The Stovebolt Site Forums The Shop Area Driveline Floating Kingpin Bushings

I'm replacing the kingpins on a 1956 half-ton. I understand that the bushings are the floating type and are designed to move around (somewhat) in their bores in the steering knuckle. From my reading here, I see that some guys prefer to fasten them in place with Loctite or something similar. What's the advantage to this?
Also, I understand that the bushings themselves do not need reaming and the new pins should fit with no trouble. Is this right? I got my parts at LMC, for what it's worth.

Loctite between the outside of the bushing where it mates with the steering knuckle will prevent movement in this area preventing wear of the knuckle if you were to neglect to properly lubricate the kingpins. The only part that is supposed to move is the kingpin inside the inner surface of the bushing. Generally when a kingpin is in need of replacement, it is due to lack of grease on the kingpin, causing it to seize to the inside of the bushing, therefore forcing the outer surface to turn on the inside of the steering knuckle, causing damage to the steering knuckle.

Thanks, Carl. But as I understand it, they were designed to "float," correct? Also, can anyone tell me if the inside diameter of the bushing needs honing? Everything I've read says the bushings are produced to finished dimensions and need no reaming or honing.
I took the parts to the machinist today assuming the bushings would have to be pressed in and then reamed. He called me back to tell me the bushings were too small for the steering knuckles. Turns out he's never heard of floating bushings and he's been in business for 37 years. I think he still doesn't believe me!

Yes, on 1/2 tons, the bushings are designed to float. Also, on 1/2 ton, they are already at the finished diameter, no reaming necessary. Here's the Manual Page explaining it. The page is from the '55 manual, but '56 is the same.

Thanks Bill. I have that page bookmarked already. I'm thinking of just letting the bushings float as designed, unless one of you can convince me I ought to use Loctite and fix them in place.

Joe,

If he has only been in the business for 37 years, he can be forgiven for not knowing about floating king pin bushings that were used on 1/2 ton trucks up to at least 54 years ago.

When I have a snug fit of the bushings to the knuckle, I do not use Loctite. I grease them every year (or, every 1,000 miles).

The problem with not using loctite on the bushings is the wear in the spindles(unless you are using NOS spindles). Even with new bushings you will end up with play between the bushing and spindle when done giving play in the front end. By loctiting the bushings in place you end up with a slop free front end.
If you decide to loctite them in make sure you put a pin through the two bushings while the loctite sets up to keep them inline.

If they float free then at some point down the road you'll have worn out bores in the spindle and be looking for replacement spindles. Fixing them in place now all that will wear are the replaceable bushing and pin.


Grigg

Every time the subject of "full floating bushings" comes up it
always seems to cause confusion. Most of us are not used to a
bushing that is not pressed into on member so the second one
can rotate freely in the bushing.
The bushings should be a snug fit in the steering knuckle, but
not snug enough to keep them from pressing thru when lightly
oiled with thumb pressure. When all the parts are new and on
size the bushing should be free to rotates in the steering
knuckle and around the king pin. If they were manufactured to
the proper dimensions then there is no need for any reaming or
honing, they should slip together snugly when lightly oiled,
assuming all the parts are spotlessly clean and there are no
burrs scratches or high spots on any of the bearing surfaces.
The kit comes with new bushings and new pins so they should be
fine. The problem comes in to play with the steering knuckle.
If you are lucky, or should I say, extremely lucky there will
not be any wear in the bore and the bushing would press thru
with thumb pressure. If you are like 99% of the population then
the steering knuckle will show some wear. That is why the
manual specifies reaming the bore for a .010" oversize bushing,
which should still float freely in the bore.
The quick fix that Dave was referring to is to Locktite the
stock size bushing which comes in the kits in the worn steering
knuckle's bore. Locktite thread locker such as 242 or similar
will not work for that. Locktite retaining compound like their
620 might work if the clearance isn't to much. But by doing
that you have just re-engineered your full floating king pin
bushings to a semi-floating design.
I don't know if .010" over bushing are available. If the
bushings that came with the kit will not slip into the steering
knuckle than I suppose they could be over size. In which case
the machinist should be instructed to hone the steering knuckle
bore to a snug slip fit, meaning a few ten thousands of an inch.

That's the way I've always interpreted the design, hope it helps
clear things up.

Denny Graham
Sandwich, IL

Thanks, everyone, for your responses. I'm going to get the parts back from the machine shop and see how well it all goes together as designed. I haven't had a chance to check the fit of the bushings myself. Thanks for all the advice.

Joe

I just checked the specs for over-size kingpin kit at Classicparts and the outside diameter of the bushings is the same as those for the standard kingpins. The over-size is in the kingpin and the inside diameter of the bushing only. So my question has always been, why would anyone ever need this over-sized kingpin/bushing? If the wear is between the kingpin and the inside surface of the bushings, why not just replace with the standard kingpin/bushing kit? What am I missing? (I am prone to missing stuff.) Also, where does one find over-sized outside diameter bushings?

The over-sized king pin is common because it was common for the loose-bushings-pins to wear/enlarge the holes in the axle. The over-sized pin will fit tight in an axle hole that was reamed to the over-sized diameter of that pin. Often .020 over-sized pin-sets are available.

What is needed is a set with over-sized king pin diameter and over-sized outer diameter of the bushing.

Someone recently posted the MOOG part number for such a replacement set.

This discussion arises fairly regularly. The wallowed-out knuckle-journals seem to be almost as common as wallowed-out holes in axles?

Not sure who originally posted it (might have been me, I don't recall for sure), but I do have a Moog catalog handy. Seems there's 3 different numbers; 8444B for '55-'56, 8457B for '57-Early '58, 8468 for Late '58-'59. Not sure what the exact differences are, the dimensions for the pins themselves is the same for all 3 sets, .8660 x 5.312".
Something I did not mention in my earlier post, I did secure my bushings in the knuckles with Locktite 640.

Guess it wasn't me. Looks like that thread covers Advance design, which uses different part numbers from the Task Force.

If the wear is minor Bill, your choice of the 620 is fine, but
it's a medium viscosity retainer. I'd use it where the inner
or outer race of a bearing was supposed to be a press fit and
was slightly loose for one reason or another.
If someone is going down to their local bearing supply to buy a
bearing retainer compound for a badly worn bore, I'd recommend
the 620 simply because it's a higher viscosity and will fill a
larger gap, like up to an 1/8" on the total diameter. Also
before they ring you up it wouldn't hurt to pick up a
primer for that compound, #7649.
All that being said, these retaining compounds are just plastic
and I'm not sure just how much hammering they will take before
they get knocked out of place. I mean look at the damage that
was done to the steel, no way plastic is going to take that
much stress. The load on the king pins is a bending load, and
they take an orful beating which is evidenced by the common
need for replacement.
Bearing retainers are mainly compounded for use where the
bearing or bearing race is supporting a radial load.
I gotta say that from my point of view using a bearing retaining
compound in this application is just a quick and dirty
temporary fix, like if you wanted to dump the vehicle
on someone and didn't what to spend the cash to do it
right.
If it were me, the only repair that I would trust would be
reaming to take an over size bushing.
Denny Graham
Sandwich, IL

Denny,
Not for these old trucks, but plastic king pin bushings are common. I'm not a fan of them but that's what's in my front axle (mid 90's GM) because that is all that I could find at time of rebuild.
So, my thinking is if plastic bushings themselves don't get pounded out, and that's the wearing surface as well. Then using something like Loctite 660 which is designed to fill a gap and support a bearing/bushing is OK. All it needs to do is fill the space and stay in place, the load and wear is in the pin and bushing, all the plastic needs to do is not squish. So the filler needs to be good in compression, which I expect it is, that's it's job.

I understand your hesitation but personally feel the 660 and similar filler/bearing retainers is a good fix for moderately worn spindle bores as well as a good way to prevent wearing out spindles even if the bushings fit as new, better to lock them in place.

Best I can figure the full floating king pin bushing was simply a quick cheap way to assemble axles on an assembly line. I see absolutely no advantages in life and function. To do it right (as nearly all other king pins and bushings are) they should have pressed bushings in and reamed them to fit the king pins.

Grigg

When I was looking for the KP's for my 58 I found RockAuto handy, as they showed the actual inner and outer dimensions for the different pins available.

Your reasoning about the assembly line labor savings is as good
as any I've heard Grigg, and it might have entered into the
equation. It does however give you twice the bearing surface of
a fixed bushing, which could reduce the friction giving you
easier steering, could even result in less wear than a single
surface bearing all of the stress.

You know me Grigg, the eternal doubting Dennis. I sort of doubt
that any of anaerobic compounds, resulting in a cast filler,
could stand the loads imposed on the king pins, especially upon
impact with poor roads surfaces. Just taxing down a smooth
asphalt runway before take off at only a few miles per hour
with my 750lb. Pitts special would peg the recording G-meter at
over nine G's. I'd shudder to think what sort of impact loads
the front end of a 3500 lb. vehicle would encounter at fifty or
sixty mph but I'd bet it would be well into the double 'G' figures.
The plastics used in your newer truck is most likely an
injection molded material which gets much of it's strength from
the long molecular chains as opposed to a cast part. Probably
something like a "T-series" resin which can handle pressures up
to 32,000 pounds per square inch and temperatures up to 619F.
The Loctite 620 has a shear strength of about 3500 psi. Not
familiar with the "660" but there is a Loctite 680 high
strength that has a shear strength of 4000psi, but it's only
designed to fill a loose slip fit no more than .015".


Have to take a look at Rock Auto's site Caso, I'd like to add
those dimensions to my reference file, thanks for pointing that out.

Denny Graham
Sandwich, IL

All I can add Denny is, I have been using Loctite on king pin bushings for at least 30 years with no come backs.

Well, I finally finished this job. I used a sleeve retaining compound by Permatex. I made that choice before seeing all of the back and forth here. We shall see what happens. Only real difficult thing I ran into was that the new tie rod ends were an absolute #%#^ to thread on. Seems like the inside diameter was slightly smaller than the outside diameter of the tie rod. I made it work but man it takes some torque to thread those things on.
Everything feels nice and tight but I got a weird steering thing going on that I'll talk about in a separate thread.

Denny, I always use high strength red Loctite. Right now I am using Red #271 permanent.
This is when using standard outside diameter NOS full floating bushings in worn spindles.
As far as GM's thought on this, I will have to add this to my long list of questions I will ask the engineers when I meet them, LOL.
The replacement king pin sets I have seen are press in style and need to be reamed. I happen to have a lifetime supply of NOS king pins and bushings to use.

I recently had the same experiance - my shop was also a little surprised. I believe that the shop manual recommended installing the bushing with anti-sieze compound.

Bob

So, the only time one needs an over-size kingpin for a full floater is when the axle hole is worn?

Correct for any kingpin; the "oversize" is to correct worn out bore in the axle.

That is correct.

If you have significant looseness in the bushing journals in the steering knuckle/spindle, you have another problem that is not solved by using the over-sized kingpin.

Yep.