Modifying Spring Hanger Question

[Bruzilla]

Ok, so I'm having a helluva time installing a set of MP SS springs onto my 74 Roadrunner. The rear wheels are sitting too far back in the well.

I think I've found out what one of the problems is, and that is that contrary to published reports the A measurement on 71-74 B bodies is not all the same. I keep hearing how 22" is that A length on all cars, but now I'm seeing references that state beginning with 74 cars, the A length is 21.25" vice 22".

Based on this, here's my plan, and if someone sees something that's gonna bite me in the butt please let me know. I have a set of 68-70 spring hangers that are about 6" long. From what I've read they're about an inch longer than than the hangers for the 71-74 cars (actually 71-73). So I am going to align the original OEM hangers with the 68-70 hangers, mark a location that's 1.25" from the center of the stock mounting hole, and drill a new hole as shown below.

The SS springs have a 20" A measurement, so that should bring me to the correct length.

Thoughts???

 

[Cranky]

I like to move my axle as far forward as possible so long as the tire doesn't rub the forward lower edge of the fender or anywhere else in the wheel house.....but what you're doing looks like it should be fine if that's where your want to locate the axle.

 

[Badvert65]

Do you still have your OE springs? If so, compare the two to get the exact difference of the front (and rear) segments.

 

[mopar 3 B]

I would go the direction you have mapped out that way the drive shaft will not need to be altered. Only question will the rear of the leaf and shackle location align or will it have to be moved forward. If it needs to be move forward I am with Cranky on moving the front eye forward and put more weight behind the axle.

 

[Cranky]

Moving the axle forward an inch is almost as good as moving the engine back an inch. Placing weight between the wheel base actually makes the car pitch rotate quicker than placing weight behind the axle does.

 

[Bb70charger500]

Correct me if I'm wrong but if he go's this route won't it pivot the axle? I would think this would rock the springs in a forward position. It might no be enough to cause a problem. Or it might cause a bad vibration or throwing the drive shaft.
Agen I'm just thinking out loud but isn't this a possibility?

 

[Bruzilla]

If I do it this way, the location of the axle and it's pinion angle should be the same as stock I believe.

 

[Daves69]

If I do it this way, the location of the axle and it's pinion angle should be the same as stock I believe.

Moving the differential nose forward increases the angle I believe. Not sure it would be significant enough to require a shim.
Measure twice, cut once. Also take a look at slip spline depth into the trans.

 

[Bruzilla]

True, but how am I moving the differential nose forward? By placing the hole 1.25" from the stock hole, that should make the 20" front length of the Super Stock springs identical to the 21.25" A length of the stock springs shouldn't it? So the differential should be in the exact same spot.

 

[DoctorDiff]

'73-'74 B-body ISO-springs are shorter than standard '71-'72 B-body springs.

 

[miller]

Still have your old springs? Why don't you measure from the front hanger holes on the springs, to the locating pin that the axle housing mount pads sit in. That's what sets your axle the right distance.

It will also give you the distance your new springs need, to set the axle right.

 

[Bruzilla]

So I started executing my plan, and got rewarded with a rain storm after drilling the holes in the hangers. Rain stopped long enough for me to get the driver's side in and it looks good. Then it started pouring again, so I'll have to wait until tomorrow to get the passenger side in.