Hi all, new to the hroup and 1st post.
so heres my issue. I ahave a 2002 grand cherokee laredo. I am having pulsating brakes when braking above 45mph. I cannot figure this one out. I rotated tires, no fix. Replaced both frount rotors and brakes. Replaced both upper and lower control arms and bushings. Replaced wheel hubs both sides. None of this helped. Only thing i can think of left to do is a front end alignment.
has anyone experienced this before? I am stumped, and out of ideas.

Ken

 

Also, forgot to mention, this shake is on drivers front, and I replaced that caliper in the hopes that it was sticking. No joy.
ken

 

Here's a list of stuff you can check that I found here.

 

Sounds like a warped rotor (from heat). Could be from pins hanging up, or rust on the sliding surfaces not allowing the brake pads or calipers from backing off a little like they should. Take the calipers off and run each caliper's piston in/out (each brake separately) at least 3x each. Squeeze the piston in with a C-clamp, then back the clamp off ..in place, and push the piston back out with brake pressure. Do both sides. The rubber pin bushings often get sticky and don't slide very well. Drizzle a couple drops of oil on it and move in/out with the hex/allen wrench till it's lubed up.

This sounds hard to believe, but if you had new rotors put on, often rotors come pre-warped. And most shops just slap on new rotors and send the car out the door. Maybe it was a shaving under the lathe during production, or an out-of-spec machine, hard to say. But it happens a lot. My buddies at NAPA once told me they had a whole period when they were getting rotors back left and right. Doesn't really matter weather they are import or not, or how much you spend in my experience.

To really get smooth brakes what a mechanic needs to do (and most don't) is to verify new rotors with a dial indicator. Often the run-out will be, say 5-6 thousands and that's too much. Then, usually they can rotate the rotor on the hub, remeasure, maybe rotate again ...sometimes even swap the rotor from the other side (the other wheel) ...if that's what it takes until they get the run-out to be essentially as close to zero as possible. And given enough diligence you CAN usually get the run-out down to 0, even if it means getting a different rotor. On our old Jeep Grand Cherokee Laredo I spent a lot of time and all those wheels were at 0. It's the smoothest brakes I ever had!!

The other problem could be the hub itself. I have that issue on my Cherokee. The mounting surface is slightly not 'true'. Then a guy needs to perhaps put a paper shim under half of it.

If you want to get super-smooth brakes, pick up a dial indicator and a magnetic base from like Harbor Freight, and six 3/4" nuts from the hardware store (to hold down the rotor). Before starting the test, you need to make sure the hub mating surface is 100% free of debris or anything that might throw off your reading (even a SINGLE grain of sand or rust flake). That usually means taking a file and some sandpaper and taking time to clean off any rust or scale down to the machining marks. Put the large nuts (like 3/4") over the studs and snugly tighten with the lug nuts. They don't have to be super tight, just decent snug. Then set up your dial indicator on a non-moving item (could be the steering knuckle, or bucket with a heavy piece of steel on it) and perform the test.

Rotate the rotor one stud at a time if it's out of spec (usually .003"). If you can't get it within that range, try another rotor. If that doesn't work, try a 3rd rotor from a different parts store. I've actually HAD multiple rotors which were no good! I stopped buying NAPA rotors a long time ago. Just too many problems. Price doesn't seem to be a determining factor. The Oreiley rotors I've gotten recently were right on the nuts. Once you've finished, apply anti-seize to the hub mating surfaces. Make sure no flakes of dirt or rust fall into it while putting the rotor on.

If you do the rear axle rotors, bear in mind that you need to HOLD the axle inward ...with like a long screwdriver (at the axle center) to your chest as you rotate the axle. Whatever it takes to keep the axle from any in/out movement.

Rarely rotors can be out of parallel too. If the outside measures good but you still have pulsating, measure the inside surface.

So, if you go about the process above, it'll take a lot more time, but you can achieve a brake system SO smooth you'll want to ride them all the time! (but don't). Nothing beats great brakes. But don't expect a shop to take that amount of time..

 

The wheel stud thread is 1/2-20 UNF. A 3/4 wrench fits them. Use washers under the nuts to make sure there's enough thread to clamp the rotor securely. When Jeep came out with the dual piston calipers on the WJ model Grand Cherokee, they had lots of problems with pulsating brakes. I read a Service Bulletin about what to do to cure this. One of the main points was to insure that the rotors ran out less that .001". This may require turning brand new rotors or replacing the hub units. These were brand new jeeps under warranty!

 

Well i checked runout on the hubs. They are dead on, at least the drivers side where my main problem is. I checked runout on on the rotor, it was out about .005 thousandth. I replaced it as ut was in warranty. New one was out about .0015 thousands. I replaced it. No luck problem still persists. I didnt check the passenger side, as you can feel it in the drivers side.
at this point i am will ling to upgrade the calipers to acubono. I presently have the teevs. I am trying to source parts at a reasonable price. It sucks being this close to christmas.

 

YES! Change to Akebono at your earliest convenience. I didn't realize we were talking about a GRAND Cherokee or I would have suggested that before. BIG difference! Stay away from Powerstop! I had nothing but heartaches with them. Also drilled and slotted rotors. Not worth the price. Mine turned blue around the holes and made grooves in the pads. Also stay with semi-metallic pads. Be aware the rear calipers stay Teves because they never had problems with single piston Teves. rockauto.com has the Akebono at a reasonable price and they'll accept the Teves as cores, although at a reduced value. You'll need caliper brackets as well, but you'll get them if you buy fully loaded calipers. They are different from the Teves. When you buy new pads, make sure you get them for Akebono because unless you specify, most counter guys will give you Teves because of your production year in their books. Use the pad clips also because you'll have problems with dragging pads if you don't. BTW, the Powerstop were supposed to be powder-coated red. They were just painted and that burnt off in a week!

PLEASE change you signature block to say Grand Cherokee and post in that section in the future. Keep on Jeepin'