Ladder bar car - Radials
Wishbone
ARB
9" Rear Housing
PG

I have been getting in some pretty good test hits, but I have a vibration that has taken out 2 tail shaft seals

At ride height
Engine/Trans - 3.3 degrees down towards the back of the car
DS - 2.2 degrees down towards the back of the car
Pinion Centerline - 2.6 degrees down towards the front of the car
Rear separates 2.5" like this

Operating angle 1 is 1.2 degrees
Operating angle 2 is 4.8 degrees

The burnout is where I noticed the vibration, not after the hit and down the track.

I have since installed a reid roller tailshaft housing + the correct mark williams yoke.

I can't raise my engine/trans angle. I have a front motor plate and a mid-motor plate. I tried loosening up the mounting bolts on the motor plate and mid motor plate. Then got 2 washer stacked between the cross member and tail shaft housing. My engine trans went from 3.4 degrees to 3.3 degrees down

My shocks have a full extension of 21.50". When I bought the car, the shock bolts were set at 18.00" and the engine/trans had a -2.1 degrees down. I lowered the springs to give a ride height of 15.50" from shock bolt to shock bolt. The thought process was to give more available shock extension. But what I've done works. I've been 1.29 60' on a lazy launch.

I'm planning to hit the track on 9/26. I could leave the 15.50" alone and raise the shock brackets on the lower bolt. That would leave the shocks at the 15.50 but raise the back of the car, which would raise the engine/trans angle.

I want to get rid of the vibration, but not sacrife the traction that I've gained. I had went to 4 track visits before I got the traction dialed in.

Is this true? The pinion center line will never get above zero on a ladder bar car?

I understand that under perfect conditions, the pinion center line would be matched to the trans output shaft. So the pinion would be up at 3.4 degrees, but is that possible in a ladder bar car?

Any suggestions or advice would be appreciated. I've read and read and watched countless videos. The more I read and the more I watch, the less clear it becomes.

Any suggestions or advice would be appreciated.

 

Your pinion angle is the problem. It's pointed down too far at ride height (-2.6°). When the car squats, the pinion rises too high and creates a bad angle, causing the vibration.

Adjust your ladder bar brackets down on the rear housing. This will point the pinion nose more toward the ground while the car is sitting still. Shoot for a ride height pinion angle between -1° and 0°. This should fix the vibration when it squats.

 

@Robbi18

You mentioned squat a couple of times in your message. Does anything change about your direction if the car separates vs squats? Im running radials.

Just to summarize, take the pinion center line and raise it from -2.6 degrees to -1 or zero at ride height. Is that correct?