lurching when braking

[mlhoward]

2019 2500 6.4 laramie coil sprung rear suspension. Bought it a year ago and have put about 17,000 miles on it with 35,000 miles on it now. Couple questions of things I notice now:

The brake pedal feels like old 2 ton truck brakes. Meaning, old 2 ton truck brakes you can pump a couple times to get a firmer feel on the pedal. Well, my truck can do the same thing. Initial push goes pretty far to the floor. Then if I push the pedal again, the pedal feels firmer and doesn't go nearly as far to the floor. Anybody else's do that? I"m not too concerned with this as much as the next.

Secondly, maybe this is related to the first, when slowing down i can feel the whole truck lurch like it has warped rotors. I know when I've had warped rotors in the past on other vehicles, I could feel the pulsation through the pedal. I don't feel any pulsation through the pedal in this instance. That leads me to believe that the front rotors are ok since that's where most the braking power comes from, and possibly the rear rotors are warped and maybe the pads are lightly grabbing the warped part. Will i feel pedal pulsation if the rear rotors are warped?

Thinking about pulling the rear rotors and having them turned. I suppose I could have a caliper hanging up too.

Is there any other component on a coil sprung rear suspension that could be wore out causing this? The shock absorber above the axle?

Thanks for any ideas you have.

 

[RKCRLR]

In my experience a lot of brake issues get blamed on warped rotors that aren't actually warped. I'd put a dial indicator on them to measure the runout to determine if they are out of spec before I replaced them.

If front rotors are warped then you can often feel it in the steering wheel but you can sometimes feel both front and back rotors in the brake pedal although that is more common with drum brakes.

The pulsation felt is frequently caused by uneven pad material deposition on the rotors. This can sometimes be resolved by some hard stops. Do a Google search for brake pad break in procedures. Turning or replacing the rotors can also fix the uneven pad deposition but it may not be necessary, and it sometimes can be removed by sanding the rotors.

 

[Rockcrawlindude]

Your rotors are not warped.
Brake rotors don’t warp.
It’s a myth.
Your brake pads cannot generate enough heat to warp a rotor.

 

[Wanderlust073]

Pedal issue sounds like a master cylinder problem.

 

[mlhoward]

Your rotors are not warped.
Brake rotors don’t warp.
It’s a myth.
Your brake pads cannot generate enough heat to warp a rotor.

I'd like to hear more on this. Why do you think rotors don't warp? Not being ornery or anything, I've just never heard of someone saying you can't warp rotors.

 

[mlhoward]

In my experience a lot of brake issues get blamed on warped rotors that aren't actually warped. I'd put a dial indicator on them to measure the runout to determine if they are out of spec before I replaced them.

If front rotors are warped then you can often feel it in the steering wheel but you can sometimes feel both front and back rotors in the brake pedal although that is more common with drum brakes.

The pulsation felt is frequently caused by uneven pad material deposition on the rotors. This can sometimes be resolved by some hard stops. Do a Google search for brake pad break in procedures. Turning or replacing the rotors can also fix the uneven pad deposition but it may not be necessary, and it sometimes can be removed by sanding the rotors.

I'll give it some good brake stabs. Seems the harder you push them, the less it gives a warped rotor sensation.

 

[RKCRLR]

I'll give it some good brake stabs. Seems the harder you push them, the less it gives a warped rotor sensation.

You want to do some hard braking to get the brakes hot but you don't want to come to a full stop. If you come to a full stop with the brakes hot the pads can imprint on the rotors which is one of the causes of uneven pad buildup on the rotors.

 

[Rockcrawlindude]

I'd like to hear more on this. Why do you think rotors don't warp? Not being ornery or anything, I've just never heard of someone saying you can't warp rotors.

They just can’t and they don’t. They can crack, they can get scored from grit and stuff but they can’t “warp” due to heat because you can’t make enough of it

Ive seen an axle fall out truck that was on a lift and land on the rotors and split them in half so I know they can crack.

 

[Rockcrawlindude]

Brake pads simply can’t generate the heat needed to warp a brake rotor.

At 550°F – 650°F— The organic binding resins in the friction material begin to melt and smear, creating a lubrication effect that reduces braking. The melted resin is what causes a “glazed” pad. At higher temperatures, the melting resins and the metallic elements begin to vaporize, resulting in “off-gassing. ” Off-gassing also acts as a lubricant, causing brake fade or loss of braking power. You can smell the melting brake pad resin odor in this temperature range.
At 850°F— Brake pads begin to smoke. Again, 850°F is not hot enough to warp a rotor.
At 1,100°F— The brake pad friction, the material begins to oxidize (burn up). The rotors react with moisture and oxygen in the air to form iron oxide, causing blue spots on the rotor.
At 1,250°F—Brake rotors turn cherry red.
At 1,400°F you’re finally reaching the point where you overheat the rotor to the point where it can soften.

In other words, long before your vehicle has reached the temperature needed to warp a rotor, your pads would be burned up, and your rotors would have blue marks on them.

To warp a rotor, you have to change the metallurgy, and that takes almost 2,000°F. There’s no street vehicle braking system that can generate that kind of heat

Brake temperature info from interweb to support my statements

Basically you would melt the pads before you could potentially warp a rotor. Keep in mind the pads are designed to wear and the rotor is not.

You cant tear up something hard with something soft that’s why brass hammers exist.

When you score your rotors it’s not the pads it’s because you got foreign material up in there like small rocks / grit etc from mud or whatever.

** I will admit there may be some Chinese Amazon brake rotors out there that aren’t made of good material and MAYBE (big maybe) those could warp but any OEM quality or better will not

 

[Rockcrawlindude]

Btw I think there’s a mega thread on this forum about soft/ spongy brakes somewhere.

 

[jsalbre]

Btw I think there’s a mega thread on this forum about soft/ spongy brakes somewhere.

I think the TL;DR of it is “big truck, not small car, brakes work different, still stop fine”.

 

[mlhoward]

Brake temperature info from interweb to support my statements

Basically you would melt the pads before you could potentially warp a rotor. Keep in mind the pads are designed to wear and the rotor is not.

You cant tear up something hard with something soft that’s why brass hammers exist.

When you score your rotors it’s not the pads it’s because you got foreign material up in there like small rocks / grit etc from mud or whatever.

** I will admit there may be some Chinese Amazon brake rotors out there that aren’t made of good material and MAYBE (big maybe) those could warp but any OEM quality or better will not

Well that is some good info. The more you know. Thank you for taking the time to explain that to me without being a jerk about it. I am mechanically inclined, I am a farmer after all, but I admit I don't know everything including the nitty gritty about brakes!

 

[Riz!]

@mlhoward

To me that sounds like a small air bubble in the line that has to get compressed first before the cylinders can generate enough force to slow you down. Maybe just need to bleed the lines?

 

[Rockcrawlindude]

I think the TL;DR of it is “big truck, not small car, brakes work different, still stop fine”.

Yes I believe that was the gist of the thread

 

[pyrorobert]

2019 2500 6.4 laramie coil sprung rear suspension. Bought it a year ago and have put about 17,000 miles on it with 35,000 miles on it now. Couple questions of things I notice now:

The brake pedal feels like old 2 ton truck brakes. Meaning, old 2 ton truck brakes you can pump a couple times to get a firmer feel on the pedal. Well, my truck can do the same thing. Initial push goes pretty far to the floor. Then if I push the pedal again, the pedal feels firmer and doesn't go nearly as far to the floor. Anybody else's do that? I"m not too concerned with this as much as the next.

Secondly, maybe this is related to the first, when slowing down i can feel the whole truck lurch like it has warped rotors. I know when I've had warped rotors in the past on other vehicles, I could feel the pulsation through the pedal. I don't feel any pulsation through the pedal in this instance. That leads me to believe that the front rotors are ok since that's where most the braking power comes from, and possibly the rear rotors are warped and maybe the pads are lightly grabbing the warped part. Will i feel pedal pulsation if the rear rotors are warped?

Thinking about pulling the rear rotors and having them turned. I suppose I could have a caliper hanging up too.

Is there any other component on a coil sprung rear suspension that could be wore out causing this? The shock absorber above the axle?

Thanks for any ideas you have.

 

[pyrorobert]

I was trying to quote your question. And also hoping if anyone has an answer for this. I have the same issue and I know that the lurching forward is not the brakes. It has to do either with the suspension or transmission. I just can't find anything loose that may cause the reaction. I have taken it to the dealer for this and I gave a ride to the mechanic with me to show them how it feels. They were not able to find the source of this. It does not happen every time I am stopping but it does happen quite often. It typically feels like someone hits you from behind. It almost feels like the rear end is wrapped up and it releases when you are coming to a stop. I going to try to put a gopro below to see if it will record it. Just don't like the feeling anymore.

 

[Rockcrawlindude]

I was trying to quote your question. And also hoping if anyone has an answer for this. I have the same issue and I know that the lurching forward is not the brakes. It has to do either with the suspension or transmission. I just can't find anything loose that may cause the reaction. I have taken it to the dealer for this and I gave a ride to the mechanic with me to show them how it feels. They were not able to find the source of this. It does not happen every time I am stopping but it does happen quite often. It typically feels like someone hits you from behind. It almost feels like the rear end is wrapped up and it releases when you are coming to a stop. I going to try to put a gopro below to see if it will record it. Just don't like the feeling anymore.

I agree it’s not the brakes.

Sounds like a loading/ unloading of the driveshaft from your transmission downshifting. Could confirm or deny this by coasting in neutral and braking (as long as you could do this safely… that’s what I would try)