Thump, when releasing brake (1 Viewer)

[Super77]

Need a little ‘Mud wisdom on tracing and diagnosing:

When I release the brakes after a full stop (like a stop sign), I feel a soft “thump,” which may be coming from the rear of the vehicle. It’s more a feeling in the brake pedal, as reaches it reaches the point where I take my foot off, than an audible noise. It happens before I hit the gas, but as the car starts moving on its own in D. It’s fairly consistent, but not 100%, and I cannot replicate it by lightly pumping the brakes.

I’m taking a look at the brakes and the driveline. My rear driveshaft has about 1/4” of rotational play, which I figure is normal backlash in the differential and transfer case? There’s no movement in the U joints, which look solid. Haven’t yet looked at the brakes.

What should I be looking at to diagnose this?

 

[Coin]

Front axles
Hub flanges
And all the rear suspension bushings

 

[3_puppies]

in addition to above
front diff bushings also

 

[Super77]

in addition to above
front diff bushings also

To rule out the front bushing, could I remove the front driveshaft and see if the noise goes away? Or would that damage the FT4WD system?

I believe this is the more failure prone one, yes? Alongside the rearward end of the front differential shaft, offset to the passenger side?

 

[pvhobo]

Check the gas tank and brackets.
I read a post a while back about a guy with the same issue.
The post said something about the brackets being lose and when the gas rushes forward when slowing or stopping the tank shifted, then settled back once stopped.
Good luck with this.

 

[rexington14]

Check the rear brakes and specifically inspect the rotors for damage

 

[Coin]

So, be sure to check everything under the truck

 

[Todrn55]

Lots of option…I got this too. Thinking sticky caliper..,but I have plans for new from CV/front axles. Also waiting on the two front diff supports. Lots of old bushings that play into this from 20+ years ago. Too many dancing in concert parts to tell. Go with the usual suspects, the pray it goes away.

 

[SteveH]

Can believe no one has suggested lubricating the driveshaft splines, on both front and rear shafts. They can stick and then slip upon stopping and starting, causing a faint thump that you can feel.

My GX 470 was recalled for this and has a new rear driveshaft (and still does it), and my LX does it, but a lot less.

 

[Super77]

Can believe no one has suggested lubricating the driveshaft splines, on both front and rear shafts. They can stick and then slip upon stopping and starting, causing a faint thump that you can feel.

My GX 470 was recalled for this and has a new rear driveshaft (and still does it), and my LX does it, but a lot less.

Yeah, I don’t know how I missed this thread, but it sounds a lot like what I’m experiencing.

To my knowledge, the driveshafts on my truck have never been greased. I don’t see it anywhere on the service paperwork, so unless it’s just an invisible and free part of dealer service (yeah, right), I’ve still got the original 1999 factory fill in there. The PO was not the type to even know to ask.

When I grab the rear driveshaft and wiggle it, I can feel play in it. Not rotational play, like backlash in the diff and transfer case, but more like an awareness that the driveshaft is made of two pieces. I recall that when I did this exact service in my 62, the fresh packed grease made the driveshaft feel solid.

Seems like a good place to start, for the cost of a couple tubes of grease.

 

[excessive]

grease your driveshaft, including the slip yokes

 

[2001LC]

Spare tire!

 

[Exiled]

Since we've named every possible thing under the sun, I will reinforce one of the earlier suggestions since this happened on my '99 recently. Grease the driveshafts and u-joints, what you are describing is the exact same thing that I was experiencing, right after coming to a complete stop and with the brake pedal still all the way down, a sizable "thump" that I felt through the pedal but could also audibly hear. I need new front diff bushings (still on the original ones) but greasing the rear driveshaft solved the issue (I greased both DS and all u-joints while I was down there).

 

[dbfw]

Another vote for greasing the driveshafts. My 99 does this as well when it's been too long since I last greased them, it's also a bit temperature dependent but this is always my reminder that they're ready to be greased again.

 

[Super77]

Spare tire!

I recently dropped, aired up, and re-snugged the spare. Incidentally, it’s the original spare from 1999 . Never used. Still has the little “whiskers” in the rubber. Yes, it will be replaced as soon as I figure which tires I want.

 

[Mike NXP]

Are you on stock rear coils? I have heavy coils in the rear and sometimes I feel like when my vehicle isn't loaded down and I come to a stop like the situation you described I sorta hear something back there..... Any chance you could try and recreate the noise by rocking / bouncing the rear end a bit with the help of a fat friend