Any OTHER ideas on source of brake pulsations?

ZJ JIM 96 · Apr 15, 2006

I am about at my wits' end with the pulsating brakes on my ZJ. Just this week, I have replaced the front rotors with brand new Wagners from O'Reilly ($40 each), brand new Morse pads from Autozone ($40 ceramics) and new hardware and boots ($27) from NAPA.

The net result...NOTHING! I still get terrible pulsations when coming to a gentle stop.

My calipers seem to be fine. No leaks, and I don't think they're sticking (how do you test for that?). Is it possible it's the back brakes? Could it be the brake lines? Would bleeding be any help (the pedal is fine, not soft at all, but the fluid has never been bled)?

Any help or ideas would be greatly appreciated.

Thanks,
--Jim

JayH · Apr 15, 2006

Does the Jeep itself shimmy? or just a pulsating feeling in the pedal? If the former, check for bent flanges/shafts/housing in the rear. If the latter, its possible you got bad rotors. Probably some other things as well...

NRV95ZJ · Apr 15, 2006

rear rotors?

ZJ JIM 96 · Apr 15, 2006

JayH said:
Does the Jeep itself shimmy? or just a pulsating feeling in the pedal? If the former, check for bent flanges/shafts/housing in the rear. If the latter, its possible you got bad rotors. Probably some other things as well...

The whole Jeep surges or pulsates. It's not really a shimmy, but also not really in the pedal at all.

I agree it could be that I got bad rotors, but it is exactly the same pulsation that I got with the rotors I just took off, so I find it a little strange that both sets would be identically warped.

As for the shafts and housing in the rear, they look straight, and have never taken a bad beating. What are the flanges you are referring to? I will check them, but am not sure exactly how.

What other things do you think it could be? Think it's worth changing the original rear rotors?

XMech · Apr 16, 2006

You should get the rotors turned instead of just replacing them, unless you've got money to burn! Also, if you weren't feeling the pules in the steering wheel, then it probably is in the rear. Just take the rotors to a shop where they can machine them and see if it helps. Only replace them if their too thin from previous machinings. The shop will tell you.

Edit: Oh yeah. I'm not familiar with your year GC, so maybe it's drum brakes in the rear, but those can warp too, same deal about getting them machined.

Lou C · Apr 16, 2006

At this point, you want to have the rotors mearured for run out to see if it exceeds the specs. I put new Wagner rotors on 50K miles ago that are still good. When you install rotors, make sure the hubs are clean, wire brush off any rust, and put a coating of anti-seize or marine grease to make the next removal easier. What I do is mount them, and check run out with a dial indicator (they are not that expensive and a good tool to have if you do your own brake jobs). I then check the run out with the rotor mounted in different positions on the hub, and wind up with it mounted in the position where it has the least run out. That gives the longest life from the rotor. You definitely could be getting a vib from the rear rotors.

Silkstone · Apr 16, 2006

easiest wat to tell, at 50 mph start appling the brakes if the pedal pulses
and the steering wheel shakes. its the front, if you get a vehicle vibration
or pedal pulse but no steering wheel shake its the rear...lines and air will not cause a pulse.. if its rear disc don't forget about your e-brake shoes
when doing your service if they're cracked replace them, sometimes its less
expensive to replace the rear rotors than to have the pad surface and the drum surface machined on the same rotor..... good luck.

JeepCachr · Apr 17, 2006

Rotors these days are made so thin that your lucky to get one turn out of them. If they are badly scored or warped you won't even get that. Are your bearings good? Is there any play in the ball joints or tie rods?

ZJ JIM 96 · Apr 17, 2006

XMech said:
...Also, if you weren't feeling the pules in the steering wheel, then it probably is in the rear.

Silkstone said:
...if the pedal pulses
and the steering wheel shakes. its the front, if you get a vehicle vibration
or pedal pulse but no steering wheel shake its the rear...

Thanks for clarifying that. In fact, I don't feel them in the steering wheel, it's just that the whole Jeep lunges. I will definitely turn or replace the rear rotors (and maybe change pads while I'm at it) and see if that helps.

If it's not the rear brakes, I'll go ahead and check the other stuff in front (runout on the new rotors, ball joints and tie rod ends--bearings should still be good, as hub was replaced not too long ago).

I appreciate the advice.

--Jim

paris · Apr 17, 2006

The pedal is fine, not soft at all, but the fluid has never been bled ...

Have the brakes power bled. Although you say that the pulsing occurs when going at low speeds, pulsing at higher speeds, or when the brakes are hot, can be caused by moisture in the brake fluid. What happens is that the water in the brake fluid gets hot enough to flash into steam, forcing the piston against the disc. When the the steam re-condenses into water, the pressure on the piston is released, causing you to press harder on the pedal, which causes more heat, which in turn causes the moisture to flash into steam once again, and so on, and so on, making your brakes feel as if they are pulsing.

canadian_driver · Apr 17, 2006

ABS rings?

the're only $15 and when doing brake work will often rust or bend in spots engagin the abs causing the brakes to feel wierd. its an easy fix too.

ZJ JIM 96 · Apr 19, 2006

Sure enough it was the rear rotors. Replaceing them not only got rid of the pulsating on slow stops, but also got rid of some shimmy at 55-60mph that I thought was bumpsteer, and it got rid of a consistent light thud that seemed like a flat-spotted tire while driving. Wow was that ever worth it!

Thanks for everybody's input. I really appreciate the help.

--Jim

thewooddogg · Apr 27, 2006

Glad to hear you got it fixed! It's on my list of
"to-do's" for the ZJ I just bought. I've also heard 2 two things, that could cause problems but I'm not 100% sure they are true or accurate (definitely possible though).

1.) I was told that it's possible for a brand new set of rotors to be warped (not entirely sure I believe what this mechanic was telling me), and that if you buy some cheapos that you should have them turned right away. Once again, I dunno if I believe this...

2.) If you put the tire on incorrectly even the slightest amount it will warp new rotors. Or if you, being silly like I once did, try to tighten the pads back up to the rotor without the tire back on... LOL *sigh*

Turning rox, when it can be done!

Tphoto · May 1, 2006

Your Fix Posted!

ThanKyou! for posting your solution to your problem! Many a thread dies an incomplete topic! Tphoto
96Limited
5.2Liter
Strong Stock!

Any OTHER ideas on source of brake pulsations?

ZJ JIM 96

JayH

NRV95ZJ

ZJ JIM 96

XMech

Lou C

Silkstone

JeepCachr

ZJ JIM 96

paris

canadian_driver

ZJ JIM 96

thewooddogg

Tphoto

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