47-55.1 MII Axle Center

[Mains52]

Alright guys I want to get my cross member tacked in this weekend. What are your guys' axle center measurements? I want to see how close everyone is.
Thanks

[dsraven]

the axle centerline depends on the ride height because the front fender wheel opening tapers on the rear and is more rounded on the front. if you lower the truck down over the wheel with the stock axle centerline the wheel/tire looks like it is being stuffed into the rear of the wheel opening. you need to have the tire size and rim offset that you will finish the project with and then set it in the opening with the truck at ride height and the rake angle you like. then you will need to choose the look you like. less drop would mean less axle movement towards the front. a stock ride height and rake angle would mean the axle centerline could be left as is, theoretically. there are lots of threads on the subject but it is a personal preference thing and is really dependent on the tire size. smaller tire would have less visual effect because the tire has more clearance between the outside of the tire and the wheel opening so the air gap looks more uniform around the tire. larger tire or more drop is more visually noticeable.

[mr48chev]

As Dsraven said there is the "standard" spot and the there is the perfectly centered spot.

I'd start with the instructions for the kit you have though.

This the link to Heidt's pfd instructions for putting their MII kit on the AD truck if it works.

[mr48chev]

The measurement that you are looking for to start with is Fig 2 which is 18-1/8 from the center of the front spring bolt hole in the frame to the center line of the axle.

NOTE do not remove those cast pieces at the front of the frame horns that the spring bolts were in. They also keep your front bumper brackets located correctly. I've seen some guys take them out thinking they were "cleaning up" the front of the frame when in fact they were making a lot more hassle for themselves when they bolted the bumper brackets back on.

[dsraven]

umm, mains. it would probably help if you mentioned what year of truck you are working with, what ride height you are striving for, what tire size you would like to finish with and what sort of wheel offset you want.

[Mains52]

Originally Posted by dsraven

umm, mains. it would probably help if you mentioned what year of truck you are working with, what ride height you are striving for, what tire size you would like to finish with and what sort of wheel offset you want.

Thanks everyone. I have a 52 and I’m looking for around 10inches at ride height but I will also be on air bags so it should be somewhat adjustable. I have no clue what tire size and offset I’ll be using. I plan on running 17” steel wheels with an average tire size. Maybe I should wait to get it tacked in until I buy my wheels and tires.
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[Mains52]

Hey guys,
I am bringing this thread back up top because its time to dig back into my truck. I still haven't installed my crossmember due to breaking my leg in September and being pretty much down for a long while. I still don't have the tires and wheels I want. I don't have a clue on what I actually want either. I am going to be running air ride so I don't know if that changes things for axle center, but I really want to get this thing put in so I can get the 4 link put in the rear and get this thing rolling. Any more info would be appreciated. It's a 52 3100 if you need to know info.

[MiraclePieCo]

It's my observation that it's always better to error on the forward side.

[whitedog76]

Originally Posted by MiraclePieCo

It's my observation that it's always better to error on the forward side.

I’ll second that. I dropped a plumb bob on my 54 before I demo’d the frontend. I got 17.75, if I remember correctly. Of course that was on 65 year old leaf springs. I believe the the 18 1/8 measurement is based on an IFS with manual steering and stock spindles. Most folks with power steering will set castor anywhere from 4-7 degrees. If you do the math, that could move your centerline 1/2-7/8 rearward. Drop spindles will also affect the centerline in the same manner, but with a smaller effect.

The ideal way would be to tack everything together, put the front clip and wheels on and see how it looks. That’s not realistic for most folks. I would stick with the directions, if you do anything, maybe move it ahead to 18, that’s it.

[Mains52]

Originally Posted by whitedog76

I’ll second that. I dropped a plumb bob on my 54 before I demo’d the frontend. I got 17.75, if I remember correctly. Of course that was on 65 year old leaf springs. I believe the the 18 1/8 measurement is based on an IFS with manual steering and stock spindles. Most folks with power steering will set castor anywhere from 4-7 degrees. If you do the math, that could move your centerline 1/2-7/8 rearward. Drop spindles will also affect the centerline in the same manner, but with a smaller effect.

The ideal way would be to tack everything together, put the front clip and wheels on and see how it looks. That’s not realistic for most folks. I would stick with the directions, if you do anything, maybe move it ahead to 18, that’s it.

Where were you measuring from? WhiteDog

[whitedog76]

I dropped a plumb bob from the from the frame to the center of the straight axle and measured to the front shackle center.

Chris.