Constant *thud* Noise Over 80Km/h

[Rekin]

Hello all,

During a trackday training day i went backwards over a ripple strip and heard a massive bang underneath the car. Assumed I smashed the dump pipe on the ripple strip. Turned back around and kept on driving as normal. Everything seemed to be fine till the end of the day.

When driving back i noticed a constant thud noise coming from the car when Im over 80km/h.

It sounds like a flat spot or buckled rim; *thud* *thud* *thud*. From 80kmh+ the sound is quite noticeable.

Clutch in; Sound still there

Clutch in, neutral, clutch out, rolling at speeds above 80km/h sound still present.

This would mean its related to suspension, diff, tyres, rims, tailshaft?

Wheels have been balanced and aligned. Rims have been checked for any buckling and seem fine.

The kicker is that the thud sound comes and goes! If i drive up to the city, the thud noise is quite loud. However, after a couple of hours and driving back the sound is completely gone! Its hard to replicate it to any mechanic as it seems to come and go and Im not sure why

Any help would be greatly appreciated.

Might chuck on a set of stockies for a week and see if i can still hear/feel it. That would eliminate tyres/rims as being the problem.

Thanks all...

[MBS206]

Sounds definitely like a flat spotted tyre.

Drove a VN to Canberra from Sydney with 4 flat spotted tyres, exactly the same thing but it came at 100KM/H, and would come and go.

Could also be felt through steering and floor. They were some massive flat spots though... LOL

[Rekin]

Sounds definitely like a flat spotted tyre.

Drove a VN to Canberra from Sydney with 4 flat spotted tyres, exactly the same thing but it came at 100KM/H, and would come and go.

Could also be felt through steering and floor. They were some massive flat spots though... LOL

both rear tyres have been replaced and sound still there. Unless i flat spotted the fronts, however dont get any steering wheel shake/wobble... Will swap to stockies and see what happens!

cheers

[Moodles2]

Could the castrate inside the cat converter have been dislodged from it's body?

[NickR33]

both rear tyres have been replaced and sound still there. Unless i flat spotted the fronts, however dont get any steering wheel shake/wobble... Will swap to stockies and see what happens!

cheers

my bet is bent rim... I went straight on at turn 1 sandown over the ripple strip... thought I had knocked a wheel weight off or flat spotted a tyre... turned out to be a slightly bent rim as the tyre place couldn't balance it... it only needs to be a few mm out and will thud like that at certain speeds

[Birds]

Swap wheels first, if that doesn't work, get it up on hoist (if you can) and drive it at 80km/h+

If it makes the sound then you know it's drivetrain related. Could be the diff or a loose driveshaft.

[GTRsean]

Sounds definitely like a flat spotted tyre.

Drove a VN to Canberra from Sydney with 4 flat spotted tyres, exactly the same thing but it came at 100KM/H, and would come and go.

Could also be felt through steering and floor. They were some massive flat spots though... LOL

Hmm, maybe from texi?????????!!! Not as smooth as she used to be

[Rekin]

Could the castrate inside the cat converter have been dislodged from it's body?

interesting, although you can feel the thud through the body of the car and its always at a constant rate. Will suss it out.

my bet is bent rim... I went straight on at turn 1 sandown over the ripple strip... thought I had knocked a wheel weight off or flat spotted a tyre... turned out to be a slightly bent rim as the tyre place couldn't balance it... it only needs to be a few mm out and will thud like that at certain speeds

haha yeah i went off backwards on turn 1 at Sandown over the ripple strip

Swap wheels first, if that doesn't work, get it up on hoist (if you can) and drive it at 80km/h+

If it makes the sound then you know it's drivetrain related. Could be the diff or a loose driveshaft.

Will swap wheels over and then drive it on a hoist

Cheers