New 99 Cobra owner with questions

[marcoc]

I just picked up a Rio red Cobra with 73k miles. It has a Flowmaster cat-back. The car is in excellent shape and will be my new weekend toy. I have plans for suspension upgrades, intake, maybe a tune upgrade, rear wheel spacers, and possibly a catted H-pipe. The car moves and drives very strong but It was purchased at a used car dealer here in CT where the car was originally purchased and I have no history as far as what was done. I will be doing basic stuff such as plugs, fuel filter, tranny fluid, oil, and maybe a new drive belt. The car has a rear clung when I engage it into gear like play or something but only when I put it in gear and get on gas if I feather the clutch and engage slowly you cant really tell, what is it? rear end? someone on another forum said there was a TSB years ago about re-torquing rear suspension to stop clunk. Tranny engages fine so I know its coming from the rear of the car. only under load. Also speedo is way off like 20mph off! the car also seems like it realy goes on the highway in 4th gear not like another Cobra I drove. Do I have aftermarket gears? RPM's on highway in 5th gear doing 70mph are over 2500rpm's that seems high. How can I tell if I have 3:73 or something? Any help would be great since I am new to the mustang world.

 

[sdg97232]

I just picked up a Rio red Cobra with 73k miles. It has a Flowmaster cat-back. The car is in excellent shape and will be my new weekend toy. I have plans for suspension upgrades, intake, maybe a tune upgrade, rear wheel spacers, and possibly a catted H-pipe. The car moves and drives very strong but It was purchased at a used car dealer here in CT where the car was originally purchased and I have no history as far as what was done. I will be doing basic stuff such as plugs, fuel filter, tranny fluid, oil, and maybe a new drive belt. The car has a rear clung when I engage it into gear like play or something but only when I put it in gear and get on gas if I feather the clutch and engage slowly you cant really tell, what is it? rear end? someone on another forum said there was a TSB years ago about re-torquing rear suspension to stop clunk. Tranny engages fine so I know its coming from the rear of the car. only under load. Also speedo is way off like 20mph off! the car also seems like it realy goes on the highway in 4th gear not like another Cobra I drove. Do I have aftermarket gears? RPM's on highway in 5th gear doing 70mph are over 2500rpm's that seems high. How can I tell if I have 3:73 or something? Any help would be great since I am new to the mustang world.

The "clunk" is a pretty infamous problem with the I.R.S. you can start by searching "cobra clunk" on this forum lots of good info on the subject here. Most likly you need to replace your differential bushings or maybe your carrier bolts are lose. Most say replacing all the bushing in the I.R.S. will make the clunk go away for the most part.

 

[3B99SVT]

Congrats on the Cobra purchase. If you can put the rear end on jack stands and spin the wheels, you can check the gears. Just make sure you don't lift the rear end by the differential like a SRA. After it's in the air, put a mark on the inside sidewall of the tire (or line up something unique on the tire/wheel that you can see from under the car) and put another mark on the drive shaft. Then, while spinning the rear tire one full revolution, count how many times the driveshaft goes around. If it goes around a little over 4 times, you've got 4.10s, around 3 3/4 turns will be 3.73s, etc. A tuner can usually adjust for different gears and tire sizes.

I'm not sure about the clunk since (knock on wood) I don't have it, but there are a lot that can chime in to help you w/it.

You'll need to get some pics up when you can to let us all see your car. And if you haven't already, read through the stickies at the top of this forum. There's a lot of good info there. Let the modding begin!!

 

[marcoc]

Well did research and sounds like I have "cobra Clunk" hopefully its safe to drive the car this way. ordered the rear IRS Urethane Differential Mounts today so hopefully this helps. Gotta check the driveshaft also.

 

[Brutal Metal]

The car is plenty dafe to drive, just make sure the rear axle bolts are torqued over 200 ft lbs!

 

[Roots-type]

Could be worn differential mounts allowing the nose to raise up when a load is applied and/or excessive back lash in the ring and pinion causing the clunk. While the diff is out for the new urethane mounts, I'd rebuild it and eliminate it as a possibility. Will also be good to have fresh clutches back there.

 

[marcoc]

yea ordered new differential mounts so probably start with those first for cost reasons.

 

[Gallows]

yea ordered new differential mounts so probably start with those first for cost reasons.

Cograts on the new ride:rockon: What brand of bushings did you go with? FTBR is the top dog when it comes to IRS bushings.

 

[pbeechner]

I have had the cobra clunk since I bought the car last year, no driveability or safety problems here.

Sounds to me like you've got 4.10s... my rpms are usually about 2500-2700 cruising on the highway in 5th. Thats good though! 4.10s make the car a hell of a lot more fun!

Congrats on the cobra! :beer:

 

[marcoc]

Going to figure out what gears are on the car this weekend once I install the mounts on the diff and replace the fuel filter. Went with Maximum Motorsports bushings and removal tool for $60. only doing diff mounts for now. Found no play in the pinion, driveshaft, u-joints, and nothing felt loose. hopefully this fixes the clunk.