Pulsing Brakes?

All,
My father-in-law has a 2006 Ranger with maybe 45K on it (never had a brake job). Over the last number of months it has developed a pulsing action when braking the vehicle. It can be noticed/felt during an abrupt stop from high speeds or during a very gradual stop from low speeds. I automatically assuming warped rotors - easy fix.

When I pulled the front wheels, I dial indicated the rotors' interior and exterior faces at a few locations near the OD. One rotor's worst runout was .0015" and .0005" and the other's was .0025" and .0010". I'm not sure what the runout spec limit is for this vehicle's rotor is, but I've never seen a vehicle requiring less than a .0030" spec limit. I realize .0025" is a little high on one of the surfaces, but if you felt how bad this thing is pulsing you wouldn't think .0025" would be the culprit either. Both rotors and all pads had tons of life left on them, so let them be and I moved to the rear drum brakes thinking the cause might be there.

I lifted the entire rear end, put the truck in gear, and let the wheels turn as it idled. I then applied the brakes mildly braking expecting the to see/hear the drums grabbing every half rotation or so if one of the drums was out of round, but no such luck. I removed the drums and inspected everything. I didn't have a mic capable of measuring the drum's ID. Again everything was in order and the shoes had plenty of life in them, so I put it all back together and scratched my head.

I'm stumped, there is no ABS light, no weird noises, and no pulsing/shimmying unless the brakes are applied. Does anyone have any ideas as to the cause for the pulsing? I could have the rotors turned to true them up a little more, but really feel like I'll still have the same problem when I'm done.

Thanks for any help,
Jerrold

Generally, when you feel a pulsating while braking, it is usually due to warped rotors. Whether it's front or rear, depends on where you feel it. Front, in the steering wheel. Rear, in the seat. But having drums/shoes on the rear, that might not be an issue. I'd suspect the fronts and here's why. Measuring with a mic won't give you the whole story. The rotors may still be warped. The mic measurements won't tell you if the entire rotor itself is warped, only if the thickness is different in areas around the rotor. Having them turned could be an option, but the price of rotors nowadays, turning them is steadily becoming nonexistent. Most often people buy new rotors if in doubt. Turning a rotor may cost 15 bucks each, while a new rotor may be 30 each for new, so it's really up to you. I'd bet the fronts are warped.

82Stang, thanks for the response. I did measure the front rotor thickness with a mic, that's how I knew they had plenty of life left in them (they are well over min spec). But as I stated I checked runout too, with a mag mounted dial indicator. This check will show the warpage in the disc surfaces. I listed the runout values above. The runouts are kinda small to fell the heavy pulse that I do when driving the truck.

Just looking for ideas on whether it might be something else (maybe even non-brake related). Let me know. I will post back I'm able to solve it.

ditto on the warped rotors.

Check your calipers to see if they're seized or tight. If the caliper isn't moving it'll force the rotor sideways when you apply the brakes,
Take the the stainless steel sliders off and clean everything up and lube them sparingly with a good silicone caliper brake grease.....Mike

But as I stated I checked runout too, with a mag mounted dial indicator.

Didn't mean to imply you didn't check runout, BUT I believe they are indeed still warped enough. It doesn't take much for them to pulsate like heck going down the road.

1 hot rotor + 1 cold puddle = warped rotor$

I've seen cases where it could even be tires (but don't ask me why we don't feel it when we're not on the brakes, i don't know that one). A Chevy work van is doing the same thing. Before changing tires, it would shake so bad when braking that it would knock stuff off the shelves, especially when braking down a mountain. With new meats, it has smoothed way out. The brakes were not serviced at this time.

I forgot to post my results. I opted to have the rotors turned to true them up a bit, since they had enough life left. Re-installed and the pulse is gone. Go figure, I never would have (and didn't) believed the .0025" runout would cause that much of a pulse. Glad I did it because the bearings' grease seals on these rotors were starting to leak a little so I replaced them while I was at it.

Thanks to those who posted!
Jerrold