Featured Technical 40-41 FORD PICKUP PARALLEL LEAFS

This is something that I had not contemplated prior to my telephone conversation with Dale the other day. Those raised shackles in the back (like we ran in HS) screw with the pinion angle of the diff. Effectively tilting the pinion up, how much is the question. I would guess that my 4.25" shackles (stock was 2" eye to eye), will raise the truck 1.125" (half the shackle raise). The spring is 48" long so the ce625nter point is halfway (24"), so I could be lifting the pinion .625"? If so, I would need to drop the *** end of my transmission the same and I don't recall building in any downward adjustment to the crossmember and mount. I guess I could raise the Hemi on its mounts?

I'll check it once it back together and on the ground. I may be overthinking it. That happens, regardless of what you hear from my wife and a few on here.

 

Wondering since you are basically putting back to where it was originally if the angle would be wrong.

But if it is off, there is no need to change mounts, instead use wedge shims on the spring pads.

 

Energy Suspension (I should get a commision) offers their GM style trans/crossmember mounts in two thicknesses, not sure what your current arrangement is but the shorter one could be a problem solver.

 

Yup I think if you are just putting it back to where you started that you are probably going to be pretty close to correct on the opinion regardless of method.

 

I bet you are correct. In fact, I mentioned to @Pist-n-Broke one day a couple of months back that the PU had developed a vibration. Smooth as silk until 40 PMH, then a harmonic brump, brump, brump, like you are running over the turtles (Bott's dots) in the lane divider. Gone by 50 MPH. That may be due to the rear end sagging and changing the pinion angle. Lifting it may fix the ride height and the vibration. Hmmm

Correct, I have some wedges around here somewhere if it necessary. Interesting.

 

I believe we touched on pinion angle at that time. The vibe wasn't there initially and slowly came on. You also hadn't mentioned the ride height was changing. I won't be surprised when you learn the two go hand in hand.

 

Just me thinking outside the circle, what about keeping the original (sagged) spring setup you have to locate/mount the diff, and run coil over shocks to get the ride height where you want it??
Leaves and coils working in harmony..
Or is that a bit of a Hmmmmmm suggestion.. Lol

 

That would make for a harsh ride.

 

It would only be harsh if you were running the total weight of the pickup rear on the sagged springs, plus the coils, my suggestion was to take the weight on the coil-overs (raising the rear 2''), and nothing/minimal on the leaf springs, they would only be locating everything, and taking the drive forces..

 

But if the leaf springs are still connected they will still be doing their share of carrying the vehicles m***. Any extra coilover springs fitted would need to have a very low spring rate because they would only need to bear the proportion of the m*** that is not already being dealt with by the leaf springs. There is no way for the coilovers to carry the entire vehicle m*** unless the leaf springs are completely disconnected from the system, at which point they would then no longer be able to locate the rearend.

 

This was my advice to B-B several days ago.

I firmly disagree. B-B was also confused with my explanation as to my opinion (I've only been doing this for 50 years so I'm no pro) and was going to do some follow-up with a spring manufacture. I haven't heard anything either way back from him. I'm no longer calling what's under his Truck, "springs" because if they were they'd be doing there job instead of letting the Axle rest on the Snubbers. Ther's NO Spring left in them.

 

As the Wizard summed up in that last post, we discussed this on the phone in particularly the potential ride harshness caused by two sets of springs. Secondarily, the inability to control ride height if I install coil overs.

Addressing the first point, those springs may be holding up the truck and they have just come to rest on the bump stops, I will confirm that once the stops are removed. If they are supporting the truck to that level it will be a game to configure a spring rate that will allow for an ***ist to raise the truck without jacking it up in the air (ick). For example if the truck only needs 100 lbs of ***ist to raise it the required amount (to ***ist the leaves) and I use a 250-pound spring on each side it may ride like a Sherman tank. In my mind (that's a dark, Vicodin powered place) I figure I could place a bathroom scale (not my wife's gl*** one) on a floor jack saddle and slide it under the diff, jack it up a stroke or two until I have my lift and that should tell me what is required, yes? There is likely a better way to that, but it at least illustrates my point. If it only takes 100 pounds to lift the truck, I doubt I can buy 50-pound springs. (Just an example)

To the latter issue, the ride height is paramount. I must get that whitewall spacing corrected and of course obtain the 2-3" clearance the rear end needs for compression. Rear coil overs are not height adjustable other than spring rate and dampening, unlike their forward mounted cousins that are pushing against the frame. Too much spring and the back end will be in the air, and I do not want to see the top of those tires.

 

I have to think the leaf springs would still be doing some percentage of their job, even if they have sagged. It will be interesting to see what happens if @Bandit Billy does his weighing experiment.

This would tell you what proportion of the load, if any, is being dealt with by the leaf springs. Wouldn't you have to place the floor jack and scale under the frame, not under the diff?

 

Duh, brain fart on my part there, thanks for the correction. Yes the frame is what needs to be measured. Maybe a 4x4 paid across the frame at nearest the diff. No, the exhaust is under there...I'd have to build a little 4x4 with frame supports on either end. That's easy and free. Good catch.

 

I hope you actually do this. I am interested as to what the outcome would be. Enquiring minds like mine want to know.......

 

Ah, but they are adjustable, for that very reason. Modern coilovers aren't the fixed rate 'helper shocks' our fathers bought to put on their station wagon for towing or loading up on camping gear. Most I've seen have at least 4 inches of ride height adjustment if not more. Yes, changing the ride height will also change the spring preload and rate, but using the correct length/rate spring will address that.

Cost-wise it appears to be a wash, but will be far easier to 'tune' as well as a much easier install.

 

Steve, if the top of the spring is under a retainer plate under the top shock eye, and the bottom is on the adjuster nuts, how does that effect elevation? The top of the spring would have to ride on the frame, yes? I suppose a guy could fabricate an upper pocket for the coil to sit in and use a post top mount to locate the shock body but simply "eye hole to eye hole" bolt in shock replacement doesn't provide body lift, only spring compression and thus a little adjustment but much increased ride stiffness in return.

I put a pair under the back of my 442 for drag racing to replace the factory coils. I used them more for the dampening control so the back would sink at launch and add some traction. They do little if any to adjust body height. Or am I missing something you are referring to?