[dascenc]

Hello Everyone,

WK noob here. I recently purchased my first Wk, 09 3.7L V6 Brilliant Black with 69k miles almost a month ago. Ive only put just over 1k miles on it when it started pulsing during braking, it kinda feels like the brakes are gripping then letting go but ever so slightly and its only felt at slow speeds. Its not a vibrating feeling. I dont feel it in the pedal, its the whole vehicle (I can feel myself lurch forward just a bit) so I believe it might be warped rotor. Ill be ordering a clamping dial indicator to test the rotors for runout but I was looking for any other ideas of what it might be. Any input is greatly appreciated.

Thank You

 

[SvenskaJeepGuy]

warped rotor or air in the brake fluid would be my guesses

 

[2005JGC]

thickness variation in the rotor... the repair would be new rotors or have your current ones machined.

 

[jeepgcoman]

This is more than likely caused by "hot spots" on the rotors, and is really quite common. They can also happen for the reasons ID'ed above too, or excessive grooving/irregular wear patterns. Hot spots happen predominantly on the front rotors, as they take the brunt of the braking load and generate much more heat than the rears. If there are spots on both front rotors, the "pulsing" can come and go or it may even move the steering wheel back and forth (shimmy) when braking, depending if the rotor rotation is in sync or out of sync with each other. You'll also probably notice it more at higher speeds (may even get a good shutter/vibration) than lower speeds (mostly surging/pulsing). You should also be able to see these "hot spots" on the rotors, by looking between the spokes in the wheels. They will appear as bluish colored spots, some round, some elongated. They can be machined out, but usually return in short order, because the spots had been "hardened" previously and, unless you can completely machine them out, you'll be back where you started. I've got a small amount on mine, and I'll just drive it until it irritates me too much, or I wear the brakes out, whichever comes first. When you replace rotors, make sure you get good OEM quality (or better), and not the Chinese (low cost) ones. Some of those, new, are worse than what you take off. Been there, done that.

 

[ChrisWk]

I had this problem I hope I fixed it I just replaced my front rotors looks like hot spots I will take a picture of my rotors let you see this. I have not tested them to tired from replacing rotors , was a easy job with the right tools back soon

 

[ChrisWk]

Here picture of my rotors I changed today

 

[jeepgcoman]

Chris, can you get a closer pix of some of those hot spots? Looks like you have some long ones there. Also, what kind of rotors did you put on? Where were they made? What kind of pad did you use?

 

[ChrisWk]

Chris, can you get a closer pix of some of those hot spots? Looks like you have some long ones there.

Will do heading to dinner, my brake pedal pulsed like crazy lite braking and hard braking.

 

[dascenc]

Thanks for the info everyone. Ill probably wait till it gets real annoying before I tackle it with a complete rotor swap.

 

[dmsfun]

Mine did that too before installing new rotors and pads. I went with Centric solid rotors from Tirerack, not costly and very high quality..Centric is a division of Stoptech.

 

[ChrisWk]

I installed Centric rotors and Wagner Thermo pads, my front pads factory had cracks in them the back did not look that bad. So your front rotors looked like my set? I got about 45k out of the rotors.

 

[jeeper_57]

rotor problem , i've seen it on WJ we machined the rotors and since then no problem

 

[jeepgcoman]

Chris, mine don't look anywhere near as bad as yours appear to be (need those closeups), but I have just a few on each front. When I bought mine it had new front brakes (don't know if new rotors though), and I've got almost 40K on it since then.

 

[ChrisWk]

Here are some close up pictures, also I was going to bleed the brake , I sucked out the resovior and I got alot of sediment I got pics too this is the same fluid from the factory, will this sediment stop up a brake line

 

[jeepgcoman]

Thanks for the pix. Yours were much worse than mine are. You bet that crap can contaminate the whole system, especially the calipers. I think I'd be doing a complete flush and renewal of the fluid. Make sure you get the proper stuff though. What kind of sediment stuff is it? Is it hard or does it dissolve when rubbed between your fingers?

From the FSM:

BRAKE FLUID
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The brake fluid used in this vehicle must conform to DOT 3 specifications and SAE J1703 standards. No other type of brake fluid is recommended or approved for usage in the vehicle brake system. Use only Mopar brake fluid or an equivalent from a tightly sealed container.​

​

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CAUTION: Never use reclaimed brake fluid or fluid from an container which has been left open. An open container of brake fluid will absorb moisture from the air and contaminate the fluid.​

CAUTION: Never use any type of a petroleum-based fluid in the brake hydraulic system. Use of such type fluids will result in seal damage of the vehicle brake hydraulic system causing a failure of the vehicle brake system. Petroleum based fluids would be items such as engine oil, transmission fluid, power steering fluid, etc.​

BRAKE FLUID CONTAMINATION
Indications of fluid contamination are swollen or deteriorated rubber parts. Swollen rubber parts indicate the presence of petroleum in the brake fluid. To test for contamination, put a small amount of drained brake fluid in clear glass jar. If fluid separates into layers, there is mineral oil or other fluid contamination of the brake fluid.
If brake fluid is contaminated, drain and thoroughly flush system. Replace master cylinder, proportioning valve, caliper seals, wheel cylinder seals, Antilock Brakes hydraulic unit and all hydraulic fluid hoses.​

All the above being said, you may be able to "get away with" just the flush and new fluid, depending on what that stuff is. I would probably try that first and see how it goes, especially if it is "soft" material. If it's hard or gritty, for sure do as said above. That'll run some $$$ though. Hope you can save it.​

 

[ChrisWk]

Thanks for the reply it disolves when you rub it, I was going to bleed the brakes the gravity fed way so not to get air in the lines and get all the fluid out put in new fluid I was going to use Valvoline dot3 dot4 synthetic brake fluid.

 

[jeepgcoman]

If it dissolves when you rub it, you'll probably be OK. Let us know how it goes.

 

[dascenc]

So I finally found time to do a runout check one of my rotors and is was 0.007. I'm pretty sure that's past the max tolerance but can anyone verify? The cheap dial indicator from harbor freight was such a pain in the ass to get right that I didn't even bother checking the others. The cost of buying a good quality American made one will cost more than having the rear rotors turned so that's probably what I'll do.

 

[2005JGC]

Runout spec is .002". You need to measure the hub runout too. The hub may have runout that wont be fixed with rotors. Realistically runout can contribute to braking concerns and can lead to a pulsation but runout by itself is NOT an indication that that is where your pulsation is coming from. Rotor parallelism as measured with a micrometer is what causes a pulsation. The pulsation comes from the thickness of the rotor not being even all around so it grabs-slips-grabs-slips... Runout will just cause the caliper to walk back and fourth on the slides but typically wont translate to any noticeable concerns.

When you did the runout you had run lug nuts back on to firmly hold the rotor evenly in place correct?

 

[dascenc]

I replaced the lug nuts during the runout check. Since i'm returning the dial indicator to harbor freight and I dont own a outside micrometer I'm just gonna replace all four rotors with some R1 concepts or stocks, still havent decided. Not gonna bother finding out which ones are bad since I'd have to buy new tools. Thanks for the promp reply.