Thud when starting off from a stop

[Bdc101]

I have noticed this the past year or two, whenever I come to a stop and then go again, I hear a thud noise and the car jerks a little bit. It is not a metallic sound like I found when searching. It is definitely a damped sort of thud, accompanied by a slight jerk. It seems like it is worse when I am giving it more throttle in first. Once the car thuds, it doesn't do it again until I come to a stop, or if it does, at least, I don't notice it.

Note: I have about 110k miles on my X, and I believe the clutch is original (it is a manual transmission car). Here are some things I was thinking it might be:

Rear subframe bushings
Giubo
Transfer case chain?
Suspension links?

Anybody have any insight to help me narrow it down?

[andrewwynn]

Mine does the same and I had thought it was the subframe bushings but prob just as likely the rear diff bushings.

Get a look while somebody is in the car and with the brakes on change between forward and reverse a few times and see where the drivetrain slop is.

It's normal to have some backlash so you'll see the drive shaft turn a bit before ir binds and the thud could simply be the result of the backlash winding out and coming to an abrupt end.

You may notice that the thud is quite metallic "tink" when under the car vs. behind the wheel.

(I noticed a very metallic sound when shifting between fwd rev when I had my gas tank access panel off.

I have learned to ease on the throttle until the drivetrain loads up before hitting the gas to avoid the big thud.

[crystalworks]

I get this only when the X is cold. Happens when changing from forward motion to backwards (while applying brake to come to stop), or vice versa. I was leaning towards diff and/or subframe bushings. Have 126k on the vehicle. Will report what I find if I ever get time to investigate.

[andrewwynn]

I want to set up my inspection camera to watch the back suspension when I change direction and finally determine what is causing the "thunk". I already have new subframe bushings and the tool but it moves with less force than I would expect from SFB so I'm thinking the diff mounts or just the backlash in the drive train. I can't hear inside the car but when the fuel trap doors were off wow was the slack in the drive train obvious. ; I've heard it many many times on virtually every rwd car over worked on. Any time change transmission direction with the brakes on the drive train has to wind up and it slaps at the end makes a pretty metallic "tink".

It's possibly that sound is just getting muffled into thud or the "wind up" has enough momentum behind it that it shakes something like the differential in it's mounts. I'm dying to find out the answer.

[crystalworks]

Originally Posted by andrewwynn

It's possibly that sound is just getting muffled into thud or the "wind up" has enough momentum behind it that it shakes something like the differential in it's mounts. I'm dying to find out the answer.

Going to set up a GoPro under the truck and check it out. Maybe I'll make some time for it this weekend. It's a very noticeable thud. I can hear it with all panels in place. Not a "tink" or "clink" type of tinny sound in my case. Will follow up.

[Bdc101]

My manual transmission car won't apply the same pressure to the drivetrain when switching between fwd and rev though -- but I will try to dink around with it in a parking lot and see if I can consistently replicate the problem.



Actually I could put the car in the air on my new QuickJack and actually have my wife put it in gear while I was under the car. Hmm

[nick325xit 5spd]

FWIW, if you're really chasing your tail on finding a noise, a set of chassis ears can help a lot. They are cheaper than firing the parts cannon.

Of course, given the age of the E53, it often makes sense to just fire the parts cannon anyway.

[andrewwynn]

Originally Posted by Bdc101

My manual transmission car won't apply the same pressure to the drivetrain when switching between fwd and rev though -- but I will try to dink around with it in a parking lot and see if I can consistently replicate the problem.



Actually I could put the car in the air on my new QuickJack and actually have my wife put it in gear while I was under the car. Hmm

You can use parking brake to load the drive train fwd rev. Definitely best bet to do the wife option.

[1100russ]

Originally Posted by nick325xit 5spd

FWIW, if you're really chasing your tail on finding a noise, a set of chassis ears can help a lot. They are cheaper than firing the parts cannon.

Of course, given the age of the E53, it often makes sense to just fire the parts cannon anyway.

Fire the parts cannon. Lol. Never heard that one.

[andrewwynn]

Originally Posted by 1100russ

Fire the parts cannon. Lol. Never heard that one.

Sometimes "shotgun". I first heard it on XO