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Discussion Starter #1
I have a 99 gt with a t-56 tranny and 31 spline upgrade with carbon fiber clutches and 3:73 gears. It also has a vortec v-2 at 13.5 lbs non intercooled. I noticed the other day a clunking, sounds like driveshaft related. Jacked it up to find a new greaseable joint at the rear but the front appears stock. I can feel no play in the shaft or joints, could it be the front joint being stock? Have checked the tranny mounts and bbk upper and lower control arms already. Any help would be appreciated. Brian
 

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Have you checked pinion angle? If I'm not mistaken the pinion going past 0 on acceleration/deceleration can cause a clunk? I'm definitely not an expert on the subject but I think I recall hearing that symptom. Maybe someone else has some input on that.
 

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That and make sure the axle tubes aren't rotating in the center section. Had a girl that used to work for me and her mustang was doing the same thing..found the left tube loose in the center section. We moved it to where it was supposed to be and welded it(both sides) and it fixed it.
 

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I will check both of those today, the axle tube makes more sense to me, its a new noise and pinion angle hasnt been touched. Thanks guys and I will keep you posted.
 

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So I checked to see if the tubes moved and I see no evidence of it, rear is jacked up so hard to check the pinion angle. Putting a front driveshaft joint in today to see if it fixes it. Any other thoughts?
 

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The way I found hers was having it on a drive on rack and with it in gear rocked it forward and backwards and saw the tube moving.
 

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it could be many reason. Start with the cheapest and change the ujoint. Check your upper and lower control arms. I would also give a check on the torque boxes as well. I was getting a clunk when I ripped a torque box out
 

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Did the u-joint and its better but not fixed. I checked the upper and lowers in the rear and there tight. What do the torque boxes do? Can they be removed? I assume these are the shock looking things parralel with the ground bebind the tires?
 

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Did the u-joint and its better but not fixed. I checked the upper and lowers in the rear and there tight. What do the torque boxes do? Can they be removed? I assume these are the shock looking things parralel with the ground bebind the tires?
LOL - No, not those shock looking things...

The torque boxes are somewhat slang for where the rear suspension attachment points tie into the body.

If you have a healthy engine and have been using the power regularly then what happens is the bolt attachment holes get elongated. Manual transmission cars are harder on these than a comparable auto application.

The best way to check this is not easy. You have to remove suspension components to "unload" the attachment points. Then you can wiggle the control arms or simple unbolt them and look. In severe cases you can crack then tear the attachment points right off the chassis.

I beefed up mine a long time ago. Got lazy and reused the stock bolts. Broke the bolt on the lower left control arm one night at the track. Fortunately, it was right out of the gate and I only hurt a tire when the body "settled" on it. I immediately went to a better/larger diameter bolt and haven't had any problems since.
 

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Discussion Starter #10 (Edited)
Ok, I will have a look at them next.. Will 411 hp at the wheels do this? It has never hooked hard, I had to the track once with micket thompson et streets at 32 lbs....spinning needles to say. Thank you. Brian
 

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A couple of 10 thousand miles of aggressive driving with a healthy engine can be enough. A lot depends on what type of suspension components you have. Rubber bushing will absorb a lot, poly-urethane will soften it slightly and solid joints will work it hard.

Mine was originally a 4 cyl car with rubber bushings. It didn't take me very long with at around 500hp level to kill that bolt. That was a long time ago before the car was really running hard. And yes, the original attachment hole was elongated when I did the repair.
 
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