I have owned this 1991 LX 5.0 for about 3 months. It has this weird thumping in the driver floor board since I purchased it. I have checked and replaced all wheel bearings. Checked motor and tranny mounts. All are good. Checked all of the suspension. It all appears good. I only feel it when I hit light bumps in the road. I feel it in the brake pedal when coming to a stop and I hit bumps in the road. It is starting to bother me. Everything drives great with the car it does not pull and it drives straight. The steering wheel does not shimmy or anything. Let me know if anyone has experienced this or has a guess of what this could be.
Weird Thumping in Driver Floor Board??????
- Thread starter roadrunner19va
- Start date
sunil6784
Member
sunil6784
Member
If there's one thing that Fast and the Furious taught us its that a bad floor board is because of a bad intake manifold. Be careful...this can lead to the floor pan falling off. 
j/k
I vote for exhaust. Give all the exhaust pipes a good shake under there.
j/k
I vote for exhaust. Give all the exhaust pipes a good shake under there.
5ive.oh
Founding Member
That thumping is from the kid you ran over while zooming through a school zone - he's clinging to the sway bar and kicking the floorboard. I'd suggest jacking up the car and luring him out with apologies and a candy bar, and hoping his parents don't sue. 
Seriously, though, it could be a lot of things. I'd lean more towards a loose crossmember bolt or rotted-out crossmember bushing. Might also be a tranny mount gone bad by chance - does the shifter jump up and down on bumps or at WOT? How well does the exhaust clear the two humps of the crossmember? (My UPR X-pipe has given me headaces for over a year now with clearance problems - I had to notch the crossmember to make it clear without bumping.)
Try to pinpoint exactly where in the floor the sound's coming from, then crawl under there and wiggle n' jerk on everything until you find something that replicates the sound or moves enough that it could be suspect.
Seriously, though, it could be a lot of things. I'd lean more towards a loose crossmember bolt or rotted-out crossmember bushing. Might also be a tranny mount gone bad by chance - does the shifter jump up and down on bumps or at WOT? How well does the exhaust clear the two humps of the crossmember? (My UPR X-pipe has given me headaces for over a year now with clearance problems - I had to notch the crossmember to make it clear without bumping.)
Try to pinpoint exactly where in the floor the sound's coming from, then crawl under there and wiggle n' jerk on everything until you find something that replicates the sound or moves enough that it could be suspect.
Glaze
New Member
I have had this same problem before but again it may differ from yours.
I had new ball joints installed on my 91 GT and the installer never lubed them up. I would get this thump every so often but it got progressively worse and I did feel it in the chassis. It normally happened going over light bumps and hard turns. To test push down on each front corner of the car and see if occurs than. Note I did not feel any problems steering car because it was so minimal. Also check for bad control arm bushings (or loose nuts) and loose strut tower nuts. Check K member mounting areas while your at it.
I would also double check clearances of exhaust as stated above.
I had new ball joints installed on my 91 GT and the installer never lubed them up. I would get this thump every so often but it got progressively worse and I did feel it in the chassis. It normally happened going over light bumps and hard turns. To test push down on each front corner of the car and see if occurs than. Note I did not feel any problems steering car because it was so minimal. Also check for bad control arm bushings (or loose nuts) and loose strut tower nuts. Check K member mounting areas while your at it.
I would also double check clearances of exhaust as stated above.
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