PDA

View Full Version : "Thump" noise


pr cobra
11-18-2004, 10:13 PM
When I shift the car into first gear, there is a "thump" noise that comes from the rear diff. Also, it will sound when shifting gears without any hard racing. Is this normal? I just bought the car recently and the previous owner said that was normal.

Any ideas or thoughts?

Thanks:eek:

Butcher
11-18-2004, 10:17 PM
When I shift the car into first gear, there is a "thump" noise that comes from the rear diff. Also, it will sound when shifting gears without any hard racing. Is this normal? I just bought the car recently and the previous owner said that was normal.

Any ideas or thoughts?

Thanks:eek:
This is a normal thing, for me it was anyway until I changed all the bushings to urethane. Seemed like it was more of a thunk than a thump to me, but my hearing has been thoroughly abused through the years. I'm refering to an IRS though too. Changing the bushings will resolve this noise, although imo its not a big worry.

Jimmie

pr cobra
11-19-2004, 06:27 AM
Thanks! Now I know what will be my next mod...:D

ausie
12-14-2004, 06:59 AM
That almost sounds like the differential damper is hitting something (like the exhaust) or is loose. I never heard any thumps but I did hear clunks when making a very tight slow turn ( which came from the differential itself since both wheels are trying to turn at the same speed and not enough torque to get it to slip, you get the same thing with 4wd vehicles when the 4wd is engaged but it usually comes from the front end). Sometimes noise may be attributed to bad u-joints. If you feel vibration while driving too it is definately a u-joint or out of balance drive shaft. As for hearing the noise when shifting that would concern me a bit. The differential housing may not be secure in it's nest. Then again not all Cobras have the same issues or generate the same noises. I hope I am wrong in all accounts and the noise is just the typical clunk we all have heard from time to time. If your shifting is at low speed and you are using higher gears than needed, that is normal since it is windage that is spooling up and the drive line is actually rotating faster than the transmission. If you apply throttle you will get a thump especially when in 4th or 5th gear at 35 mph. If that is what you are experiencing, that is normal.

JenRem
12-14-2004, 08:20 AM
I heard the same thing in my car and posted to the board asking about it...I thought I was going crazy because it would not do it for my fiancee for awhile...he was like, "You just can't drive!" :(

At least I know it's not me now.

Lumpydogs
12-16-2004, 04:21 PM
Hey All,

Any chance it's the IRS bushings. I know that some of the Cobras
were built with the wrong size bolt, too small. I bought a Urethane bushings kit and they came with the correct size bolts. Unfortunately I have not installed them yet. That may help explain why the bushing swap reduces or eliminates the "Thump". Just my thought.

Butcher
12-17-2004, 02:02 AM
That almost sounds like the differential damper is hitting something (like the exhaust) or is loose. I never heard any thumps but I did hear clunks when making a very tight slow turn ( which came from the differential itself since both wheels are trying to turn at the same speed and not enough torque to get it to slip, you get the same thing with 4wd vehicles when the 4wd is engaged but it usually comes from the front end). Sometimes noise may be attributed to bad u-joints. If you feel vibration while driving too it is definately a u-joint or out of balance drive shaft. As for hearing the noise when shifting that would concern me a bit. The differential housing may not be secure in it's nest. Then again not all Cobras have the same issues or generate the same noises. I hope I am wrong in all accounts and the noise is just the typical clunk we all have heard from time to time. If your shifting is at low speed and you are using higher gears than needed, that is normal since it is windage that is spooling up and the drive line is actually rotating faster than the transmission. If you apply throttle you will get a thump especially when in 4th or 5th gear at 35 mph. If that is what you are experiencing, that is normal.That almost sounds like the differential damper is hitting something (like the exhaust) or is loose. I never heard any thumps but I did hear clunks when making a very tight slow turn ( which came from the differential itself since both wheels are trying to turn at the same speed and not enough torque to get it to slip, you get the same thing with 4wd vehicles when the 4wd is engaged but it usually comes from the front end).Hello. That sums it up pretty much in a nutshell. Your going to eat the aftermarket urethane bushings up totally, depending on your application. :) I put in a Moser Engineering solid axle, 33 spline axles exactly; Moser Engineering spool, 4.10 gears, put Moser 9" ends on it, did away with the 8.8" C-clips. UPR solid axle parts, drag launch, the whole enchilada. actually a 5 link. If your going to drag race a Cobra with an IRS, seriously; consider a solid axle and put real horsepower to the Wheels. Otherwise, the open track is where you need to be. These 4.6 Mods will rape the rear diff with violent wheelstarts, without cracking a valvecover. These NMRA rules are, well, for lack of better terms, lax ;)

Well, hell...gotta love these power-adders. Imagine them with a 150 shot of nitrous. Hell, they can handle a 250 shot easy...solid forged from the factory. Imagine a 351 10 hole motor...christ.

Jimmie

Arch Angel
12-31-2004, 03:49 PM
It's called driveline slack. I fixed mine permanently with a solid axle swap. :D

smashedheadcat
01-01-2005, 03:34 PM
It's called driveline slack. I fixed mine permanently with a solid axle swap. :D

Agreed!!! What your're referring to is know to the terminator guys as "the clunk". What this is, is exactly what arch angel said..... driveline slack or slop. I believe it's actually pinion gear meshing with the ring gear that causes this noise. As far as pushing the shifter into first gear, more than likely the clutch needs adjusted. You can do this by pumping the clutch 4 or 5 times with the shifter in neutral. Or, try taking out the floor mat, or sliding it back. Make sure the clutch pedal is down to the floor when pushing the shifter into first. When you shift to first, it takes a little extra effort to get into gear. The thump is you hear is just slop in the driveline. Basically, your cluch isn't completely disengaging. This can be caused by a worn clutch, floor mat preventing the clutch pedal from full travel, or clutch cable out of adjustment. Which can be remedied by pumping the pedal quickly, or lifting the pedal up towards you, then pumping the clutch. If this doesn't help, and you've got some hard earned miles on the clutch, it may be time to switch it out. A firewall adjuster can also fix the problem. Hope this helps.

Josh

Lumpydogs
01-01-2005, 04:36 PM
Regarding the clutch pedal. Put your shoe underneath the pedal and
lift it upwards with the top of your foot. If there is too much wear the
clutch with self adjust like a ratchet (assuming you still have adjustment left).
This will allow the clutch pedal to disengage the clutch in a higher position
and thus creating more disengagement when the clutch pedal is all the way
to the floor.

Check it out, it's in your Ford Manual. :thumbsup: