Rear end Placement.

[keeks]

I was checking the car over and noticed that my rearend placement in the car is not correct. Basic setup calls for 15-3/4" from 90/10 plate to the center of the RR frame rail. It was 17-1/2, but I've managed to get it to 16-1/4" but I have to get a part to do that. What are the biggest differences I am going to see in the car? I'm thinking it will be much freer everywhere.

[Matt49]

I was checking the car over and noticed that my rearend placement in the car is not correct. Basic setup calls for 15-3/4" from 90/10 plate to the center of the RR frame rail. It was 17-1/2, but I've managed to get it to 16-1/4" but I have to get a part to do that. What are the biggest differences I am going to see in the car? I'm thinking it will be much freer everywhere.

Be sure you're measuring that at ride height because that is pretty far off. If you've got the correct length j-bar, then you are either in the wrong slot on the chassis slider or using the wrong slider. Check with your chassis manufacturer to be sure.
But going from 17-1/2 to 15-3/4 is a significant move of the rear end to the right which is going to free you up a bunch.

[powerslide]

The measurements I have seen are usually to the inside or outside of the frame rail. Maybe read the book again and be sure its the center. How does the driveshaft look now?

[MBR Performance]

Mastersbilt measures to the center of the frame rail

[Matt49]

Mastersbilt measures to the center of the frame rail

Correct and 15-3/4" is the measurement for a smack car.

Keeks, is this a smack car?
What length j-bar is it and is the frame side even with the 2x2 or inboard of that?
I get the feeling that you're running the short j-bar (18-3/8") but you're in the slot for the long bar which is why the rear end is pulled so far to the left.

[keeks]

It is a smack car. My jbar is at 21" now, and is mounted right of the pinion, and on the right mount on the frame.(so inboard)

[TheJet-09]

The frame side should be about centered on the square upright (part of the frame that the J-Bar mount bolts to/around). At your original setting how did your RR tire not rub the frame? Which would bring into question...is it the right rearend for the car (axle tube lengths)? And for anyone, are you measuring from the outside of the 90/10 plate or the inside, which would technically be the outer edge of the RH bell on the rearend? My 90/10 plate is 3/8" thick (not the issue you had to begin with, but what does the spec call for?).

[keeks]

The pic in the setup book definitely shows from the outer edge of the 90/10 plate. I suppose the thickness of the plate could alter the measurement.

The rear end is a 33-35 as per Masters.

[rakracing]

I never had a masters car but have to wander what the j=bar angle is most cars are no more than 9" of angle difference from pinion bolt to frame bolt.

[keeks]

rak, I'll check that tomorrow.

[hucktyson]

Keeks the 21" j bar is for when your mount is close to
The centerline of the panhard upright.

[Matt49]

Something is definitely out of whack here. With a 21" bar and then mounted in the slot inboard of the proper slot (like you said, inline with the 2x2), the measurement from 90/10 to RR frame rail should be SHORT but it was long. Something doesn't add up.

Rear end tube axle/tube lengths shouldn't effect this measurement.

I wonder if the j-bar pinion mount is something non-standard that has the mount way further right than usual.

Keeks, can you take pictures of your mounts on each end of the j-bar and post them? And also be sure you are taking all of these measurements with the car at ride height.

[hatchet]

The frame mount might have been changed . ?

[Austin34471]

How are these measurements figured? Do chassis builders square the left side tires then just pick an arbitrary measurement from some point on the rear end to some fixed point to basically do a quick check to make sure the rearend is in the right spot? How are the left sides usually oriented in these cars?

[rakracing]

every builder has some measurement to center the rear, all birdcage and shock mount locations are based on this, you will chase your tail with handling with these cars if the measurements are off, matt, did the smack down cars have a update for there frame mount that it may have been altered.