Bad shake when applying brakes

Have you checked if the rotors are warped? Or prehaps not seated correctly?

The only other thing i could think of is the drive shafts or lose control arms. Typically a loose control arm is just a thump noise under acceleration though.

The driveshaft angle or joint may be causing it though when you're braking. If the brakes check out it may be worth while pulling 1 shaft at a time and do a test ride.

Just tossing out idea's that dont cost money to test.

Firstjeepbuild said:

This is the second time I have had a bad shake in my 99 TJ it has happened when going down hill applying brakes and slowing at 45 to 50 miles an hour. The steering and the whole jeep shake bad until I take my foot off the brake and start to slow down. The brakes have been replaced. I will look at them again. The front hubs . differential bearing and ball joints have recently been replaced. Can I get some thoughts on my issue.

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When you state you have a bad shake when applying the brakes; do you mean the brakes are pulsating due to a warped rotor or hot spots on the rotor OR is the shaking more like the beginnings of Death Wobble caused by loose control arms or worn control arm bushings that move or deflect under heavy braking ??

Is song like hard spots in the rotor(s) or warped rotor(s).

Doesn't take much to warp rotors. And it's easy to check...jack up the Jeep, pull the tire and put a lug nut back on to hold the rotor tight to the hub...then rotate and observe it going through the caliper... bonus points for a dial indicator!

-Mac

Shimmying/pulsations during braking is very likely to not be caused by warped rotors. I had that problem many times and was a regular at my local brake shop to have my rotors turned believing they were warped. However, as I eventually learned from Blaine, It's most commonly caused by hot brake pad material transferring itself to the rotors and forming into a repetitive pattern much like what happened to rough washboard desert roads. He told me it commonly happens from doing too many "limousine stops" and keeping the brake pedal pressed hard during long stops at traffic lights when the brakes are hot which is when the pad material gets transferred to the rotor.

Since learning that and changing my braking style have not had any brake pulsations/vibrations since. I no longer do nearly as many "limousine stops" (slow smooth braking so you don't feel the vehicle stop) and I now just keep the brake on just enough to prevent it from rolling at a stop.

Jerry Bransford said:

I no longer do nearly as many "limousine stops"

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My mother used to do what I'd call binary braking... either all the way or or all the way off! Maybe she learned that growing up driving grain trucks in Idaho.

-Mac

macleanflood said:

My mother used to do what I'd call binary braking... either all the way or or all the way off! Maybe she learned that growing up driving grain trucks in Idaho.

-Mac

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My wife does that with the gas pedal.

Not very pleasant.

Alex01 said:

My wife does that with the gas pedal.

Not very pleasant.

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Even more annoying when they do it to something they are listening to on the radio.

macleanflood said:

Doesn't take much to warp rotors. And it's easy to check...jack up the Jeep, pull the tire and put a lug nut back on to hold the rotor tight to the hub...then rotate and observe it going through the caliper... bonus points for a dial indicator!

-Mac

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There are several things there. That isn't really a warped rotor, that is an out of true rotor caused by wobble as it runs through the pads and wears it so it resembles something warped. The biggest one is called DTV or disc thickness variation where a layer of imprinted pad material heats up as it runs through the pads while driving. The difference in temperature at the localized area creates the formation of cementite in the iron composition of the rotor which is harder than the surrounding iron. As the brakes are used, that wears down the softer iron leaving a high spot. It only takes about .001 difference in rotor surface to cause severe brake judder that yanks the steering wheel back and forth and at certain speeds will cause death wobble, especially in a slight turn.

The actual reality is there is almost no such thing as a "warped" rotor, there are lots of things that create the impression that they are warped, but they are made the way they are simply due to how much resistance cast iron in certain alloys has to being warped by heat since that is their main function, to survive an abusive high heat cyclical environment. If they warped easily, that would be a very poor material choice.

I've had them with very severe cases of DTV and you could spend 10 minutes with a microment trying to find the high spot(s) and it just isn't easy to do. Faster and easier to get them turned or replace them. Of note, the longer a case of DTV goes, the deeper the formation of hard material goes into the rotor. That means it will come back with a quickness after turning.

What does cause most of our "warp" issues after the front friction imprint is a bent rear axle that wobbles the rotor through the pads, the indicator you referenced will certainly show something out of whack there, but replacing the wobble worn rotor will only delay the inevitable which is fixing the bent axle. Easy way to check that one is idle it in gear on jackstands and watch to see if the calipers are moving back and forth.

Passing through water when brakes are hot enough will warp the rotor, especially if a shade tree mechanic didn’t properly torque rotor to hub. Which means the wheel lug nut torque. common thing here in the Deep South Louisiana. One thing that people tend to overlook is a bent/ out of round hub bearing will cause pulsing when applying brakes.

Jerry Bransford said:

Shimmying/pulsations during braking is very likely to not be caused by warped rotors. I had that problem many times and was a regular at my local brake shop to have my rotors turned believing they were warped. However, as I eventually learned from Blaine, It's most commonly caused by hot brake pad material transferring itself to the rotors and forming into a repetitive pattern much like what happened to rough washboard desert roads. He told me it commonly happens from doing too many "limousine stops" and keeping the brake pedal pressed hard during long stops at traffic lights when the brakes are hot which is when the pad material gets transferred to the rotor.

Since learning that and changing my braking style have not had any brake pulsations/vibrations since. I no longer do nearly as many "limousine stops" (slow smooth braking so you don't feel the vehicle stop) and I now just keep the brake on just enough to prevent it from rolling at a stop.

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Yep. I keep the brake on just long enough to stop, then put both feet flat on the floor, setting the parking brake as needed. Auto transmissions get shifted into neutral.

macleanflood said:

My mother used to do what I'd call binary braking... either all the way or or all the way off! Maybe she learned that growing up driving grain trucks in Idaho.

-Mac

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Riding the brake or using it as a speed maintenance device will also cause strange and wonderful problems - if you manage to stop the vehicle at all that is.

CajunJeepNate said:

Passing through water when brakes are hot enough will warp the rotor,

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If that were even remotely true, every time it rains in SoCal every single mechanic shop would have lines of cars to get rotors replaced. There isn't. The other way you know that isn't remotely accurate is due to the non-existence of floating rotor hats on OEM vehicles. The race world uses a rotor hat with a rim that has holes for bolts and some easy misalignment mechanism that allows the rotor to run slightly out of perpindicular to the bearing axis when high loads in turns tilt the hubs on the bearings. The rotor bolts to the hat typically with a spring mechanism of some sort.

CajunJeepNate said:

especially if a shade tree mechanic didn’t properly torque rotor to hub. Which means the wheel lug nut torque. common thing here in the Deep South Louisiana.

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That is exceptionally rare and you have listed two entirely different methods of damaging a rotor, one is nearly impossible, the other was addressed above.