Knocking under the car when slowly releasing clutch pedal?

X3FBrian

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Cheers folks, I am trying to help a friend solve an issue.

He has an 03 cobra, stock t56, some bolt ons, IRS car, nothing wild.

The issue is, when you're in first, and at a stop, when you let out of the pedal to get moving there is a loud, almost hammer slapping the bottom of the car, noise.

Changing gears while driving the noise isn't there. Only when you take off, it gets really bad if you're turning. I've had a few Cobra's with the "clunk" and this is much more violent than that.

He put a brand new clutch in the car, RXT twin disc, and a replacement differential out of another cobra.

I recommended him put stock axles in the car to eliminate that scenario.

Any ideas?? My buddy is really bummed out because he recently acquired this car.
 

hotcobra03

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Does this happen in reverse also?

Front of differential bushings will do this. .

Also Front rear subframe bolts.

Ford put a 3/8 bolt in a 9/16 hole. Really. Expecting it to hold
 

Rambro

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I just did FTBR diff mounts and mine is doing this. Need to go under there and make sure everything is torqued properly in the rear, then I guess I’ll try the larger subframe bolts.
 

03cobra#694

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I just did FTBR diff mounts and mine is doing this. Need to go under there and make sure everything is torqued properly in the rear, then I guess I’ll try the larger subframe bolts.
Larger bolts are a must. I did it forever ago.
 

Rambro

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Are there any tips for installing these bolts? Going to throw them in this weekend and see if it makes a difference.
 

03cobra#694

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Where are these bolts? Got a pic of them? I need to check them on my car too

Are there any tips for installing these bolts? Going to throw them in this weekend and see if it makes a difference.
Godstang had done a write up years ago about it the Terminator section. I'll see if I can find it when I get a minute. I do remember using a impact to get them in.
 

03cobra#694

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Here's a few I found. I actually used the 9/16", as they fit a little tighter. Bruce talks about this in the 3rd link, post 16.
 

hotcobra03

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For me to Install ,,

A floor jack.

Than a cable ratchet to pull subframe forward.

Bolt will just fit,may have to actually use a wrench to screw bolt through,,no need to hammer it.

Did mine in driveway with car backed up on a ramp ,
Wheels were always on the ground , just jack under subframe.
 

X3FBrian

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I just did FTBR diff mounts and mine is doing this. Need to go under there and make sure everything is torqued properly in the rear, then I guess I’ll try the larger subframe bolts.
Hey, we fixed my buddies car. It was a bolt that ran from the drivers to the passenger side, into a bracket that bolts to the rear end. There's two bolts that run from the passenger to the drivers side, that bolt the diff and the bracket together, then the other bolt. The other bolt, had a factory nut welded on one side, then the bolt runs in and grabs it. That nut had broken lose which had a lot of play in that bracket. It was impossible to get it to move when the rear was fully assembled but we noticed it when removing the axles. We put an impact on that bolt, and a small pry bar on the nut to hold it, sent that bolt home and it fixed 100% of his issues. I've attached a picture of the bracket I'm talking about, I would verify the two bolts that go into the side are good and tight, and the last bolt, you have to get it from the drivers side and some extensions, put an impact on that and send it home. A second set of eyes on the nut to make sure it isn't spinning would be very helpful. That piece rocks back and forth if it isn't tight and creates that really harsh thump.

Hope this helps.
 

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Rambro

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Hey, we fixed my buddies car. It was a bolt that ran from the drivers to the passenger side, into a bracket that bolts to the rear end. There's two bolts that run from the passenger to the drivers side, that bolt the diff and the bracket together, then the other bolt. The other bolt, had a factory nut welded on one side, then the bolt runs in and grabs it. That nut had broken lose which had a lot of play in that bracket. It was impossible to get it to move when the rear was fully assembled but we noticed it when removing the axles. We put an impact on that bolt, and a small pry bar on the nut to hold it, sent that bolt home and it fixed 100% of his issues. I've attached a picture of the bracket I'm talking about, I would verify the two bolts that go into the side are good and tight, and the last bolt, you have to get it from the drivers side and some extensions, put an impact on that and send it home. A second set of eyes on the nut to make sure it isn't spinning would be very helpful. That piece rocks back and forth if it isn't tight and creates that really harsh thump.

Hope this helps
Yes checking those 3 bolts is on my agenda.
 

Rambro

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I didn’t have these three rear bolts torqued properly, that was the source of my noise.
 

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