Vibration - pinion angle? Need advice.

[Jcharger]

Well I put her up on jack stands yesterday and leveled the car to zero according to the rockers. The Trans is down 4.40° and the rear was at 0°. I couldn't go up with the Trans due to tunnel hump clearance so I shimmed the rear up 4° and things are better but I still have that rattle snake in the shifter between 3-4000 rpm in every gear while accelerating. The higher the gear, the stronger the rattle and the harder I accelerate, the stronger the rattle. The rattle is not there in neutral regardless of clutch position. Engine is new and balanced, Trans is new directly from Libertys Gears. Bell housing was checked and aligned to perfection and pilot bearing is brand new from Hurst. The last thing I think to check is the worthless flimsy Keisler crossmember and mount. I just ordered a new member and poly mount from Hurst.

A thought. If it is pinion angles and close, it can shake on acceleration or deceleration depending on whether the torque on the differential pushes it up or down. It may be that your rear is torqueing up to more than 4 up on acceleration.

 

[74Beeper]

A thought. If it is pinion angles and close, it can shake on acceleration or deceleration depending on whether the torque on the differential pushes it up or down. It may be that your rear is torqueing up to more than 4 up on acceleration.

I have Calvert split mono leafs and CalTracs bars. Little to no deflection

 

[383man]

Dont forget the trans and rear diff centerlines need to be parallel when under a load on the gas. Just an example is if the trans was at o then on a leaf spring car I would put the rear 3 degrees down as the rear will move about that much under a load. I would try to get your trans as close to 0 as you can and then set the rear about 3 down from the same centerline as the trans. If the trans is 5 down then the rear should be about 2 up so it will go to about 5 up when on the gas. Ron

 

[74Beeper]

Well, I ended up ditching the flimsy Keisler crossmember and trans mount in favor of a beefier Hurst member and poly mount, then removed the shifter bracket attached to the back of the trans and welded in a couple of flat plate gussets. This helped out A LOT but I still had a BAD high speed vibration. So.... I pulled the trigger on a custom QA1 carbon fiber driveshaft. Holy moly this sucker is awesome. Without the slip yoke and joints it weighs a massive 7 pounds! My vibration issues are GONE!!!!

 

[747mopar]

Wow, that's a beauty! If you don't mind, what did that set you back? Glad to hear it's all good, so are you figuring it was a bad balance, bent driveshaft or something along those lines?

 

[74Beeper]

Just a hair under $1500...... The problem was the driveshaft was reaching critical mass failure. I have such low gears and an engine capable of 7600rpm. My 3.5" steel shaft was turning into a jump rope at about 100mph. After about a dozen or so jump rope distortions, the shaft had a permanent bow.