Backlash in drivetrain

Grady

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I have a 2004 Cobra with 12k. It seems like there is excessive back lash when letting off the gas peddle. The clunking is annoying. Is it normal? The only thing not original is the shifter which should not have anything to do with it. Any reply would be helpful. Jack
 

MG0h3

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So you can get some from ring and pinion, u joints, or trans wear.

But the most common clunk complaint with our cars is from the front IRS subframe bolts being the wrong diameter.

I believe they came with half and you need 9/16”. Been a while since I did mine so can’t recall for sure the size


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Grady

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So you can get some from ring and pinion, u joints, or trans wear.

But the most common clunk complaint with our cars is from the front IRS subframe bolts being the wrong diameter.

I believe they came with half and you need 9/16”. Been a while since I did mine so can’t recall for sure the size


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Grady

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Thank you for the reply. It just seem excessive. I also have a 04 Mach 1 with very little play. Are you talking about big X shaped sub frame ?
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MG0h3

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No, the IRS subframe.

Bolts into unibody.

This generates more of a clunk than backlash.

Prob time for an inspection under there.


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Grady

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No, we are talking about two different things here. This play in the driveline. The car only has 12k on it. It is definitely up front. Was also thinking drive shaft, but with the miles it does not make a lot of sense.
 

01yellercobra

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It's the Cobra clunk. It's a mix of the bolts mentioned, the diff moving, and gear lash. Do a search as It's been mentioned many times.

I have the FTBR bushing kit with bigger cradle bolts and I don't have the clunk anymore.
 

IllCobra

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Not to hijack your thread, but would an unbalanced driveshaft cause a clunk? I traded my irs to someone with a MM Race bushing kit installed on their irs (simialir to FTBR full busing kit) and it makes a clunk when i am in 5th and 6th when i get on the gas, even super lightly.... and it's for sure NOT coming from trans, i can hear it's somewhere in the driveshaft or diff...but what would cause it to only do it in 5th and 6th? I didn't get the driveshaft balanced (i kept mine, we didn't trade this), or could it be that I didn't tighten the diff's pinion bolt hard enough? Or could it be an alignment issue?
 

Grady

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It's the Cobra clunk. It's a mix of the bolts mentioned, the diff moving, and gear lash. Do a search as It's been mentioned many times.

I have the FTBR bushing kit with bigger cradle bolts and I don't have the clunk anymore.
Thank you guys for the input. I am starting to believe that this is the nature of the beast
 

01yellercobra

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Not to hijack your thread, but would an unbalanced driveshaft cause a clunk? I traded my irs to someone with a MM Race bushing kit installed on their irs (simialir to FTBR full busing kit) and it makes a clunk when i am in 5th and 6th when i get on the gas, even super lightly.... and it's for sure NOT coming from trans, i can hear it's somewhere in the driveshaft or diff...but what would cause it to only do it in 5th and 6th? I didn't get the driveshaft balanced (i kept mine, we didn't trade this), or could it be that I didn't tighten the diff's pinion bolt hard enough? Or could it be an alignment issue?
An unbalanced drive shaft would cause a vibration. Worn u-joints could cause a clunk. You might only hear it in 5th and 6th due to loading. I would get under and check all the bolts. Did you upgrade the front cradle bolts? Don't forget aftermarket bushings will let more sounds through.
 

IllCobra

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An unbalanced drive shaft would cause a vibration. Worn u-joints could cause a clunk. You might only hear it in 5th and 6th due to loading. I would get under and check all the bolts. Did you upgrade the front cradle bolts? Don't forget aftermarket bushings will let more sounds through.
Bolt wise, except for the subframe bolts, all bolts are original. Should I have got new cradle bolts? At first, I didn't think it would be the the driveshaft or u-joints since they were fine before the swap but coincidences like this do happen. Checking under the car would be my best bet
 

01yellercobra

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Bolt wise, except for the subframe bolts, all bolts are original. Should I have got new cradle bolts? At first, I didn't think it would be the the driveshaft or u-joints since they were fine before the swap but coincidences like this do happen. Checking under the car would be my best bet
The front cradle bolts are too small from the factory. That's what was mentioned earlier in the thread. Changing them to 9/16" (I think) gets rid of that slop.
 

03cobra#694

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It's the Cobra clunk. It's a mix of the bolts mentioned, the diff moving, and gear lash. Do a search as It's been mentioned many times.

I have the FTBR bushing kit with bigger cradle bolts and I don't have the clunk anymore.
This, changing the bolts mentioned makes a huge difference.
 

Grady

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Guys I am still yrying to figure out which bolts you are talking about. My car was up on my lift all winter to continue to detail the under carriage. How many bolts are you talking about and what do they connect. I just can’t picture in my mind these bolts. I am at work. Jack
 

JaCobro

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Guys I am still yrying to figure out which bolts you are talking about. My car was up on my lift all winter to continue to detail the under carriage. How many bolts are you talking about and what do they connect. I just can’t picture in my mind these bolts. I am at work. Jack
There is 4 bolts that mount rear subframe to chassis. 2 before axle and 2 after the axle. You want to upgrade the front bolts.
 

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