Rythmic thump when braking to a stop | Ford Explorer Forums - Serious Explorations

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Rythmic thump when braking to a stop

mark2016

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January 2, 2016
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City, State
Glen Burnie, MD
Year, Model & Trim Level
2001 Explorer XLT 4.0SOHC
Just started on mine, when on the brakes slowing to a forward stop a get a rhythmic thumping that slows as vehicle speed slows. Sound is coming from the rear center differential or driveshaft area and is not felt through steering or the brake pedal, only heard. It doesn't do anything unusual when accelerating or when braking in reverse. Any suggestions? Brakes are new all around (rear pads and rotors within a week, fronts within 6 months), shocks new all around within 6 months, all ball joints new within the year, and tires are one year old with only 8K miles. Any suggestions?
 



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bad u-joint? .. check diff gear oil?
 






bad u-joint? .. check diff gear oil?

I was thinking U-Joint, would it only be symptomatic in the one way though and not all the time in motion? Gear oil was done last about 7 months ago, around 4K miles, I use Royal Purple.
 






Well, could crawl under and wiggle the driveshaft back and forth to look for play in the u joints.

The rear diff usually takes synthetic gear oil and friction modifier if you have limited slip.
 






Well, could crawl under and wiggle the driveshaft back and forth to look for play in the u joints. The rear diff usually takes synthetic gear oil and friction modifier if you have limited slip.
Used RP which is synthetic and added the friction modifier since mine is 4.10LSD. How much play should there be?
 












Shouldn't be any play in the u joints, you'll end up with vibration, squeaking and or clunking with a bad u joint.

Ah yes, the slip yolk where the driveshaft meets the transmission, it should be under the rubber boot there and needs to be able to slip back and forth on the splined shaft.. should check that also and make sure it's greased, good call.

So, I was thinking for a second and thought if you were going to lube your slip joint without taking the driveshaft off, you'd jack the rear of the truck up so the rear suspension is fully extended so the driveshaft is pulled back as far as it goes.
 






Add one note here, this just started after replacing the rear brakes last weekend. Could be coincidence I suppose. I had the truck jacked under the rear diff itself and my jackstands under the rear end near the leaf springs on each side with both wheels in the air. Definitely not the brakes though as I pulled the wheels this weekend again and triple checked everything there.
 






Last note, the slip yoke grease has been on my to do list, it has the original boot with original clips still in place. Previous owner was also first owner and did have all maintenance done by dealership with records but none show where it was ever lubed. It'll be the first thing I try as it is at 144K miles.
 






Only thing I can think of is the transfer case getting ready to go, although the sound you describe doesn't exactly match up to what I've heard before. So just throwing that in as a remote possibility.
 






The more and more I think on this it has to be related to braking. Last Saturday I replaced the original rear rotors and pads which were in bad condition. No symptoms at all at that point. During this I discovered the parking brake shoes were frozen and on one side actually the pads had separated, so I pulled both sides of parking brake with the intention to replace (haven't yet, this isn't a DD and the brake hadn't been used in my year and a half with it). I only replaced one side of caliper bolts and left the slides alone as they moved ok (I should've greased at least thinking on it now). One caliper I noticed had a torn piston boot but again I was in a rush and didn't replace it. More thoughts?
 






Driving again just now the brakes feel great, just the thump persists when slowing and becomes audible below about 20mph with foot on the brake. When braking in reverse the same way there is no noise. Caliper? Bad rotors (Duralast Gold)? Bad Pads (Duralast gold)?
 






Going to check my diff fluid also, noticed a slight bit of seepage around the pinion seal.
 






I'm thinking you might could rule out bad u-joints. When my front went bad I'd get a nasty vibration at 30+ mph and always acceleration. Decelerating/gas off was smooth. The only audible and feelable clunk I'd get was when shifting into Drive from Park. Loose u-joints will do that. Didn't really have any issues with braking. Replaced them both and no issues at all. Sounds like your problems might be brake related.
 






I'm thinking you might could rule out bad u-joints. When my front went bad I'd get a nasty vibration at 30+ mph and always acceleration. Decelerating/gas off was smooth. The only audible and feelable clunk I'd get was when shifting into Drive from Park. Loose u-joints will do that. Didn't really have any issues with braking. Replaced them both and no issues at all. Sounds like your problems might be brake related.

Tried also just letting speed drop without throttle or brakes and it doesn't do it then either. Only while pressing the brake.
 






Update: After isolating the noise to the rear passenger wheel I replaced the caliper on that brake, it was sticking as the piston retracted and advanced. Problem solved for $40 replacement.
 






Good to hear. And better that it was only $40.
 






Good to hear. And better that it was only $40.

Best I can figure the boot around the piston was torn (original 15yo caliper, rotor, and pads on the rear) and the piston was sitting extended to the limit of its travel. The pads were down to less than a millimeter and the metal backing was showing through. When I replaced them I forced the piston back in to fully retracted position and had a ridge where the sides had rusted. When braking with new pads and rotors it was catching on the rusted ridges, thus the thump rythmically with reducing wheel rotations when braking. Glad it was simple.
 






Update Again:

Even with both calipers replaced noise returned. Ultimately I replaced the Duralast Gold Rotors and pads that were brand new under warranty with the standard Duralast Rotors and new pads and voila. Problem solved, could have been a warped rotor brand new out of the box or bad pads.
 



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Chinese rotors and drums are crap. I had such a problem on my Taurus I returned five drums, some I opened at the parts house and they had so many weights on them I refused to purchase them. More specifically the problem was lateral run out of half an inch at the tire sidewall! I finally ponied up for a Motorcraft and alas it was Chinese as well! Geez!
 






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