Hey fellas,

I changed my front brakes this past weekend, and since then, I notice a slight thumping noise when I apply the brakes. I can also feel the thump coming up through the floorboard. The harder I apply the brakes, the more I can hear/feel the thump. The thump is in rhythm with the wheel rpm as the truck is rolling. I know it wasn't there before I replaced the pads, so I'm thinking it has to do with something with the brakes. Prior to replacement, I was getting brake pulsating, I checked the rotors, and they were warped about .010", so I turned them, and they are running true and parallel within .0005". Pulsating is gone. I used OEM pads. When I removed the calipers, I removed the brake line, so I could drain out the burnt fluid from the caliper, rather then flushing it back into the system when I collapsed the caliper piston, and bled the brakes with nearly a full 30oz bottle of fresh brake fluid. The calipers were in good shape, nothing was seized, slide pins moved freely. Everything came apart and went back together easily. I plan on pulling off the wheels again to do some more inspecting, to see if there is anything obvious that is causing the thump. But in the meantime, I was hoping someone could shed some light. I did a search on the issue, and found that it seems to be a rather common problem, but I didn't find any solid answers on the causes.

Thanks for any help.

 

It is a common problem but the cause is often different no common cause it can be anything or a combination of things.

Your just going to have to look again more carefully.

 

Did you use the new rattle clips that come with the pads?

 

Yes, new rattle clips, re-greased slide pins.

I've been doing some research on this, and some have mentioned that it could be caused by the ABS. I'm just not sure why the noise would sync up with the wheel rotation, almost like something is hitting every time the wheel comes around, but only when braking. The sound is not audible during acceleration or cruising.

 

Are your ball joints good??

 

I just pulled off both front wheels and calipers again, just to see if anything looked out of the ordinary. Rotors spun freely, calipers are mounted good, and pads are able to move side to side easily. I bled both fronts one more time too.

Ball joints feel solid, no play in the wheel. Stabilizer bar and bushings look and feel pretty good.

When I feel the thumping, it sounds like it's coming from the drivers side wheel, but feels like it coming from right underneath the drivers seat, almost like the drive shaft from the transfer case to the front differential.
I have manual locking hubs on my truck, so while I had the front end jacked up, I locked the hubs and rotated the wheels to see if I could hear anything, but nothing.
I'm a little stumped at this point???

 

0.0005" parallelism variation is not an insignificant amount. Considering you already had pulsation earlier you most likely also would have developed hard spots within the rotor. Since the turning bits tend to not cut as deep into these areas compared to the softer regions, that would account for the 0.0005" thicker areas. These harder areas also do not develop as high of friction as the rest of the rotor.

You need to replace one or both rotors.

If you meant 0.0005" runout then that is fine.

 

Just wanted to give an update on this issue I was having.

So I feel confident that I found the cause of the "thumping" noise I was hearing. What it boiled down to was the machined surface finish on the contact surfaces of the rotor. When I initially machined them, I used too fast of feedrate on the cutting tool, which essentially left fine grooves on the rotor similar to what you see on a vinyl record. The groove were course enough that when I applied the brake, the pad wanted to follow the grooves, similar to what a stylus would do on a record players. So when the caliper/pad ran out of travel room, it skipped out or the groove and started all over again.
So I pulled off the rotors and resurfaced them with a finer finish, then added a non directional finish to them with a scotchbrite wheel while the rotor was still on the lathe. The finish was much smoother than the previous one, and now the noise has stopped and everything sounds, feels, and works like new.

 

Awesome thanks for the update always helpful we problem is resolve in its thread.

Sent from my SPH-L900 using IB AutoGroup