'73 D20 to '72 D18 Front Axle Swap?

[Firsttimebuyers]

Sent: 7/24/2007 2:17 PM

hey folks! getting ready for the jam!Dave wants to know if we can switch the front end from the crushed 73 d20 to the front end on our newly acquired d18? The new one needs a new kingpin, but he was wondering if it would be possible to use the whole axle and all from the crushed one since we know everything is good on that front end  before the big tree incident. He says everything seems to measure up the same, any reasons why  or why not?The d18 is a 72 I believe, thanks, mary and dave

[MSN Member]

From: firehart2
Sent: 7/26/2007 9:01 PM

Dodges were famous for mid year changes and identical units useing different parts. If you have both VIN numbers, I would check all the parts numbers.

[denisondc]

Sent: 7/27/2007 10:39 AM

If both of the front axles use the 8 bolt hubs, they are probably the same axle rating, or very close. You might wind up with different brake components - and would eventually need to ensure the inside diameter of the front wheel cylinders was the same.
The things to check though: is the frame width the same? This would have to do with whether the new axle could fit under the original springs. Are the springs the same width. This would have to do with whether the U-bolts would fit into the new axle.
Is the drag link the same length, and does it have the same size 'nut' on the taper where it fits to the steering arm on the drivers side spindle assembly? You would need to have the drag link fit to the steering arm and have the steering wheel 'straight' ahead, with the wheels also 'straight' aheard.
Will the brake hoses fit - i.e. are the threads and fittings the same. Its possible the D18 would have different wheel cylinders - involving different braking pressures relative to the rear axle brakes.
What is wrong with the existing kingpin, and how loose is the wheel on the end of the axle? If you adjust the toe-in on the D18, and lube the kingpins, it should hold up for a while. Do you know how to assess the wear on the kingpins? Many mechanics (and safety inspectors) are used to McPherson strut suspensions with ball joints. Zero play is the only acceptable wear on those - but this is NOT true for beam axles with kingpins and bushing. With my front wheels jacked up, I can move the top of the wheel in-out by pushing hard on it. It will move about 1/4" at the tire edge. This is still within acceptable limits. (I had a 29 Sterling chain drive heavy truck where the top of the front tire could move in-out more than 1.5 inches, and it still steered nicely - with the toe-in set properly.

[DaveVA78Chieftain]

Sent: 7/27/2007 10:54 AM

M300 used the same 4500lb drum brake axle P/N from 69-73.  They changed the axle P/N when they went to front disk brakes for the RM300 chassis.  M400 chassis used a 5000lb axle which obviously is a different P/N and setup.  So, are both chasis' M300s with drum brakes?  If so, then yes they interchange.  If your trying to convert from drum to disk then there are other issues to address.

Dave

[Slantsixness]

Sent: 7/28/2007 7:35 PM

Mary and Dave,

Switching out the whole front axle is almost as easy as it seems.

But... before I tell you how easy it is, you do know that the kingpins aren't that hard to change, right? (and still available.. relatively cheaply too..)

Another thought is, just how bad is the one kingpin? If it moves an inch, its too bad to drive (or something else could be wrong?). If it moves 1/16" or less, it's still ok. (jack the rig up, tape a straight edge to the tire and muscle it back and forth like you check ball joints. put a ruler on the ground and see how far the straight edge moves. Also assuming that the front spindle bearings aren't the problem...) I don't think I've ever seen a Kingpin go bad or wear out from normal driving, usually there has been some kind of impact (accident, big pothole..etc..).

moving along.... here's what it takes to swap it out:
(I admit this sounds like a lot, but a couple of strong freinds and an afternoon is all the time you would need to pull off the swap... I might add that I'm assming that you're fairly mechanically inclined and not afraid of a little knuckle busting...)

First off, the 73 was Disc brakes. A D18, has to be a 69-72 model year to have Drum brakes, (73 up is a D19, and has disc brakes). ALL D18/19/20/21's are 8 lug Dodge/Ford, as long as its a Dodge drivetrain. There were some that had 6 lug wheels, but I think that was '66-68.

down to the nitty gritty:

If you have good drum brakes, they are a bolt in swap to the disc brake axle. Just remove the brakes, and all mounting hardware. The disc brake spindle has two holes (one per side) that are Tapped out for the caliper mounting plate, and a bolt and nut are used in lieu of the larger threaded bolt for the discs. (a little trick here.. suspend the backing plate on the Winnie and leave the brake hoses connected... saves a lot of headaches when the lines won't come undone, plus you wont even have to bleed the brakes!)

Remove the drum brakes in their entirety from the older rig. Remove the axle. (just take the leaf spring mounts loose, the shocks and the steering arm and it'll basically fall out... WITH the Steering links and tie rod ends still attached... saves time, use the other steering gear from the 73)

Removing the 73 axle will require you to remove the same things, however, the 73 axle you will see has the anti-roll arms and rods and the shocks moved rearward about 14". All of these items unbolt, leaving you with a bare axle, quite the same as the 69-72 axle in the D18.


This all brings me to one last idea.... if you still have the 73 (as it seems you do) why not convert the D18 to disc brakes? It's as simple as changing the master cylinder and proportioning valve, and you're already taking the axle and brakes out (they could even be left wholly intact....hmmm....)
A word of caution though: IF YOU CONVERT THE BRAKES, YOU MUST USE THE MASTER CYLINDER AND PROPORTIONING BLOCK FROM A DISC BRAKE WINNIE.
And after that, prepare to be able to stop on a dime.

There are no necessary modifications to the rear brakes in the conversion: They are THE SAME (or at least hydraulically and "size wise" they are). 

I did just exactly this to my 72 D20. And I mean to tell you.. it was worth every grunt and groan.

Alignment??  If you removed the steering arm from the drag link, there wil be no adjustments required, except that you get the springs mounted up straight and smoothly into the original mounting holes and it "Looks straight". Straight axles aren't that finicky... "set the toe and let it go"
But its pretty simple to do if you want to check it: measure the distance between the front edges of the backing plate, brake drum edge or wheel (whatever you think is the straightest) on each side, and same for the rear edges. Make this measurement exactly 1/16" shorter in the front (Toe in) And she'll drive like a dream.
Since you would be taking the enitre axle for the swap, there would be no alignment necessary, unless something is really wrong in the installation ( and... you CAN put the whole axle in backwards, by the way.. that's why you want to leave the steering gear on!)

Ok, I've run out of breath. Good luck... I'm off the soap box!

Tom

[denisondc]

Sent: 7/29/2007 5:59 AM

I would agree with all that Tom said, except that for checking kingpin/bushing tolerance by moving the wheel in/out, he said "1/16th or less is okay". I believe, and have read in literature from companies that make kingpin/bushing sets, that up to 3/8ths movement is okay. This is for tires with a 31" diameter. The more conservative limit for school buses in North Carolina (which get inspected each month) is 1/4". I have two 72 Winnies. On the one with 103,000 miles the wheels move in/out 3/16th", of which about 1/16th is due to the wheel bearings clearance. On the one with about 75,000 miles on it they move in/out less than 3/16ths. I wont be able to meaure them accurately until I can drive it around some.
I check my toe-in before any long trip. With having that set properly and greasing the kingpins frequently, (about each 1000 miles) I expect the kingpins/bushings will last to at least 200,000 miles.

[Slantsixness]

Sent: 7/30/2007 10:47 AM

3/8" is ok too.
The main problem, as Dave describes, is that there are states that are too lenient on the specs, and states that also expect "0" torlerance for front end wear.

Who is right? well.. it depends on what Dana spec'd the axle at, at the rated weight of the axle (not Dodge or Ford, who by the way has their own "looser" spec for the kingpins...)

So you can see it's a gray area. In Virginia, when (if) they inspect it, they don't bother to look up the proper specification, so the rule is 0 tolerance, but anybody with any brains can tell you that's almost impossible... heck the whole rig and axle, whell, bearings etc.. moves a little.....

Anyway... unless the thing is REALLY bad... Drive it. Save the axle and or brake swap for another time.

[denisondc]

Sent: 7/30/2007 12:21 PM

When the Dodge chassis under my Winnebago was new, the spec was .002" clearance between kingpin and bushing. This would result in .050" of movement at the tire rim. In VA I take my RV to a truck dealership that sells Kenworths and services any type of heavy truck. Their inspector knew about solid beam axles.
Years ago I would take my 52 Ford F1 in for inspection, and the inspector (who was middle aged) figured that 1/4" of movement at the wheel rim of the Ford was fine. The Ford had floating bushings - meaning the bushings were a 'float' fit in the axle, and the kingpin was a 'float' fit in the bushings.

[Slantsixness]

Sent: 7/30/2007 12:41 PM

Of course, to the naked eye (which is all they use for inspections) It's impossible to tell .050" of play, let alone .002", so their rule of thumb is "if it moves noticeably, it's bad"

And that's the way the State Police put it when I had the old Dodge School Bus inspected. I fought with the inspector (a atruck place in Chantilly) for two days, and finally brought the state police to the shop to have the bus passed. Why? I had just spent $400 of the Church's money getting new Kingpins installed... (the bus was a D900 with a 413 and 5 speed auto (single speed rear). Nice setup... was a dog on the highway though... max speed 60...at 3700 rpm OWWW! I think the rear ratio was somewhere in the mid 5's

[xerofall]

I'm bumping this old thread up because I had a question about king pins for a 1973 Winnebago D20. (I used the search and found this thread, but not my answer.) My mechanic is having me fix what I can before taking it too him for repairs. The kingpins need to be replaced and he said I need to get the axle code to make sure he orders the correct ones. However after reading Dave's replay above, it was the same axle used from 69-73, something the mechanic wanted to make sure of before he ordered them.

So my ultimate question, should I still try to locate the code? (I have no idea where to look.) Or should I just tell him they were all the same from 69-73? Also there was talk about converting to disk brakes if all that stuff needs to come off anyway... is that a huge expense? (I used to drive a 1969 Ford Fairlane, so I'm used to the drum brakes and their weaknesses.)

[DaveVA78Chieftain]

D20 would use a Dodge M300 chassis (confirm that using your Dodge VIN plate).  Same kingpin set P/N for all M300 chassis from 69 to 77

Dodge P/N 2275522