Drop axle pivots & radius arm bracket for RWD, unicorn or duh?

[3WVNflip]

My '84 F150 Std RWD 351 Auto has a very high back end, from the 235/75R15 rear tires to the wheel arch is 6 1/2" and up front it's 3 1/2" (normal?). I thought the front springs were tired so if replacing I thought I would raise the nose a bit. Wanted to do it without messing up alignment because the truck drives nice (only a tiny bit of wander, but it's best to keep your hands on the steering wheel anyway! lol). So if you put in longer springs it makes sense to drop the suspension down and maybe the steering linkage. I found 2" drop axle pivot brackets and there is a kit for 2.5" lift (2" in the rear) but those are for 4WD only. I called the manufacturer of the brackets and they said there is a note on their internal catalog that says 'not for RWD, 4WD only'. Elsewhere I found reports of taking the 4WD axles, transfer case, driveshafts etc. and bolting them onto a RWD Bullnose (with no mention of changing the mounting brackets). The Bible uses some numbers for those items on the 4WD & RWD suspension diagrams that are identical. Am I overthinking this and it's done all the time without consulting Google? Any help will be greatly appreciated, want to get this truck on the level for a summer project... thanks. Am I correct in thinking that the back end doesn't care if the front is 2" higher up?

[ArdWrknTrk]

Diagram numbers are only the base numbers, and the same for every Ford/Lincoln/Mercury part going way back.

You need to refer to the Master Parts Catalog to find your application, and that will give you the prefix code and the engineering revision suffix.

[Gary Lewis]

Jim is right - 3B095 is just the base part number. And and Bracket (Front Suspension Radius Arm Mounting) used by Ford on any vehicle anywhere in the world carried the number 3B095.

As for using the same brackets on a 4wd conversion, here are the listings from the MPC and it looks to me like it will work save for the 1980 models. In fact, even the F250 LD's use the same bracket. (I want y'all to see that Ford actually called them F250 LD. )

And the 1980 F100 & F150's will after a build date of 12/79, and all F250's will after 4/80 up until 6/84 when the F250 HD's got a different bracket. But the F250 LD's will all the way through.

[85lebaront2]

When aligning these trucks with either twin I-beam or twin traction beam front suspension, the rear height is part of the alignment procedure (if done correctly) as it affects the caster angle (which is what helps returning to center). If you look at the alignment charts in the service manual, there is a section for front and rear height that contains a large chart.

Due to the design of the front suspension, travel of the wheel up or down from it's ride position causes change in both caster and camber. Caster is affected by the radius arm (one going back to the frame) and camber is affected by the axle motion. Actual alignment on these trucks is one of two ways, if you have king pins, the axle beam must be bent to change camber and possible caster, but there are some methods for changing caster at the radius arm attachment. If you have ball joints, the upper ball joint has eccentric bushings to allow caster and camber to be adjusted.

The good thing on the king pin models, properly done, it will last a long time. Darth's last full alignment was done in 1994 not long after I bought him. My last set of front tires were bought in 2014 and are wearing dead even across the tread.

[3WVNflip]

Thanks for the primer and a good start. I will see if the truck has caster bushings or kingpins. Did anyone mention the steering linkage or pitman arm? (I was reading through the Lift Links in the Resources section when I noticed these replies, short term memory limit reached, lol). thanks! as long as I drop all the suspension contact points up front equally to allow for the longer springs the caster 'should' stay where it is, yeah? So the idea of getting the 2.5" kit (Rough Country #42230) and leaving the rear as it is doesn't sound like a really bad idea?

[ArdWrknTrk]

Thanks for the primer and a good start. I will see if the truck has caster bushings or kingpins. Did anyone mention the steering linkage or pitman arm? (I was reading through the Lift Links in the Resources section when I noticed these replies, short term memory limit reached, lol). thanks! as long as I drop all the suspension contact points up front equally to allow for the longer springs the caster 'should' stay where it is, yeah? So the idea of getting the 2.5" kit (Rough Country #42230) and leaving the rear as it is doesn't sound like a really bad idea?

Caster will change when you change the rake of the truck because the inclination of the axis through the ball joints (or kingpin) has to change if the front and rear are leveled.

Dropping the steering components doesn't change the fact that the frame itself is no longer raked.

The radius arms or torsion beams are attached to the frame.

A straight axle (like a D-60 front) is attached only to the leaf springs, and can be wedged.

[3WVNflip]

I believe this truck has forged axles with caster bushings. But with the generous coating of surface rust it has on everything I couldn't see without getting under there if there was a bushing in that upper ball joint area. Looks a lot more formidable than the '08 California Ford van I removed all the front suspension from although looks familiar to that operation. Just to confirm; kingpin axles slip inside the upper & lower of the knuckle and caster bushing axles sit on top of the upper and on top of the lower on the knuckle, yes? Will spraying it all down with several treatments of pb blaster and driving it for a week be worth the $8 & effort?

[3WVNflip]

Working this out on 'paper' is helping a bit I think:

So when the frame pivots around the rear axle axis (as it raises up in front) it changes the angle of the new front axle drop brackets, setting the position of the knuckle, which changes the purple triangle's orientation affecting caster (reducing I think), that assumes that the brackets do not take this into account in their design. the ball joints allow enough movement around this axis to affect the caster. So I guess the question is with 2" vertical change how much of an effect will this have?

Note: I realized I did not draw the purple triangle in perspective, I only add this in the event my technical drawing teacher is reading the forum, lol.

[ArdWrknTrk]

Working this out on 'paper' is helping a bit I think:

So when the frame pivots around the rear axle axis (as it raises up in front) it changes the angle of the new front axle drop brackets, setting the position of the knuckle, which changes the purple triangle's orientation affecting caster (reducing I think), that assumes that the brackets do not take this into account in their design. the ball joints allow enough movement around this axis to affect the caster. So I guess the question is with 2" vertical change how much of an effect will this have?

Note: I realized I did not draw the purple triangle in perspective, I only add this in the event my technical drawing teacher is reading the forum, lol.

We didn't have tools like this when I took drafting and print reading.

NASA didn't have tools like that when I had drawing class!

it's going to increase caster, because as the front rises, the axis through which the truck steers is going to move more forward of the tire's contact patch.

You seem to have the program.

Why don't you plug in the truck wheelbase (133" for a 8' bed) and see how much 2 1/2" lift in the front changes the trail?

Then your have a good idea of how much offset the camber bushings need to get it back into spec.

 

[85lebaront2]

We didn't have tools like this when I took drafting and print reading.

NASA didn't have tools like that when I had drawing class!

it's going to increase caster, because as the front rises, the axis through which the truck steers is going to move more forward of the tire's contact patch.

You seem to have the program.

Why don't you plug in the truck wheelbase (133" for a 8' bed) and see how much 2 1/2" lift in the front changes the trail?

Then your have a good idea of how much offset the camber bushings need to get it back into spec.

Jim as the front of the truck rises, the radius arms will swing down to maintain tire contact with the road surface, this has the effect of reducing the caster angle (positive caster is the backwards tilt of the steering axis that helps center the wheels) Camber is the in or out tilt of the steering axis, most vehicles have a slight positive camber which helps in maintaining a good contact patch on the outside front wheel when cornering.

Extreme (somewhat) example. When Shelby set up the front ends on the 1965 GT350s, the upper control arms were lowered 1", and the alignment specs were 2° + caster, 0° camber, the caster + the 3.5 turns lock to lock meant the wheel would return to center with a vengeance if you let go of it. The 0 camber put the front tires straight up and the relocated upper control arms made the outside front tire tilt in under load so it remained vertical with respect to the track surface. This was done for the bias ply race tires of the 60s, put radials on these cars and they were squirrely as all get out.