Chassis - Dropped Axle/Spring Installation Tech Article

[modifieddriver]

I was reading Harrison's post/thread about installing a dropped axle in his '38.

I remembered giving him some tips on what to do.

Here's a tech article I wrote for another website a couple of years ago. They considered it good enough to be included in their Old Ford Tech Library. Here it is:


<CENTER>Dropped Axles & Stuff</CENTER>

This will be a little lengthy, but I thought I'd share what technical information I've learned doing five dropped axle installations along with the reversed arch spring thing on my own cars (1936 thru 1948).

SPRING:

1) If you try to lower the front end a significant amount by just reversing the arch of the front spring and removing leaves, you can have a problem with the stock radius rods hitting the frame rails, especially on the stock steering box mounting bracket (it can be heated and bent for more clearance with no saftey issues). With this solution you've lowered the front end but have sacrificed suspension travel. You can alter the length of the axle rubber bump stops to limit suspension travel to prevent the radius rods from hitting the frame but it will "bottom out when hitting a significant bump.

2) An advantage of a thinner spring "package" is you can shim between the frame and spring to get "your" desired ride height or "look".

3) Another problem with this method a reduction in shock absorber travel. Lever action shocks will have the arms pointed "uphill" unless you shorten the shock links. Make sure tube shocks aren't bottoming out in their travel. I've had to go with shorter shocks to correct this problem.

DROPPED AXLES:

1) I've used Bell, Chassis Engineering, Magnum and Mor-Drop I-beam axles. All are OK depending upon what you're doing. Most importantly with a dropped axle you retain most of your suspension travel. Depending upon the amount of "drop" you want, you may not have to reverse the arch of the front main leaf. Removal of a few spring leaves might be all that's needed, primarily to improve ride comfort. Remember to install shim(s) of equal thickness to what's taken out so your stock U-bolts will clamp the spring tight in the crossmember.

2) The Magnum and Mor-Drop(a stock axle with ends heated and reformed) have stock perch pin (or radius rod mount) spacing. If you're using the stock transmission or just want to retain the stock radius rod mount on the frame, this is the way to go. Why? Because the stock radius rods can stay the same length. Looking at the radius rods as a triangle, none of the dimensions have to be changed. The axle is "almost" a bolt in replacement. I even use the stock lever action shocks and sway bar under my '40 Coupe.

3) Bell and Chassis Engineering(CE) have a reduced perch pin spacing. This changes the dimensions of the radius rod triangle and moves the pivot ball location to the rear of the car. If you're doing an engine and later model transmission swap, plan on using a radius rod split kit with these axles. They work great! Also, plan on a shorter spring main leaf because the distance has been reduced between the shackle pivots.

STEERING ARMS:

1) I have heated and bent steering arms, but don't like to because it can mess up the Ackerman, other geometry and cause safety issues.

2) I like to use the dropped steering arms made by each individual axle manufacturer. You have to cut the stock steering arms off the spindles to do this. But spindles are plentiful because all the hi-tech street rodders are installing Mustang II "stuff" under their cars and selling off the "good old stuff". So, if you want to back to original some day, pick up some spares at the swap meet.

3) When you are cutting off the steering arms I prefer to use a pair of later '46-'48 square back spindles, if you have access to them. #1) The later spindles use a longer kingpin, which I like. #2)The later right front spindle has the tie rod entering from the bottom and the drag link entering from the top. The round backs have both entering from the bottom. So, if I'm going to destroy a pair of spindles for this swap, I opt to use the square backs. My personal preference.

TIE ROD and DRAG LINK:

1) I think the Magnum axle is about 1" shorter from king pin to king pin. I think the CE and Bell are even narrower. This tucks the rims and tires inside a little to gain needed tire to fender clearance when turning.

2) Because I'm pretty frugal, I use the stock tie rod and drag link with the Magnum axle swap. Because the kingpin spacing is reduced you have to shorten the tie rod an equal amount. I cut off the right hand threaded end of the tie rod and rethread with a right hand thread tap I bought from Travers Supply. I reslit the tie rod with a thick hacksaw blade or zizz wheel and reinstall the clamping collar and tie rod end. The tap is special, you won't get it at Lowes or Home Depot! Cost about $10.

3) Because you only have to shorten the drag link about 1/2", you can usually get that much distance out of the adjusting sleeve. This is using a stock steering box.

SHOCK ABSORBERS:

As I mentioned before, make sure the shocks have enough travel so they don't "bottom out". I've used both lever action and tube shocks. It's amazing how good the old lever action shocks work!

TIRES:
The best "hot rod look" I've obtained is with a 165/80R15 (26.5" diameter) on a 5" wide rim on the front and a P235/75R15 (29" diameter) on a 6" or 7" rim on the rear. If you're using a stock spring in the rear you'll probably only be able to use a 6" rim with close to original back spacing. Otherwise, the rim will contact the spring shackle mount. Also, you'll have to heat and bend the stock shock arms toward the frame, otherwise they'll hit the tire inner sidewall.

ALIGNMENT:

Assuming we all know what the terms mean. I run 1/16" to 1/8" toe in with radial tires. Camber on these replacement axles has been consistently correct, about 1 - 1.5 degrees positive. After dropping the front end down, usually I have to adjust the caster back to 5 - 7 degrees positive. This "stuff" is not rocket science and can be done in your "well" equipped home garage. I'll save the procedure for another day if someone wants to know.

OVERALL:

For me, the dropped axle front end is the best way to go. My cars with this set-up handle great, track down the road straight and have plenty of ride comfort. My '40 pick-up with only the spring thing done works OK, but lacks the ride comfort of the dropped axle cars. It's slated for an axle change in the future!

I've owned old Fords with Mustang II independent front ends and didn't like 'em for a variety of reasons. Sometime in the future I envision hot rod parts suppliers selling kits to convert Mustang II front end old Fords back to straight front axles!!!!

Modifieddriver

Positive and/or negative comments are welcomed .

[HOTRODPRIMER]

Well written Frank,,,HRP

[fab32]

Originally Posted by HOTRODPRIMER

Well written Frank,,,HRP

Ditto

Frank

[19Fordy]

Modifieddriver:Thanks for the very good article. I dropped the front of my 40 ford by using the 4 inch Magnum dropped axle and dropped steering arms along with a posie reversed eye spring. Front tires are 5:60 x 15. Rears are 7:60 x 15. Toe in is 1/16 in. Do I need to adjust the camber and if so how is it done? Thanx

[modifieddriver]

Thanks for the positive comments.

I'll do another thread on bending axles to adjust camber. It's a "piece of cake" to do in your home workshop.

[Tindall]

This will deffinitly come in handy in the future

[Harrison]

This information was a blessing while I did the deed on my '38. It should really be put in the Tech-O-Matic for future reference.

One thing I'd agrue though - those 15" tires. It don't get any better than this...

JH

[Flat Ernie]

We'll send to to Tech-O-Matic soon - it's marked!

[29-a-freak]

i'ma need this in bout a month....hope it hangs around!

[modifieddriver]

Originally Posted by 29-a-freak

i'ma need this in bout a month....hope it hangs around!

If ya' need help, send me a PM.

I may do a reversed arch/rebuilding spring tech and a camber adjusting tech. Besides Harrison, I have had several folks asking for tech info.

[casper]

This is an awesome post! I am going thru this right now and I'm having major clearance problems with the spindle arms hitting the drop axle. This explained everything plain and clear that I need to fix the problem. Viva la H.A.M.B.!