Thump in front end

[9755]

Car is an 01 Jetta with a manual trans. Long story short, I replaced the trans due to 5th gear shearing off the teeth on the highway and junking 4th gear as well. Trans went in no problem. All clutch parts were swapped over and looked great.
The issue is starting around 40-45 mph, there was a thump in the floor. No steering wheel vibration and the car stayed straight when letting go of the wheel.
I noticed both front springs were broke and the struts were about useless. So I put a set of ecs street coilovers in. Including new mounts and bearings. That made the car ride great again, but the thump is still there.
Also changed the driver inner and outer tie rods. Ball joints look good.
Motor and trans mounts don’t appear to be torn and dogbone seems fine. I’m leaning towards the engine mount being worn. I had the car on stands higher than I probably should. But I wanted extra room for trans positioning. The engine was slanted a lot when I dropped the trans. And trying to move the engine and trans shows no visible movement. Any thoughts

 

[csstevej]

Check your sway bar bushings…..I bet there bad…..

 

[9755]

I will do that tomorrow afternoon and report back

 

[snakeye]

What do you mean by starting at 40-45 mph there was a thump? What exactly do you do that causes it?

 

[Pancake Slap]

I had a similar issue. No issue with ride quality but a random thunk. I checked everything over and it seemed fine, took me forever to realize that if I turned the wheel lock to lock it would separate the ball joint.

 

[9755]

That’s just it. Once I get to around 40 mph, there’s a thump I can feel in the floor. That’s with both normal and I guess more aggressive driving. The car still drives straight and doesn’t wander at all. The thump is there turning also. As long as I’m at or above 40 mph

 

[snakeye]

You need to figure out what driver input causes it. I bet that if you're hearing a thump at over 40mph, soon enough you'll start hearing it below that speed as well.

I would inspect every bushing, and also check the front control arm bolts. Sometimes they come loose, as do the captive nuts that they bolt onto inside the subframe.

 

[9755]

I replaced sway bar end links, as I already had them. Sway bar bushing look good and no slop. Control arm bolts are all tight and the bushings don’t seem to have any play. Now on my way home I went a different way than usual. I noticed the thump went away while going left around a turn. Is that telling me it’s something towards the passenger side?

 

[Pancake Slap]

Could be. This sounds exactly like my ball joint issue. Can you replicate the noise while the car is not moving?

 

[9755]

I haven’t. I got a friend stopping by tonight to look it over. I’m obviously not noticing something. For the price off ball joints, I might just replace them

 

[RexNICO]

Doesn't necessarily align with the speed you mention, but have you checked the LCA bushings? The rear one (per side) could be close to the "thump in the floor" sounds you are reporting.

 

[9755]

I have. They didn’t seem to have any slop. But I will definitely look them over again. Just seems odd to me that this happened right after a trans replacement

 

[BobnOH]

To help narrow it down, does it match engine speed or car rolling speed?

 

[RexNICO]

I have. They didn’t seem to have any slop. But I will definitely look them over again. Just seems odd to me that this happened right after a trans replacement

Trans mount?
Was the trans mount (upper engine mount & lower dogbone) bolts with the recent trans replacement?

 

[9755]

I did not change the bolts this time. Didn’t even cross my mind somehow. It matches rolling speed

 

[9755]

Ok guys, here’s an update. I haven’t had time to look at the car for a week. I took a video of the engine idling and shutting off. It shook pretty bad. I got all 3 mounts, but only had time tonight to change the trans and dogbone. Those seemed to have cured the majority of the thump. The old mounts, especially the dogbone had tons of play in them. There is a slight thump under hard throttle on the driver side. I did change that axle during trans swap. The boot was torn a little. I checked and the bolts were not exactly loose, but not super tight either. They are now tight. Didn’t have time to go for a ride unfortunately. But that’s were I’m at