Mopar SS spring question

[Montclaire]

Hello, I have a 74 Barracuda (yeah, I know - E-body) with an 8-3/4 and Mopar SS springs. The car has what looks like the Mopar front hangers with two bolt locations, and the springs are in the lower hole. I am getting a driveline vibration above 3,000 rpm/50-55 mph (the car has 3.91s). Checked the pinion angle and found it to be one degree positive.

I ordered a pair of four degree wedges to correct the pinion angle. The wedges are 3/8” thick at the midpoint, and I am assuming engagement of the center pin is going to be an issue. Does anyone know the length of the Mopar center pins? I’d like to pick up a new set in advance so I don’t make this into a two day project.

I have already done a precursory search and can’t find a length listed anywhere. I believe they are 5/16”. I’ve seen guys suggest using allen head bolts, although I have a few spring shops local to me so I probably won’t need to go that route. Would grade 8 allen bolts be sufficient if I do?

Thanks in advance.

 

[Sixpactogo]

I have the Super Stock springs in my Charger also..The spring perch bolts are 5/16" If you are going to need 4 degree shims you will need longer bolts. I bought mine from Mega Parts. They are 2 3/4" in length. My car has a rear stabilizer bar that mounts in between the perch and the spring so I needed a taller head to make up that distance plus the 4 degree shim. I found a chunk of 3/8 ID (1/2" OD) steel pipe and cut a pair of 1/2" long pieces to add to the bolts.
A long story short, my 4 degree shims were not enough to correct my pinion angle so I ended up cutting the perches and welding new ones in at the correct angle. Here are a couple pics of the longer bolts and spacers I used but no longer need because of relocating my perches.

By the way. I did a lot or research on Pinion angle and there is a lot of bad info out there IMO. People tell you that with leaf springs, you get 5-6 degree of axle windup which I found to be bogus. Maybe with a drag car with high HP and 12" sticky tires but not a street machine with stock tires. My car has a 6.1 Hemi with around 360 hp to the wheels and my axle windup is less than 2 degrees.

 

[Montclaire]

Perfect, thank you. The old Direct Connection literature wanted a lot of negative pinion angle. As you said, for racing, sure. I'm looking to get around 2-3 degrees negative, even as much as 5 degrees I think I'm fine for the street. I may play with the trans mount at some point as well. It depends on what the result is after the wedges are in.

 

[Sixpactogo]

5 degrees is way too much for Super Stock springs. My engine/trans is 4 degrees down. Driveshaft is 1 degree down. I set my pinion at 1.8 degrees down. (nose up) I figured if I get 2-2.5 degrees of axle windup, I would be perfect. When it is all said and done, on a hard take off, I am in good shape with no issues. While at part throttle, my pinion is probably closer to 3 degrees nose up. If I were you, I would not go much more than 2-2.5 degrees lower than your trans angle unless you have lots of room to go up with your transmission. I have a 545RFE 5 speed auto in my Charger and with my tunnel mods, I can't go up at all. As I said, all that drivel about 5-8 degrees axle windup does not happen with a street car with decent leaf springs. I doubt if I could get 3 degrees even with sticky tires.