New car shakedown... a few issues (long)

[Speed Raycer]

I had a very good shakedown of the new car but there were a few issues. We did not build the car and it was our first outing with it, but are going to rebuild it soon.

At first there was some high rpm missfire (dual msds) according to the VDO tach. The shift light would flash when the car got to about 6 and the needle would bounce a little, then it would go away (shift light setting was 7,200. This went away as the day went on and never happened after the 4th or 5th session. Any ideas?

Braking (newer hawk blues & blacks, braided lines, new rotors) was great and never gave me a problem but during braking after the long Nascar straight (Turn 1, 100+ brake to set the car, slight left over a transition dip back into the infield) there would be a "groan" from the rear. This was the only place I recall the sound and it didn't happen when I was hard on the brakes for turn 2 4 seconds later. Any ideas on the groan?

There was a huge backfire upon lifting on turns where I wasn't left foot braking. This was a little unnerving at first. I swapped the trailing wires to the leading spots on the cap later and the backfires became more muffled. Coincidence, or am I burning off more of the fuel before the backfire?

There was a high rpm vibration in 5th at about 6K. It would accelerate out of it, but if I tried to take it easy on the car it would stay until I lifted or braked/downshifted. 4.88s and a 81-85 tranny. Overdrive issue with the 4.88's? Could this be related to the groan fom above?

Anybody ever bend the G-Force panhard bar diagonal brace? Did a heavier wall tube fix it? I'm thinking that I'd rather have it bend than something else break. Any other issues with the G-Force setup?

TIA for any thoughts or ideas!

------------------
Scott
It's not what you build...
it's how you build it

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[miketrier]

The groan may be the black pads. I tried a set last year on the rears and not only did they groan, they grabbed. Went back to blues and everything was fine.

[Allen Brown]

The only thing I can comment on is the high rpm driveshaft vibration in 5th. Assuming your 5th gear is .824...That amounts to a 1.214 times your rpm. So your driveshaft is only spinning at 7281....Hmmm...This seems very low. Is there any vibration at the upper rpm range in 4th? If not, then my thoughts about the driveshaft being the issue is unfounded. (U joints, shaft out of balance, or rear bushingin trans is worn and the yolk moves around slightly)

[dickita15]

are you runnung the tri link. there is a lot of rod end buzz with the tri link and the panhard rod. seems to go away when loaded with hard accel/decel but at part throttle it is real buzzy.
dick

[moto62]

Another possibility for the groan could be a worn axle bearing. Either the bearing itself is bad or the play in the bearing will cause the rotor to contact the caliper bracket, usually when turning.
Ray

[Speed Raycer]

Allen BrownIs there any vibration at the upper rpm range in 4th? If not, then my thoughts about the driveshaft being the issue is unfounded. (U joints, shaft out of balance, or rear bushingin trans is worn and the yolk moves around slightly)

I didn't notice any vibration in 4th which is why I really noticed it in 5th. I will check on the U-joints and the trans mount just to make sure.

dickita15 are you runnung the tri link. there is a lot of rod end buzz with the tri link and the panhard rod. seems to go away when loaded with hard accel/decel but at part throttle it is real buzzy.

Yes, I am running the tri-link. It would only "buzz" for about 500 rpm once I hit 6K in 5th and kept accelerating. If I tried to baby it in 5th the buzz would stay all the way down the straight until braking/downshift.


moto62 Another possibility for the groan could be a worn axle bearing. Either the bearing itself is bad or the play in the bearing will cause the rotor to contact the caliper bracket, usually when turning.
Will definitely check that one out!

Thanks for the possibilities guys!