem to feel any movement.

I’m looking for suggestions….could it be a bad wheel cylinder? Drums warped? I’m sort of at a loss, since it only happens at high speeds when brakes are warm.

Before replacing front end parts, I’m just wondering whether anyone has some advice on where to look next

Thanks

Ps; I recently installed four Koni red shocks….any chance new shocks could cause this strange issue when high speed braking??

Sounds to me like warped rotors or drums. You could use a dial indicator to check run-out. It is always more pronounced at higher speeds. Another option is to replace the front drums with rotors and calipers.

I’m trying to keep the car stock and original., so will hold off on the disc brake conversion for now.

I found a local shop that’s willing to turn my brake drums today, so hoping that it will correct the problem. Since I was told the previous dealer already did turned the drums, it’s a long shot…but hey maybe they did a poor job last time. We’ll know by tomorrow when it’s back together.

I’ll keep you posted

Update…..I had the drums turned at O’Reilly’s. It seems to have fixed the problem!! 😀😀👍👍