mod newbie

[oldgold]

i bought my grandson a mod he has championships on asphalt at 16 and now wants to try dirt .
i found a 73-77 chevelle mod and it has 4 links on rearend a j-bar and long pullbar with a biscuit on it . he put the car on hoist to look everything over. I am guessing it is called a B mod it looks like inca with a 9 inch but non floater.it has a floater on the left housing .it has what i term sliders on the springs and we noticed that the springs are screwed in so tight that the car is at the extended up end of the slider.should the springs be pinched in this tight? we thought of mounting the springs up on the housing .I am not sure of spring rates yet or shock values .we are going to a fun nite this sat and will see what it does any site we can get setup or notes? we cant find any markings on who built it so not sure what copy.thank you

[js11]

I wouldn't say the 9" differential makes it a B mod...lots of guys still run those and win. Not knowing your chassis make or bracket placement, you could try the following to get started. Also this assumes that this is a 4 bar both sides (not z-link with four bars):

That year Chevelle takes a little more front spring than some of the other chassis. After you get your motor in the car, fill the fuel tank and account for driver's weight, take a look at your rear springs again, then adjust (a little preload is good). My dad's car is a similar clip and we run 900 to 750 ln the LF, 750 to 650 on RF (might need a bump rubber on RF if too much travel), 175 to 200 on the LR (spring behind on slider with 1/4 pre-load), 225 to 175 RR. The long pull-bar will work, but if it's a single or two rubber design, it might too soft. You need about 1000, to 1200 spring rate on the pull-bar (progressive or not), is my guess. Shocks to start would be 74 across the front (an extra 763 tiedown for either side for tuning), and 938 or 937 stand up on LR (stiffer comp to help turn on entry) with a 94 or 93 RR...for starters (if clamping the RR spring, start with a 935). I would leave the R-side floating, mount spring on bird cage (floating); then spring behind LR, floating if you can (or clamped in front [mounted on shock bracket with slider], which is easier to dial in). Rates also vary, depending on angles, placement away from tires, etc. But these are ball-park guesses. For the J-bar, maybe someone else has a starting point. Just don't get too radical on the angle to start. You want 4 to 4.75 of LR drop (don't let the shock stop travel...use a chain).

It's hard to say what your ride height and bar angle baselines should be without knowing the chassis maker, but most cars work with 6.5 to 7' ride at the corners behind the wheels (10 to 15 degrees upper A angles in front and a downward slope of tire rods from spindle arm to drag link [hard to say how much]). The rear: search this site for the upper and lower trail arm and J-bar angles...I usually find a lower link that's one hole up from the bottom (again, hard to say without seeing what you have) to get zero degrees at ride height (both sides) then raise the LR bottom to 5 degrees to start, and the 5 to on RR bottom (raise to help turn and lower to tighten. The top bars, I cant say for sure, 17 to 20 on the LR and about 5 degrees less on RR. String the car with the same offsets on front rear from the driver's side. Run rear tracking on passenger side to get about 1/4 trail (longer than driver side wheel base), and run even or shorter on passenger side if the car is too loose out or skating.

Run 1 degree stagger front tires and 2 to 1.5 in rear. use the same offsets all around (a lot of folks run 2 ' or 3') and have a 4' RR read for the slick track conditions.

Scale with drive and fuel at 80 lbs LR bite, 53-54 left side and 55 to 58 rear percent. Dont worry about cross weight.

I hope this helps. There are guys on this site who are sharper on setups, so maybe they can chime it also.